MONKLANDS DIVER MEDIC MANUAL
This course is designed to equip the candidate to deal with medical crises, which
may occur under pressure and at sea level.
In order to pursue the underwater perspective a short resume of underwater
physiology is given below.
In underwater diving a facemask is worn. In the air most of the refraction (bending)
of light takes place by the cornea, which is the front part of the eye. Underwater this
refraction is lost, resulting in blurred vision and most of the focusing ability of the eye
is lost. The facemask traps a pocket of air in front of the eye, improving the situation
but light is refracted at the faceplate, which makes objects, appear larger and closer
than they actually are.
2. Pressure Changes
Gas varies its volume according to pressure, water does not. For example, if the
pressure in a given volume of gas is increased, the volume decreases (Boyle’s Law).
If the pressure in a given amount of gas is doubled the volume is reduced by half but
if the pressure in a given volume of water is increased the volume remains virtually
At sea level (barometric pressure of 760mmHg) the weight of air produces a pressure
of 14.7 psi - referred to as one Ata of pressure. If the water pressure on a diver is
taken to be one Ata absolute (1Ata) at the surface, it has been shown that water
pressure increases by 1 Ata for every 10 metres that the diver descends. The
following table demonstrates the effect of water depth on Ata and volume mass of
DEPTH (Metres) PRESS. (Ata) VOLUME (Fixed Mass of Gas)
0 1 1
10 2 ½
20 3 1/3
30 4 ¼
It is important to stress that the body has pockets of air e.g. airway and lungs, gastro-
intestinal tract (oesophagus, stomach and bowels), middle ears, sinuses and behind
fillings in teeth. As the depth increases, so does the pressure within these gas
pockets. However inequalities in pressure can result in symptoms related to these
areas - both during ascent and descent.
3. Ears and Sinuses
During a descent the eardrums bend resulting in pain unless pressure is equalised
through the Eustachian tubes. This equalisation does not happen automatically. It
can be achieved by using the valsalva manoeuvre. “Squeezing” of the sinuses of the
head may cause facial pain.
4. Breath Hold Diving
Hyperventilation before diving can result in loss of consciousness by causing a delay
in the urge to breathe which is normally caused by an increase in the level of arterial
C02. Hyperventilation “blows off” some of the C02 and this reduction in CO2 prolongs
the time the breath can be held. There is no significant increase in the amount of O 2
stored in the body by hyperventilation. Oxygen is consumed during the dive but low
levels do not cause much urge to breath but may result in unconsciousness before
the C02 level is high enough to compel the diver to breath and thus the diver will have
no insight or warning of the risk.
5. Affects of changes in Pressure on Air Spaces
If a diver takes a deep breath at 4Ata below the surface and proceeds to the surface
without exhaling. Trapped gas within the chest will expand the lung beyond normal
size and cause rupture of the alveoli, which are the smallest and most vulnerable air
spaces in the lung. Severe rupture results in shattering of lung tissues, capillaries
and veins and propels gas into the circulation where it can cause further damage.
The injury to the lung can result in it collapsing (Pneumothorax - pneumo - air,
thorax - chest) and the passage of air along the circulation can result in brain
damage or death (air embolism)
6. Air embolus
In an air embolism, air bubbles are forced by the above mechanism into torn blood
vessels in the lung and subsequently travel along the circulation to the heart, where
they can impair its pumping action and/or be pumped to any part of the body,
resulting in circulatory blockage, causing paralysis, coma and death. The presence
of gas in the blood triggers mechanisms, which damage and derange the blood.
