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					                    CHAPTER 5                          and Observations on Different Kinds of Air”          nitrous oxide for the medical faculty in Boston,
           niTRous oxidE – n2o                         (1775), where he described how to produce the        leaving his colleagues doubtful regarding its
                   (5 CE Hours)                        preparation of “nitrous air diminished” by heating   efficacy and safety.
Learning objectives                                    iron filings dampened with nitric acid.           The method did not come into general use until
!   Review the history of nitrous oxide.               Early use (1794-1843)                             1863, when Colton successfully started to use it
!   Describe the production of nitrous oxide.       The first important use of nitrous oxide was made in all his Colton Dental Association clinics, which
!   List the uses of nitrous oxide.                 possible by Thomas Beddoes and the renowned          he just had established in New Haven and New
!   Explain the use of nitrous oxide in dental      engineer James Watt, who worked together to          York City. Over the following three years, Colton
    operatories.                                    publish the book “Considerations on the Medical and his associates successfully administered
!   Describe the hazards in the workplace.          Use and on the Production of Factitious Airs”        nitrous oxide to more than 25,000 patients.
!   Review the methods of engineering control       (1794). This book was important for two reasons. With its efficacy and safety now demonstrated
    and training.                                   First, James Watt had invented a novel machine to by large numbers, the usage of nitrous oxide
                                                    produce “factitious airs” (i.e. nitrous oxide) and   rapidly became the preferred anesthetic method in
introduction
                                                    a novel “breathing apparatus” to inhale the gas.     dentistry. Because the gas is mild enough to keep
Sedation dentistry, sometimes called relaxation
dentistry, refers to the way dentists manage pain   Second, the book also presented the new medical a patient in a conscious and conversational state
and anxiety during dental appointments.             theories by Thomas Beddoes, that tuberculosis and but in most cases is strong enough to suppress
                                                    other lung diseases could be treated by inhalation the pain caused by dental work, it remains the
Conscious sedation is defined as a minimally        of factitious airs.                                  preferred agent in dentistry today.
depressed level of consciousness that retains                                                            In hospitals, however, nitrous oxide was found not
the patient’s ability to independently and          The machine to produce factitious airs was
                                                    comprised of three parts: a furnace to burn the      to be a strong enough for use in large operations.
continuously maintain an airway and respond                                                              A stronger and more potent anesthetic, sulfuric
appropriately to physical stimulation and verbal    needed material, a vessel with water where the
                                                    produced gas passed through in a spiral pipe (in     ether, was instead demonstrated and accepted for
command that is produced by pharmacological or                                                           use in October 1846, along with chloroform in
nonpharmacologic method or a combination of         order for impurities to be “washed off”), and
                                                                                                         1847. When Joseph Thomas Clover invented the
both. Nitrous oxide is only one of the 14 different finally the gas cylinder with a gasometer where
ways that sedation drugs can be administered.       the produced air could be tapped into portable air “gas-ether inhaler” in 1876, it became a common
                                                    bags (made of airtight oily silk). The breathing     practice at hospitals to initiate all anesthetic
There are three primary ways that sedation is                                                            treatments with a mild flow of nitrous oxide, and
administered in the dental office: IV sedation,     apparatus was one of the portable air bags
enteral conscious sedation and inhalation           connected with a tube to a mouthpiece. With this then gradually increase the anesthesia with the
conscious sedation or nitrous oxide.                new equipment engineered and produced already stronger ether/chloroform. Clover’s gas-ether
                                                    in 1794, the way was now paved for clinical          inhaler was designed to supply the patient with
                                                    trials, which began when Thomas Beddoes in           nitrous oxide and ether at the same time, with
                                                    1798 established the Pneumatic Institution for       the exact mixture controlled by the operator of
                                                    Relieving Diseases by Medical Airs in Clifton        the device. It remained in use by many hospitals
                                                    (Bristol). In the basement of the building, a large- until the 1930s. Although hospitals today are
                                                    scale machine was producing the gases under          using a more advanced anesthetic machine, these
                                                    the supervision of a young Humphry Davy, who         machines still use the same principle launched
                                                    was encouraged to experiment with new gases          with Clover’s gas-ether inhaler, to initiate
                                                    for patients to inhale. The first important work of the anesthesia with nitrous oxide before the
                          N2O                       Davy was to examine the nitrous oxide, with the administration of a more powerful anesthetic.
Inhalation conscious sedation or the use of nitrous    results being published in his book: “Researches,    Production
oxide, commonly known as laughing gas, is a            Chemical and Philosophical” (1800).              Nitrous oxide is most commonly prepared by
chemical compound with the formula N2O. It is       Despite the valuable finding made by Davy,          careful heating of ammonium nitrate, which
an oxide of nitrogen. At room temperature, it is    that inhalation of nitrous oxide could relieve a    decomposes into nitrous oxide and water vapor.
a colorless non-flammable gas with a pleasant,      conscious person from pain, another 44 years        The addition of various phosphates favors
slightly sweet odor and taste. It is used in surgerywould elapse before doctors attempted to use it for formation of a purer gas at slightly lower
and dentistry for its anesthetic and analgesic      anesthesia.                                         temperatures. One of the earliest commercial
effects. It is known as “laughing gas” because of                                                       producers was George Poe in Trenton, New
the euphoric effects of inhaling it, a property thatAnesthetic use                                      Jersey.
has led to its recreational use as a dissociative   At a “popular science” exhibition in Hartford,       NH4NO3 (s) → 2 H2O (g) + N2O (g)
hallucinogen. It is also used as an oxidizer in     Connecticut, where volunteers inhaled nitrous            Š This reaction occurs between 170-240
rocketry and in motor racing to increase the power  oxide, local dentist Horace Wells noted one of               degrees C, temperatures where ammonium
output of engine. At elevated temperatures, nitrous them, a man who had injured his leg, seemed                  nitrate is a moderately sensitive explosive
oxide is a powerful oxidizer similar to molecular   unaware of any pain from the injury. Thus                    and a very powerful oxidizer. Above 240
oxygen. For example, nitrous oxide in a test tube   was the born the first use of nitrous oxide as               degrees C, the exothermic reaction may
will re-ignite a smoldering splint.                 anesthetic drug. Wells himself, with assistance by           accelerate to the point of detonation, so
                                                    Gardner Quincy Colton and John Mankey Riggs,                 the mixture must be cooled to avoid such
Nitrous oxide reacts with ozone and is the main
                                                    demonstrated insensitivity to pain from a dental             a disaster. Superheated steam is used
naturally occurring regulator of stratospheric
                                                    extraction in December 1844. In the following                to reach reaction temperature in some
ozone. It is also a major greenhouse gas and air
                                                    weeks, Wells treated the first 12-15 patients with           turnkey production plants.
pollutant. Considered over a 100-year period, it
                                                    nitrous oxide in Hartford, and according to his
has 298 times more impact per unit weight than                                                          Downstream, the hot, corrosive mixture of gases
                                                    own record, only failed in two cases. In spite of
carbon dioxide.                                                                                         must be cooled to condense the steam and filtered
                                                    these convincing results reported by Wells to the
                                                                                                        to remove higher oxides of nitrogen. Ammonium
History                                             medical society in Boston in December 1844,
                                                                                                        nitrate smoke, as an extremely persistent colloid,
The gas was first synthesized by English chemist this new method was not immediately adopted
                                                                                                        will also have to be removed. The cleanup is often
and Unitarian minister Joseph Priestley in 1772,    by other dentists. This probably was because in
                                                                                                        done in a train of three gas washes, base, acid
who called it phlogisticated nitrous air. Priestley January 1845, Wells had been partly unsuccessful
                                                                                                        and base again. However, significant amounts of
published his discovery in the book “Experiments at his first public demonstration of the use of
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nitric oxide (NO) may not necessarily be absorbed      combination of nitrous oxide with hydroxyl-        in a reciprocating engine is that it can produce
directly by the base (sodium hydroxide) washes.        terminated polybutadiene fuel has been used by     enough power to damage or destroy the engine.
The nitric oxide impurity is sometimes chelated        SpaceShipOne and others. It is also notably used   Very large power increases are possible, and if the
out with ferrous sulfate, reduced with iron metal      in amateur and high power rocketry with various    mechanical structure of the engine is not properly
or oxidized and absorbed in base as a higher           plastics as the fuel.                              reinforced, the engine may be severely damaged
oxide. The first base wash may (or may not)                                                               or destroyed during this kind of operation. It is
                                                       Nitrous oxide can also be used in a
react out much of the ammonium nitrate smoke.                                                             very important with nitrous oxide augmentation
                                                       monopropellant rocket. In the presence of a heated
However, this reaction generates ammonia gas,                                                             of internal combustion engines to maintain proper
                                                       catalyst, N2O will decompose exothermically
which may have to be absorbed in the acid wash.                                                           operating temperatures and fuel levels to prevent
                                                       into nitrogen and oxygen, at a temperature of
                                                                                                          “pre-ignition” or “detonation” (sometimes referred
other routes                                           approximately 1,300 degrees C. Because of the
                                                                                                          to as “knocking” or “pinging”). Most problems
The direct oxidation of ammonia may someday            large heat release, the catalytic action rapidly
                                                                                                          that are associated with nitrous do not come from
rival the ammonium nitrate pyrolysis synthesis         becomes secondary as thermal autodecomposition
                                                                                                          mechanical failure due to the power increases.
of nitrous oxide mentioned above. This capital-        becomes dominant. In a vacuum thruster, this
                                                                                                          Since nitrous allows a much denser charge into
intensive process, which originates in Japan, uses     can provide a monopropellant specific impulse
                                                                                                          the cylinder, it dramatically increases cylinder
a manganese dioxide-bismuth oxide catalyst:            (Isp) of as much as 180s. While noticeably less
                                                                                                          pressures. The increased pressure and temperature
 2 NH3 + 2 O2 → N2O + 3 H2O                           than the Isp available from hydrazine thrusters
                                                                                                          can cause problems, such as melting the piston
    Š Higher oxides of nitrogen are formed as          (monopropellant or bipropellant with nitrogen
                                                                                                          or valves. It may also crack or warp the piston or
         impurities. In comparison, uncatalyzed        tetroxide), the decreased toxicity makes nitrous
                                                                                                          head and cause pre-ignition due to uneven heating.
         ammonia oxidation (i.e. combustion or         oxide an option worth investigating.
         explosion) goes primarily to N2 and H2O.      Specific impulse (Isp) can be improved by blending   Aerosol propellant
                                                       a hydrocarbon fuel with the nitrous oxide inside     The gas is approved for use as a food additive
Nitrous oxide can be made by heating a solution
                                                       the same storage tank, becoming a nitrous            (also known as E942), specifically as an aerosol
of sulfamic acid and nitric acid. Many gases are
                                                       oxide fuel blend (NOFB) monopropellant. This         spray propellant. Its most common uses in this
made this way in Bulgaria.
                                                       storage mixture does not incur the danger of         context are in aerosol whipped cream canisters,
 HNO3 + NH2SO3H → N2O + H2SO4 + H2O
                                                       spontaneous ignition because N2O is chemically       cooking sprays and as an inert gas used to displace
    Š There is no explosive hazard in this
                                                       stable. When the nitrous oxide decomposes by         oxygen and inhibit bacterial growth when filling
        reaction if the mixing rate is controlled.
                                                       a heated catalyst, high-temperature oxygen is        packages of potato chips and other similar snack
        However, as usual, toxic higher oxides of
                                                       released and rapidly ignites the hydrocarbon fuel    foods.
        nitrogen are formed.
                                                       blend. NOFB monopropellants are capable of           The gas is extremely soluble in fatty compounds.
Nitrous oxide is produced in large volumes as
                                                       Isp greater than 300 seconds, while avoiding the     In aerosol whipped cream, it is dissolved in
a byproduct in the synthesis of adipic acid, one
                                                       toxicity associated with hypergolic propulsion       the fatty cream until it leaves the can, when it
of the two reactants used in nylon manufacture.
                                                       systems. The low freezing point of NOFB eases        becomes gaseous and thus creates foam. Used in
This might become a major commercial source,
                                                       thermal management compared to hydrazine and         this way, it produces whipped cream four times
but will require the removal of higher oxides
                                                       dinitrogen tetroxide – a valuable property for       the volume of the liquid, whereas whipping air
of nitrogen and organic impurities. Currently,
                                                       space storable propellants.                          into cream only produces twice the volume. If
much of the gas is decomposed before release for
                                                                                                            air were used as a propellant, oxygen would
environmental protection. Greener processes may        internal combustion engine
                                                                                                            accelerate rancidification of the butterfat; nitrous
prevail that substitute hydrogen peroxide for nitric In vehicle racing, nitrous oxide (often referred
                                                                                                            oxide inhibits such degradation. Carbon dioxide
acid oxidation; hence no generation of oxide of      to as just “nitrous” or as NOS after the name of
                                                                                                            cannot be used for whipped cream because it is
nitrogen by-products.                                the brand Nitrous Oxide Systems) allows the
                                                                                                            acidic in water, which would curdle the cream and
                                                     engine to burn more fuel and air, resulting in
Hydroxylammonium chloride can react with                                                                    give it a seltzer-like “sparkling” sensation.
                                                     a more powerful combustion. The gas itself is
sodium nitrite to produce N2O as well:
                                                     not flammable, but it delivers more oxygen than        However, the whipped cream produced with
 NH3OH Cl + NaNO2 → N2O + NaCl + 2 H2O
              +   −
                                                     atmospheric air by breaking down at elevated           nitrous oxide is unstable and will return to a liquid
    Š If the nitrite is added to the hydroxylamine
                                                     temperatures.                                          state within half an hour to one hour. Thus, the
         solution, the only remaining byproduct is
                                                                                                            method is not suitable for decorating food that will
         salt water. However, if the hydroxylamine Nitrous oxide is stored as a compressed liquid;
                                                                                                            not be immediately served.
         solution is added to the nitrite solution   the evaporation and expansion of liquid nitrous
         (nitrite is in excess), then toxic higher   oxide in the intake manifold causes a large drop       Similarly, cooking spray, which is made from
         oxides of nitrogen are also formed.         in intake charge temperature, resulting in a denser    various types of oils combined with lecithin (an
                                                     charge, further allowing more air/fuel mixture         emulsifier), may use nitrous oxide as a propellant;
Applications                                         to enter the cylinder. Nitrous oxide is sometimes      other propellants used in cooking spray include
Rocket motors                                        injected into (or prior to) the intake manifold,       food-grade alcohol and propane.
Nitrous oxide can be used as an oxidizer in a        whereas other systems directly inject right before
rocket motor. This has the advantages over other the cylinder (direct port injection) to increase           Users of nitrous oxide for recreational use as a
oxidizers that it is non-toxic, and because of its                                                          euphoria-inducing inhalant drug, often obtain it
                                                     power.
stability at room temperature, easy to store and                                                            from whipped cream dispensers that use nitrous
relatively safe to carry on a flight. As a secondary The technique was used during World War II by          oxide as a propellant. It is not harmful in small
benefit, it can be readily decomposed to form        Luftwaffe aircraft with the GM-1 system to boost       doses, but risks due to lack of oxygen do exist (see
breathing air. Its high density and low storage      the power output of aircraft engines. Originally       Recreational use below).
pressure enable it to be highly competitive with     meant to provide the Luftwaffe standard aircraft
                                                     with superior high-altitude performance,
                                                                                                            Recreational use
stored high-pressure gas systems.                                                                           Nitrous oxide (N2O) is a dissociative drug that
                                                     technological considerations limited its use to
In a 1914 patent, American rocket pioneer Robert extremely high altitudes. Accordingly, it was              can cause analgesia, depersonalization, dizziness,
Goddard suggested nitrous oxide and gasoline as only used by specialized planes like high-altitude          euphoria and some sound distortion. Research
possible propellants for a liquid-fueled rocket.                                                            has also found that it increases suggestibility
                                                     reconnaissance aircraft, high-speed bombers and
Nitrous oxide has been the oxidizer of choice                                                               and imagination. Inhalation of nitrous oxide for
                                                     high-altitude interceptor aircraft.
in several hybrid rocket designs (using solid                                                               recreational use to cause euphoria and slight
fuel with a liquid or gaseous oxidizer). The         One of the major problems of using nitrous oxide       hallucinations began as a phenomenon for the
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British upper class in 1799 at “laughing gas           “marred by substance abuse, and in some cases,           patient without an assistant in the operatory, high
parties.” When equipment became more widely            criminal convictions.”                                   concentrations of nitrous oxide, and failure to
available for dentistry and hospitals, most                                                                     titrate the patient to avoid extension of therapeutic
                                                       The Herald Courier told the story of a Big Stone
countries also restricted the legal access to buy                                                               sedation.
