Decompression sickness (DCS), the diver’s disease,
the bends, or caisson disease is the name given to a variety of symptoms
suffered by a person exposed to a reduction in the pressure surrounding their
body. It is a type of diving hazard and dysbarism.
Contents
Introduction
Decompression sickness can happen in these situations:
* A diver ascends rapidly from a dive or does not carry out decompression stops
after a long or deep dive.
* An unpressurized aircraft flies upwards.
* The cabin pressurization system of an aircraft fails.
* Divers flying in any aircraft shortly after diving. Pressurized aircraft are
not risk-free since the cabin pressure is not maintained at sea-level pressure.
Commercial aircraft cabin pressure is often maintained to about 8,000 feet above
sea level.
* A worker comes out of a pressurized caisson or out of a mine, which has been
pressurized to keep water out.
* An astronaut exits a space vehicle to perform a space-walk or extra-vehicular
activity where the pressure in his spacesuit is lower than the pressure in the
vehicle.
This surfacing diver must enter a recompression chamber to avoid the bends.
This surfacing diver must enter a recompression chamber to avoid the bends.
These situations cause inert gases, generally nitrogen, which are normally
dissolved in body fluids and tissues, to come out of physical solution (i.e.,
outgas) and form gas 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 can or
bottle. When you remove the cap from the bottle, you can clearly hear gas
escaping and see bubbles forming in the soda. This is carbon dioxide gas coming
out of solution as a result of the pressure inside the container reducing to
atmospheric pressure.
Similarly, nitrogen is an inert gas normally stored throughout the human body,
such as tissues and fluids, in physical solution. When the body is exposed to
decreased pressures, such as when flying an un-pressurized aircraft to altitude
or during a scuba ascent through water, the nitrogen dissolved in the body
outgases. If nitrogen is forced to come out of solution too quickly, bubbles
form in parts of the body causing the signs and symptoms of the "bends" which
can be itching skin and rashes, joint pain, sensory system failure, paralysis,
and death.
An air embolism, caused by other processes, can have many of the same symptoms
as DCS. The two conditions are grouped together under the name decompression
illness or DCI.
History
Wikisource has an original article from the 1911 Encyclopædia Britannica about:
Caisson Disease
The first documented case of DCS were reported in 1841 by a mining engineer who
observed the occurrence of pain and muscle cramps among coal miners exposed to
air-pressurized mine shafts designed to keep water out. The submarine pioneer
Julius H. Kroehl died of decompression sickness during experimental dives with
the Sub Marine Explorer in 1867. Another early case resulting from diving
activities while wearing an air-pumped helmet was reported in 1869.
Predisposing factors
* Magnitude of the pressure reduction: A large pressure reduction is more likely
to cause DCS than a small one. For example, the ambient pressure halves by
ascending during a dive from 10 metres / 33 feet (2 bar) to the surface (1 bar),
or by flying from sea level (1 bar) to an altitude of 16,000 feet / 5,000 metres
(0.5 bar) in an un-pressurized aircraft. Diving and then flying shortly
afterwards increases the pressure reduction as does diving at high altitude.
* Repetitive exposures: Repetitive dives or ascents to altitudes above 18,000
feet within a short period of time (a few hours) also increase the risk of
developing altitude DCS.
* Rate of ascent: The faster the ascent, the greater the risk of developing
altitude DCS. An individual exposed to a rapid decompression (high rate of
ascent) above 18,000 feet 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 flight to altitudes of 18,000
feet 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 supply, nitrogen is stored in greater
amounts in fat tissues. Although fat represents only 15 percent of a normal
adult body, it stores over half of the total amount of nitrogen (about 1 litre)
normally dissolved in the body.
* Exercise: When a person is physically active, or performing strenuous activity
before or after a dive (such as rowing to and from a dive site), there is
greater risk of DCS.
* Rate of Air Consumption: If you tend to consume more air than what may be
considered "normal" for scuba diving, you will certainly be more susceptible to
DCS if you skirt the no-decompression limits.
* Alcohol consumption/dehydration: While conventional wisdom would have one
believe that the after effects of alcohol consumption increase the
susceptibility to DCS through increased dehydration and decreased motor
coordination/mental acuity, one study concluded that alcohol consumption did not
increase the risk of DCS.[1]. The high surface tension of water is generally
regarded as helpful in controlling bubble size, hence staying hydrated is
recommended by most experts.
* Patent foramen ovale: A hole between the atrial chambers of the heart in the
fetus is normally closed by a flap with the first breaths at birth. In up to 20
percent of adults the flap does not seal, however, allowing blood through the
hole with coughing or other activities which raise chest pressure. In diving,
this can allow blood with microbubbles in the venous blood from the body to
return directly to the arteries (including arteries to the brain, spinal cord
and heart) rather than pass through the lungs, where the bubbles would otherwise
be filtered out by the lung capillary system. In the arterial system, bubbles
(arterial gas embolism) are far more dangerous because they block circulation
and cause infarction (tissue death, due to local loss of blood flow). In the
brain, infarction results in stroke, in the spinal cord it may result in
paralysis, and in the heart it results in myocardial infarction (heart attack).