7. Pneumothorax (Entry of air into the Chest Cavity)
Following the rupture of lung tissue (alveoli) there may be an accumulation of air in
the chest cavity (pneumothorax). As the diver continues his/her ascent, the air in the
pleural cavity will expand further resulting in a collapsed lung. A continuous
expansion of the air will result in a collapsed lung and the heart being pushed to the
opposite side of the chest (tension pneumothorax). This constitutes a life threatening
crises where the pumping action of the heart will be severely impaired to the point
that the diver will become unconscious and the heart will eventually arrest (stop
beating effectively - cardiac arrest). This situation can be remedied by draining the
entrapped gas in the chest. Passing a tube into the affected side of the chest does
8. Decompression Sickness
Helium and Nitrogen are inert gases (the body does not naturally consume it unlike
oxygen). As the diver descends the pressure around the diver increases, forcing the
inert gases into the solution within the blood and tissues. The greater the depth, the
longer the time of the dive, the higher the exercise intensity and the warmer the diver
the more inert gas will go into solution in the tissues. Helium and Nitrogen dissolves
quite rapidly in the blood. The inert gas in the tissues is not a problem until the diver
ascends towards the surface. The decrease in pressure may lead to bubble
formation in the blood or tissues and cause circulatory blockage and tissue damage.
A very fast ascent by the diver has been compared to the removal of a cap of soda
bottle in that the dissolved gas is liberated and forms the bubbles. A diver can reach
the surface from 30 metres (4Ata) in 2 or 3 minutes, the diver will breath air at
atmospheric pressure on the surface but will have inert gas dissolved in his blood
and tissues at a pressure equivalent to his dive depth of 4 Ata. Another complication
includes bubbles reaching the heart and brain, cutting off the blood supply to these
organs, triggering a heart attack or causing brain or nerve damage. Paralysis of the
legs can result from bubble formation in the spinal cord. By and large the sooner
symptoms occur after a dive the more serious the decompression illness, but there
can be a delay. (For these reasons any discomfort and illness after a dive must be
presumed to be decompression illness until proven otherwise.)
Prevention of Decompression Illness
1. The dive is restricted in depth (10m or 2 Ata).
Although most tables allow unrestricted diving to shallower depths, it should be
remembered that repeated descents and ascents would result in the accumulation
of inert gas within the tissues, thereby resulting in the possibility of DCI.
2. Divers who descend more than 2 Ata but limit their time at depth based on
3. Beyond certain limits of depth and time the accumulation of inert gas requires a
decompression period i.e. the return to the surface must be slowed to permit
elimination of inert gas through the lungs to avoid large bubble formation which
can cause damage. If this has been omitted or cannot be arranged then rescue
treatment is by use of recompression i.e. - the DDC pressure is raised to a level,
which controls symptoms. The increased pressure results in the inert gas being
forced back into solution. With slow decompression the inert gas is allowed to
come slowly from the solution without bubble formation and be exhaled. Oxygen
breathing at safe pressures (1.6 Ata or less) will speed up this process.
Nitrogen narcosis - Nitrogen in the air at high pressure acts like an anaesthetic gas.
That is to say it impairs the action of the brain and nerves. The greater the depth, the
worse the effect. CNS, the central nervous system is affected by nitrogen narcosis.
The symptoms include dizziness, impaired judgement and euphoria. While nitrogen
narcosis is not in itself fatal, it can impair judgement and ability at depth, which may
lead, to serious accidents. The greater depth, the more nitrogen is forced into
solution in the body. It should be noted that the effects are individualistic. The depth
at which divers are affected varies, and there is marked variation in the severity of
9. High Pressure Neurological Syndrome
This was described in 1965 following some Royal Navy experiments as a condition
found in depths in excess of 160 metres. The developments of symptoms are related
to the rate of compression at great depths. The serious symptoms include in order of
progression - course tremor, inco-ordination, and disorientation, leading to poor
judgement, apathy and confusion. These effects are minimised by the use of Tri-mix
i.e. oxygen, nitrogen and helium. Other means of avoiding this syndrome are slow
compression to saturation depth from which short excursions may be carried out at
greater depths with fairly rapid compression rates, which would otherwise not be
When subjects are exposed to extreme depth for prolonged periods a condition
known as hydrostatic pressure syndrome can occur. This is not related to the rate of
compression but to the duration of it. Treatment for both these conditions is gradual
decompression until symptoms disappear.
Section 1a Circulation and 1b Bleeding & 1 c Shock and 1d Management of
For this section the following are your learning objectives. There is a short self-test
questionnaire at the back.
