Laparoscopic Energy Sources UNM Health Sciences Center

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Laparoscopic Energy Sources UNM Health Sciences Center Powered By Docstoc
					                Physics and General Concepts of Laparoscopic Energy Sources
                               Lonika Majithia, MS III. UNM SOM

Laparoscopy uses several different sources of energy including monopolar electrosurgery, bipolar
electrosurgery, argon beam coag, laser, and ultrasonic coag and scalpel. A new source using thermal
electrocautery has recently been released but is not evaluated in this review. All sources have
approximately the same rate of conversion to open abdominal surgery.

1. Electrosurgery:
The basics of electricity: V=IR. In an AC system, there is the skin effect which decreases resistance due to
the decrease in cross-sectional area of conduction (R=(length X resistivity)/cross sectional area). The
resistivity is temperature dependent. As electrolytes are considered semi-conductors there resistivity
decreases with temperature, and therefore conduction increases. In the biologic system conduction
occurs by the ions carrying the electric charge and passing through ion channels.

The electrosurgery techniques use alternating current input at a frequency of ~300 kHz to 2 MHz
(radiofrequeny) depending on the function (coag vs cut). The reason thermal energy is produced is due
to the quick change in conductivity from the electrode to the tissue. The contact point (or near contact
point) between the electrode and tissue has a small cross sectional area and the tissue has more internal
e- resistance. Therefore energy conservation laws with high tissue current density cause local heat
production (150-400˚C).

Settings include coag, cut, and blend. The difference between these settings is variations in the
amplitude and waveform.
    a. Cutting mode uses continuous low-voltage conduction. It can be used without tissue contact
        creating a clean cut with no coag or can be placed in direct contact with tissue (dissection)
        causing local coag.
    b. The blend mode uses intermediate voltage with rest cycles. The times when current is running is
        the cutting stages and the resting periods between are coag stages. The mode is used for cutting
        with hemostasis.
    c. Coag mode uses a high voltage with long rest cycles and short duration of conduction. It can be
        used with tissue contact for dissection or non-contact as a spray/fulguration to cause diffuse
        coag. The spray approach should only be used for a small amount of time to cause a superficial
        injury, if used longer it can cause deeper tissue damage. Also the low voltage coag should be
        used for laparascopic procedures to reduce insulation failure and capacitive coupling.

Complications with electrosurgery include thermal and electrical injury, particularly with a monopolar
source. There can be injury from operator error, such as incorrect location, inadequate blunt dissection,
or direct coupling (electrode too close to another metal instrument allowing current passage through
that instrument to tissue which can be visualized as a spark or arc). Injury can also occur due to
characteristics of the instrument such as insulation failure. There is an insulator surrounding the
electrode that, over time, wears down or can be cut which can form a stray current which can injure the
part of the body in contact with the insulation break. Another cause of insulation failure is frequent use
of the coag mode which uses a much higher voltage than the cutting mode, increasing insulation
breakdown. Capacitive coupling occurs between the monopolar electrode and the metal cannula it is
encased in. There is an insulation layer between then which acts as a capacitor and can conduct an
electrostatic field from the electrode out, which again can cause contact burn or abnormal return paths.
Late tissue injury can occur from these abnormal return paths if the cross-sectional area condenses to
create a power density >7.5 W/cm2. These stray currents can cause symptoms (fever, abd pain) several
days post-op due to the internal burns causing necrosis and abscess formation which can further
develop into adhesions, peritonitis, septic shock, hemorrhage, etc which can require further surgery and
increase mortality. A good tool for detection of insulation failure and capacitive coupling is active
electrode monitoring (AEM) which is a conduction shield in the wire lining that stops current flow if any
stray current is identified. Patients with pacemakers and ICDs are at an increased risk for current flow
from, particularly, monopolar pole to the pacemaker/ICD. This risk has been reduced with use of a
grounding pad in monopolar electrocautery; however, other precautions are routinely use including
assessing good function of pacemaker/ICD, turning off pacemaker/ICD (place on monitor only mode)
before surgery, placing magnet over pacemaker/ICD, use short bursts with monopolar, placing
grounding pad away from thorax, and keeping all wires from direct contact with the thorax.

1a. Monopolar electrosurgery(Bovie) uses a single electrode with a grounding pad usually placed on the
thigh. The current passes through the electrode to the pad, via the tissue/electrolytes in a direct path.
There is an increased risk of local and distal thermal damage with monopolar vs bipolar due to operator
imprecision, insulation breakdown, direct coupling, and capacitive coupling (see above). A monopolar
source can also increase the incidence of bowel injury, though minimally (0.07%, El-Banna). Monopolar
source causes more lateral and deep tissue injury, and depending on the tissue and voltage settings, can
cause necrosis 1-6 mm below area of use and lateral spread 2.5 mm away.

1b. Bipolar electrosurgery uses two electrodes, a conducting pole (or tine) and receiving pole. The tissue
is placed between the two electrodes and current is run until no further current can pass (no ions
present). Bipolar is considered to cause less thermal damage to nearby tissue compared to monopolar
due to the local completion of the circuit, but can still cause significant lateral thermal tissue injury.
Bipolar does not make a clean cut and has no fulguration mode.

