Arterial gas embolism, sometimes simply called gas embolism, is caused by entry
of gas bubbles into the arterial circulation which then act as blood vessel obstructions
called emboli. These emboli are frequently the result of pulmonary
barotrauma caused by the expansion of gas taken into the lungs while breathing
under pressure and held in the lungs during ascent. The gas might have been
retained in the lungs by choice (voluntary breathholding) or by accident (blocked
air passages). The gas could have become trapped in an obstructed portion of the
lung that has been damaged from some previous disease or accident; or the diver,
reacting with panic to a difficult situation, may breathhold without realizing it. If
there is enough gas and if it expands sufficiently, the pressure will force gas
through the alveolar walls into surrounding tissues and into the bloodstream. If the
gas enters the arterial circulation, it will be dispersed to all organs of the body. The
organs that are especially susceptible to arterial gas embolism and that are responsible
for the life-threatening symptoms are the central nervous system (CNS) and
heart. In all cases of arterial gas embolism, associated pneumothorax is possible
and should not be overlooked.
Arterial gas embolism may develop within
minutes of surfacing, causing severe symptoms that must be diagnosed and treated quickly and correctly. Because the supply of blood to the central nervous system is
almost always involved, unless treated promptly and properly by recompression,
arterial gas embolism is likely to result in death or permanent brain damage.
Gas embolism can strike
during any dive where underwater breathing equipment is used, even a brief,
shallow dive, or one made in a swimming pool. As a basic rule, any diver who has
obtained a breath of compressed gas from any source at depth, whether from
diving apparatus or from a diving bell, and who surfaces unconscious or loses
consciousness within 10 minutes of reaching the surface, must be assumed to be
suffering from arterial gas embolism. Recompression treatment shall be started
immediately. A diver who surfaces unconscious and recovers when exposed to
fresh air shall receive a neurological evaluation to rule out arterial gas embolism.
Divers surfacing with any
obvious neurological symptoms (numbness, weakness, or difficulty in thinking)
should be considered as suffering from an arterial gas embolism. Commence
recompression treatment as soon as possible.
Appendix 5A contains a set of guidelines
for performing a neurological examination and an examination checklist to assist
nonmedical personnel in evaluating decompression sickness cases.
A diver suffering from an arterial gas embolism with absence of a pulse or respirations
(cardiopulmonary arrest) requires Advanced Cardiac Life Support.
Performing ACLS requires that special medical training and equipment be readily
available. ACLS procedures include diagnosis of abnormal heart rhythms and
correction with drugs or electrical countershock (cardioversion or defibrillation).
Though patient monitoring and drug administration may be able to be performed
at depth, electrical countershock must be performed on the surface.
If an ACLS-trained medical provider or a Basic Life Support–Defibrillation
(BLS-D) provider with the necessary equipment can administer the potentially
life-saving therapies within 10 minutes, the stricken diver should be kept at the
surface until pulse and/or respirations are obtained. It must be realized that unless
ACLS procedures—especially defibrillation—can be administered within 10
minutes, the diver will likely die, even though adequate CPR has been begun. If a
Diving Medical Officer cannot be reached or is unavailable, the Diving Supervisor
may elect to compress to 60 feet, continue Basic Life Support, and attempt to
contact a Diving Medical Officer.
If ACLS becomes available within 20 minutes, the pulseless diver shall be brought
to the surface at 30 fpm and defibulated on the surface. (Current data shows there
is 0-percent recovery rate after 20 minutes of cardiac arrest with BLS.) If the
pulseless diver does not regain vital signs with ACLS procedures, continue CPR
until trained medical personnel terminate resuscitation efforts. Never recompress a
pulseless diver who has failed to regain vital signs after defibrillation or ACLS.
Resuscitation efforts shall continue until the diver recovers, the tenders are unable
to continue CPR, or trained medical personnel terminate the effort. If the pulseless
diver does regain vital signs, compress to 60 fsw and follow the appropriate treatment
table.
CAUTION
If the tender is outside of no-decompression limits, he should not be
brought directly to the surface. Either take the decompression stops
appropriate to the tender or lock in a new tender and decompress the
patient leaving the original tender to complete decompression.
The potential hazard of arterial gas embolism
may be prevented or substantially reduced by careful attention to the
following:
-
Proper, intensive training in diving physics and physiology for every diver, as
well as instruction in the correct use of various diving equipment. Particular
attention must be given to the training of scuba divers, because scuba operations
produce a comparatively high incidence of embolism accidents.
-
A diver must never interrupt breathing during ascent from a dive in which
compressed gas has been breathed.
-
A diver making an emergency ascent must exhale continuously. The rate of
exhalation must match the rate of ascent. For a free ascent, where the diver uses natural buoyancy to be carried toward the surface, the rate of exhalation
must be great enough to prevent embolism, but not so great that the buoyancy
factors are canceled. With a buoyant ascent, where the diver is assisted by a
life preserver or buoyancy compensator, the rate of ascent may far exceed that
of a free ascent. The exhalation must begin before the ascent and must be a
strong, steady, forceful exhalation. It is difficult for an untrained diver to execute
an emergency ascent properly. It is also often dangerous to train a diver in
the proper technique. No ascent training may be conducted unless fully qualified
instructors are present, a recompression chamber and Diving Medical
Technician are on scene, and a Diving Medical Officer is able to provide an
immediate response to an accident. Ascent training is distinctly different from
ascent operations as performed by Navy Special Warfare groups. Ascent operations
are conducted by qualified divers or combat swimmers. These
operations require the supervision of an Ascent Supervisor but operational
conditions preclude the use of instructors.
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Other factors in the prevention of gas embolism include good planning and
adherence to the established dive plan. Trying to extend a dive to finish a task
can too easily lead to the exhaustion of the air supply and the need for an
emergency ascent. The diver shall know and follow good diving practices and
keep in good physical condition. The diver shall not hesitate to report any illnesses,
especially respiratory illnesses such as colds, to the Diving Supervisor
or Diving Medical Personnel prior to diving.