                                                       Gap, Va., dentist who “huffed nitrous oxide in the
pure nitrous oxide gas cylinders to those sectors.
                                                       mid-1970s and quit only after a temporary loss           “Nitrous oxide should be employed with
A low availability of equipment to produce the gas
                                                       of feeling in his hands.” From there, the dentist        confidence. Employing simple guidelines will
combined with a low usage of the gas for medical
                                                       descended into alcoholism and took Valium and            ensure there are no difficulties with sexual issues
purposes meant recreational use was a relatively
                                                       Hydrocodone from his office, the newspaper said.         and the administrator of nitrous oxide,” they said.
rare phenomenon that mainly took place among
students at medical universities. That apparently      A grassroots drug-recovery group of Virginia             in medicine
continued into the 20th century. A poll taken in       dentists directed the man to a rehab program. The        Nitrous oxide has been used for anesthesia in
1979 indicated that between 1 and 2 percent of         state board of dentistry got an anonymous call           dentistry since December 1844, when Horace
medical and dental students used nitrous oxide         about his situation. Instead of disciplinary action,     Wells made the first dental operations with the
for recreational purposes, according to Theodore       the board helped monitor his recovery. According         gas in Hartford. Its debut as a generally accepted
J. Jastak in a 1991 article in the Journal of the      to the newspaper, keeping addictions confidential        method came in 1863, when Gardner Quincy
American Dental Association.                           is at the discretion of either a Department of           Colton introduced it more broadly at all the Colton
                                                       Health Professions investigator or a licensing           Dental Association clinics. The first devices
In the 1960 and ’70s, the recreational use of
                                                       board.                                                   used in dentistry to administer the gas, known as
inhalants became somewhat fashionable again,
                                                       A board of medicine official said the policy             nitrous oxide inhalers, were designed in a very
according to a Consumers Union report in
                                                       protected the public by “making sure the                 simple way, with the gas stored and breathed
1972 based on reports of use in Maryland and
                                                       individual is identified and investigated, set           through a breathing bag made of rubber cloth,
Vancouver and a survey at the University of
                                                       for an evaluation and treatment, and continue            without a scavenger system and flow meter, and
Michigan in 1970.
                                                       with monitoring. They (the Virginia monitoring           with no addition of oxygen/air.
According to the Michigan survey: “It was not
                                                       program) will not OK a doctor to go back into            Today these simple and somewhat unreliable
uncommon [in the interviews] to hear from
                                                       practice until he or she is believed to be safe.”        inhalers, of course, have been replaced by the
individuals who had been to parties where a
                                                       That is a common practice. The Federation of             more modern relative analgesia machine, which
professional (doctor, nurse, scientist, inhalation
                                                       State Physician Health Programs Inc. (FSPHP)             is an automated machine designed to deliver
therapist, researcher) had provided nitrous oxide.
                                                       evolved in 1990 from an initiative of the                a precisely dosed and breath-actuated flow of
There also were those who work in restaurants
                                                       American Medical Association and individual              nitrous oxide mixed with oxygen for the patient
who used the N2O stored in tanks for the
                                                       state physician health programs that focus upon          to inhale safely. The machine used in dentistry
preparation of whip cream. Reports were received
                                                       rehabilitation and monitoring of physicians with         is designed as a more simplified version of the
from individuals who used the gas contained in
                                                       psychoactive substance abuse disorders as well           larger anesthetic machine used by hospitals, and it
aerosol cans both of food and non-food products.
                                                       as mental and physical illness. The nonprofit            doesn’t feature the additional anesthetic vaporizer
At a rock festival, nitrous oxide was widely sold
                                                       organization includes members from 42 state              and medical ventilator. The machine allows for
for 25 cents a balloon. Contact was made with
                                                       programs.                                                a more simple design, because it only delivers
a ‘mystical-religious’ group that used the gas
                                                                                                                a mixture of nitrous oxide and oxygen for the
to accelerate arriving at their transcendental-        FSPHP serves as a resource for state programs;           patient to inhale to depress the feeling of pain
meditative state of choice. Although a few more        helps to establish monitoring standards; serves as       while keeping the patient in a conscious state.
sophisticated users employed nitrous oxide-            an informational source; advocates for physicians
oxygen mixes with elaborate equipment, most            and their health issues at local state and national      The relative analgesia machine typically features
users employed balloons or plastic bags. They          levels; and helps states in their quest to protect the   a constant-supply flow meter, which allows the
either held a breath of N2O or rebreathed the gas.     public. The organization promotes confidentiality        proportion of nitrous oxide and the combined gas
There were no adverse effects reported in the          for health care professionals who chose to address       flow rate to be individually adjusted. The gas is
more than 100 individuals surveyed.”                   their substance problems and submit to rigorous          administered by dentists through a demand-valve
                                                       monitoring of their progress.                            inhaler over the nose, which will only release
Although recreational use is believed to be
                                                                                                                gas when the patient inhales through the nose.
somewhat limited today, government data on         A 2003 report in the Journal of the California               Because nitrous oxide is minimally metabolized
substance abuse of youths shows that inhalants,    Dental Association [Malamed and Clark] cited                 in humans (with a rate of 0.004 percent), it
including nitrous oxide, are being used by young   concerns about abuse of nitrous oxide by health              retains its potency when exhaled into the room
people.                                            care professionals. The authors said nitrous                 by the patient and can pose an intoxicating and
The Substance Abuse and Mental Health Services oxide causes euphoria and can include “sexual                    prolonged exposure hazard to the clinic staff
Administration (SAMHSA) said in its 2007           phenomena,” including increased feelings of                  if the room is poorly ventilated. Where nitrous
report on trends in drug use that almost 1 million sexuality and arousal, and therefore has the                 oxide is administered, a continuous-flow fresh-air
youth had used inhalants within the past year. The potential for abuse. “This abuse is usually not              ventilation system or nitrous scavenger system is
percentage of young people aged 12-17 who had as addictive as some drugs, but nonetheless can                   used to prevent a waste-gas buildup.
used all inhalants within the past year was lower be a steppingstone to other drugs and can cause
                                                   incapacitation of the affected person. Nitrous               Hospitals are administering nitrous oxide as one
in 2007 (3.9 percent) than in 2003 (4.5 percent),
                                                   oxide should be given the same respect as all                of the anesthetic drugs delivered by anesthetic
in 2004 (4.6 percent), and in 2005 (4.5 percent).
                                                                                                                machines. Nitrous oxide is a weak general
Among first-time users, the rate of use of nitrous drugs.”
                                                                                                                anesthetic, and so is generally not used alone
oxide, or “whippets” – usually canisters of the    The typical abuser of nitrous oxide is older and             in general anesthesia. In general anesthesia it is
propellants to create whipped cream – declined     middle- or upper class, they said. If the abuser has         used as a carrier gas in a 2:1 ratio with oxygen
between 2002 and 2007 among males (40.2            an inhalation sedation unit available, it may have           for more powerful general anesthetic, drugs
percent to 20.2 percent) and females (22.3 percent been altered to deliver a higher concentrate of gas,
                                                                                                                such as sevoflurane or desflurane. It has a MAC
to 21.2 percent).                                  they said.                                                   (minimum alveolar concentration) of 105 percent
However, an investigation in 2009 by the Bristol       The authors noted there have been reports of             and a blood gas partition coefficient of 0.46.
(Va.) Herald Courier reported that the records of      sexual abuse of patients under anesthetics,          When nitrous oxide is inhaled as the only
46 health care professionals in the area – including   including nitrous oxide. They noted there are three anesthetic drug, it is normally administered as
doctors, nurses, pharmacists and dentists – were       elements that put a practitioner at risk: treating a
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a mixture with 30 percent gas and 70 percent        Euphoric effect                                        parts with fuels have been implicated in rocketry
oxygen.                                             In rats, N2O stimulates the mesolimbic reward          accidents, where small quantities of nitrous/fuel
                                                    pathway via inducing dopamine release and              mixtures explode due to “water hammer-like”
neuropharmacology                                                                                          effects (sometimes called “dieseling” – heating
                                                    activating dopaminergic neurons in the ventral
The pharmacological mechanism of action of N2O
                                                    tegmental area and nucleus accumbens,                  caused by adiabatic compression of gases that
in medicine is not fully known. However, it has
                                                    presumably through antagonization of NMDA              can reach decomposition temperatures). Some
been shown to directly modulate a broad range of
                                                    receptors localized in the system. This action         common building materials, such as stainless
ligand-gated ion channels, and this likely plays
                                                    has been implicated in its euphoric effects,           steel and aluminum, can act as fuels with
a major role in many of its effects. It moderately
                                                    and notably, appears to augment its analgesic          strong oxidizers such as nitrous oxide, as can
blocks NMDA and β2-subunit-containing nACh
                                                    properties as well.                                    contaminants, which can ignite due to adiabatic
channels; weakly inhibits AMPA, kainate, GABAC
                                                                                                           compression.
and 5-HT3 receptors; and slightly potentiates       However, it is remarkable that in mice, N2O
GABAA and glycine receptors. It has also been       blocks amphetamine-induced and dopamine                There have also been accidents where nitrous
shown to activate two-pore-domain K+ channels. release in the nucleus accumbens and behavioral             oxide decomposition in plumbing has led to the
While N2O affects quite a few ion channels,         sensitization, abolishes the conditioned place         explosion of large tanks.
its anesthetic, hallucinogenic and euphoriant       preference (CPP) of cocaine and morphine, and
                                                                                                           Biological
effects are likely caused predominantly or fully    does not produce reinforcing (or aversive) effects
                                                                                                           Nitrous oxide inactivates the cobalamin form of
via inhibition of NMDAR-mediated currents. In       of its own. Studies on CPP of N2O in rats is
                                                    mixed, consisting of reinforcement, aversion and       vitamin B12 by oxidation. Symptoms of vitamin
addition to its effects on ion channels, N2O may
act to imitate nitric oxide (NO) in the central     no change. In contrast, it is a positive reinforcer    B12 deficiency, including sensory neuropathy
nervous system as well, and this may relate to its in squirrel monkeys, and is well known as a                              and encephalopathy, can occur
analgesic and anxiolytic properties.                drug of abuse in humans. These discrepancies                            within days or weeks of exposure
                                                    in response to N2O may reflect specie variations                        to nitrous oxide anesthesia in
Anxiolytic effect                                   or methodological differences. It is noteworthy                         people with subclinical vitamin
In behavioral tests of anxiety, a low dose of N2O that in human clinical studies, N O was found                             B12 deficiency. Symptoms are
                                                                                      2
is an effective anxiolytic, and this anti-anxiety   to produce mixed responses similarly to rats,                           treated with high doses of vitamin
effect is associated with enhanced activity of      reflecting high subjective individual variability.                      B12, but recovery can be slow and
GABAA receptors as it is partially reversed by                                                                              incomplete. People with normal
benzodiazepine receptor antagonists. Mirroring      neurotoxicity
                                                                                                                            vitamin B12 levels have stores to
this, animals that have developed tolerance to the Similarly to other NMDA antagonists like
                                                                                                                            make the effects of nitrous oxide
anxiolytic effects of benzodiazepines are partially ketamine, N2O has been demonstrated to
                                                                                                                            insignificant, unless exposure is
tolerant to N2O. Indeed, in humans given 30         produce neurotoxicity in the form of Olney’s
                                                                                                                            repeated and prolonged (nitrous
percent N2O, benzodiazepine receptor antagonists lesions (damage to the posterior cingulate and
                                                                                                                            oxide abuse). Vitamin B12 levels
reduced the subjective reports of feeling “high,”   retrosplenial cortices) in rodents upon prolonged
                                                                                                                            should be checked in people with
but did not alter psychomotor performance in        (e.g., several hours) exposure. However, it also
                                                    simultaneously exerts widespread neuroprotective                        risk factors for vitamin B12
human clinical studies.
                                                    effects via inhibiting glutamate-induced and it        deficiency prior to using nitrous oxide anesthesia.
Analgesic and anti-nociceptive effect               has been argued that on account of its very short      A study of workers and several experimental
The analgesic effects of N2O are linked to the      duration under normal circumstances, N2O may           animal studies indicate that adverse reproductive
interaction between the endogenous opioid           not share the neurotoxicity of other NMDA              effects for pregnant females may also result from
system and the descending noradrenergic system. antagonists. Indeed, in rodents, short-term
                                                                                                           chronic exposure to nitrous oxide.
When animals are given morphine chronically,        exposure results in only mild injury that is rapidly
they develop tolerance to its pain-killing effects, reversible, and permanent neuronal death only          Flammability
and this also renders the animals tolerant to       occurs after constant and sustained exposure.          Nitrous oxide is a non-flammable gas at room
the analgesic effects of N2O. Administration of                                                            temperature.
antibodies that bind and block the activity of      safety
                                                                                                           The National Fire Protection Association has not
some endogenous opioids (not β-endorphin) also The major safety hazards of nitrous oxide come
                                                                                                           assigned a flammability rating to nitrous oxide:
block the anti-nociceptive effects of N2O. Drugs    from the fact that it is a compressed liquefied gas,
                                                                                                            Flash point: Not applicable.
that inhibit the breakdown of endogenous opioids an asphyxiation risk and a dissociative anesthetic.
                                                                                                            Autoignition temperature: Not applicable.
also potentiate the anti-nociceptive effects of     Exposure to nitrous oxide causes short-term
                                                                                                            Flammable limits in air: Not applicable.
N2O. Several experiments have shown that opioid decreases in mental performance, audiovisual
                                                                                                            Extinguishant: For small fires, use dry
receptor antagonists applied directly to the brain  ability and manual dexterity. Long-term exposure
                                                                                                               chemical or carbon dioxide. Use water spray,
block the anti-nociceptive effects of N2O, but      can cause vitamin B12 deficiency, numbness,
                                                                                                               fog or standard foam to fight large fires
these drugs have no effect when injected into the reproductive side effects and other problems.
                                                                                                               involving nitrous oxide.
spinal cord.
                                                    The National Institute for Occupational Safety
                                                                                                           Fires involving nitrous oxide should be fought
Conversely, α2-adrenoceptor antagonists block       and Health recommends that workers’ exposure
                                                                                                           upwind from the maximum distance possible.
the anti-nociceptive effects of N2O when given      to nitrous oxide should be controlled during the
                                                                                                           Keep unnecessary people away; isolate the hazard
directly to the spinal cord, but not when applied   administration of anesthetic gas in medical, dental
                                                                                                           area and deny entry. Isolate the area for ½-mile
directly to the brain. Indeed, α2B-adrenoceptor     and veterinary operators.
                                                                                                           in all directions if a tank, rail car or tank truck is
knockout mice or animals depleted in
                                                                                                           involved in the fire. For a massive fire in a cargo
norepinephrine are nearly completely resistant to Chemical/physical
                                                                                                           area, use unmanned hose holders or monitor
the anti-nociceptive effects of N2O. It seems N2O- At room temperature (20 degrees C), the saturated
                                                    vapor pressure is 58.5 bar, rising up to 72.45         nozzles; if this is impossible, withdraw from the
induced release of endogenous opioids causes
                                                                                                           area and let the fire burn. Emergency personnel
disinhibition of brain stem noradrenergic neurons, bar at 36.4 degrees C – the critical temperature.