1. Understanding the circulatory mechanism
2. Full understanding of the significance and signs of shock
Understand and describe the treatment for shock
a) Circulation (see Diagram 1, pages 9-11)
The heart is a muscular pump with four chambers, which drive two circuits of blood
round the body. If the circulation fails the body sacrifices less important cells and
tissues in order to maintain the brain. It receives used blood from all the major
organs e.g. brain, internal organs and limbs, pumps this blood through a moderately
high pressure system round the lungs where the blood obtains oxygen and carbon
dioxide is expelled into the lungs. This blood is received back into the left side of the
heart where it is pumped round the main organs of the body to provide them with
oxygen and other essential items. The vessels, which deliver the blood to these
organs, are called arteries. They have thick muscular walls and deliver blood in
pulses under high pressure. A pulse can be felt by an examining finger at various
sites in the body e.g. neck (carotid), wrist (radials) and groins (femorals). The
significance of all these sites is that when a subject is talking to you they must have a
carotid pulse as the heart clearly is delivering blood to the brain. If they do not have
a radial pulse there is a significant reduction in the blood pressure (shock). If they do
not have a femoral pulse then the reduction in blood pressure is even more serious.
Pressures required to produce pulses in the various areas are given below.
Radial 80mmHg pressure
Femoral 70mmHg pressure
Carotid 60mmHg pressure
Normal blood pressure is 120/80mmHg. (systolic/diastolic BP mmHg)
The reason for the normal blood pressure being expressed in this way is that it is in
the form of a pressure wave. The highest figure is the high point of the wave and the
lower figure is the minimum level to which the arterial pressure drops. If someone
has lost a significant amount of blood the first change one would note in the blood
pressure would be a change from 120/80 to 120/90. This is because the muscular
arteries squeeze the remaining blood to increase the pressure to normal and for this
reason the lower figure is raised slightly. If even more blood is lost both figures drop
alarmingly. Once the pressure drops to levels of about 80-60 then the circulation to
the kidneys is at risk and replacement of blood loss or even just giving plasma or
fluids to increase the blood pressure could rescue the kidneys at this point. Blood is
delivered to the main organs by the arterial system it is then delivered to the cells of
these organs by a tree like branching of increasingly smaller blood vessels, the
smallest of which are known as capillaries. The thinness of these vessels allows the
blood to be spread over a very large area and also allows oxygen and nutrients to
easily pass from the blood to the tissues.
Once the blood has been delivered to the organs, it then returns to the head by the
low-pressure collection system known as the venous system, which returns to the
right side of the heart where once again it is pumped back to the lungs. The heart is
situated slightly to the left of the midline within the chest. It is well protected by the
ribs. Its main vulnerability in a diving situation is that if a diver sustains a
pneumothorax which goes under tension, this can impair the hearts function to the
point where the pulses are progressively lost i.e. radial, then femoral then ultimately
carotid resulting in death. Its inability to pump can also be impaired if gas is
propelled into the main vessels as this will seriously impair the hearts ability to propel
blood it will simply act to compress the gas within it’s chambers rather than pump
blood. The blood volume is body weight in Kg x 80mls i.e.
1. For a 70Kg man a blood volume of 5.6L would be present.
The blood itself consists of about 50% red cells which are the component of the
blood designed to carry oxygen round the body and is responsible for it’s colour. The
other portion of the blood is mainly fluid which contains factors which control clotting
and also contain the various nutrients, and waste products propelled around the
Diagram 1 (a)
The initial diagram shows a simplified circulation of the flow of blood through the
heart and the remainder of the body. The heart, as is well known, is situated in the
centre of the chest. Its two main neighbours are the lungs and consequently any
upset to these organs can have impact on the others e.g. tension pneumothorax (see
diagram 3) can significantly impair the heart action as can mediastinal emphysema.
The important pulses to look for in the body are in the neck (carotids), the wrists
(radials) and in the groins (femorals) and at the ankle during assessment of leg
injuries. diagram 1(b)
This is where there is failure of the heart to maintain normal circulation. The features
of it are:-
Subject is/has - pale
may have altered consciousness
low blood pressure
shallow and weak breathing
rapid thready pulse (rate >100)
On examination of the periphery it will be noted that the capillary return is
lengthened, the peripheral pulses may disappear in the following order according to
the severity of shock - radials and then femorals. The usual cause of shock in
trauma is either external or internal bleeding. The significance of the latter is that it
cannot be controlled without surgical help and, as such the subject having an injury
like this requires rapid transfer to a hospital facility.
