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understand that breathing 100% oxygen only during
flight (ascent, enroute, descent) does not decrease
the risk of altitude DCS and should not be used in
lieu of oxygen prebreathing.
Although 100% oxygen prebreathing is an effective
method to provide individual protection against
altitude DCS, it is not a logistically simple or an
inexpensive approach for the protection of civil
aviation flyers (commercial or private). Therefore,
at the present time, it is only used by military flight
crews and astronauts for their protection during high
altitude and space operations.
Table 1. Signs and symptoms of Altitude Decompression Sickness.
DCS Type Bubble Location Signs & Symptoms (Clinical Manifestations)
BENDS Mostly large joints
of the body (elbows,
shoulders, hip, wrists,
knees, ankles)
• Localized deep pain, ranging from mild (a “niggle”) to excruciating. Sometimes a
dull ache, but rarely a sharp pain.
• Active and passive motion of the joint aggravates the pain.
• Pain can occur at altitude, during the descent, or many hours later.
NEUROLOGIC
Manifestations
Brain • Confusion or memory loss
• Headache
• Spots in visual field (scotoma), tunnel vision, double vision (diplopia), or blurry
vision
• Unexplained extreme fatigue or behavior changes
• Seizures, dizziness, vertigo, nausea, vomiting and unconsciousness may occur
Spinal Cord • Abnormal sensations such as burning, stinging, and tingling around the lower chest
and back
• Symptoms may spread from the feet up and may be accompanied by ascending
weakness or paralysis
• Girdling abdominal or chest pain
Peripheral Nerves • Urinary and rectal incontinence
• Abnormal sensations, such as numbness, burning, stinging and tingling
(paresthesia)
• Muscle weakness or twitching
CHOKES Lungs • Burning deep chest pain (under the sternum)
• Pain is aggravated by breathing
• Shortness of breath (dyspnea)
• Dry constant cough
SKIN BENDS Skin • Itching usually around the ears, face, neck arms, and upper torso
• Sensation of tiny insects crawling over the skin
• Mottled or marbled skin usually around the shoulders, upper chest and abdomen,
accompanied by itching
• Swelling of the skin, accompanied by tiny scar-like skin depressions (pitting edema)
3
PREDISPOSING FACTORS
Altitude
There is no specific altitude that can be considered
an absolute altitude exposure threshold, below
which it can be assured that no one will develop
altitude DCS. However, there is very little evidence
of altitude DCS occurring among healthy individuals
at altitudes below 18,000 ft. who have not been
SCUBA (Self Contained Underwater Breathing
Apparatus) diving. Individual exposures to altitudes
between 18,000 ft. and 25,000 ft. have shown a low
occurrence of altitude DCS. Most cases of altitude
DCS occur among individuals exposed to altitudes
of 25,000 ft. or higher. A US Air Force study of
altitude DCS cases reported that only 13% occurred
below 25,000 ft. The higher the altitude of exposure,
the greater the risk of developing altitude DCS. It
is important to clarify that although exposures to
incremental altitudes above 18,000 ft. show an
incremental risk of altitude DCS, they do not show
a direct relationship with the severity of the various
types of DCS (see Table 1).
Repetitive Exposures
Repetitive exposures to altitudes above 18,000
ft. within a short period of time (a few hrs.) also
increase the risk of developing altitude DCS.
Rate of Ascent
The faster the rate of ascent to altitude, the greater
the risk of developing altitude DCS. An individual
exposed to a rapid decompression (high rate of
ascent) above 18,000 ft. has a greater risk of
altitude DCS than being exposed to the same
altitude but at a lower rate of ascent.
Time at Altitude
The longer the duration of the exposure to altitudes
of 18,000 ft. and above, the greater the risk of
altitude DCS.
Age
There are some reports indicating a higher risk of
altitude DCS with increasing age.
Previous Injury
There is some indication that recent joint or limb
injuries may predispose individuals to developing
“the bends.”
Ambient Temperature
There is some evidence suggesting that individual
exposure to very cold ambient temperatures may
increase the risk of altitude DCS.
Body Type
Typically, a person who has a high body fat content
is at greater risk of altitude DCS. Due to poor blood
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Pilot Safety Brochures飞行员安全手册(14)