                                                                                                           should stay out of low areas and ventilate closed
which release norepinephrine into the spinal cord The pressure curve is thus unusually sensitive to
                                                    temperature. Liquid nitrous oxide acts as a good       spaces before entering. Vapors are an explosion
and inhibit pain signaling. Exactly how N2O
                                                                                                           hazard indoors, outdoors or in sewers. Containers
causes the release of endogenous opioid peptides solvent for many organic compounds; liquid
                                                    mixtures may form shock-sensitive explosives.          of nitrous oxide may explode in the heat of the
is still uncertain.
                                                                                                           fire and should be moved from the fire area if it is
                                                    As with many strong oxidizers, contamination of        possible to do so safely. If this is not possible, cool
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fire-exposed containers from the sides with water   gas cylinder rules (1985) permit the transfer of       epidemiologic studies, no dose-effect relationship
until well after the fire is out. Stay away from    gas from one cylinder to another for breathing         could be established.
the ends of containers. Firefighters should wear a  purposes. This law benefits remote hospitals,          Exposure to high concentrations of waste
full set of protective clothing and self-contained  which would otherwise suffer because of                anesthetic gases – even for a short time – may
breathing apparatus when fighting fires involving   India’s geographic immensity. Nitrous oxide            cause the following health effects:
nitrous oxide.                                      IP is transferred from bulk cylinders (17,000           Headache.
                                                    liters capacity gas) to smaller pin-indexed valve       Irritability.
Environmental                                       cylinders (1,800 liters of gas), which are then
Nitrous oxide is a greenhouse gas, accounting for                                                           Fatigue.
                                                    connected to the yoke assembly of Boyle’s               Nausea.
about 6 percent of the heating effect of greenhouse
                                                    machines. Because India’s Food and Drug                 Drowsiness.
gases in the atmosphere. According to 2006 data
                                                    Authority (FDA-India) rules state that transferring     Difficulties with judgment and coordination.
from the United States Environmental Protection
                                                    a drug from one container to another (refilling) is     Liver and kidney disease.
Agency, industrial sources make up only about 20
                                                    equivalent to manufacturing, anyone found doing
percent of all anthropogenic sources, and include                                                          Workers exposed
                                                    so must possess a drug-manufacturing license.
the production of nylon and the burning of fossil                                                          In 1983, the American Dental Association (ADA)
fuel in internal combustion engines. Human          nitrous oxide in dental operatories                    reported that 35 percent of all dentists used N2O
activity is thought to account for 30 percent;      The Engineering Control Technology Branch              to control pain and anxiety in their patients [ADA
tropical soils and oceanic release account for 70   (ECTB) of the Division of Physical Sciences and        1983]. The ADA 1991 Survey of Dental Practice
percent. However, a 2008 study by Nobel Laureate Engineering studies the aspects of health hazard          indicated that 58 percent of dentists reported
Paul Crutzen suggests that the amount of nitrous prevention and control in the workplace. Nitrous          having N2O anesthetic equipment, and 64 percent
oxide release attributable to agricultural nitrate  oxide (N2O) mixed with oxygen has been used            of those practitioners also reported having a
fertilizers has been seriously underestimated,      in dentistry as an analgesic and as a sedative for     scavenging system. The percentage of pediatric
most of which would presumably come under           more than 100 years. Today, more than 424,000          dentists using N2O increased from 65 percent in
soil and oceanic release in the Environmental       workers who practice dentistry (such as dentists,      1980 to 88 percent in 1988.
Protection Agency data. Nitrous oxide also causes dental assistants and dental hygienists) in the
ozone depletion. A recent study suggests that N2O United States are potentially exposed to N2O.            occupational exposure limits
emission currently is the single most important                                                            The Occupational Safety and Health
                                                    In a technical report published in 1977, the           Administration (OSHA) does not currently have a
ozone-depleting substance (ODS) emission and is National Institute for Occupational Safety and
expected to remain the largest throughout the 21st Health recommended controlling exposure limits          standard for N2O.
century.                                            of nitrous oxide waste to 25 parts per million parts The NIOSH recommended exposure
                                                      (ppm) of air during dental surgery. The report     limit (REL) for N2O is 25 ppm as a time-
Legality                                                                                                 weighted average (TWA) during the period
In the United States, possession of nitrous oxide is presented methods for limiting the waste during
                                                                                                         of anesthetic administration [NIOSH 1977b].
legal under federal law and is not subject to DEA administration, based on the technical feasibility
                                                      of existing controls. Since publication of this    This REL is intended to prevent decreases in
purview. It is, however, regulated by the Food
                                                      technical report, data collected by NIOSH have     mental performance, audiovisual ability and
and Drug Administration under the Food Drug
and Cosmetics Act; prosecution is possible under      shown occupational exposures as high as 300 ppm manual dexterity during exposures to N2O. A
                                                                                                         recommended exposure limit to prevent adverse
its “misbranding” clauses, prohibiting the sale or in hospital operating rooms and exposures higher
                                                      than 1,000 ppm in dental operatories equipped      reproductive effects cannot be established until
distribution of nitrous oxide for the purpose of
                                                      with scavenging systems (properly operating        more data are available.
human consumption.
                                                      scavenging systems have been shown to reduce       The American Conference of Governmental
Many states have laws regulating the possession, N O concentrations by more than 70 percent). The Industrial Hygienists’ (ACGIH) threshold limit
                                                        2
sale and distribution of nitrous oxide. Such laws     scavenging systems use local exhaust ventilation value (TLV) for N2O is 50 ppm as an eight-hour
usually ban distribution to minors or limit the       to collect waste gases from anesthetic breathing   time-weighted average [ACGIH 1993]. The 1991
amount of nitrous oxide that may be sold without systems and remove them from the workplace.             Documentation of the Threshold Limit Values and
special license.                                                                                         Biological Exposure Indices states that “control
                                                      Effects of exposure to high concentrations to this level should prevent embryo-fetal toxicity
In the state of California, possession for
                                                      Animal studies have shown adverse reproductive
recreational use is prohibited and qualifies as a                                                        in humans and significant decrements in human
                                                      effects in female rats exposed to airborne
misdemeanor.                                                                                             psychomotor and cognitive functions or other
                                                      concentrations of N2O. Data from these studies
                                                                                                         adverse health effects in exposed personnel”
In some countries, it is illegal to have nitrous      indicate that exposure to N2O during gestation can
                                                                                                         [ACGIH 1991].
oxide systems plumbed into an engine’s intake         produce adverse health effects in the offspring.
manifold. These laws are ostensibly used to                                                              Medical surveillance
                                                      Several studies of workers have shown that
prevent street racing and to meet emission                                                               OSHA is currently developing requirements for
                                                      occupational exposure to N2O causes adverse
standards. Nitrous oxide is entirely legal to possess                                                    medical surveillance. When these requirements
                                                      effects such as reduced fertility, spontaneous
and inhale in the United Kingdom, although                                                               are promulgated, readers should refer to them for
                                                      abortions and neurologic, renal and liver disease.
supplying it to others to inhale, especially minors,                                                     additional information and to determine whether
                                                      A recent study reported that female dental
is more likely to end up with a prosecution under                                                        employers whose employees are exposed to
                                                      assistants exposed to unscavenged N2O for five
the Medicines Act.                                                                                       nitrous oxide are required to implement medical
                                                      or more hours per week had a significant risk of
                                                                                                         surveillance procedures.
In New Zealand, the Ministry of Health has            reduced fertility compared with unexposed female
warned that nitrous oxide is a prescription           dental assistants. The exposed assistants had a    Medical screening
medicine, and its sale or possession without a        59 percent decrease in probability of conception   Workers who may be exposed to chemical
prescription is an offense under the Medicines        for any given menstrual cycle compared with        hazards should be monitored in a systematic
Act. This statement would seemingly prohibit all the unexposed assistants. For dental assistants         program of medical surveillance that is intended
non-medicinal uses of the chemical, though it is      who used scavenging systems during N2O             to prevent occupational injury and disease. The
implied that only recreational use will be legally administration, the probability of conception         program should include education of employers
targeted.                                             was not significantly different from that of the   and workers about work-related hazards, early
                                                      unexposed assistants. Because environmental        detection of adverse health effects and referral
In India, for general anesthesia purposes, nitrous
                                                      exposures were not measured during these           of workers for diagnosis and treatment. The
oxide is available as nitrous oxide IP. India’s
Elite CME - www.EliteCME.com                                                                                                                           Page 5
occurrence of disease or other work-related          to determine the worker’s medical status at the      Use the guidelines in the following section to
adverse health effects should prompt immediate       end of his or her employment. Any changes in the       minimize worker exposures to N2O.
evaluation of primary preventive measures (e.g.,     worker’s health status should be compared with
                                                                                                         Guidelines for minimizing worker
industrial hygiene monitoring, engineering           those expected for a suitable reference population.
controls, and personal protective equipment).                                                            exposures
                                                     Biological monitoring                               Exposure monitoring
A medical surveillance program is intended to
                                                     Biological monitoring involves sampling and        Exposure monitoring should be the first step in
supplement, not replace, such measures. To detect
                                                     analyzing body tissues or fluids to provide        developing work practices and worker education
and control work-related health effects, medical
                                                     an index of exposure to a toxic substance or       programs, because measurements of N2O are
evaluations should be performed (1) before job
                                                     metabolite. No biological monitoring test          needed to determine the type and extent of
placement, (2) periodically during the term of
                                                     acceptable for routine use has yet been developed  controls that are necessary. Follow the guidelines
employment, and (3) at the time of job transfer or
                                                     for nitrous oxide.                                 below to minimize worker exposures:
termination.
                                                     Workplace monitoring and measurement                Monitor for N2O when the anesthetic
Preplacement medical evaluation                                                                             equipment is installed and every three months
                                                     Determination of a worker’s exposure to airborne
Before a worker is placed in a job with a potential                                                         thereafter. Include the following types of
                                                     nitrous oxide can be made using one of the
for exposure to nitrous oxide, a licensed health                                                            monitoring:
                                                     following techniques:
care professional should evaluate and document                                                              Š Leak testing of equipment.
                                                      A Landauer Passive Dosimeter badge, which
the worker’s baseline health status with thorough                                                           Š Monitoring of air in the worker’s personal
                                                          can be used for a minimum sampling duration
medical, environmental and occupational                                                                          breathing zone.
                                                          of one hour (maximum duration 40 hours).
histories, a physical examination, and physiologic                                                          Š Environmental (room air) monitoring.
                                                          Analysis is performed by the manufacturer
and laboratory tests appropriate for the anticipated                                                     Prepare a written monitoring and maintenance
                                                          of the badge as described in the OSHA
occupational risks. These should concentrate                                                                plan for each facility that uses N2O . This
                                                          Computerized Information System.
on the function and integrity of the respiratory,                                                           plan should be developed by knowledgeable
                                                      An ambient air or bag sample with a minimum
reproductive, central nervous and hematological                                                             persons who consider the equipment
                                                          collection volume of two spectrophotometer
systems. Medical surveillance for respiratory                                                               manufacturers’ recommendations, frequency
                                                          cell volumes. Analysis is conducted
disease should be conducted using the principles                                                            of use and other circumstances that might
                                                          using a long-path-length portable infrared
and methods recommended by the American                                                                     affect the equipment.
                                                          spectrophotometer as described in NIOSH
Thoracic Society. A preplacement medical                                                                 Perform air monitoring by gasbag sampling or
                                                          Method No. 6600.
evaluation is recommended to assess medical                                                                 real-time sampling.
conditions that may be aggravated or may result      Personal hygiene procedures                         When real-time sampling is conducted to
in increased risk when a worker is exposed to        If liquid nitrous oxide contacts the skin, workers     obtain personal exposure data, attach the
nitrous oxide at or below the prescribed exposure should flush the affected areas immediately with          sampling train to the lapel of the worker
limit. The health care professional should consider tepid water to reduce the likelihood of frostbite.      on the side closest to the patient; N2O
the probable frequency, intensity and duration of                                                           concentrations in this location are most
                                                     A large population of health care workers
exposure as well as the nature and degree of any                                                            representative of those in the worker’s
                                                     is potentially exposed to N2O, and NIOSH
applicable medical condition. Such conditions                                                               breathing zone. Diffusive samplers (referred
                                                     has documented cases in which exposures
(which should not be regarded as absolute                                                                   to as passive dosimeters) are commercially
                                                     substantially exceed existing recommended
contraindications to job placement) include a                                                               available and may be useful as initial
                                                     exposure limits. NIOSH has concluded that
history and other findings consistent with diseases                                                         indicators of exposures.
                                                     exposure to N2O causes decreases in mental
of the respiratory, reproductive, central nervous or
                                                     performance, audiovisual ability and manual        Engineering controls and maintenance
hematological systems.
                                                     dexterity. Data from animal studies demonstrate    procedures
Periodic medical evaluations                         that exposure to N2O may cause adverse             The following engineering controls and
Occupational health interviews and physical          reproductive effects. Studies of workers exposed maintenance procedures have been shown to be
examinations should be performed at regular          to N2O have reported adverse health effects        feasible and effective in reducing exposure to N2O
intervals during the employment period, as           such as reduced fertility, spontaneous abortion,   during anesthetic administration.
mandated by any applicable federal, state or local and neurological, renal, and liver disease. The
standard. Where no standard exists and the hazard recommendations in a 1994 NIOSH alert should          Anesthetic delivery. Excessive exposure to N2O
is minimal, evaluations should be conducted          therefore be followed to minimize worker           may occur as a result of leaks from the anesthetic
every three to five years or as frequently as        exposures.                                         delivery system during administration. The
recommended by an experienced occupational                                                              rubber and plastic components of the anesthetic
                                                     Recommendations                                    equipment are potential sources of N2O leakage
health physician. Additional examinations may
                                                     Engineering controls, work practices and           because they may be degraded by the N2O and the
be necessary if a worker develops symptoms
                                                     respirators (when necessary) should be used        oxygen as well as by repeated sterilization.
attributable to nitrous oxide exposure. The
                                                     to minimize the exposure of workers to N2O.
interviews, examinations and medical screening                                                          Take the following steps to control N2O exposure
                                                     Employers should ensure that their workers are
tests should focus on identifying the adverse
                                                     adequately protected from N2O exposure by taking from anesthetic delivery systems:
effects of nitrous oxide on the respiratory,                                                             Use connection ports with different-diameter
                                                     the following steps:
reproductive, central nervous or hematological                                                              hoses for N2O and O2 to reduce the possibility
                                                      Monitor airborne concentrations of N2O.
systems. Current health status should be compared                                                           of incorrectly connecting the gas delivery and
                                                      Implement appropriate engineering controls,
with the baseline health status of the individual                                                           scavenging hoses.
                                                          work practices and maintenance procedures.
worker or with expected values for a suitable                                                            Check all rubber hoses, connections, tubing
                                                      Institute a worker education program that:
reference population.                                                                                       and breathing bags daily and replace them
                                                          Š Describes standard operating procedures
Termination medical evaluations                                for all tasks that may expose workers to     when damaged or when recommended by the
The medical, environmental and occupational                    N2O.                                         manufacturer.
history interviews; the physical examination; and         Š Informs workers about proper work            Following visual inspection, perform leak
selected physiologic or laboratory tests that were             practices, controls, equipment and           testing of the equipment and connections by
conducted at the time of placement should be                   protective gear that should be used when     using a soap solution to check for bubbles
repeated at the time of job transfer or termination            working with N2O.                            at high-pressure connections. For a more
                                                                                                            thorough inspection of all connectors, use a
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    portable infrared spectrophotometer (such as a          manufacturer’s recommendations.                        system.