Signs and symptoms
Bubbles can form anywhere in the body, but symptomatic sensation is most
frequently observed in the shoulders, elbows, knees, and ankles.
This table gives symptoms for the different DCS types. The "bends" (joint pain)
accounts for about 60 to 70 percent of all altitude DCS cases, with the shoulder
being the most common site. These types are classifed medically as DCS I.
Neurological symptoms are present in 10 to 15 percent of all DCS cases with
headache and visual disturbances the most common. DCS cases with neurological
symptoms are generally classified as DCS II. The "chokes" are rare and occur in
less than two-percent of all DCS cases. Skin manifestations are present in about
10 to 15 percent of all DCS cases.
Table 1. Signs and symptoms of 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.
* The pain may be reduced by bending the joint to find a more comfortable
position.
* If caused by altitude, pain can occur immediately or up to many hours later.
NEUROLOGIC Brain
* Confusion or memory loss
* Headache
* Spots in visual field (scotoma), tunnel vision, double vision (diplopia), or
blurry vision
* Unexplained extreme fatigue or behaviour changes
* Seizures, dizziness, vertigo, nausea, vomiting and unconsciousness may occur,
mainly due to labyrinthitis
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,
with itching
* Swelling of the skin, accompanied by tiny scar-like skin depressions (pitting
edema)
Treatment
Recompression is the only effective treatment for severe DCS, although rest and
oxygen (increasing the percentage of oxygen in the air being breathed via a
tight fitting oxygen mask) applied to lighter cases can be effective.
Recompression is normally carried out in a recompression chamber. In diving, a
high-risk alternative is in-water recompression.
Oxygen first aid treatment is useful for suspected DCS casualties or divers who
have made fast ascents or missed decompression stops. Most fully closed-circuit
rebreathers can deliver sustained high concentrations of oxygen-rich breathing
gas and could be used as an alternative to pure open-circuit oxygen
resuscitators.
Common pressure reductions that cause DCS
The main cause of DCS is a reduction in the pressure surrounding the body.
Common ways in which the required reduction in pressure occur are:
* leaving a high atmospheric pressure environment
* rapid ascent through water during a dive
* ascent to altitude while flying
Leaving a high pressure environment
The original name for DCS was caisson disease; this term was used in the 19th
century, when large engineering excavations below the water table, such as with
the piers of bridges and with tunnels, had to be done in caissons under pressure
to keep water from flooding the excavations. Workers who spend time in high
pressure atmospheric pressure conditions are at risk if they leave that
environment and reduce the pressure surrounding them.
DCS was a major factor during construction of Eads Bridge, when 15 workers died
from what was then a mysterious illness, and later during construction of the
Brooklyn Bridge, where it incapacitated the project leader Washington Roebling.
Ascent during a dive
DCS is best known as an injury that affects scuba divers. The pressure of the
surrounding water increases as the diver descends and reduces as the diver
ascends. The risk of DCS increases by diving long or deep without slowly
ascending and making the decompression stops needed to eliminate the inert gases
normally, although the specific risk factors are not well understood. Some
divers seem more susceptible than others under identical conditions.
There have been known cases of bends in snorkellers who have made many deep
dives in succession. DCS may be the cause of the disease taravana which affects
South Pacific island natives who for centuries have dived without equipment for
food and pearls.
Two linked factors contribute to divers' DCS, although the complete relationship
of causes is not fully understood:
* deep or long dives: inert gases in breathing gases, such as nitrogen and
helium, are absorbed into the tissues of the body in higher concentrations than
normal (Henry's Law) when breathed at high pressure.
* fast ascents: reducing the ambient pressure, as happens during the ascent,
causes the absorbed gases to come back out of solution, and form "micro bubbles"
in the blood. Those bubbles will safely leave the body through the lungs if the
ascent is slow enough that the volume of bubbles does not rise too high.
The physiologist John Haldane studied this problem in the early 20th century,
eventually devising the method of staged, gradual decompression, whereby the
pressure on the diver is released slowly enough that the nitrogen comes
gradually out of solution without leading to DCS. Bubbles form after every dive:
slow ascent and decompression stops simply reduce the volume and number of the
bubbles to a level at which there is no injury to the diver.
Severe cases of decompression sickness can lead to death. Large bubbles of gas
impede the flow of oxygen-rich blood to the brain, central nervous system and
other vital organs.
