Civil aviation can result
in some unique medical problems that are unfamiliar to most physicians.
One such problem, decompression sickness, is not mentioned in most medical
texts, and is not included in most medical school instruction. If not
promptly recognized and treated, decompression sickness can result in
permanent disability or death. I report a case of altitude-induced
decompression sickness after a flight in an unpressurised aircraft.
DECOMPRESSION SICKNESS (DCS)
is an illness caused by a reduction in ambient pressure, resulting in the
formation of bubbles of inert gas (usually nitrogen) within body tissues. DCS can occur as a result of high altitude exposure.
risk of DCS is increased when a compressed air dive is immediately
followed by exposure to reduced atmospheric pressure, such as a flight in
an aircraft. The risk is further increased when a flight is accomplished
after several deep dives in succession without adequate time for
re-equilibration. The incidence of DCS among private pilots is unknown.
Many cases of DCS probably go unrecognized, with spontaneous recovery.
Even when the illness is recognized and treated, there is no requirement
for reporting DCS by either the pilot or treating physician.
A healthy, experienced,
59-year-old private pilot planned a cross-country flight from Missouri to
California. He had an uneventful ascent to an altitude of 28,000 feet
above mean sea level (MSL) in the unpressurized airplane, and began using
supplemental oxygen after passing 12,000 feet MSL, as required by federal
aviation regulations. After 1 hour at his cruising altitude, the pilot
noticed the onset of weakness and paresthesias of the right arm. A few
minutes later, he felt extreme fatigue and chest tightness associated with
a dry cough. These symptoms progressively worsened, and were soon
accompanied by left arm weakness and paresthesias. He had no dyspnea,
diaphoresis, visual or auditory symptoms, or alteration in consciousness.
There was no previous history of similar symptoms or of pulmonary,
cardiac, or neurologic problems. The pilot remained on oxygen by mask, and
began to slowly descend, landing his aircraft in New Mexico. He remained
ill, and was immediately transported to a local hospital.
Upon arrival at the
emergency department, he was diaphoretic and ashen. He continued to
complain of weakness and paresthesias of both arms, but more severe on the
right. Supine blood pressure was 115/88 mm Hg, supine pulse rate 98/min,
and respiratory rate 20/min. When the patient was standing, blood pressure
dropped to 75/41 mm Hg, with pulse unchanged. There was no skin rash,
mottling, or oedema. Head and neck examination was unremarkable. Cardiac
rate and rhythm were regular, with normal heart sounds. Mild crackles were
heard at both lung bases. Abdominal examination was unremarkable. On
neurologic examination, the patient was alert and fully oriented. All
cranial nerves were normal. Examination of the right upper extremity
revealed severe flexor weakness at the elbow and wrist, severe weakness of
grip strength, numbness of the forearm, and severely impaired fine motor
control. The left upper extremity also showed flexor weakness and
decreased grip strength, but not as severe as on the right. Sensation was
normal. Strength and sensation in the lower extremities was normal. Gait
was not tested because of orthostasis.
Chest x-ray films showed
mild increase in interstitial markings. Electrocardiogram showed a 1 mm
elevation in ST segments in leads V2 and V5. Perfusion scans of the lungs
were normal. Arterial blood gas values, with the patient breathing room
air, were pH 7.40, P02 111 mm Hg, Pco2 33.4 mm Hg, and oxygen saturation
96%. Serum potassium level was 3.3 mg/dL; remaining electrolyte values
A diagnosis of
altitude-induced decompression sickness was made. The patient was
maintained on 100% oxygen by mask, and transported by pressurized aircraft
to the Hyperbaric Medicine Division at Brooks Air Force Base in Texas,
arriving approximately 12 hours after landing his aircraft. Upon arrival,
findings on physical examination were unchanged. The patient was
immediately placed in the hyperbaric chamber for compression therapy.
Following a standard hyperbaric treatment, some neurologic improvement was
noted, although the deficits of the right upper extremity persisted. Over
the next 4 days, the patient received an additional seven treatments. The
first 5 of these treatments produced improvement. The decision to
terminate treatments was made when there was no further improvement after
the final two treatments. At the conclusion of hyperbaric therapy, there
was persistent weakness of the right shoulder and weakness of the
intrinsic muscles of the right hand. At follow-up 1 year later, the
patient had complete recovery in the muscles of the right hand, but
continued to have mild weakness in the right shoulder.
One of the most serious
physiologic problems associated with aviation is decompression sickness (DCS).
As early as 1917, Henderson predicted the possibility of DCS in aviators
flying at more than 20,000 feet. DCS occurs when a person is subjected to
a reduction in ambient pressure. During decompression, body tissues become
supersaturated with inert gas (nitrogen). Excess nitrogen in the tissues
diffuses into the blood, is carried to the lungs, and eliminated in
expired air. The amount of nitrogen remaining in body tissues is directly
proportional to the nitrogen partial pressure around the person. If the
amount of dissolved nitrogen exceeds some threshold, the critical
supersaturation point, some of the nitrogen comes out of solution in the
form of bubbles. These bubbles are the basis for the development of
symptoms of DCS. The etiology, pathophysiology, epidemiology, and clinical
manifestations of altitude decompression sickness were described by Fryer
in his 1969 monograph.
Decompression sickness is
rare for unpressurised flights that do not exceed an altitude of 29,000
feet. There has been a recent proliferation of unpressurised private
aircraft that can exceed altitudes of 24,000 feet; Beech, Piper, Cessna,
and Mooney all currently manufacture such aircraft.
manifestations of DCS are variable, with many of the symptoms being
protean. The varied nature of DCS has led Behnke to compare it with the
spirochete as the "great imitator." The many signs and symptoms of DCS can
occur in any combination, which can make the diagnosis difficult.
Wirjosemito, et al. noted that the clinical manifestations of serious
altitude DCS include, in descending order of frequency, joint and limb
pain, headache, visual disturbances, extremity paresthesia, mental
confusion, extremity weakness, fatigue, cerebella signs, pulmonary
manifestations (chokes), and extremity numbness.
Several factors may
predispose a pilot to the development of DCS. Risk of DCS increases as the
altitude of exposure increases, as the rate of ascent increases, and as
the duration of exposure lengthens. Personal factors that increase risk of
DCS include age (susceptibility increases with age), body build (obese
individuals are at greater risk), and recent joint injury.
Initial management of
decompression sickness consists of hydration, delivery of 100% oxygen, and
transfer to a compression chamber for the compression therapy. Serious
cases of DCS may require other supportive measures (e.g., intubation and
therapy is the definitive treatment of DCS. The longer the delay in
treatment, the poorer the outcome. Rudge and Shafer, in a study of
altitude-induced DCS cases treated by the United States Air Force, noted
that patients treated rapidly with compression therapy recovered faster
than patients whose treatment was delayed.
The Divers Alert Network,
located at Duke University, provides 24-hour information regarding the
diagnosis and management of DCS, and can supply up-to-date information on
compression chamber locations. The number for this service is (919)
A requirement for the
treatment of any disease process is a full understanding of the clinical
picture of the disease. This can be especially difficult in DCS, with its
broad spectrum of presenting signs and symptoms. In many cases, the
patient must be relied on to present an accurate and truthful description
of the problem. Pilots should be educated to promptly seek medical
treatment when problems develop during or after flying. Health care
providers must be able to identify individuals at risk for DCS, to
recognize the bewildering array of possible presentations, and to initiate
prompt treatment. When doubt exists, consultation with a trained flight
surgeon or hyperbaric physician should be obtained.