    Miran 1A or 1B) calibrated for N2O detection.          Use scavenging vacuum pumps that are                  Encourage patients to minimize talking
   Check both high- and low-pressure                       powerful enough to maintain a scavenging               and mouth-breathing during dental surgery.
    connections (such as O-rings) regularly,                flow rate of at least 45 L/min at each nasal           When mouth-breathing is apparent, avoid the
    as they may become worn; replace them                   mask, regardless of the number of scavenging           patient’s breathing zone to the extent possible.
    periodically, according to the manufacturer’s           units in use at one time.
                                                                                                               Respiratory protection
    recommendations.                                       Vent N2O from all scavenging vacuum pumps
                                                                                                               Workers should wear respiratory protection when
   Evaluate the N2O and oxygen mixing                      to the outside of the building away from fresh
                                                                                                               N2O concentrations are not consistently below
    system for leaks when it is first installed             air intakes, windows or walkways. Scavenging
                                                                                                               25 ppm; however, practical considerations may
    and periodically thereafter, according to the           system exhaust should not be vented into a
                                                                                                               prevent them from wearing such protection.
    manufacturer’s recommendations.                         recirculating ventilation system.
                                                                                                               Therefore, it is essential that employers use
   Ensure that gas cylinders are safely handled,
                                                        Room ventilation. Take the following steps to          the engineering controls and work practices
    used and stored as specified by the National
                                                        assure that the ventilation system effectively         described in a 1994 NIOSH alert to reduce N2O
    Research Council and as required by OSHA
                                                        removes waste N2O:                                     concentrations below 25 ppm.
    Federal Code Rule Title 29, 1910.101.
                                                         If concentrations of N2O are above 25 ppm in When N2O concentrations are not consistently
    Š Sec. 1910.101 Compressed gases (general
                                                            work areas, increase the airflow into the room
                                                                                                       below 25 ppm, workers should take the following
        requirements).
                                                            or increase the percentage of outside air to
                                                                                                       steps to protect themselves:
    Š (a) Inspection of compressed gas
                                                            allow for more air mixing and further dilution
                                                                                                        Wear air-supplied respirators. Air-purifying
        cylinders. Each employer shall determine
                                                            of the anesthetic gas. Maintain a balanced air respirators (that is, respirators that remove
        that compressed gas cylinders under his
                                                            supply and exhaust system so that N2O does     N2O from the air rather than supply air from
        control are in a safe condition to the extent
                                                            not contaminate adjacent areas.                a clean source) should not be used because
        that this can be determined by visual
                                                         If concentrations of N2O are still above 25      respirator filters do not efficiently remove
        inspection. Visual and other inspections
                                                            ppm, use supplementary local ventilation       N2O.
        shall be conducted as prescribed in the
                                                            in conjunction with a scavenging system to  As specified by the NIOSH respirator
        Hazardous Materials Regulations of
                                                            reduce N2O exposure in the operatory. The      standards, the minimum level of protection
        the Department of Transportation (49
                                                            effectiveness of this ventilation depends on   for an air-supplied respirator is provided by a
        CFR parts 171-179 and 14 CFR part
                                                            its location with respect to the patient and the
                                                                                                           half-mask respirator operated in the demand
        103). Where those regulations are not
                                                            airflow rates. Do not work between the patient or continuous-flow mode. More protective
        applicable, visual and other inspections
                                                            and the exhaust duct, where contaminated       air-supplied respirators are described in the
        shall be conducted in accordance with
                                                            air would be drawn through the worker’s        NIOSH respirator decision logic.
        Compressed Gas Association Pamphlets
                                                            breathing zone.                             When respirators are used, the employer
        C-6-1968 and C-8-1962, which is
                                                         Dilute N2O and remove contaminated air           must establish a comprehensive respiratory
        incorporated by reference as specified in
                                                            from the work area by placing fresh-air vents  protection program as outlined in the NIOSH
        Sec. 1910.6.
                                                            in the ceiling; direct the supply of fresh air Guide to Industrial Respiratory Protection
Scavenging systems. Control of N2O at the                   toward the floor and the operating area. Place [NIOSH 1987a] and as required by the OSHA
scavenging mask is the next priority after control          exhaust-air vents at or near the floor.        respiratory protection standard [29 CFR
of N2O leakage from the anesthetic equipment.                                                              1910.134]. Important elements of this standard
Leakage from the scavenging mask can be one
                                                     Work practices
                                                     Use the following work practices to control N2O       are:
of the most significant sources of N2O exposure                                                            Š An evaluation of the worker’s ability
                                                     exposures:
because the breathing zone of a dentist or                                                                      to perform the work while wearing a
                                                      Inspect the anesthetic delivery systems and
dental assistant is within inches of the mask.                                                                  respirator.
                                                        all connections before starting anesthetic gas
NIOSH research has reported breathing-zone                                                                 Š Regular training of personnel.
                                                        administration. Make sure that breathing bags,
concentrations of N2O above 1,000 ppm.                                                                     Š Periodic environmental monitoring.
                                                        hoses and clamps are in place before turning
Take the following steps to control N2O exposure        on the anesthetic machine.                         Š Respirator fit testing.
from anesthetic scavenging systems:                   Connect the scavenging mask properly to the         Š Maintenance, inspection, cleaning and
 Supply scavenging masks in a variety of sizes         gas delivery hose and the vacuum system.                storage.
    so that the mask always fits comfortably and  Do not turn on the machine delivering N2O               Š Selection of proper NIOSH-approved
    securely over the patient’s nose or face.           until:                                                  respirators.
 Use an automatic interlock system to assure           Š The vacuum system scavenging unit is          The respiratory protection program should be
    that the N2O cannot be turned on unless the              operating at the recommended flow rate of     evaluated regularly by the employer.
    scavenging system is also activated. N2O                 45 L/min.                                 signs and symptoms of exposure
    should never be used without a properly             Š The scavenging mask is secured over the  Acute exposure: The signs and symptoms
    operating scavenging system.                             patient’s nose or face.                       of acute exposure to nitrous oxide include
 Make sure that the scavenging system exhaust  Fasten the mask according to the                          dizziness, difficult breathing, headache,
    rates (flow rates) are approximately 45 liters      manufacturer’s instructions to prevent leaks       nausea, fatigue and irritability. Acute exposure
    per minute (L/min) to minimize leakage of           around the mask during gas delivery.               to nitrous oxide concentrations of 400,000 to
    N2O. Flow rates of less than 40 L/min may         Do not fill the breathing bag to capacity with      800,000 ppm may cause loss of consciousness.
    result in significant leakage around the mask.      N2O; an overinflated bag can cause excessive  Chronic exposure: The signs or symptoms
    Monitor the flow rate with a flow meter that is:    leakage from the scavenging mask. The              of chronic overexposure to nitrous oxide
    Š Validated to measure airflow within 5             breathing bag should collapse and expand as        may include tingling, numbness, difficulty
        percent of actual airflow.                      the patient breaths. This bag activity shows       in concentrating, interference with gait, and
    Š Permanently connected to the scavenging           that the proper amounts of N2O and air are         reproductive effects.
        system vacuum line.                             being delivered to the patient.
    Š Positioned so that it is always visible to      Flush the system of N2O after surgery by        storage
        the operator.                                   administering oxygen to the patient through    Nitrous oxide should be stored in a cool, dry, well-
 Maintain the flow meter by cleaning                   the anesthetic equipment for at least five     ventilated area in tightly sealed containers that
    and recalibrating it according to the               minutes before disconnecting the gas delivery are labeled in accordance with OSHA’s Hazard
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Communication Standard [29 Code of Federal          RCRA, EPA requires employers to treat waste as        personal protective equipment (PPE) (e.g., gloves,
Regulations (CFR)1910.1200]. Containers of          hazardous if it exhibits any of the characteristics   sleeves, encapsulating suits) should be based on
nitrous oxide should be protected from physical     discussed above. Providing detailed information       the extent of the worker’s potential exposure to
damage and should be stored separately from         about the removal and disposal of specific            liquid nitrous oxide and the PPE material’s ability
cylinders containing oxygen. Nitrous oxide          chemicals is beyond the scope of this guideline.      to protect workers from frostbite. There are no
should also be stored separately from aluminum,     The U.S. Department of Transportation, EPA, and       published reports on the resistance of various
boron, hydrazine, lithium hydride, phenyllithium,   state and local regulations should be followed        materials to permeation by liquid nitrous oxide.
phosphine, sodium, tungsten carbide, hydrogen,      to ensure that removal, transport and disposal
                                                                                                          To evaluate the use of PPE materials with liquid
hydrogen sulfide, organic peroxides, ammonia and    of this substance are conducted in accordance
                                                                                                          nitrous oxide, users should consult the best
carbon monoxide.                                    with existing regulations. To be certain that
                                                                                                          available performance data and manufacturers’
                                                    chemical waste disposal meets EPA regulatory
spills and leaks                                                                                          recommendations. Significant differences have
                                                    requirements, employers should address any
In the event of a spill or leak involving nitrous                                                         been demonstrated in the chemical resistance of
                                                    questions to the RCRA hotline at (703) 412-9810
oxide (liquid or gas), persons not wearing                                                                generically similar PPE materials (e.g., butyl)
                                                    (in the Washington, D.C. area) or toll-free at 800-
protective equipment and clothing should be                                                               produced by different manufacturers. In addition,
                                                    424-9346 (outside Washington, D.C.). In addition,
restricted from contaminated areas until cleanup                                                          the chemical resistance of a mixture may be
                                                    relevant state and local authorities should be
has been completed. The following steps should                                                            significantly different from that of any of its neat
                                                    contacted for information on any requirements
be undertaken following a spill or leak:                                                                  components.
                                                    they may have for the waste removal and disposal
 Do not touch the spilled material; stop the leak
                                                    of this substance.                                    Any chemical-resistant clothing that is used
    if it is possible to do so without risk.
                                                                                                          should be periodically evaluated to determine its
 Use water spray to protect persons attempting Respiratory protection
                                                                                                          effectiveness in preventing dermal contact. Safety
    to stop the leak.                               Conditions for respirator use                         showers and eye wash stations should be located
 Notify safety personnel of large spills or leaks. Good industrial hygiene practice requires that
                                                                                                          close to operations that involve nitrous oxide.
 Minimize all sources of ignition because a        engineering controls be used where feasible to
    fire may cause nitrous oxide to accelerate      reduce workplace concentrations of hazardous          Splash-proof chemical safety goggles or face
    the burning of other combustibles; keep         materials to the prescribed exposure limit.           shields (20 to 30 cm long, minimum) should be
    combustible materials (wood, paper, oil, etc.) However, some situations may require the use           worn during any operation in which a solvent,
    away from the spilled material.                 of respirators to control exposure. Respirators       caustic or other toxic substance may be splashed
 Isolate the area until the gas has dispersed.     must be worn if the ambient concentration of          into the eyes.
special requirements                                nitrous oxide exceeds prescribed exposure limits.     In addition to the possible need for wearing
United States Environmental Protection Agency       Respirators may be used (1) before engineering        protective outer apparel (e.g., aprons,
(EPA) requirements for emergency planning,          controls have been installed, (2) during work         encapsulating suits), workers should wear work
reportable quantities of hazardous releases,        operations such as maintenance or repair activities   uniforms, coveralls or similar full-body coverings
community right-to-know and hazardous waste         that involve unknown exposures, (3) during            that are laundered each day. Employers should
management may change over time. Users are          operations that require entry into tanks or closed    provide lockers or other closed areas to store work
therefore advised to determine periodically         vessels, and (4) during emergencies. Workers          and street clothing separately. Employers should
whether new information is available.               should only use respirators that have been            collect work clothing at the end of each work shift
                                                    approved by NIOSH and the Mine Safety and             and provide for its laundering. Laundry personnel
Emergency planning requirements                     Health Administration (MSHA).                         should be informed about the potential hazards
Nitrous oxide is not subject to EPA emergency                                                             of handling contaminated clothing and instructed
planning requirements under the Superfund           Respiratory protection program
                                                    Employers should institute a complete respiratory     about measures to minimize their health risk.
Amendments and Reauthorization Act (SARA)
(Title III) in 42 CFR 11022.                        protection program that, at a minimum, complies       Protective clothing should be kept free of oil and
                                                    with the requirements of OSHA’s Respiratory           grease and should be inspected and maintained
Reportable quantity requirements for                Protection Standard [29 CFR 1910.134]. Such           regularly to preserve its effectiveness.
hazardous releases                                  a program must include respirator selection, an
Employers are not required by the emergency                                                               Protective clothing may interfere with the body’s
                                                    evaluation of the worker’s ability to perform
release notification provisions in 40 CFR Part                                                            heat dissipation, especially during hot weather
                                                    the work while wearing a respirator, the regular
355.40 to notify the National Response Center of training of personnel, respirator fit testing,           or during work in hot or poorly ventilated work
an accidental release of nitrous oxide; there is no periodic workplace monitoring, and regular            environments.
reportable quantity for this substance.             respirator maintenance, inspection and cleaning.      More on personal protective equipment
Community right-to-know requirements                The implementation of an adequate respiratory            Personal protective equipment should not be
Employers are not required by EPA in 40 CFR         protection program (including selection of the            used as a substitute for engineering, work
Part 372.30 to submit a Toxic Chemical Release      correct respirator) requires that a knowledgeable         practice and/or administrative controls in
Inventory form (Form R) to EPA reporting the        person be in charge of the program and that the           anesthetizing locations and post anesthesia
amount of nitrous oxide emitted or released from program be evaluated regularly. For additional               care units (PACUs). In fact, exposure to waste
their facility annually.                            information on the selection and use of respirators       gases is not effectively reduced by gloves,
                                                    and on the medical screening of respirator users,         goggles and surgical masks. A negative-
Hazardous waste management                          consult the latest edition of the NIOSH Respirator        pressure, high-efficiency particulate air
requirements                                        Decision Logic [NIOSH 1987b] and the NIOSH                (HEPA) filter used for infection control is also
EPA considers a waste to be hazardous if it         Guide to Industrial Respiratory Protection                not appropriate to protect workers from waste
exhibits any of the following characteristics:      [NIOSH 1987a].                                            gases. Air-supplied respirators with self-
ignitability, corrosivity, reactivity or toxicity                                                             contained air source are ideal for eliminating
as defined in 40 CFR 261.21-261.24. Under           Personal protective equipment
                                                                                                              exposure but are not a practical alternative.
the Resource Conservation and Recovery              Workers should use appropriate personal
                                                                                                             During cleanup and containment of spills of
Act (RCRA) [40 USC 6901 et seq.], EPA               protective clothing and equipment that must be
                                                                                                              liquid anesthetic agents, personal protective
has specifically listed many chemical wastes        carefully selected, used and maintained to be
                                                                                                              equipment should be used in conjunction
as hazardous. Although nitrous oxide is not         effective in preventing skin contact with liquid
                                                                                                              with engineering, work practice and/
specifically listed as a hazardous waste under      nitrous oxide. The selection of the appropriate
                                                                                                              or administrative controls to provide for
Page 8                                                                                                                          Elite CME - www.EliteCME.com
    employee safety and health. Gloves, goggles,        in anesthesia equipment systems, components,            Gas flow in the anesthesia machine and
    face shields and chemical protective clothing       and accessories are identified, and appropriate         breathing system
    (CPC) are recommended to ensure worker              methods are described that limit excessive leaks.       The internal piping of a basic two-gas anesthesia
    protection. Respirators, where needed,              Inhaled anesthetic agents include two                   machine is shown in Figure 1 The machine has
    should be selected based on the anticipated         different classes of chemicals: nitrous oxide           many connections and potential sites for leaks.