Subclavian Artery Left Common Carotid Artery
Arch of Aorta
Brachial Abdominal Aorta
Left Renal Artery
Left Common Iliac Artery
Posterior Tibial Artery
b) Bleeding (see Diagram 2, page 18-22)
Uncontrolled bleeding is a threat to life. If significant amounts of blood are lost e.g.
half to a third of normal blood volume (normal blood volume of a 70 Kilo subject is 5.6
litres). Then the blood pressure drops and the heart’s ability to produce a normal
pulse is lost. It responds by increasing its rate of pumping.
If a blood vessel is damaged, such as an artery it will be under high pressure. The
simplest way of controlling this bleeding is by direct pressure to the wound and then
a pad can be secured by a dressing and hence the situation remedied. The blood
vessels themselves tend to respond to injury by curling up to the extent that the
leaking hole is closed. This control of bleeding is further reinforced by the body
producing a plug of red cells which stick to the hole and this is further reinforced by
clotting factors forming a rigid framework and hence some kind of repair is achieved.
Loss of sufficient amount of blood to derange the pulse and blood pressure will result
in a condition known as shock. The subject will respond to this state of affairs by
becoming pale, sweaty, anxious or confused and will feel cold to the touch. The
normal signs one would expect e.g. a pulse of 60 at the radial or wrist, blood
pressure of 120/80mmHg will be progressively deranged, the pulse will increase for
example to 100 and the blood pressure will drop for example to 100/80mmHg. In
early shock the lower figure -120/80mmHg may become slightly higher -
120/90mmHg. This is because the body’s response to the situation is for the high-
pressure vessels to stiffen and contract and this acts to maintain pressure but reduce
flow. For this reason the pulse is very difficult to feel. Part of the response of the
skin to this situation is that the blood supply is reduced and it is therefore cold. This
can be confirmed when the pulse is taken, the capillary return test indicates this. The
test is done by squeezing a finger tip until it whitens and then noting the time it takes
to pink up again, normally 2 seconds, shock 3 seconds +. Sweating is also part of the
response and indicates that adrenaline a stress and survival hormone has been
produced in response to this injury.
If this state of affairs continues the blood supply to certain organs can be reduced to
the point where they are seriously damaged. The most important ones are the
kidneys. As blood is progressively lost, the subject will lose consciousness and
ultimately the heart will stop pumping (cardiac arrest). The treatment then is that
external bleeding should be controlled immediately it has occurred by local pressure.
If the subject has lost significant blood then, the treatment is to give 2 litres of Saline
intravenously or replace with blood if available (if necessary this treatment will need
to be repeated). This requires a plastic tube to be inserted into a vein, which is the
part of the circulation that propels fluid back towards the right side of the heart. This
procedure can be life saving. In the case of error i.e. a normal subject does not
require 2 litres of Saline and it is given by mistake, it will not cause any harm. The
act replacing fluid, which returns the circulation to normal and controlling bleeding will
result in the following –
i. heart function returns to normal
ii. the pulse slows down
iii. the blood pressure comes back up to normal
iv the vital organs are spared a potentially serious insult
Other important points:-
1. If inappropriate amounts of intravenous fluids are given in the management of
shock for example more than 2 litres of saline given rapidly in a person who has
normal vital signs i.e. pulse 60, blood pressure 120/80 or so, the first sign of them
coming into difficulty would be anxiousness followed by breathlessness either
difficulty in breathing and or increased rate of breathing.