2. Ligasure Vessel Sealing Systems (Ligasure lap, 5 mm, Advance, Atlas, etc)
The Ligasure devices use electrocautery to fuse blood vessels <7mm in size along with lymphatics and
tissue bundles in 2-4 sec. It causes less thermal injury to local tissue (radius of 2 mm outside of applied
field with even less using Ligasure Advance). The Ligasure devices are RF generators which are
controlled by a microprocessor system. The seal is formed by heating the vessel and reshaping the
collagen and elastin in the wall. The microprocessor monitors the tissue properties and stops the current
flow and allowing the area to cool which solidifies the seal.

3. Harmonic /Ultrasound :
Ultrasound started being used in laparascopic surgery in place of electrosurgery was due to decrease in
thermal tissue injury and no electrical injury.

Ultrasound coag devices use an electric generator which sends current into the device. The electrical
energy activates the transducer which emits ultrasonic mechanical waves, which are transmitted to the
blade/forceps with amplification to 55.5 kHz. Of the two blades one is stationary and the other applies
the ultrasound wave to the field. Therefore the stationary blade can be rested on tissue to stabilize the
instrument. There are low and high power dissectors which are differentiated by their effect on tissue.
Low power (used for liver surgery) dissectors cause inertial cavitation with cellular injury but does not
damage vessels or bile ducts. High power (gyn/GI) causes inertial cavitation along with coaptation.
Cavitation causes a lower pressure region to form (bubble) in cellular fluid, which oscillates with the
incoming waves (non-inertial cavitation). Once the bubble and incoming waves are out of sync the
bubble collapses (inertial cavitation) causing cellular rupture and heat production. The vapor produced
can separate the tissue planes which helps surgeons locate proper dissection limits. There is also the
question of sonoluminscence in these collapsing structures. Copatation is the transfer of mechanical
energy into friction which breaks H bonds and denatures proteins, which causes a sticky coagulum to
form and seals vessels with a temp production <100˚C. Overall ultrasound devices decrease thermal
injury, nerve injury, and smoke. Thermal injury does still occur and this can be minimized by using lower
transduction energy and not using energy continuously.

The harmonic scalpel or shear is used to divide and seal small and medium sized vessels (<5mm) by
tamponade and heat production. It also causes less tissue to stick to the blade allowing for safer
dissections in critical areas.

4. Argon Beam Coag (ABC):
Argon-18 is the 3rd noble gas and is colorless. Current is applied to the tissue by a directed beam of
ionized argon gas. This method causes a uniform and shallow coag surface. There is less tissue damage,
faster coagulation, and less smoke production. Literature sites use in pulmonary wedge resection and tx
for spontaneous PTX. There have been several case reports of fatal venous gas emboli formation with
laparascopic ABC. With argon beam application the abdominal CO2 can be displaced, causing an
increasein intra-abdominal pressures (one case increased to 33mmHg), which can exceed venous
pressure (3-18 mmHg at IVC) creating argon-enriched gas emboli. The increased abdominal pressure can
also cause mechanical injury to the CV and respiratory systems by compressing the IVC and elevating the
diaphragm.

5. Laser:
Not generally used in laparascopic procedures previously due to expense, gas toxicities, and
maintenance. With the development of solid state diode lasers newer applications are being tried.
Lasers are EM radiation so their effects are similar to electrosurgery in that they cause thermal damage,
retinal injury to surgeon, accidental burns, etc. Currently gyn use for laser surgery is for endometriosis
ablation. Following are types of lasers:
-Argon (above): used for endometriosis ablation, the Hb absorbs more than the tissue, changing the
vascular nature of lesions.
-CO2 laser: thin superficial ablation, does not coag, can cause distal abdominal injury.
-Contact Nd:YAG laser: used laparascopically more than any other, does not produce deep hemostasis as
well as monopolar electrosurgery.

Sources:
-Electrosurgical safety during laparoscopic surgery. Willson P.D., et al. Minimally Invasive Therapy & Allied
Technologies. 1995, Vol. 4, No. 4, Pages 195-201.
-Cardiac Arrest During Laparotomy With Argon Beam Coagulation of Metastatic Ovarian Cancer. Kizar N, et al.
International Journal of Gynecological Cancer. 02/2009. Vol 19, Issue 2. pp 237-238.
- An overview of laparoscopic dissection modalities. Sangster T.P., et al. World Laparascopic Hospital. 11/2008.
http://www.laparoscopyhospital.com/dissection.htm
- Management of laparoscopic-related bowel injuries. El-Banna, M et al. Surgical Endo(2000):14, 779-82.
- Maintenance of Electrosurgical Accessories. Guide to Maintenance of Electrosurgical Accessories National Panel
on Clinical Engineering/BEAG(NSW). 02/2000.
-Harmonic energy. McCarus SD., Nezhat C. Advanced Laparoscopic Surgery. 2006.