Pulmonary overinflation syndromes are disorders that are caused by gas
expanding within the lung. The disorders encountered in diving are arterial gas
embolism, mediastinal and subcutaneous emphysema, and pneumothorax.
Normally, only arterial gas embolism (AGE) requires recompression therapy
(Chapter 20, paragraph 20-2).
Mediastinal emphysema is caused
by gas expanding in the tissues behind the breast bone. Symptoms include mild to
moderate pain under the breast bone, often described as a dull ache or feeling of
tightness. Deep inspiration, coughing, or swallowing makes the pain worse, and
the pain may radiate to the shoulder, neck or back.
Subcutaneous emphysema results from
movement of the gas from the mediastinum to the region under the skin of the
neck and lower face. Mild cases are often unnoticed by the diver. In more severe
cases, the diver may experience a feeling of fullness around the neck and may
have difficulty in swallowing. The diver’s voice may change in pitch. An observer
may note a swelling or apparent inflation of the diver’s neck. Movement of the
skin near the windpipe or about the collar bone may produce a cracking or
crunching sound (crepitation).
Suspicion of mediastinal
or subcutaneous emphysema warrants prompt referral to medical personnel
to rule out pneumothorax. Treatment of mediastinal or subcutaneous emphysema
with mild symptoms consists of breathing 100 percent oxygen at the surface. If
symptoms are severe, shallow recompression may be beneficial. Recompression
should only be carried out upon the recommendation of a Diving Medical Officer
who has ruled out the occurrence of pneumothorax. Recompression is performed
with the diver breathing 100 percent oxygen and using the shallowest depth of
relief (usually 5 or 10 feet). An hour of breathing oxygen should be sufficient for
resolution, but longer stays may be necessary. Decompression will be dictated by
the tender’s decompression obligation. The appropriate air table should be used,
but the ascent rate should not exceed 1 foot per minute. In this specific case, the delay in ascent should be included in bottom time when choosing the proper
decompression table.
A pneumothorax is air outside the lung that is trapped in the chest
cavity. This condition can result from a severe blow to the chest or a rupture of
lung tissue due to overpressurization.
Pneumothorax is usually accompanied by a sharp
unilateral (one side) pain in the chest, shoulder, or upper back that is aggravated
by deep breathing. To minimize the pain, the victim will often breathe in a
shallow, rapid manner. The victim may appear pale and exhibit a tendency to bend
the chest toward the involved side. A collapsed lung may be detected by listening
to both sides of the chest with the ear or a stethoscope. A completely collapsed
lung will not produce audible sounds of breathing. In cases of partial pneumothorax,
however, breath sounds may be present and the condition must be
suspected on the basis of history and symptoms. In some instances, the damaged
lung tissue acts as a one-way valve, allowing gas to enter the chest cavity but not
to leave. Under these circumstances, the size of the pneumothorax increases with
each breath. This condition is called tension pneumothorax. In simple pneumothorax,
the respiratory distress usually does not get worse after the initial gas
leakage out of the lung. In tension pneumothorax, however, the respiratory distress
worsens with each breath and can progress rapidly to shock and death if the
trapped gas is not vented by inserting a catheter, chest tube, or other device
designed to remove gas from the chest cavity
Mild pneumothorax can be treated by breathing 100
percent oxygen. Cases of pneumothorax that demonstrate cardiorespiratory
compromise may require the insertion of a chest tube, large-bore intravenous (IV)
catheter, or other device designed to remove intrathoracic gas (gas around the
lung). These devices should only be inserted by personnel trained in their use and
the use of other accessory devices (one-way valves, underwater suction, etc.)
necessary to safely decompress the thoracic cavity. Divers recompressed for treatment
of arterial gas embolism or decompression sickness, who also have a
pneumothorax, will experience relief upon recompression. A chest tube or other
device and a one-way relief valve may need to be inserted at depth to prevent
expansion of the trapped gas during subsequent ascent. If a diver’s condition deteriorates
rapidly during ascent, especially if the symptoms are respiratory, tension
pneumothorax should always be suspected. If a tension pneumothorax is found,
recompression to depth of relief is warranted to relieve symptoms until the
thoracic cavity can be properly vented. Pneumothorax, if present in combination
with arterial gas embolism or decompression sickness, should not prevent immediate
recompression therapy. However, a pneumothorax may need to be vented as
described before ascent from treatment depth.
The potential hazard of the
pulmonary overinflation syndromes may be prevented or substantially reduced by
careful attention to the following:
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Medical selection of diving personnel, with particular attention to eliminating
those who show evidence of lung disease or who have a past history of
respiratory disorders. Divers who have had a spontaneous pneumothorax have
a high incidence of recurrence and should not dive. Divers who have had
pneumothorax from other reasons (e.g., surgery, trauma, etc.) should have
their fitness for continued diving reviewed by an experienced Diving Medical
Officer, in consultation with appropriate respiratory specialists.
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Evaluation of the diver’s physical condition immediately before a dive. Any
impairment of respiration, such as a cold, bronchitis, etc., may be considered
as a temporary restriction from diving.
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Proper, intensive training in diving physics and physiology for every diver, as
well as instruction in the correct use of various diving equipment.