This is due to the fact that the fluid which has been given inappropriately has leaked
out of the circulation of the lungs i.e. from the vessels in the lungs into lung tissue
making them stiffer which increases the difficulty in breathing and also reduces the
efficiency of the lungs. This can progress to become life threatening with the subject
starting to cough up pink frothy fluid from the lungs and losing consciousness. The
treatment for this is first of all to avoid it by only giving appropriate amounts of fluid
intravenously and observing the subject for the return of pulse and blood pressure to
normal. In this situation one would not continue with aggressive fluid replacement
treatment. If, however, the situation has arisen then the fluid should be stopped
immediately, the subject sat up to improve the efficiency of breathing, given oxygen
and even some drugs to improve the breathing. These drugs would be Morphine,
which helps reduce the pressure on the lungs, which is one of the mechanisms by
which the fluid leaks into the lungs. It also makes the subject feel better. A drug
known as a diuretic promotes removal of fluid from the lungs by increasing the
amount of urine production by the kidneys and so reducing the excess fluid the
subject has in their circulation
2. Bleeding can be regarded as two types either external where it is visible to the
observer or internal. Usually the latter results from damage of an organ or a blood
vessel to an organ. Bleeding into the body cavities can occur for example following
injury to the abdomen, chest or the pelvis and can result in serious or even fatal
shock. Bleeding into the abdomen is usually recognised by the subject complaining
of abdominal pain and touching the abdomen even gently can provoke severe pain
(peritonism). Bleeding into the chest can result in the collapse of a lung which may
not be immediately life threatening. Bleeding into the area between the lung and the
heart can impair the heart action. This will result in the heart producing a smaller
volume pulse which is increasingly more difficult to feel, the heart sounds becoming
quieter and the veins becoming filled with blood because the blood returning to the
heart has not been pumped out of it. (Cardiac tamponade)
This can be evident on examining the neck where the neck veins, which are normally
not visible, can become very obvious and firm. This situation is called cardiac
tamponad and can be remedied by removing the blood from the space between the
heart and the lungs using a long needle and syringe, this is not a procedure
commonly done and requires expert care.
c) Shock - Occurs when the circulation cannot adequately oxygenate the body.
1. Loss of fluid either by bleeding from injury or from internal medical disorder or
losses of fluid e.g. burns, prolonged vomiting and diarrhoea.
2. Heart problems such as coronary thrombosis, abnormality of the heart action,
mechanical impairment of the heart action by for example barotrauma, tension
3. Other factors which impair the circulation such as severe allergy, which may result
from a sting from a poisonous animal, or allergy to drug or other materials.
4. Neurological - in a high spinal injury the automatic control of the blood vessels is
loss. This results in a drop in blood pressure. The importance of this cause of shock
is that the state of shock is accepted and not treated with intravenous fluids. Such
treatment would be highly dangerous and can result in death from pulmonary
The treatment of shock is
1. Recognise the cause, control it if possible e.g. splint fractures where possible,
control external bleeding and give fluid in the following circumstances:-
iii) abnormal losses from vomiting/diarrhoea
2. Check for mechanical conditions, which can complicate the picture, e.g.
tension pneumothorax. Conditions such as this should always be sought and
3. Heart attack. Someone suffering a coronary thrombosis can have a
sufficiently severe event to impair the hearts action. The usual way this is evident is
that the subject complains of severe chest pain, usually described as tight or
gripping. The pain can stretch from the breastbone across to both sides of the chest,
can sometimes go into the neck or the jaw or left arm. It is usually accompanied with
pallor, sickness and has been traditionally described and regarded as the worse pain
imaginable. In this situation an ECG would give the qualified person useful
information. The main treatment here is to give oxygen, reassure the subject to
reduce adrenaline levels, which are highly dangerous in this situation, controls pain
and obtain a defibrillator. The highest risk after a heart attack is the first four hours
when cardiac abnormalities such as arrhythmias can occur and result in death. The
treatment does not vary under hyperbaric conditions but defibrillation is a fire risk in
the presence of an increased partial pressure of oxygen.
d) Management of Bleeding
Bleeding can be of two types, either external i.e. there has been a skin wound for
whatever reason, blood escapes from it and is visible to the attendant and internal
bleeding by an indirect injury for example blast injury to the lung or blunt trauma to
the abdomen or a fall from a height can result in damage to the internal organs and
skeleton. This will result in bleeding which is not visible but nevertheless highly
significant as evident by shock (pulse more than 100, systolic BP less than 100,
capillary return more than 2 seconds).