    contamination level.                                and halogenated agents. Halogenated agents              Both oxygen and N2O may be supplied from
   When selecting gloves and chemical                  currently in use include halothane (Fluothane®),        two sources (Figure 2): a pipeline supply source
    protective clothing, some of the factors to         enflurane (Ethrane®), isoflurane (Forane®),             (central piping system from bulk storage) and
    be considered include material chemical             desflurane (Suprane®), and sevoflurane (Ultane®).       a compressed gas cylinder supply source. In
    resistance, physical strength and durability,       Methoxyflurane (Penthrane®), once in general            hospitals, the pipeline supply source is the primary
    and overall product integrity. Permeation,          use, is now only infrequently used, primarily in        gas source for the anesthesia machine. Pipeline-
    penetration and degradation data should             veterinary procedures. At present, OSHA has             supplied gases are delivered through wall outlets
    be consulted if available. Among the most           no permissible exposure limits regulating these         at a pressure of 50-55 psig through diameter
    effective types of gloves and body protection       agents.                                                 indexed safety system (DISS) fittings or through
    are those made from Viton®, neoprene                                                                        quick-connect couplings that are gas-specific
    and nitrile. Polyvinyl alcohol (PVA) is also        The basic anesthesia machine                            within each manufacturer’s patented system.
    effective, but it should not be exposed to water    An anesthesia machine is an assembly of various
    or aqueous solutions.                               components and devices that include medical             Because pipeline systems can fail and because
   When the gloves and the CPC being used have         gas cylinders in machine hanger yokes, pressure         the machines may be used in locations where
    not been tested under the expected conditions,      regulating and measuring devices, valves, flow          piped gases are not available, anesthesia
    they may fail to provide adequate protection.       controllers, flow meters, vaporizers, CO2 absorber      machines are fitted with reserve cylinders of
    In this situation, the wearer should observe the    canisters, and breathing circuit assembly. The          oxygen and N2O. The oxygen cylinder source is
    gloves and the chemical protective clothing         basic two-gas anesthesia machine has more than          regulated from approximately 2,200 psig in the
    during use and treat any noticeable change          700 individual components.                              tanks to approximately 45 psig in the machine
    (e.g., color, stiffness, chemical odor inside) as                                                           high-pressure system, and the N2O cylinder
                                                        The anesthesia machine is a basic tool of the           source is regulated from 745 psig in the tanks
    a failure until proved otherwise by testing. If     anesthesiologist/anesthetist and serves as the
    the work must continue, new CPC should be                                                                   to approximately 45 psig in the machine high-
                                                        primary work station. It allows the anesthesia          pressure system.
    worn for a shorter exposure time, or be of a        provider to select and mix measured flows of
    different generic material. The same thickness      gases, to vaporize controlled amounts of liquid         Figure 1
    of a generic material such as neoprene or           anesthetic agents, and thereby to administer            The flow arrangement of a basic two-gas
    nitrile supplied by different manufacturers         safely controlled concentrations of oxygen and          anesthesia machine. A, The fail-safe valve in
    may provide significantly different levels          anesthetic gases and vapors to the patient via a        Ohmeda machines is termed a pressure sensor
    of protection because of variations in the          breathing circuit. The anesthesia machine also          shut-off valve; in Dräger machines it is the oxygen
    manufacturing processes or in the raw               provides a working surface for placement of             failure protection device (OFPD). B, Second-stage
    materials and additives used in processing.         drugs and devices for immediate access and              oxygen pressure regulator is used in Ohmeda (but
   Professional judgment must be used in               drawers for storage of small equipment, drugs,          not Dräger Narkomed) machines. C, Second-stage
    determining the type of respiratory protection      supplies and equipment instruction manuals.             nitrous oxide pressure regulator is used in Ohmeda
    to be worn. For example, where spills of            Finally, the machine serves as a frame and source       Modulus machines having the Link 25 Proportion
    halogenated anesthetic agents are small,            of pneumatic and electric power for various             Limiting System; not used in Dräger machines.
    exposure time brief and sufficient ventilation      accessories such as a ventilator, and monitors that     D, Pressure relief valve used in certain Ohmeda
    present, NIOSH-approved chemical cartridge          observe or record vital patient functions or that are   mchines; not used in Dräger machines. E, Outlet
    respirators for organic vapors should provide       critical to the safe administration of anesthesia.      check valve used in Ohmeda machines
    adequate protection during cleanup activities.
   Where large spills occur and there is               Figure 1
    insufficient ventilation to adequately reduce
    airborne levels of the halogenated agent,
    respirators designed for increased respiratory
    protection should be used. The following
    respirators, to be selected for large spills, are
    ranked in order from minimum to maximum
    respiratory protection:
    Š Any type C supplied-air respirator with a
         full facepiece, helmet or hood operated in
         continuous-flow mode.
    Š Any type C supplied-air respirator with
         a full facepiece operated in pressure-
         demand or other positive-pressure mode.
    Š Any self-contained breathing apparatus
         with a full facepiece operated in pressure-
         demand or other positive-pressure mode.
Workplace exposures
Workplace exposures to anesthetic gases occur
in hospital-based and stand-alone operating
rooms, recovery rooms, dental operatories and
veterinary facilities. Engineering, work practice
and administrative controls that help reduce
these exposures in all anesthetizing locations
are identified and discussed. Sources of leaks
Elite CME - www.EliteCME.com                                                                                                                                 Page 9
Figure 2                                                                                                   The circle system shown in Figure 4 is the
                                                                                                           breathing system most commonly used in
                                                                                                           operating rooms (ORs). It is so named because
                                                                                                           its components are arranged in a circular manner.
                                                                                                           The essential components of a circle breathing
                                                                                                           system (Figure 5) include a site for inflow of
                                                                                                           fresh gas (common [fresh] gas inlet), a carbon
                                                                                                           dioxide absorber canister (containing soda lime
                                                                                                           or barium hydroxide lime) where exhaled carbon
                                                                                                           dioxide is absorbed; a reservoir bag; inspiratory
                                                                                                           and expiratory unidirectional valves; flexible
                                                                                                           corrugated breathing tubing; an adjustable
                                                                                                           pressure-limiting (APL) or “pop-off” valve for
                                                                                                           venting excess gas; and a Y piece that connects to
                                                                                                           a face mask, tracheal tube, laryngeal mask airway
                                                                                                           (LMA) or other airway management device.
                                                                                                           Once inside the breathing system, the mixture of
                                                                                                           gases and vapors flows to the breathing system’s
                                                                                                           inspiratory unidirectional valve, then on toward
                                                                                                           the patient. Exhaled gases pass through the
                                                                                                           expiratory unidirectional valve and enter the
                                                                                                           reservoir bag. When the bag is full, excess gas
                                                                                                           flows through the APL (or pop-off) valve and
                                                                                                           into the scavenging system that removes the
except Modulus II Plus and Modulus CD models;          common manifold to the concentration-calibrated waste gases. On the next inspiration, gas from the
not used in Dräger machines. The oxygen take-off       vaporizer and then via the machine common gas reservoir bag passes through the carbon dioxide
for the anesthesia ventilator driving gas circuit is   outlet to the breathing system. The high pressure absorber prior to joining the fresh gas from the
downstream of the main on/off switch in Dräger         system of the anesthesia machine comprises those machine on its way to the patient. The general use
machines, as shown here. In Ohmeda machines,           components from the compressed gas supply           of fresh gas flow rates into anesthetic systems in
the take-off is upstream of the main on/off            source to the gas (O2 and N2O) flow control         excess of those required to compensate for uptake,
switch. (Adapted from Check-out: a guide for           valves. The low pressure system of the anesthesia metabolism, leaks, or removal of exhaled carbon
preoperative inspection of an anesthesia machine,      machine comprises those components downstream dioxide results in variable volumes of anesthetic
ASA, 1987. Reproduced by permission of the             of the gas flow control valves.                     gases and vapors exiting the breathing system
American Society of Anesthesiologists, 520 N.                                                              through the APL valve.
                                                       Once the flows of oxygen, N2O, and other medical
Northwest Highway, Park Ridge, Ill.)
                                                       gases (if used) are turned on at their flow control When an anesthesia ventilator is used, the
Figure 2                                               valves, the gas mixture flows into the common       ventilator bellows functionally replaces the circle
The supply of nitrous oxide and oxygen may             manifold and through a concentration-calibrated     system reservoir bag and becomes a part of the
come from two sources: the wall (pipeline) supply      agent-specific vaporizer where a potent inhaled     breathing circuit. The APL valve in the breathing
and the reserve cylinder supply. (Reproduced           volatile anesthetic agent is added. The mixture of circuit is either closed or excluded from the circuit
by permission of Datex·Ohmeda, Madison,                gases and vaporized anesthetic agent then exits the using a manual (“bag”)/automatic (ventilator)
Wisconsin). Compressed gas cylinders of oxygen,        anesthesia machine low pressure system through circuit selector switch. The ventilator incorporates
N2O, and other medical gases are attached to      the common gas outlet and flows to the breathing
the anesthesia machine through the hanger yoke    system.
assembly. Each hanger yoke is equipped with the
pin index safety system, a safeguard introduced   Figure 3
to eliminate cylinder interchanging and the
possibility of accidentally placing the incorrect
gas tank in a yoke designed for another gas tank.
(Reproduced by permission of Datex·Ohmeda,
Madison, Wisconsin).
Figure 3 shows the oxygen pathway through the
flow meter, the agent vaporizer, and the machine
piping, and into the breathing circuit. Oxygen
from the wall outlet or cylinder pressurizes the
anesthesia delivery system. Compressed oxygen
provides the needed energy for a pneumatically
powered ventilator, if used, and it supplies the
oxygen flush valve used to supplement oxygen
flow to the breathing circuit. Oxygen also
“powers” an in-line pressure-sensor shutoff valve
(“fail-safe” valve) for other gases to prevent their
administration if the O2 supply pressure in the
O2 high-pressure system falls below a threshold
value.
Oxygen and N2O flow from their supply sources
via their flow control valves, flow meters and
Page 10                                                                                                                          Elite CME - www.EliteCME.com
Figure 4                                                                                               Minute absorbent particles that may have been
                                                                                                       spilled on the rubber seal around the absorber
                                                                                                       canister(s) may also prevent a gas-tight seal when
                                                                                                       the canister(s) in the carbon dioxide absorber is
                                                                                                       (are) reassembled). The exhaust from a sidestream
                                                                                                       sampling respiratory gas analyzer and/or
                                                                                                       capnograph should also be connected to the waste
                                                                                                       gas scavenging system because the analyzed gas
                                                                                                       sample may contain N2O or halogenated vapors.
                                                                                                       Figure 5
                                                                                                       Checking anesthesia machines
                                                                                                       Prior to induction of anesthesia, the anesthesia
                                                                                                       machine and its components/accessories should
                                                                                                       be made ready for use. All parts of the machine
                                                                                                       should be in good working order with all
                                                                                                       accessory equipment and necessary supplies
                                                                                                       on hand. The waste gas disposal system should
                                                                                                       be connected, hoses visually inspected for
                                                                                                       obstructions or kinks, and proper operation
                                                                                                       determined. Similarly, the anesthesia breathing
                                                                                                       system should be tested to verify that it can
                                                                                                       maintain positive pressure. Leaks should be
                                                                                                       identified and corrected before the system is used.
                                                                                                       The ability of the anesthesia system to maintain
                                                                                                       constant pressure is tested not only for the safety
                                                                                                       of the patient dependent on a generated positive
a pressure-relief valve that permits release of    from loose-fitting connections, defective and worn pressure ventilation but also to test for leaks and
excess anesthetic gases from the circuit at end-                                                       escape of anesthetic gases, which may expose
                                                   seals and gaskets, worn or defective breathing
exhalation. These gases should also be scavenged.                                                      health-care personnel to waste anesthetic gases.
                                                   bags, hoses, and tubing, loosely assembled or
sources of leaks within the anesthesia             deformed slip joints and threaded connections, and General workplace controls
machine and breathing system                       the moisture drainage port of the CO2 absorber,     Occupational exposures can be controlled by the
 No anesthesia machine system is totally           which may be in the “open” position.                application of a number of well-known principles,
leak-free (Emergency Care Research Institute       Low-pressure system leaks also may occur at the including engineering and work practice controls,
1991). Leakage may originate from both the         gas analysis sensor (i.e., circuit oxygen analyzer) administrative controls, personal protective
high-pressure and low-pressure systems of the      and gas sampling site(s), face mask, the tracheal   equipment and monitoring. These principles may
anesthesia or analgesia machine.                   tube (especially in pediatric patients where a leak be applied at or near the hazard source, to the
                                                   is required around the uncuffed tracheal tube),     general workplace environment, or at the point
The high-pressure system consists of all piping
                                                   laryngeal mask airway (over the larynx), and        of occupational exposure to individuals. Controls
and parts of the machine that receive gas at
                                                   connection points for accessory devices such as     applied at the source of the hazard, including
cylinder or pipeline supply pressure. It extends
from the high-pressure gas supply (i.e., wall      a humidifier, temperature probe, or positive end- engineering and work practice controls, are
                                                   expiratory pressure (PEEP) valve. Inappropriate     generally the preferred and most effective means
supply or gas cylinder) to the flow control
                                                   installation of a calibrated vaporizer(s) or        of control. In anesthetizing locations and PACUs,
valves. Leaks may occur from the high-pressure
connections where the supply hose connects to the misalignment of a vaporizer on its manifold can
wall outlet or gas cylinder and where it connects also contribute to anesthetic gas leakage.
to the machine inlet. Therefore, gas-supply hoses
should be positioned to prevent strain on the      Figure 5
fittings (ASTM Standard F1161-88; Dorsch and
Dorsch 1994) and constructed from supply-hose
materials designed for high-pressure gas flow and
minimal kinking (Bowie and Huffman 1985).
High-pressure leakage may also occur within the
anesthesia machine itself. Other potential sources
of leaks include quick-connect fittings,cylinder
valves, absent or worn gaskets, missing or worn
yoke plugs in a dual yoke assembly, and worn
hoses.
The low-pressure system of the anesthesia
machine (in which the pressure is slightly above
atmospheric) consists of components downstream
of the flow-control valves. It therefore includes the
flow meter tubes, vaporizers, common gas outlet
and breathing circuit, (i.e., from the common gas
outlet to the patient). Low-pressure system leaks
may occur from the connections and components
anywhere between the anesthesia gas flow control
valves and the airway. This leakage may occur
Elite CME - www.EliteCME.com                                                                                                                       Page 11
where employees are at risk of exposure to waste                                                           systems at reducing excess waste anesthetic gas
anesthetic gases, exposure may be controlled            The gas disposal assembly, which conveys          concentrations because leaks in the scavenging
by some or all of the following: (1) effective           the excess gases to a point where they can be     system do not result in an outward loss of gas.
anesthetic gas scavenging systems that remove            discharged safely into the atmosphere. Several
excess anesthetic gas at the point of origin; (2)        methods in use include a nonrecirculating
                                                                                                           Passive systems
                                                                                                           HVAC systems used in health-care facilities are
effective general or dilution ventilation; (3)           or recirculating ventilation system, a central
                                                                                                           of two types: nonrecirculating and recirculating.
good work practices on the part of the healthcare        vacuum system, a dedicated (single-purpose)
                                                                                                           Nonrecirculating systems, also termed “one-pass”
workers, including the proper use of controls;           waste gas exhaust system, a passive duct
                                                                                                           or “single-pass” systems, take in fresh air from
(4) proper maintenance of equipment to prevent           system and an adsorber.
                                                                                                           the outside and circulate filtered and conditioned
leaks; and (5) periodic personnel exposure and
                                                      In general, a machine-specific interface must be     air (i.e., controlled for temperature and humidity)
environmental monitoring to determine the
                                                      integrated with a facility’s system for gas removal. through the room. Whatever volumes of fresh
effectiveness of the overall waste anesthetic gas
                                                      The interface permits excess gas to be collected in  air are introduced into the room are ultimately
control program.
