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pressures that cause inert gases (mainly nitrogen),
normally dissolved in body fluids and tissues, to
come out of physical solution and form bubbles.
DCS can occur during exposure to altitude (altitude
DCS) or during ascent from depth (mining or diving).
The first documented cases of DCS (Caisson
Disease) were reported in 1841 by a mining
engineer who observed the occurrence of pain and
muscle cramps among coal miners exposed to airpressurized
mine shafts designed to keep water out.
The first description of a case resulting from diving
activities while wearing a pressurized hard hat was
reported in 1869.
ALTITUDE-INDUCED
DECOMPRESSION SICKNESS
Altitude DCS became a commonly observed
problem associated with high-altitude balloon and
aircraft flights in the 1930s. In present-day aviation,
technology allows civilian aircraft (commercial and
private) to fly higher and faster than ever before.
Though modern aircraft are safer and more reliable,
occupants are still subject to the stresses of high
altitude flight—and the unique problems that go with
these lofty heights. A century and one-half after the
first DCS case was described, our understanding
of DCS has improved, and a body of knowledge
has accumulated; however, this problem is far from
being solved. Altitude DCS still represents a risk to
the occupants of modern aircraft.
Tiny Bubbles
According to Henry’s Law, when the pressure of
a gas over a liquid is decreased, the amount of
gas dissolved in that liquid will also
decrease. One of the best practical
demonstrations of this law is offered
by opening a soft drink. When the
cap is removed from the bottle, gas
is heard escaping, and bubbles can
be seen forming in the soda. This
is carbon dioxide gas coming out
of solution as a result of sudden
exposure to lower barometric
pressure. Similarly, nitrogen is an inert gas normally
stored throughout the human body (tissues and
fluids) in physical solution. When the body is
exposed to decreased barometric pressures (as in
flying an unpressurized aircraft to altitude, or during
a rapid decompression), the nitrogen dissolved in
the body comes out of solution. If the nitrogen is
forced to leave the solution too rapidly, bubbles form
in different areas of the body, causing a variety of
signs and symptoms. The most common symptom is
joint pain, which is known as “the bends.”
Trouble Sites
Although bubbles can form anywhere in the body,
the most frequently targeted anatomic locations are
the shoulders, elbows, knees, and ankles.
Table 1 lists the different DCS types
with their corresponding bubble
formation sites and their most
common symptoms. “The bends’’
(joint pain) account for about 60 to
70% of all altitude DCS cases, with
the shoulder being the most common
site. Neurologic manifestations
are present in about 10 to 15% of all DCS cases,
with headache and visual disturbances being the
most common symptoms. “The chokes” are very
infrequent and occur in less than 2% of all DCS
cases. Skin manifestations are present in about 10
to 15% of all DCS cases.
Medical Treatment
Mild cases of “the bends” and skin bends (excluding
mottled or marbled skin appearance) may disappear
2
during descent from high altitude, but still require
medical evaluation. If the signs and symptoms
persist during descent or reappear at ground
level, it is necessary to provide hyperbaric oxygen
treatment immediately (100% oxygen delivered in
a high-pressure chamber). Neurological DCS, “the
chokes,” and skin bends with mottled or marbled
skin lesions (see Table 1) should always be treated
with hyperbaric oxygenation. These conditions are
very serious and potentially fatal if untreated.
Facts About Breathing 100% Oxygen
One of the most significant breakthroughs in altitude
DCS research was the discovery that breathing
100% oxygen before exposure to a low barometric
pressure (oxygen prebreathing), decreases the risk
of developing altitude DCS. Oxygen prebreathing
promotes the elimination (washout) of nitrogen from
body tissues. Prebreathing 100% oxygen for 30
minutes prior to initiating ascent to altitude reduces
the risk of altitude DCS for short exposures (10-30
min. only) to altitudes between 18,000 and 43,000 ft.
However, oxygen prebreathing has to be continued,
without interruption, with inflight 100% oxygen
breathing to provide effective protection against
altitude DCS. Furthermore, it is very important to
　
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