Internal bleeding may be the result of medical conditions such as an ulcer or a
tumour of the bowel, which can bleed internally, or injury to internal organs.
Eventually the blood will leak out either upwards by being vomited or coughed up by
the patient or downwards by being passed in the motions.
Clearly if one takes care in a hazardous environment this should minimise the risk of
External bleeding - obvious.
Internal bleeding - the damaged area will be a source of pain and the affected organ
will have limited function e.g. a limb which is broken and bleeding will be sore,
swollen and the subject will be unable to use it. In the case of internal bleeding in a
cavity the local signs are very likely to be
1. Skull - confusion then coma note that shock unlikely unless the wound is open.
2. Chest - impaired breathing and local pain.
3. Abdomen - degree of pain is variable and the abdomen may be very tender to
The other signs of bleeding are (where the volume lost has been sufficient to
derange the circulation and produce shock). The subject -
i. becomes anxious
ii becomes breathless
iii has a rapid thready pulse which is difficult to feel
iv feels pale and clammy
v blood pressure being reduced (normal 120/80)
vi capillary return is lengthened
Management under normal/hyperbaric conditions is the same -
1. Control external bleeding by direct pressure followed by securing an appropriate
bandage. In the case of a limb one must take care that if the pressure required to
control the bleeding is sufficient to cut off the circulation to the distal (part of the limb
away from the body) then the dressing must be released from time to time to allow
some blood to go down the limb to ensure it’s survival.
2. In the case of internal bleeding little can be done to control it but every measure
should be made to treat the shock. Ideally two intravenous lines should be set up
with large bore cannulae and appropriate amounts of fluid given to maintain vital
signs near normality. The useful way of assessing adequate resuscitation is that the
subject is able to produce normal amounts of urine. This is sometimes best
assessed by passing a catheter into the bladder to measure urine output. Normal
urinary output is 75-150ml/hour for a 70kg subject.
A subject will have to lose approximately 1 litre or so of their blood volume (70 Kilo
male) before they will show early signs of shock. Once the external bleeding has
been controlled by local pressure of the wounds reinforced by a compression
bandage and elevation of the limb (diagram 2a), attention can be returned to
resuscitative measures, which will include the setting up of an i.v. line (these two
procedures can be run concurrently if there are 2 operators available). The most
reliable place to find a good vein is in front of the elbow. The largest cannula the
operator can confidently manage should be inserted and it would be safe to give the
subject 2 litres of saline under the above circumstances. The subject should be
continually assessed for improvement in pulse (return to normal rate) and blood
pressure (return to normal usually 120/80) and return of normal capillary return (2
seconds or less). Diagram 2b-2d
Section 1a Circulation
Question 1 What is normal blood pressure and how is this produced?
Question 2 If there is a reduction in blood volume, how can this be easily and
Question 3 What is the significance of blood loss of this magnitude?
Answer 1 Blood pressure is a combination of the pumping action of the heart and
the controlling pressure of the muscular arteries.
Answer 2 A significant drop in blood volume (>1 litre) results in the loss of first
normal capillary return, then the radial pulse felt at the wrist and then
the groin pulse.
Answer 3 A significant reduction in blood volume results in reduction of circulation
to initially non-vital organs such as skin and muscles, then later on more
vital organs such as the kidneys. Significant blood loss causes concern
due to the damage it may cause to the kidneys.
Section 1b Bleeding & 1c Shock
Question 1 Define shock?
Question 2 Describe features of shock?
Question 3 Describe the treatment of shock in a subject who has sustained
a large wound in the thigh?
Answer 1 Shock is where the circulation cannot maintain the needs of
tissues in terms of providing adequate volume of blood to them
containing oxygen. The likely causes of bleeding are mediastinal
emphysema where the entrapped gas can impair the heart’s
function and tension pneumothorax where entrapped gas in the
chest can impair the heart’s function.
Answer 2 The features of shock are that the subject feels weak, anxious, is
breathless, pale, and sweaty with a thready pulse and may have
lost capillary return.