                                                      a reservoir (bag or canister) and limits the pressureexhausted to the outside. Waste anesthetic
The following is a general discussion                 within the bag or canister. A facility’s gas disposalgases can be efficiently disposed of via this
of engineering controls, work practices,              system receives waste anesthetic gases from the      nonrecirculating system.
administrative controls, and personal protective      interface and should vent the waste gases outside
                                                                                                            When a nonrecirculating ventilation system serves
equipment that can reduce worker exposure             the building and away from any return air ducts or
                                                                                                            through large-diameter tubing and terminating
to waste anesthetic gases. However, not every         open windows, thus preventing the return of the
                                                                                                            the tubing at the room’s ventilation exhaust as the
control listed in this section may be feasible in all waste gases back into the facility.
                                                                                                            disposal route for excess anesthetic gases, disposal
settings.
                                                      Removal of excess anesthetic gases from the           involves directing the waste gases grille. The
Engineering controls                                  anesthesia circuit can be accomplished by either      sweeping effect of the air flowing into the grille
The collection and disposal of waste anesthetic       active or passive scavenging. When a vacuum or carries the waste gases away. Because all of the
gases in operating rooms and non-operating room source of negative pressure is connected to the             exhausted air is vented to the external atmosphere
settings is essential for reducing occupational       scavenging interface, the system is described as      in this type of system, the excess anesthetic gases
exposures. Engineering controls such as an            an active system. When a vacuum or negative           can be deposited into the exhaust stream either
appropriate anesthetic gas scavenging system are pressure is not used, the system is described as           at the exhaust grille or further downstream in the
the first line of defense and the preferred method a passive system. With an active system, there           exhaust duct.
of control to protect employees from exposure         will be a negative pressure in the gas disposal
                                                                                                            Concern for fuel economy has increased the use of
to anesthetic gases. An effective anesthetic gas      tubing. With a passive system, this pressure will
                                                                                                            systems that recirculate air. Recirculating HVAC/
scavenging system traps waste gases at the            be increased above atmospheric (positive) by the
                                                                                                            ventilation systems return part of the exhaust
site of overflow from the breathing circuit and       patient exhaling passively, or manual compression
                                                                                                            air back into the air intake and recirculate the
disposes of these gases to the outside atmosphere. of the breathing system reservoir bag.
                                                                                                            mixture through the room. Thus, only a fraction
The heating, ventilating and air conditioning         Use of a central vacuum system is an example of of the exhaust air is disposed of to the outside. To
(HVAC) system also contributes to the dilution        an active system: The waste anesthetic gases are maintain minimal levels of anesthetic exposure,
and removal of waste gases not collected by the       moved along by negative pressure. Venting waste air that is to be recirculated must not contain
scavenging system or from other sources such as anesthetic gas via the exhaust grille or exhaust
                                                                                                            anesthetic gases. Consequently, recirculating
leaks in the anesthetic apparatus or improper work duct of a nonrecirculating ventilation system is an
                                                                                                            systems employed as a disposal pathway for
practices.                                            example of a passive system: The anesthetic gas       waste anesthetic gases must not be used for gas
The exhalation of residual gases by patients in the is initially moved along by the positive pressure       waste disposal. The exception is an arrangement
PACU may result in significant levels of waste        from the breathing circuit until it reaches the gas that transfers waste gases into the ventilation
anesthetic gases when appropriate work practices disposal assembly.                                         system at a safe distance downstream from the
are not used at the conclusion of the anesthetic                                                            point of recirculation to ensure that the anesthetic
                                                      Active systems
or inadequate ventilation exists in the PACU. A                                                             gases will not be circulated elsewhere within the
                                                      Excess anesthetic gases may be removed by
nonrecirculating ventilation system can reduce                                                              building.
                                                      a central vacuum system (servicing the ORs
waste gas levels in this area. Waste gas emissions
                                                      in general) or an exhaust system dedicated to         Under certain circumstances, a separate duct
to the outside atmosphere must meet local, state,
                                                      the disposal of excess gases. When the waste          for venting anesthetic gases directly outside
and Environmental Protection Agency (EPA)
                                                      anesthetic gas scavenging system is connected to the building without the use of a fan may be an
regulatory requirements.
                                                      the central vacuum system (which is shared by         acceptable alternative. By this technique, excess
A scavenging system consists of five basic            other users, e.g., surgical suction), exposure levels anesthetic gases may be vented through the wall,
components (ASTM, F 1343 - 91):                       may be effectively controlled. The central vacuum window, ceiling or floor, relying only on the slight
 A gas collection assembly, such as a collection system must be specifically designed to handle            positive pressure of the gases leaving the gas
     manifold or a distensible bag (i.e., Jackson-    the large volumes of continuous suction from OR collection assembly to provide the flow. However,
     Rees pediatric circuit), which captures excess scavenging units. If a central vacuum system is         several limitations are apparent. A separate line
     anesthetic gases at the site of emission, and    used, a separate, dedicated gas disposal assembly would be required for each OR to prevent the
     delivers it to the transfer tubing.              tubing should be used for the scavenging system, cross-contamination with anesthetic gases among
 Transfer tubing, which conveys the excess           distinct from the tubing used for patient suctioning the ORs. A safe disposal site would be necessary.
     anesthetic gases to the interface.               (used for oral and nasal gastric sources as well as The possible effects of variations in wind
 The interface, which provides positive (and         surgical suctioning).                                 velocity and direction would require a means for
     sometimes negative) pressure relief and may                                                            preventing a reverse flow in the disposal system.
                                                      Similarly, when a dedicated exhaust system
     provide reservoir capacity. It is designed to                                                          Occlusion of the outer portion of such a passive
                                                      (low velocity) is used, excess gases can also be
     protect the patient’s lungs from excessive                                                             system by ice or by insect or bird nests is also
                                                      collected from one or more ORs and discharged
     positive or negative scavenging system                                                                 possible. The outside opening of a through-wall,
                                                      to the outdoors. The exhaust fan must provide
     pressure.                                                                                              window, ceiling or floor disposal assembly should
                                                      sufficient negative pressure and air flow so that
 Gas disposal assembly tubing, which conducts                                                              be directed downward, shielded and screened
                                                      cross-contamination does not occur in the other
     the excess anesthetic gases from the interface                                                         to prevent the entrance of foreign matter or ice
                                                      ORs connected to this system. Active systems
     to the gas disposal assembly.                                                                          buildup. Despite these limitations, the separate
                                                      are thought to be more effective than passive
Page 12                                                                                                                          Elite CME - www.EliteCME.com
duct without the use of a fan may be ideal in older      testing procedures for equipment checkout           approach for reducing worker exposure to waste
facilities constructed with windows that cannot be       prior to administering an anesthetic.               gases other than through the use of engineering
opened and in the absence of nonrecirculating air       If a face mask is to be used for administration     controls, work practices, or personal protective
conditioning.                                            of inhaled anesthetics, it should be available in   equipment. Administrative controls may be
                                                         a variety of sizes to fit each patient properly.    thought of as any administrative decision that
Absorbers can also trap most excess anesthetic
                                                         The mask should be pliable and provide as           results in decreased anesthetic-gas exposure. For
gases. Canisters of varying shapes and capacities
                                                         effective a seal as possible against leakage        workers potentially exposed to waste anesthetic
filled with activated charcoal have been used as
                                                         into the surrounding air.                           gases, the program administrator should establish
waste gas disposal assemblies by directing the
                                                        Tracheal tubes, laryngeal masks, and other          and implement policies and procedures to:
gases from the gas disposal tubing through them.
                                                         airway devices should be positioned precisely        Institute a program of routine inspection
Activated charcoal canisters will effectively
                                                         and the cuffs inflated adequately.                      and regular maintenance of equipment in
adsorb the vapors of halogenated anesthetics,
                                                        Vaporizers should be filled in a well-ventilated        order to reduce anesthetic gas leaks and to
but not N2O. The effectiveness of individual
                                                         area and in a manner to minimize spillage of            have the best performance of scavenging
canisters and various brands of charcoal vary
                                                         the liquid agent. This can be accomplished              equipment and room ventilation. Preventive
widely. Different potent inhaled volatile agents are
                                                         by using a specialized “key-fill” spout to              maintenance should be performed by trained
adsorbed with varying efficiencies. The efficiency
                                                         pour the anesthetic into the vaporizer instead          individuals according to the manufacturer’s
of adsorption also depends on the rate of gas flow
                                                         of pouring from a bottle into a funnel-fill             recommendations and at intervals determined
through the canister. The canister is used where
                                                         vaporizer. When feasible, vaporizers should be          by equipment history and frequency of use.
portability is necessary. The disadvantages are
                                                         filled at the location where the anesthetic will        Preventive maintenance includes inspection,
that they are expensive and must be changed
                                                         be administered and, when filled electively,            testing, cleaning, lubrication and adjustment
frequently. Canisters must be used and discarded
                                                         with the fewest possible personnel present              of various components. Worn or damaged
in the appropriate manner, as recommended by the
                                                         in the room. Vaporizers should be turned off            parts should be repaired or replaced. Such
manufacturer.
                                                         when not in use.                                        maintenance can result in detection of
General or dilution ventilation                         Spills of liquid anesthetic agents should be            deterioration before an overt malfunction
An effective room HVAC system when used in               cleaned up promptly.                                    occurs. Documentation of the maintenance
combination with an anesthetic gas scavenging           Before extubating the patient’s trachea                 program should be kept indicating the nature
system should reduce, although not entirely              or removing the mask or other airway                    and date of the work performed, as well as the
eliminate, the contaminating anesthetic gases.           management device, one should administer                name of the trained individual servicing the
If excessive concentrations of anesthetic gases          non-anesthetic gases/agents so that the                 equipment.
are present, then airflow should be increased            washed-out anesthetic gases can be removed           Implement a monitoring program to measure
in the room to allow for more air mixing and             by the scavenging system. The amount of                 airborne levels of waste gases in the breathing
further dilution of the anesthetic gases. Supply         time allowed for this should be based on                zone or immediate work area of those most
register louvers located in the ceiling should be        clinical assessment and may vary from                   heavily exposed (e.g., anesthesiologist, nurse
designed to direct the fresh air toward the floor        patient to patient. When possible, flushing of          anesthetist, oral surgeon) in each anesthetizing
and toward the health care workers to provide            the breathing system should be achieved by              location and PACU. Periodic monitoring
dilution and removal of the contaminated air from        exhausting into the scavenging system rather            (preferably at least semiannually) of waste
the operatory or PACU. Exhaust register louvers          than into the room air.                                 gas concentrations is needed to ensure
should be properly located (usually low on the          Work practices performed by biomedical                  that the anesthesia delivery equipment and
wall near the floor level) in the room to provide        engineers and technicians also contribute               engineering/environmental controls work
adequate air distribution. They should not be            significantly to the efficacy of managing waste         properly and that the maintenance program
located near the supply air vents because this will      gas exposure. It is, therefore, important for           is effective. Monitoring may be performed
short-circuit the airflow and prevent proper air         this group of workers to do the following:              effectively using conventional time-weighted
mixing and flushing of the contaminants from the         Š Monitor airborne concentrations of                    average air sampling or real-time air sampling
room.                                                         waste gases by sampling, measuring,                techniques.
                                                              and reporting data to the institution’s         Encourage or promote the use of scavenging
Work practices                                                administration. Air monitoring for waste           systems in all anesthetizing locations
Work practices, as distinct from engineering                  anesthetic gases should include both               where inhaled agents are used, recognizing
controls, involve the way in which a task is                  personal sampling (i.e., in a health-              that a waste gas scavenging system is the
performed. OSHA has found that appropriate                    care worker’s breathing zone) and area             most effective means of controlling waste
work practices can be a vital aid in reducing the             sampling.                                          anesthetic gases.
exposures of OR personnel to waste anesthetic            Š Assist in identifying sources of waste/            Implement an information and training
agents. In contrast, improper anesthetizing                   leaking gases and implementing corrective          program for employees exposed to
techniques can contribute to increased waste                  action.                                            anesthetic agents that complies with OSHA’s
gas levels. These techniques can include an              Š Determine whether the scavenging system               Hazard Communication Standard (29
improperly selected and fitted face mask, an                  is designed and functioning properly to            CFR 1910.1200) so that employees can
insufficiently inflated tracheal tube cuff, an                remove the waste anesthetic gases from             meaningfully participate in, and support,
improperly positioned laryngeal mask, or other                the breathing circuit, and ensure that the         the protective measures instituted in their
airway, and careless filling of vaporizers and                gases are vented from the workplace in             workplace.
spillage of liquid anesthetic agents.                         such a manner that occupational re-             Define and implement appropriate work
General work practices recommended for                        exposure does not occur (e.g., smoke trail         practices to help reduce employee exposure.
anesthetizing locations include the following:                tests of exhaust grilles used with passive         Training and educational programs covering
 A complete anesthesia apparatus checkout                    scavenging systems).                               appropriate work practices to minimize
    procedure should be performed each day               Š Ensure that operatory and PACU                        levels of anesthetic gases in the operating
    before the first case. An abbreviated version             ventilation systems provide sufficient             room should be conducted at least annually.
    should be performed before each subsequent                room air exchange to reduce ambient                Employers should emphasize the importance
    case. The FDA Anesthesia Apparatus                        waste gas levels.                                  of implementing these practices and should
    Checkout Recommendations should be                                                                           ensure that employees are properly using the
                                                    Administrative controls                                      appropriate techniques on a regular basis.
    considered in developing inspection and
                                                    Administrative controls represent another
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                                                      Jackson-Rees modification of the Ayre’s T-piece      Postanesthesia care in hospitals and
   Implement a medical surveillance program for      are examples of limited rebreathing systems that     stand-alone facilities
    all workers exposed to waste gases.               require appropriate scavenging equipment.            Because the patient is the main source of waste
   Ensure the proper use of personal protective                                                           anesthetic gases in the PACU, it becomes more
                                                    The following work practices may be employed
    equipment during cleanup and containment of                                                            difficult to control health-care workers’ exposures
                                                    with any of the above breathing circuits:
    major spills of liquid anesthetic agents.                                                              to waste anesthetic gases. The unique PACU
                                                     Empty the contents of the reservoir bag
   Manage disposal of liquid agents, spill                                                                environment coupled with the patient’s immediate
                                                         directly into the anesthetic gas scavenging
    containment, and air monitoring for waste                                                              condition upon arrival from surgery require
                                                         system and turn off the flow of N2O and
    gases following a spill.                                                                               different work practices than those routinely used
                                                         any halogenated anesthetic agent prior to
   Comply with existing federal, state, and                                                               in ORs. Patients undergoing general anesthesia
                                                         disconnecting the patient circuit.
    local regulations and guidelines developed                                                             usually have their airways secured using a tracheal
                                                     Turn off the flow of N2O and the vaporizer,
    to minimize personnel exposure to waste                                                                tube with an inflatable cuff that seals the tube
                                                         if appropriate, when the patient circuit is
    anesthetic gases, including the proper disposal                                                        within the trachea. The seal between the tracheal
                                                         disconnected from the patient, for example,
    of hazardous chemicals.                                                                                tube cuff and the trachea (or between the face
                                                         for oral or tracheal suctioning.
Location-specific workplace controls                 Test daily for low-pressure leaks throughout         mask and the face) is essential for maintaining a
This section describes engineering and work              the entire anesthesia system. All leaks           gas-tight system that permits effective scavenging
practice controls specific to hospital ORs, PACUs,       should be minimized before the system is          in the OR. The tracheal tube connects the patient
dental operatories and veterinary clinics and            used. Starting anesthetic gas flow before the     with the breathing circuit that is connected to the
hospitals. Operational procedures relating to            actual induction of anesthesia begins is not      scavenging system in the OR. Once the patient
engineering controls are also discussed where            acceptable. For techniques to rapidly induce      reaches the PACU, scavenging systems such as
appropriate.                                             anesthesia using inhaled agents (single-breath    those used in the OR are no longer effective, since
                                                         mask induction), the patient connector should     the patient is no longer connected to the breathing
Hospital operating rooms                                                                                   circuit. Other less-effective methods of waste gas
                                                         be occluded when filling the breathing circuit
For years, anesthesia providers tolerated exposure                                                         removal are thus relied upon.