Even when the change in pressure causes no immediate symptoms, rapid pressure
change can cause permanent bone injury called dysbaric osteonecrosis (DON) "bone
cell death from bad pressure". DON can develop from a single exposure to rapid
decompression. DON is diagnosed from lesions visible in X-ray images of the
bones. Unfortunately, X-rays appear normal for at least 3 months after the
permanent damage has occurred; it may take 4 years after the damage has occurred
for its effects to become visible in the X-ray images. [1]
Avoidance
Decompression tables and dive computers have been developed that help the diver
choose depth and duration of decompression stops for a particular dive profile
at depth.
Avoiding decompression sickness is not an exact science. Accidents can occur
after relatively shallow and short dives. To reduce the risks, divers should
avoid long and deep dives and should ascend slowly. Also, dives requiring
decompression stops and dives with less than a 16 hour interval since the
previous dive increase the risk of DCS. There are many additional risk factors,
such as age, obesity, fatigue, use of alcohol, dehydration and a patent foramen
ovale. In addition, flying at high altitude less than 24 hours after a deep dive
can be a precipitating factor for decompression illness.
Astronauts aboard the International Space Station preparing for Extra-vehicular
activity "camp out" at low atmospheric pressure (approximately 10 psi = 700
mbar) spending 8 sleeping hours in the airlock chamber before their spacewalk.
Their spacesuits can operate at 4.7 psi = 330 mbar for maximum flexibility.
Helium
Nitrogen is not the only breathing gas that causes DCS. Gas mixtures such as
trimix and heliox include helium, which can also be implicated in decompression
sickness.
Helium both enters and leaves the body faster than nitrogen, and for dives of
three or more hours in duration, the body almost reaches saturation of helium.
For such dives the decompression time is shorter than for nitrogen-based
breathing gases such as air.
There is some debate as to the decompression effects of helium for shorter
duration dives. Most divers do longer decompressions, whereas some groups like
the WKPP have been pioneering the use of shorter decompression times by
including deep stops.
Decompression time can be significantly shortened by breathing rich nitrox (or
pure oxygen in very shallow water) during the decompression phase of the dive.
The reason is that the nitrogen outgases at a rate proportional to the
difference between the ppN2 (partial pressure of nitrogen) in the diver's body
and the ppN2 in the gas that he or she is breathing; but the likelihood of
bubbles is proportional to the difference between the ppN2 in the diver's body
and the total surrounding air or water pressure.
Ascent to altitude
People flying in un-pressurised aircraft at high altitude, such as stowaways, or
passengers in a cabin that has experienced rapid decompression, or pilots in an
open cockpit, can suffer from decompression sickness. Even Lockheed U-2 pilots
experienced altitude DCS in the mid-'50s during the Cold War flying over their
targets. Divers who dive and then fly in aircraft are at risk even in
pressurised aircraft because the cabin air pressure is less than the air
pressure at sea level. The same applies to divers going into higher elevations
by land after diving.
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-a-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 is
still a risk to the occupants of modern aircraft.
There is no specific altitude threshold that can be considered safe for everyone
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 pressure altitudes below 18,000 feet who have not been scuba
diving. Individual exposures to pressure altitudes between 18,000 and 25,000
feet have shown a low occurrence of altitude DCS. Most cases of altitude DCS
occur among individuals exposed to pressure altitudes of 25,000 feet or higher.
A US Air Force study of altitude DCS cases reported that only 13 percent
occurred below 25,000 feet 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 feet 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).
Arterial gas embolism and DCS have very similar treatment because they are both
the result of gas bubbles in the body. Their spectra of symptoms also overlap,
although those from arterial gas embolism are more severe because they often
cause infarction and tissue death as noted above. In a diving context, the two
are joined under the general term of decompression illness. Another term,
dysbarism, encompasses decompression sickness, arterial gas embolism, and
barotrauma.
Ascent to altitude can happen without flying in places such as the Ethiopia and
Eritrea highland (8000 feet = about 1.5 miles above sea level) and the Peru and
Bolivia altiplano and Tibet (2 to 3 miles above sea level).
Medical treatment
Mild cases of the "bends" and skin bends (excluding mottled or marbled skin
appearance) may disappear 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-percent 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.
Effects of breathing pure oxygen
Breathing pure oxygen to remove nitrogen from the bloodstream
Breathing pure oxygen to remove nitrogen from the bloodstream
One of the most significant breakthroughs in altitude DCS research was oxygen
pre-breathing. Breathing pure oxygen before exposure to a low-barometric
pressure decreases the risk of developing altitude DCS. Oxygen pre-breathing
promotes the elimination or washout of nitrogen from body tissues. Pre-breathing
pure oxygen for 30 minutes before starting ascent to altitude reduces the risk
of altitude DCS for short exposures (10 to 30 minutes only) to altitudes between
18,000 and 43,000 feet. However, oxygen pre-breathing has to be continued
without interruption with in-flight, pure oxygen to provide effective protection
against altitude DCS. Furthermore, it is very important to understand that
breathing pure oxygen only during flight (ascent, en route, descent) does not
decrease the risk of altitude DCS, and should not be used instead of oxygen
pre-breathing.
