Decompression sickness (DCS) is a dangerous and occasionally lethal condition caused by nitrogen bubbles that form in the blood and other tissues because of abrupt changes in barometric pressure.
Decompression sickness occurs most often in scuba divers who surface too quickly. It also can occur in pilots who fly above 18,000 ft. (5,500 m) in high-altitude balloons or unpressurized aircraft, although in the twenty-first century, this is rare.
DCS was first described in 1841 by a mining engineer who noted symptoms of joint pain in bridge construction crews working under water in large pressurized enclosures called caissons. He called the disorder caisson disease, a name that is no longer used. At times the terminology adopted by writers on DCS can be confusing. Some substitute the term decompression illness (DCI) for DCS. Others treat DCI as a label encompassing both DCS and a rarer bubble problem called gas embolism, air embolism, or arterial gas embolism (AGE).
The air humans breathe is mostly a mixture of two gases, nitrogen (78%) and oxygen (21%). Unlike oxygen, nitrogen is a biologically inert gas, meaning that it is not metabolized (converted into other substances) by the body. For this reason, most of the nitrogen humans inhale is expelled when they exhale, but some is dissolved into the blood and other tissues. The amount of nitrogen that dissolves in the blood depends on the barometric or air pressure.
During a dive, divers experience water pressure on their bodies that is greater than the air pressure at sea level. For example, it is twice as great at a depth of 33 ft. (10 m). As the water pressure increases, the amount of nitrogen that dissolves in the blood and body tissues increases. It remains until divers begin their return to the surface. On the way up, decompression occurs, in other words, the water pressure drops. As the pressure decreases, the extra nitrogen gradually diffuses out of the tissues and is delivered by the bloodstream to the lungs, where it is expelled from the body.
If divers surface too quickly, however, potentially dangerous nitrogen bubbles can form and cause DCS. These bubbles can compress nerves; block arteries, veins, and lymphatic vessels; and trigger harmful chemical reactions in the blood. The precise reasons for bubble formation remain unclear.
How much extra nitrogen enters the tissues varies with the depth and duration of the dive. Dive tables prepared by the U.S. Navy and other organizations specify how long most divers can safely remain at a particular depth. If the dive table limits are exceeded, divers must pause on the way up to allow the nitrogen to diffuse gradually into the bloodstream without forming bubbles; these pauses are called decompression stops, and they are carefully calibrated.
DCS can occur even when divers obey safe diving rules. In such cases, the predisposing factors include fatigue, obesity, dehydration, hypothermia, and recent alcohol use. There is also some indication that gas bubbles form in children more readily than adults. The Divers Alert Network (DAN) recommends that children under age 12 years not make even shallow dives.
People who fly or travel to high-altitude locations without letting 12–24 hours pass after their last dive are at risk for DCS as well because their bodies undergo further decompression. This is true even when flying in commercial aircraft. Many travelers are unaware that to save money on fuel the cabin pressure in commercial aircraft is set much lower than the pressure at sea level. At 30,000 ft. (9,144 m), for instance, cabin pressure is usually equivalent to the pressure at 7,000–8,000 ft. (2,133–2,438 m) above sea level, a safe setting for most people, but not for recent divers. Exactly how long divers should wait before flying or traveling to a high-altitude location depends on how much diving they have done and other considerations. If there is uncertainty about the appropriate waiting period, the sensible course of action is to wait the full 24 hours before experiencing high altitude.
DCS is caused by nitrogen gas diffusing out of tissues in the body as pressure on the body decreases. Although nitrogen can safely diffuse out of the body when pressure changes are slow, rapid pressure decreases allow bubble formation, resulting in DCS.
Because the nitrogen bubbles that cause DCS can affect any of the body's tissues, including the blood, bones, nerves, and muscles, many kinds of symptoms are possible. Symptoms can appear minutes after divers surface and in about 80% of cases do so within eight hours. Pain is often the only symptom. This pain is sometimes called the bends, although many people incorrectly use that term as a synonym for DCS itself.
DCS pain, which ranges from mild to severe, usually is limited to the joints but may be felt anywhere. Severe itching (pruritus), skin rashes, and skin mottling (cutis marmorata) are other possible symptoms. All of these are sometimes classified as manifestations of type 1 or mild DCS. Type 2 or serious DCS can lead, among other effects, to paralysis, brain damage, heart attacks, and death. Many DCS victims experience both type 1 and type 2 symptoms.
There are no specific tests to diagnose DVS. Diagnosis requires taking a medical history, including recent activity, and conducting a physical examination. A physician knowledgeable about DCS should ask specific questions about the frequency, depth, and duration of the dive and the rate of ascent to the surface, as well as technical information about the type of gasses and equipment used and any problem the diver encountered. Many physicians are unfamiliar with DCS symptoms and fail to diagnose the disorder.
The first-line treatment for DCS is giving divers 100% oxygen. This is especially important if hospital and hyperbaric facilities are far away. Most people experiencing DCS are also treated by being placed in a hyperbaric chamber. A hyperbaric chamber is an enclosure in which the air pressure is first gradually increased and then gradually decreased. This process shrinks the bubbles and allows the nitrogen to safely diffuse out of the tissues. Air in a hyperbaric chamber also is enriched with oxygen.
Hyperbaric chamber facilities exist throughout the United States. No matter how mild DCS symptoms may appear, immediate transport to a facility is essential. Treatment is necessary even if the symptoms clear up before the facility is reached, because bubbles may still be in the bloodstream and pose a threat. DAN maintains a list of facilities and a 24-hour hotline that can provide advice on handling DCS and other diving emergencies.
DCS is not a public health problem. Response is limited to emergency care by first responders and transport to a facility with a hyperbaric chamber.
The obvious way to minimize the risk of falling victim to DCS is to follow the rules on safe diving and air travel after a dive. People who are obese, suffer from lung or heart problems, or are otherwise in poor health should not dive. Given that the effect of nitrogen diffusion on the fetus remains unknown, diving while pregnant is not recommended.
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American College of Hyperbaric Medicine, 6737 W. Washington St., Ste. 3265, West Allis, WI, 53214, (414) 269-5340, email@example.com, http://www.achm.org .
Divers Alert Network, 6 W. Colony Place, Durham, NC, 27705, (919) 684-2948, (800) 446-2671, http://www.diversalertnetwork.org .
Undersea and Hyperbaric Medical Society, 631 U.S. Highway 1, Ste. 307, North Palm Beach, FL, 33408, (919) 490-5140, Fax: (919) 490-5149, (877) 533-8467, firstname.lastname@example.org, http://www.uhms.org .
Revised by Tish Davidson, AM