                                                         with nitrous oxide or halogenated agent prior
to waste anesthetic gases and regarded it as an
                                                         to applying the mask to the patient’s face.       Engineering controls
inevitable consequence of their work. Since the
1970s, anesthesiologists have steadily worked       If the circle absorber system (Figure 6) is used,      As a result of using appropriate anesthetic gas
to improve equipment and technique to reduce        the following additional work practices can be         scavenging in ORs, the levels of contamination
workplace exposures to waste anesthetic gases,      employed:                                              have been decreased. In the PACU, however, the
and significant progress has been made. In early     Adjust the vacuum needle valve as needed             principle of scavenging as practiced in the OR is
delivery equipment, waste gases were exhausted           to regulate the flow of waste anesthetic          not widely accepted due to medical considerations
through the APL or “pop-off” valve into the face         gases into the vacuum source in an active         and consequently is infrequently employed
of the anesthesia provider and were distributed          scavenging system. Adjustments prevent the        as a source-control method for preventing the
into the room air. Present practice, which utilizes      bag from overdistending by maintaining the        release of waste anesthetic gases into the PACU
an efficient scavenging system, avoids this type         volume in the scavenging system reservoir         environment. Most PACUs provide care to
of contamination by collecting the excess gases          bag between empty and half-full. In machines      multiple patients in beds without walls between
immediately at the APL valve.                            that use an open reservoir to receive waste       them, and convective currents move the gases
                                                         gas, a flow meter is used to adjust the rate of   from their source to other areas. Therefore, in
Engineering controls                                                                                       the PACU, a properly designed and operating
                                                         gas flow to the vacuum system.
Waste gas evacuation is required for every type of                                                         dilution ventilation system should be relied upon
                                                     Cap any unused port in a passive waste gas
breathing circuit configuration with the possible
                                                         scavenging configuration.
exception of a closed circuit, because most
anesthesia techniques typically use more fresh      Figure 6
gas flow than is required. Appropriate waste gas
evacuation involves collection and removal of
waste gases, detection and correction of leaks,
consideration of work practices, and effective
room ventilation. To minimize waste anesthetic
gas concentrations in the operating room, the
recommended air exchange rate (room dilution
ventilation) is a minimum total of 15 air changes
per hour with a minimum of 3 air changes of
outdoor air (fresh air) per hour. Operating room
air containing waste anesthetic gases should not
be recirculated to the operating room or other
hospital locations.
Work practices
In most patients, a circle absorption system is
used and can be easily connected to a waste
gas scavenging system. In pediatric anesthesia,
systems other than those with a circle absorber
may be used. Choice of the breathing circuit that
best meets the needs of pediatric patients may
alter a clinician’s ability to scavenge waste gas
effectively. Breathing circuits frequently chosen
for neonates, infants and small children are
usually valveless, have low resistance and limit
rebreathing. The Mapleson D system and the
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to minimize waste anesthetic gas concentrations.      typical dental office procedure, the nasal mask is      A newer type of mask is a frequent choice in
This system should provide a recommended              placed on the patient, fitted and adjusted prior to     dental practice, a single-patient-use nasal hood.
minimum total of 6 air changes per hour with a        administration of the anesthetic agent. The mask        This mask does not require sterilization after
minimum of 2 air changes of outdoor air per hour      is designed for the nose of the patient because         surgery because it is used by only one patient and
to adequately dilute waste anesthetic gases. Room     access to the patient’s mouth is essential for dental   is disposable.
exhaust containing waste anesthetic gases should      procedures.
                                                                                                              In a dental operatory, a scavenging system is part
not be recirculated to other areas of the hospital.
                                                 A local anesthetic, if needed, is typically                  of a high-volume evacuation system used with a
Work practices                                   administered after the N2O takes effect. The                 dental unit. The vacuum system may dispose of a
PACU managers should consider:                   patient’s mouth is opened and the local anesthetic           combination of waste gases, oral fluid and debris,
 Periodic exposure monitoring with particular is injected. The dental procedure begins after                 and is not limited to waste gas removal. The
   emphasis on peak gas levels in the breathing the local anesthetic takes effect. The patient                exhaust air of the evacuation system should be
   zone of nursing personnel working in the      opens his/her mouth but is instructed to breathe             vented outside the building and away from fresh-
   immediate vicinity of the patient’s head.     through the nose. Nonetheless, a certain amount              air inlets and open windows to prevent re-entry of
   Methods using random room sampling to         of mouth breathing frequently occurs. The dentist            gas into the operatory.
   assess ambient concentrations of waste        may periodically stop the dental procedure for a
                                                                                                         The general ventilation should provide good room
   anesthetic gases in the PACU are not an       moment to allow the patient to close the mouth
                                                                                                         air mixing. In addition, auxiliary (local) exhaust
   accurate indicator of the level of exposure   and breathe deeply to re-establish an appropriate
                                                                                                         ventilation used in conjunction with a scavenging
   experienced by nurses providing bedside care. concentration of N2O in the patient’s body before
                                                                                                         system has been shown to be effective in reducing
   Because of the closeness of the PACU nurse to resuming the procedure. Depending on the nature
                                                                                                         excess N2O in the breathing zone of the dentist
   the patient, such methods would consistently of the procedure, high velocity suction is regularly
                                                                                                         and dental assistant, from nasal mask leakage and
   underestimate the level of waste anesthetic   used to remove intraoral debris and, when used,
                                                                                                         patient mouth breathing. This type of ventilation
   gases in the breathing zone of the bedside    creates a negative air flow and captures some of
                                                                                                         captures the waste anesthetic gases at their source.
   nurse.                                        the gas exhaled by the patient.
                                                                                                         However, there are practical limitations in using
 Application of a routine ventilation system    At the end of the procedure, the nosepiece is left      it in the dental operatory. These include proximity
   maintenance program to keep waste gas         on the patient while the N2O is turned off and the      to the patient, interference with dental practices,
   exposure levels to a minimum.                 oxygen flow is increased. The anesthetic mixture        noise, and installation and maintenance costs. It is
dental operatory                                      diffuses from the circulating blood into the lungs most important that the dentist not work between
Mixtures of N2O and oxygen have been used in          and is exhaled. Scavenging is continued while the the patient and a free-standing local exhaust
dentistry as general anesthetic agents, analgesics    patient is eliminating the N2O.                    hood. Doing so will cause the contaminated air
and sedatives for more than 100 years. The usual      The dental office or operatory should have a       to be drawn through the dentist’s breathing zone.
analgesia equipment used by dentists includes a       properly installed N2O delivery system. This       These auxiliary ventilation systems are not now
N2O and O2 delivery system, a gas mixing bag          includes appropriate scavenging equipment with commercially available. The Academy of General
and a nasal mask with a positive pressure relief      a readily visible and accurate flow meter (or      Dentistry also emphasizes properly installed and
valve. The analgesia machine is usually adjusted      equivalent measuring device), a vacuum pump        maintained analgesia delivery systems.
to deliver more of the analgesic gas mixture than     with the capacity for up to 45 L/min of air per    Work practices
the patient can use.                                  workstation, and a variety of sizes of masks to     Prior to first use each day of the N2O machine
Analgesia machines for dentistry are designed         ensure proper fit for individual patients.              and every time a gas cylinder is changed, the
to deliver up to 70 percent (700,000 ppm) N2O       A common nasal mask, shown in Figure 7,                low-pressure connections should be tested
to a patient during dental surgery. The machine     consists of an inner and a slightly larger outer       for leaks. High-pressure line connections
restricts higher concentrations of N2O from being   mask component. The inner mask has two hoses           should be tested for leaks quarterly. A soap
administered to protect the patient from hypoxia.   connected that supply anesthetic gas to the patient.   solution may be used to test for leaks at
In most cases, patients receive between 30 and      A relief valve is attached to the inner mask to        connections. Alternatively, a portable infrared
50 percent N2O during surgery. The amount of        release excess N2O into the outer mask. The            spectrophotometer can be used to detect an
time N2O is administered to a patient depends on    outer mask has two smaller hoses connected to a        insidious leak.
the dentist’s judgment of patient needs and the     vacuum system to capture waste gases from the        	 Prior to first use each day, inspect all N2O
complexity of the surgery. The most common          patient and excess gas supplied to the patient by       equipment (e.g., reservoir bag, tubing, mask,
route of N2O delivery and exhaust is through a      the analgesia machine. The nasal mask should            connectors) for worn parts, cracks, holes, or
nasal scavenging mask applied to the patient.       fit over the patient’s nose as snugly as possible       tears. Replace as necessary.
Some dentists administer N2O at higher              without impairing the vision or dexterity of the      Connect mask to the tubing and turn on
concentrations at the beginning of the operation, dentist. Gases exhaled orally are not captured by        vacuum pump. Verify appropriate flow
then decrease the amount as the operation           the nasal mask. A flow rate of approximately 45 L/     rate (i.e., up to 45 L/min or manufacturer’s
progresses. Others administer the same amount of min has been recommended as the optimum rate              recommendations).
N2O throughout the operation. When the operation to prevent significant N2O leakage into the room
is completed, the N2O is turned off. Some dentists air.
turn the N2O on only at the beginning of the        Figure 7
operation, using N2O as a sedative during the
administration of local anesthesia, and turn it off
before operating procedures. Based on variations
in dental practices and other factors in room air,
N2O concentrations can vary considerably for each
operation and also vary over the course of the
operation.
Unless the procedure is performed under general
anesthesia in an OR, halogenated anesthetics are
not administered, nor does the patient undergo
laryngoscopy and tracheal intubation. In the
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   A properly sized mask should be selected and      Both enflurane and desflurane are considered         The data provided by monitoring are necessary
    placed on the patient. A good, comfortable fit    hazardous wastes under the EPA regulations           to establish proper engineering, work practice,
    should be ensured. The reservoir (breathing)      because these chemicals contain trace amounts of     and administrative controls to ensure the lowest
    bag should not be over- or underinflated          chloroform (a hazardous substance), a byproduct      reasonably achievable gas levels in the operatory
    while the patient is breathing oxygen (before     of the manufacturing process. Consequently,          and PACU room air.
    administering N2O).                               sorbents that have been saturated with enflurane
                                                                                                            OSHA recommends that air sampling for
   Encourage the patient to minimize talking,        or desflurane should be managed as an EPA
                                                                                                            anesthetic gases be conducted every six months
    mouth breathing and facial movement while         hazardous waste material due to the trace
                                                                                                            to measure worker exposures and to check the
    the mask is in place.                             concentrations of chloroform present. Isoflurane
                                                                                                            effectiveness of control measures. Furthermore,
   During N2O administration, the reservoir bag      and halothane do not contain trace amounts of
                                                                                                            OSHA recommends that only the agent(s) most
    should be periodically inspected for changes      chloroform or any other regulated substance and
                                                                                                            frequently used needs to be monitored, since
    in tidal volume, and the vacuum flow rate         are therefore not considered hazardous wastes by
                                                                                                            proper engineering controls, work practices
    should be verified.                               EPA.
                                                                                                            and control procedures should reduce all agents
   On completing anesthetic administration and
                                                      To minimize exposure to all liquid anesthetic         proportionately. However, the decision to monitor
    before removing the mask, non-anesthetic
                                                      agents during cleanup and to limit exposure           only selected agents could depend not only on
    gases/agents should be delivered to the
                                                      during disposal procedures, the following general the frequency of their use, but on the availability
    patient for a sufficient time based on clinical
                                                      guidelines are recommended. The waste material of an appropriate analytical method and the cost
    assessment that may vary from patient to
                                                      should be placed in a container, tightly sealed,      of instrumentation. ASA emphasizes regular
    patient. In this way, both the patient and the
                                                      properly labeled, and disposed of with other          maintenance of equipment and scavenging
    system will be purged of residual N2O. Do not
                                                      chemical wastes sent to a facility’s incinerator or systems, daily check-out procedures for anesthesia
    use an oxygen flush.
                                                      removed by a chemical waste contractor. After         equipment, and education to ensure use of
Cleanup and disposal of liquid anesthetic             a large spill has occurred and the appropriate        appropriate work practices. It does not believe
agent spills                                          response action taken, airborne monitoring should that a routine monitoring program is necessary
Small volumes of liquid anesthetic agents such        be conducted to determine whether the spill was       when these actions are being carried out. ASA
as halothane, enflurane, isoflurane, desflurane,      effectively contained and cleaned up.                 prefers to use monitoring when indicated, such
and sevoflurane evaporate readily at normal                                                                 as in the event of known or suspected equipment
                                                      Determination of appropriate disposal procedures
room temperatures, and may dissipate before                                                                 malfunction.
                                                      for each facility is the sole responsibility of
any attempts to clean up or collect the liquid        that facility. Empty anesthetic bottles are not       Three fundamental types of air samples can be
are initiated. However, when large spills occur,      considered regulated waste and may be discarded taken in order to evaluate the workplace: personal,
such as when one or more bottles of a liquid          with ordinary trash or recycled. Furthermore, the area and source samples. Personal samples
agent break, specific cleaning and containment        facility as well as the waste handling contractor     give the best estimate of a worker’s exposure
procedures are necessary and appropriate disposal     must comply with all applicable federal, state, and level because they represent the actual airborne
is required. The recommendations of the chemical      local regulations.                                    contaminant concentration in the worker’s
manufacturer’s material safety data sheet (MSDS)                                                            breathing zone during the sampling period.
that identify exposure reduction techniques for       To minimize exposure to waste liquid anesthetic
                                                                                                            This is the preferred method for determining a
spills and emergencies should be followed.            agents during cleanup and disposal, the following
                                                                                                            worker’s time-weighted average (TWA) exposure
                                                      general guidelines are recommended by the
In addition, OSHA Standard for Hazardous Waste                                                              and should be used to assess personal exposures
                                                      manufacturers of liquid anesthetic agents:
Operations and Emergency Response would apply                                                               during anesthetic administration and in the PACU.
                                                       Wear appropriate personal protective
if emergency response efforts are performed                                                                 Where several health-care workers perform the
                                                           equipment. Where possible, ventilate area of
by employees. The employer must determine                                                                   same job, on the same shift, and in the same
                                                           spill or leak. Appropriate respirators should
the potential for an emergency in a reasonably                                                              work area, and the length, duration, and level of
                                                           be worn.
predictable worst-case scenario, and plan response                                                          waste gas exposures are similar, an employer may
                                                       Restrict persons not wearing protective
procedures accordingly. Only adequately trained                                                             sample a representative fraction of the employees
                                                           equipment from areas of spills or leaks until
and equipped workers may respond to spills.                                                                 instead of all employees.
                                                           cleanup is complete.
When the situation is unclear or data are lacking      Collect the liquid spilled and the absorbent        Area sampling is useful for evaluating overall
on the exposure level, the response needs to be the        materials used to contain a spill in a glass     air contaminant levels in a work area and for
same as for high levels of exposure. Responses             or plastic container. Tightly cap and seal the   investigating cross-contamination with other areas
to incidental releases of liquid anesthetic agents         container and remove it from the anesthetizing in the health-care facility. Source sampling can be
where the substance can be absorbed, neutralized           location. Label the container clearly to         used to detect leaks in the anesthesia delivery and
or otherwise controlled at the time of release by          indicate its contents.                           scavenging systems as well as ineffective capture
employees in the immediate release area, or by         Transfer the sealed containers to the waste         by the scavenging system. Thus, how samples are
maintenance personnel do not fall within the scope         disposal company that handles and hauls          taken is a critical point in any safety program.
of this standard.                                          waste materials.