Although pure oxygen pre-breathing is an effective method to protect against
altitude DCS, it is logistically complicated and expensive for the protection of
civil aviation flyers, either commercial or private. Therefore, it is only used
now by military flight crews and astronauts for their protection during high
altitude and space operations.
Scuba diving before flying
The rule about decompression sickness risk on ascending to lower surrounding
pressure, does not stop at sea level (even though decompression tables stop at
sea level), but continues when a diver soon after diving goes into air pressure
much less than at sea level. Altitude DCS can occur during exposure to altitudes
as low as 5,000 feet or less. This can happen:-
1. In an airliner at high altitude the cabin pressure is usually not at full sea
level pressure, but like the air pressure at say 8000 feet altitude.
2. At high altitudes on land: e.g. if you scuba dive in Eritrea, and then go
onto the Asmara plateau (where Eritrea's main airport is), which is about 8000
feet or 1.5 miles or 2400 meters above sea level.
3. Occasionally in cave diving, "Torricellian chambers" are found; they are full
of water at less than atmospheric pressure. They arise when the water level
drops and there is no way for air to get into the chamber.
What to do if altitude DCS occurs
* Put on your oxygen mask immediately and switch the regulator to 100% oxygen.
* Begin an emergency descent and land as soon as possible. Even if the symptoms
disappear during descent, you should still land and seek medical evaluation
while continuing to breathe oxygen.
* If one of your symptoms is joint pain, keep the affected area still; do not
try to work pain out by moving the joint around.
* Upon landing seek medical assistance from an aviation authority medical
officer, aviation medical examiner (AME), military flight surgeon, or a
hyperbaric medicine specialist. Be aware that a physician not specialized in
aviation or hypobaric medicine may not be familiar with this type of medical
problem. Therefore, be your own advocate.
* Definitive medical treatment may involve the use of a hyperbaric chamber
operated by specially trained personnel.
* Delayed signs and symptoms of altitude DCS can occur after return to ground
level whether or not they were present during flight.
Things to remember
* Altitude DCS is a risk every time you fly in an un-pressurized aircraft above
18,000 feet (or at lower altitude if you scuba dive prior to the flight).
* Be familiar with the signs and symptoms of altitude DCS (see Table 1). Monitor
all aircraft occupants, including yourself, any time you fly an un-pressurized
aircraft above 18,000 feet.
* Avoid unnecessary strenuous physical activity prior to flying an
un-pressurized aircraft above 18,000 feet, and for 24 h after the flight.
* Even if you are flying a pressurized aircraft, altitude DCS can occur as a
result of sudden loss of cabin pressure (in-flight rapid decompression).
* After exposure to an in-flight rapid decompression, do not fly for at least 24
h. In the meantime, stay vigilant for the possible onset of delayed symptoms or
signs of altitude DCS. If you present delayed symptoms or signs of altitude DCS,
seek medical attention at once.
* Keep in mind that breathing 100% oxygen during flight (ascent, en route,
descent) without oxygen pre-breathing before take off does not prevent altitude
DCS.
* Do not ignore any symptoms or signs that go away during the descent. This
could confirm that you are suffering altitude DCS. You should be medically
evaluated as soon as possible.
* If there is any indication that you may have experienced altitude DCS, do not
fly again until you are cleared to do so by an aviation authority medical
officer, an aviation medical examiner, a military flight surgeon, or a
hyperbaric medicine specialist.
* Allow at least 24 hours to elapse between scuba diving and flying.
* Be prepared for a future emergency by finding where hyperbaric chambers are
available in your area of operations. However, keep in mind that not all of the
available hyperbaric treatment facilities have personnel qualified to handle
altitude DCS emergencies. To obtain information on the locations of hyperbaric
treatment facilities capable of handling altitude DCS emergencies, call the
Diver's Alert Network at (USA phone number) (919) 684-8111.
Decompression sickness in popular culture
* A diver with decompression sickness flying in an aircraft was part of the plot
in the episode Airborne of House, M.D., first aired Tuesday April 11, 2007.
* Rock band Radiohead released an album entitled The Bends, a reference to
decompression sickness.
* John Roebling died from Caisson's Disease while working as the chief engineer
while building the Brooklyn Bridge in the late 1800's. Roebling's son, William,
took over as chief engineer and came down with the bends as well. He, however,
was able to survive and directed construction from his sick bed.
References
1. ^ http://depts.washington.edu/adai/pubs/pres/LeighRSAPoster.pdf