Answer 3 Treatment is to ensure there is a safe airway, and that the
subject’s breathing and circulation are satisfactory. If the subject
responds to an enquiry about their well being with an answer this
means that their airway and cerebral circulation are adequate.
In this case the first aider can immediately concern himself to
control bleeding. This is done by direct pressure over the
bleeding point, reinforced by a pressure bandage. Once this has
been achieved, two i.v. Cannulae should be inserted and it is
routine to give 2 litres of saline to help support the circulation.
Section 1e Respiratory System
For this section the following are your learning objectives. There is a short self-test
questionnaire at the back
1. Understand the function and structure of the respiratory system
2. Recognise serious respiratory events
Describe the treatment of life threatening chest problems
e) The Respiratory System (see Diagram 3, pages 31-35)
The heart’s function of delivering oxygenated blood to the brain would be futile
without a system of oxygenating the blood. This is the function of the respiratory
system. It consists of as we all know, two lungs joined together and connected to the
throat and mouth. The two lungs can each be likened to a collapsed balloon, which
contains air, and in their isolated state they will collapse down into a small volume. It
is the function of the chest wall cavity to stretch out the lungs so that they can
function to oxygenate the blood.
If the integrity of the chest cavity is compromised e.g. by a barotrauma or a
penetrating chest wound, the space between the lung and the chest wall, which in
reality is a vacuum and this vacuum is responsible for stretching the lungs up to their
normal size, is lost and for this reason the lungs collapse. If air gathers in the space
under pressure as it can do, in a tension pneumothorax (pneumothorax is the
situation where air exists within the chest cavity collapsing the lung). A tension
pneumothorax results in gas collecting under increasing pressure within the chest
wall. This collapses the lung, compresses the heart, compromises the heart’s action
and results in cardiac tamponad shock and ultimately death. The situation can be
remedied by an emergency drainage procedure to allow the gas to escape from the
The upper airway that includes the nasopharynx, mouth and throat functions to warm
and humidify the air as it is drawn into the respiratory system. It then passes down
through the throat, past the vocal cords. This is an important area as it is the
narrowest part of the airway and in serious injury the first sign of this narrow gateway
being compromised is hoarseness. This can occur when for example a patient is
subjected to a blast injury where they have experienced a burn to the upper airway
and hot air is drawn in. The airway can be burned and the first sign of this will of
course be soot to the face, throat with blistering and the most ominous sign is
increasing hoarseness followed by difficulty breathing. This difficulty results in the
subject making a whistling sound when breathing in and out (stridor).
This is a life-threatening crisis and can be controlled by having a tube passed down
the narrow space between the two vocal cords, known as intubation. (The area is
known as the trachea and the technical term for this is endotracheal intubation.) If
this fails a surgical airway can be made by cutting directly into the windpipe (trachea)
below the area of the cords (crycothyroidotomy) or below this. In the normal situation
once the air has been warmed and moistened by the upper airway, it then passes
down into the lungs. The lungs as said before amount to a large spongy air space
and the blood is oxygenated by being passed around this air space through very thin
blood vessels. This allows gas to pass between the two systems. Breathing is
controlled automatically by the brain (i.e. is not normally controlled by volition and
responds to chemical changes in the blood). The most sensitive chemical change is
increasing carbon dioxide. This has important consequences in that oxygen which is
required to keep the brain and the body alive is not responsible for control of
breathing and it is possible that the oxygen level could drop to dangerously low levels
without breathing being stimulated and the subject would have no awareness of this
situation e.g. where air is rebreathed oxygen is not replenished and C02 is extracted.
The fact that the pulmonary (lung) blood vessels are particularly fine and thin walled,
is very useful for their function but makes them vulnerable. If the lung is damaged for
example by a near drowning or inhalation of poisonous gases or by shock and by
over infusion (giving too much saline to a shocked subject), this can result in fluid
leaking from the small vessels into the air spaces in the lungs. This is known as
pulmonary oedema and its treatment has been previously discussed.