                                                                                                            The OSHA Chemical Information Manual
Because of the volatility of liquid anesthetics,       Health-care facilities that own or operate
                                                                                                            contains current sampling technology for several
rapid removal by suctioning in the OR is the               medical waste incinerators may dispose of
                                                                                                            of the anesthetic gases that may be present in
preferred method for cleaning up spills. Spills            waste anesthetics by using an appropriate
                                                                                                            anesthetizing locations and PACUs. Some of
of large volumes in poorly ventilated areas or             incineration method after verifying that
                                                                                                            the sampling methods available are summarized
in storage areas should be absorbed using an               individual incineration operating permits
                                                                                                            below.
absorbent material, sometimes called a sorbent,            allow burning of anesthetic agents at each site.
that is designed for cleanup of organic chemicals.                                                         Time-integrated sampling
“Spill pillows” commonly used in hospital
                                                      Air monitoring                                          Nitrous oxide
                                                      Air monitoring is one of the fundamental                 Personal N2O exposures can be determined
laboratories, vermiculite, and carbon-based
                                                      tools used to evaluate workplace exposures.              by using the VAPOR-TRAK nitrous oxide
sorbents are some of the materials commercially
                                                      Accordingly, this section presents some of the           passive monitor (sometimes called a
available and regularly used for this purpose.
                                                      appropriate methods that can be used to detect and       “passive dosimeter” or “diffusive sampler”)
Caution should be exercised if broken glass bottles
                                                      measure the concentration of anesthetic gases that       as referenced in the 2000 OSHA Chemical
pose a hazard.
                                                      may be present in the health-care environment.           Information Manual under IMIS:1953. The
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    minimum sampling duration for the dosimeter       attire is worn in the OR. Proper attire consists of    names. In addition, information must be provided
    is 15 minutes; however, it can be used for up     body covers such as a two-piece pantsuit (scrub        on the physical and chemical characteristics of
    to 16 hours of passive sampling. This sampler     suit), head cover (cap or hood), mask, and shoe        the hazardous chemical, known acute and chronic
    has not been validated by OSHA. Other             covers. A sterile gown is worn over the scrub suit     health effects and related health information,
    dosimeters are commercially available and can     to permit the wearer to come within the sterile        primary route(s) of entry, exposure limits,
    be used. Although not validated by OSHA at        field. Other attire such as gloves and eyewear         precautionary measures, emergency and first-
    this time, they may be validated in the future.   may be required. Some hospitals, but not all, may      aid procedures, and the identification of the
    Five liter, 5-layer aluminized gas sampling       allow persons coming into the OR to wear a clean       organization responsible for preparing the sheet.
    bags can also be used to collect a sample.        gown (in addition to the cap, the mask, and the        As a source of detailed information on hazards,
   Halogenated agents                                shoe covers) over their street clothes if they are     copies of the MSDS for each hazardous chemical
    Three chlorofluorocarbon-based anesthetic         not going to remain in the OR for longer than 10-      must be readily accessible during each work shift
    agents (halothane, enflurane, and isoflurane)     15 minutes.                                            to employees when they are in their work area(s).
    and one fluorocarbon-based agent (desflurane)
                                                      In regard to decontaminating outside equipment,        Employers must prepare a list of all hazardous
    are listed in the Chemical Information
                                                      each hospital has its own policy. However, the         chemicals in the workplace, and the list should
    Manual. The OSHA sampling procedure
                                                      common practice is to “wipe off” all surfaces          be checked to verify that MSDSs have been
    for halothane is listed under IMIS:0395; for
                                                      with a chemical disinfectant. Most hospitals use       received for each chemical. If there are hazardous
    enflurane, under IMIS:1038; for isoflurane,
                                                      Wescodyne or other phenolic solutions. Good            chemicals used for which no MSDS has been
    under IMIS:F118; and for desflurane, under
                                                      physical cleaning before disinfection helps reduce     received, the employer must contact the supplier,
    IMIS:R218.
                                                      the number of microorganisms present and               manufacturer or importer to obtain the missing
      The current recommended media sampling for enhances biocidal action.                                   MSDS.
      halothane, enflurane and isoflurane requires
                                                      Any person not familiar with the OR is usually         Health care employers must establish a training
      an Anasorb 747 tube (140/70 mg sections) or
                                                      instructed by a scrub nurse on all the safety          and information program for all personnel who are
      an Anasorb CMS tube (150/75 mg. sections).
                                                      procedures pertaining to the hospital. The scrub       involved in the handling of, or who have potential
      The sample can be taken at a flow rate of 0.5
                                                      nurse will also provide instructions on hand           exposure to, anesthetic gases and other hazardous
      L/min. Total sample volumes not exceeding
                                                      scrubbing and other procedures that may be             chemicals to apprise them of the hazards
      12 liters are recommended. The current
                                                      necessary. Persons entering the OR must follow         associated with these chemicals in the workplace.
      recommended sampling media for desflurane
                                                      these guidelines and instructions.                     Training relative to anesthetic gases should place
      requires an Anasorb 747 tube (140/70 mg
                                                                                                             an emphasis on reproductive risks. Training
      sections). The sample can be taken at a flow    In addition, it should be recognized that the
                                                                                                             and information must take place at the time of
      rate of 0.05 L/min. Total sample volumes not patient’s welfare, safety, and rights of privacy are
                                                                                                             initial assignment and whenever a new hazard
      exceeding 3 liters are recommended. All four paramount.
                                                                                                             is introduced into the work area. At a minimum,
      sampling methodologies are fully validated
                                                      Hazard communication                                   employees must be informed of the following:
      analytical procedures.
                                                      In accordance with the Hazard Communication             The Hazard Communication Standard (29
Real-time sampling                                    Standard (29 CFR 1910,1200), employers in                   CFR 1910.1200) and its requirements.
Sampling that provides direct, immediate, and         health care facilities must develop, implement          Any operations and equipment in the work
continuous (real-time) readout of anesthetic gas      and maintain at the workplace a written,                    area where anesthetic agents and hazardous
concentrations in ambient air utilizes a portable     comprehensive hazard communication program                  chemicals are present.
infrared spectrophotometer. Since this method         that includes provisions for container labeling,        Location and availability of the written
provides continuous sampling and instantaneous collection and availability of material safety data                hazard communication program including the
feedback, sources of anesthetic gas leakage           sheets (MSDSs), and an employee training and                required lists of hazardous chemicals and the
and effectiveness of control measures can be          information program. The standard also requires             required MSDS forms.
immediately determined.                               a list of hazardous chemicals in the workplace         The employee training program must consist of
                                                      as part of the written hazard communication            the following elements:
Additional sampling guidelines
                                                      program.                                                How the hazard communication program is
If it should ever be necessary to enter an operating
room to conduct air sampling, the following           Any chemicals subject to the labeling                      implemented in the workplace, how to read
guidelines provide the information needed.            requirements of the FDA are exempt from                    and interpret information on the MSDS and
Individuals performing air sampling should be         the labeling requirements under the Hazard                 label of each hazardous chemical, and how
familiar with and follow all OR procedures for        Communication Standard. This includes such                 employees can obtain and use the available
access into and out of the surgical suite with        chemicals as volatile liquid anesthetics and               hazard information.
particular attention to sterile and nonsterile areas. compressed medical gases. However, containers           The physical and health hazards of the
The patient is the center of the sterile field, which of other chemicals not under the jurisdiction of the       chemicals in the work area.
includes the areas of the patient, operating table, FDA must be labeled, tagged or marked with the            Measures employees can take to protect
and furniture covered with sterile drapes and the identity of the material and must show appropriate             themselves from these hazards, including
personnel wearing sterile attire. Sampling in the     hazard warnings as well as the name and address            specific procedures put into effect by the
breathing zone of surgeons and other nursing or       of the chemical manufacturer, importer, or other           employer to provide protection such as
technical personnel who work in the sterile field     responsible party. The hazard warning can be any           engineering controls, appropriate work
must conform to the principles of sterile field       type of message – words, pictures, or symbols              practices, emergency procedures for spill
access. Strict adherence to sound principles of       – that conveys the hazards of the chemical(s) in           containment, and the use of personal
sterile technique and recommended practices is        the container. Labels must be legible, in English          protective equipment.
mandatory for the safety of the patient.              (plus other languages if desired), and prominently      Methods and observations that may be used
                                                      displayed.                                                 to detect the presence or release of anesthetic
Generally speaking, each hospital has its own                                                                    gases and other hazardous chemicals in the
guidelines for proper OR attire and other safety      Each MSDS must be in English, although the                 work area (such as monitoring conducted by
procedures. These rules should be strictly            employer may maintain copies in other languages            the employer, continuous monitoring devices,
followed by anyone entering the OR. There are         as well, and must include information regarding            and the appearance or odor of chemicals when
standard uniform guidelines that apply to all         the specific chemical identity of the anesthetic           released).
hospitals. Only clean and/or freshly laundered OR gases or hazardous chemical and its common
Elite CME - www.EliteCME.com                                                                                                                             Page 17
Personnel training records are not required to     4       Connect mask to         Determine           8           Repeat procedure in                If personal
be maintained, but such records would assist               hose and turn on        proper vacuum                   step 7.                            exposures are
employers in monitoring their programs to ensure           vacuum pump before      pump size for                                                      less than 150
that all employees are appropriately trained.              turning on N2O.         maintaining 45                                                     ppm but greater
Employers can provide employees information                Scavenging system       lpm flow rates,                                                    than 25 ppm,
and training through whatever means are found              vacuum pump must        especially                                                         implement
appropriate and protective. Although there                 have capacity to        when                                                               auxiliary
would always have to be some training on-site              scavenge 45 lpm per     interconnected                                                     exhaust
(such as informing employees of the location               dental operation.       with other                                                         ventilation near
and availability of the written program and                                        dental                                                             the patient’s
MSDSs), employee training may be satisfied in                                      scavenging                                                         mouth. Capture
part by general training about the requirements                                    systems. If                                                        distance should
of the hazard communication standard and about                                     undersized,                                                        no greater than
chemical hazards on the job which is provided by,                                  replace pump.                                                      10 inches from
for example, professional associations, colleges,                                                                                                     the patient’s
universities, and training centers. In addition,   5       Place mask on           Secure mask
                                                           patient and assure a    with “slip”                                                        nose and
previous training, education and experience of a                                                                                                      mouth area
worker may relieve the employer of some of the             good, comfortable       ring for “good
                                                           fit. Make sure          activity”                                                          and exhaust
burdens of informing and training that worker. The                                                                                                    no less than
employer, however, maintains the responsibility to         reservoir bag is not    from patient
                                                           over- or under-         breathing.                                                         250 cfm at the
ensure that employees are adequately trained and                                                                                                      hood opening.
are equipped with the knowledge and information            inflated while the
                                                           patient is breathing.                                                                      Avoid getting
to do their jobs safely.                                                                                                                              between the
                                                   6       Check general           If smoke from                                                      auxiliary
  Step-by-step approach for controlling N2O                ventilation for         smoke tubes                                                        exhaust hood
 Step          Procedure              Control              good room air           indicate room                                                      and patient’s
 1        Visually inspect        Replace                  mixing. Exhaust         air mixing                                                         mouth and
          all N2O equipment       defective                vents should not be     is poor, then                                                      nose area.
          (reservoir bag,         equipment and/           close to air supply     increase the
          hoses, mask,            or parts.                vents (use smoke        airflow or         Conclusion
          connectors) for worn                             tubes to observe air    redesign. If       Nitrous oxide is used in many dental and
          parts, cracks, holes,                            movement in room.)      exhaust vents      medical offices and should be used with care.
          or tears.                                                                are close to air   It is the most frequently used sedation method
                                                                                   supply vents,      used in dentistry. All bodily functions remain
 2        Turn on the N2O         Determine                                        relocate (check    normal, and the patient is able to breathe on his/
          tank and check          leak source                                      with ventilation
          all high- to low-       and fix. If tank
                                                                                                      her own. The patient will not fall asleep and
                                                                                   engineers          will not have memory loss. It is best used for
          pressure connections    valve leaks,                                     to make
          for leaks. Use          replace tank;                                                       mildly anxious patients who wish only a small
                                                                                   adjustments).
          a non-oil-based         if O-rings,                                                         amount of sedation to “take the edge off” or to
          soap solution to        gaskets,             7   Conduct personal        If personal        make them less nervous. The patient is able to
          check for bubbles       valves, hoses,-          sampling of dentist     exposures          respond appropriately to physical stimulation
          at high pressure        or fittings,             and dental assistant    exceed 150         and verbal commands. It is a way for the dentist
          connectors, or use a    replace.                 for N2O exposure.       ppm during         to manage pain and anxiety during dental
          portable infrared gas   Contact the              Use diffusive           administration,    appointments, but they must also administer it
          analyzer.               manufacturer             sampler or infrared     improve
                                                                                                      wisely and with caution. Each dental or medical
                                  for parts                gas analyzer (see       mask fit and
                                                                                                      office should establish its own comprehensive
                                  replacement.             sampling methods).      make sure it
                                                                                   is secure over
                                                                                                      training program on how to maintain the
                                  For threaded                                                        equipment and proper safety standards. This
                                  pipe fittings,                                   the patient’s
                                                                                   nose. Minimize     course should help you to review your office
                                  use Teflon tape.                                                    routines and make sure you are setting the way
                                  Do not use                                       patient talking
                                                                                   while N2O is       to achieve the best safety standards for your
                                  this tape on
                                                                                   administered.      patients and for your employees.
                                  compression
                                  fittings.                                                           Bibliography
                                                                                                      s“Nitrous oxide and its abuse”; Theodore J. Jastak, Journal of the American
 3        Select scavenging       Provide a range                                                     Dental Association, 1991. Abstract accessed Sept. 15, 2010, at http://www.
          system and mask.        of mask sizes                                                       faqs.org/abstracts/Health/Nitrous-oxide-and-its-abuse-Quantification-and-
                                                                                                      analysis-of-pain-in-nonsurgical-scaling-and-or-root-p.html.
          Mask should come        for patients.                                                       s“46 Health Care Professionals Linked to Substance Abuse,” Bristol Herald
          in various sizes to     Check to see                                                        Courier, April 26, 2009.
                                                                                                      sFederation of State Physician Health Programs. http://www.fsphp.org.
          patients. Scavenging    that noise                                                          sNitrous Oxide-Oxygen: A New Look at a Very Old Technique; Stanley F.
          systems should          levels at the                                                       Malamed, DDS, and Morris S. Clark, DDS. Journal of the California Dental
                                                                                                      Association. 2003
          operate at air flow     mask are
          rate of 45 lpm.         acceptable
                                  when the
                                  scavenging
                                  system exhaust
                                  rate is operated
                                  at 45 lpm.
Page 18                                                                                                                              Elite CME - www.EliteCME.com
                                                NOTES
          niTRous oxidE – n2o
          Final Examination Exercises
        Choose True or False for questions
    1 through 5 and mark your answers on the
        Final Examination Sheet found on
        page 96 or take your test online at
           www.onlinedentalCE.com.



 1. Long-term exposure to nitrous oxide can
    cause reproductive side effects.
          True                 False

 2. The National Institute for Occupational
    Safety and Health recommended, in
    a technical report published in 1977,
    controlling exposure limits of nitrous
    oxide waste to 35 parts per million (ppm)
    of air during dental surgery.
          True                 False

 3. Inhaled anesthetic agents include two
    different classes of chemicals.
          True                 False

 4. Venting waste anesthetic gas via the
    exhaust grille or exhaust duct of a non-
    recirculating ventilation system is an
    example of an active system.
          True                 False

 5. Three fundamental types of air samples
    can be taken to evaluate the workplace;
    they are personal, area and source
    samples.
          True                 False




                                                        DCA05NOE11
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