The brain primarily controls the action of breathing although one can choose to
increase the rate and depth of breathing. The mechanism of breathing is that the ribs
are lifted up like bucket handles from a near vertical to horizontal position. A small
thin muscle, which forms the base of the chest cavity known as the diaphragm
pushes the abdominal contents down and this also, increases the space available in
the chest. The net result is to temporarily increase the vacuum between the lungs
and the inside of the chest wall and this sucks the lungs up and outwards, reducing
the pressure within them and this forces air into the lungs. Breathing out is done by
relaxation of the above mechanism and can also be done by using extra muscles to
force air out. This does not normally happen unless there is some kind of airway
obstruction such as one up in the vocal cords as described before or if the subject
has a medical condition such as asthma. This result in the small passages in the
lungs becoming smaller, increasing the resistance to flow and thus makes breathing
outwards more difficult and noisy (wheeze).
The situation in asthma is remedied by drug therapy and is usually given with oxygen
which allows the air passage in the lungs to return to normal size and this is evident
by the subjects responses returning to normal i.e. breathing becomes easier and the
wheeze is reduced.
An asthma attack results in difficulty breathing, a wheeze during the expiration
(breathing out) phase, increasing anxiety and in severe cases the subject may
become confused. An asthmatic who has trouble talking in full sentences is regarded
as having a moderately severe illness.
Protection of the airway - in the conscious subject the airway is protected by
coughing. These is stimulated by the nerves sensing that there is an object in the air
passage either in the nose, the mouth or lower down. The cough is propelled at 200
meters per second and this is forceful enough to expel any object within the airway.
However, in the unconscious subject, there are two main hazards. One the cough
reflex may be lost and if they are lying down the stomach contents can come back up
the gullet and be inhaled. For this reason unconscious subjects are placed in what is
called the “recovery position” (see Diagram 4a-d, page 36-38). This usually has
them on their left side with their head down. This anticipates leakage from the
stomach and this position will ensure that any stomach contents will leak down and
away from the airway.
In the management of the unconscious subject the important aspects of their airway
1. to keep it open and ensure that it is clear and kept so. If any fluid is there an
appropriate device removes it. The best way of protecting it is to have the subject in
the recovery position with the head down, thus allowing any drainage to come away
from the airway. The airway should be maintained (kept open).
2. They may obstruct their own airway with their tongue, there are manoeuvres (chin
lift, jaw thrust) and airway aids which can maintain this for them (diagram 5, pages
Section 1e Respiratory System
Question 1 Which chemical change in the blood controls breathing?
Question 2 Which is the narrowest part of the airway?
Question 3 How can barotrauma derange lung function?
Question 4 What is the treatment?
Question 5 What happens in secondary drowning?
Question 6 What are the airway hazards in an unconscious casualty?
Answer 1 The brain is most sensitive to levels of carbon dioxide in the
blood. If this is raised it suggests that ventilation is inadequate
and for this reason the brain automatically increases ventilation if
C02 levels increase. For this reason hyperventilation prior to
breath holding dive is particularly dangerous as the diver may
loose consciousness before he has a warning of ventilatory
Answer 2 The vocal cords which are situated in the larynx are the
narrowest part of the airway. For this reason, any peculiar noise
produced by a subject accompanied by hoarseness suggests
there is a problem here which if uncontrolled can become a life
threatening crises. Any whistling sound made during breathing in
and out related to circumstances known as stridor. To relieve
this intubation or surgical airway may require to be done.
Answer 3 Barotrauma can result in respiratory problems due to the simple
fact that the lung may collapse if gas collects in the pleural cavity.
This collects under pressure (tension pneumothorax). This can
compress the heart and impair its action.
Answer 4 If this matter is recognised by the following findings of deviation
of the trachea away from the site of injury, reduced air entry on
the affected side and increased percussion note on the affected
side. Emergency drainage of the chest on the affected side
should be carried out to relieve this.
Answer 5 This is where the lung responds to injury by flooding with fluid
which makes breathing difficult. The treatment for this is to sit
the subject up, give oxygen and give ventilatory support where
Answer 6 The hazards are that the normal structure of the airway may be
lost due to the tongue and jaw falling backwards and obstructing
it. Protective reflexes such, as cough may be lost. The subject
may inhale vomit if not placed in the proper recovery position.