decompression sickness decompression sickness decompression sickness (abbreviated dcs; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. dcs most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurisation, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. dcs and arterial gas embolism are collectively referred to as decompression illness. decompression sicknessother namesdivers' disease, the bends, aerobullosis, caisson diseasetwo united states navy sailors demonstrate treatment for decompression sickness inside a decompression chamberspecialtyemergency medicine since bubbles can form in or migrate to any part of the body, dcs can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. dcs often causes air bubbles to settle in major joints like knees or elbows, causing individuals to bend over in excruciating pain, hence its common name, the bends. individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. the classification of types of dcs according to symptoms has evolved since its original description in the 19th century. the severity of symptoms varies from barely noticeable to rapidly fatal. the risk of dcs caused by diving can be managed through proper decompression procedures, and contracting the condition has become uncommon. its potential severity has driven much research to prevent it, and divers almost universally use dive tables or dive computers to limit their exposure and to monitor their ascent speed. if dcs is suspected, it is treated by hyperbaric oxygen therapy in a recompression chamber. where a chamber is not accessible within a reasonable time frame, in-water recompression may be indicated for a narrow range of presentations, if there are suitably skilled personnel and appropriate equipment available on site. diagnosis is confirmed by a positive response to the treatment. early treatment results in a significantly higher chance of successful recovery. classification dcs is classified by symptoms. the earliest descriptions of dcs used the terms: "bends" for joint or skeletal pain; "chokes" for breathing problems; and "staggers" for neurological problems. in 1960, golding et al. introduced a simpler classification using the term "type i ('simple')" for symptoms involving only the skin, musculoskeletal system, or lymphatic system, and "type ii ('serious')" for symptoms where other organs (such as the central nervous system) are involved. type ii dcs is considered more serious and usually has worse outcomes. this system, with minor modifications, may still be used today. following changes to treatment methods, this classification is now much less useful in diagnosis, since neurological symptoms may develop after the initial presentation, and both type i and type ii dcs have the same initial management. decompression illness and dysbarism the term dysbarism encompasses decompression sickness, arterial gas embolism, and barotrauma, whereas decompression sickness and arterial gas embolism are commonly classified together as decompression illness when a precise diagnosis cannot be made. dcs and arterial gas embolism are treated very similarly because they are both the result of gas bubbles in the body. the u.s. navy prescribes identical treatment for type ii dcs and arterial gas embolism. their spectra of symptoms also overlap, although the symptoms from arterial gas embolism are generally more severe because they often arise from an infarction (blockage of blood supply and tissue death). signs and symptoms while bubbles can form anywhere in the body, dcs is most frequently observed in the shoulders, elbows, knees, and ankles. joint pain ("the bends") accounts for about 60% to 70% of all altitude dcs cases, with the shoulder being the most common site for altitude and bounce diving, and the knees and hip joints for saturation and compressed air work. neurological symptoms are present in 10% to 15% of dcs cases with headache and visual disturbances being the most common symptom. skin manifestations are present in about 10% to 15% of cases. pulmonary dcs ("the chokes") is very rare in divers and has been observed much less frequently in aviators since the introduction of oxygen pre-breathing protocols. the table below shows symptoms for different dcs types. signs and symptoms of decompression sickness dcs type bubble location signs & symptoms (clinical manifestations) musculoskeletal mostly large joints of the limbs (elbows, shoulders, hip, wrists, knees, ankles) localized deep pain, ranging from mild to excruciating. sometimes a dull ache, more rarely a sharp pain. active and passive motion of the joint may aggravate 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. cutaneous skin itching, usually around the ears, face, neck, arms, and upper torso sensation of tiny insects crawling over the skin (formication) mottled or marbled skin usually around the shoulders, upper chest and abdomen, with itching (cutis marmorata) swelling of the skin, accompanied by tiny scar-like skin depressions (pitting edema) neurologic brain altered sensation, tingling or numbness (paresthesia), increased sensitivity (hyperesthesia) confusion or memory loss (amnesia) visual abnormalities unexplained mood or behaviour changes seizures, unconsciousness neurologic spinal cord ascending weakness or paralysis in the legs urinary incontinence and fecal incontinence girdling (also referred to as girdle, banding, or tightening feeling) around the abdominal region and/or chest constitutional whole body headache unexplained fatigue generalised malaise, poorly localised aches audiovestibular inner ear loss of balance dizziness, vertigo, nausea, vomiting hearing loss pulmonary lungs dry persistent cough burning chest pain under the sternum, aggravated by breathing shortness of breath frequency the relative frequencies of different symptoms of dcs observed by the u.s. navy are as follows: symptoms by frequency symptoms frequency local joint pain 89% arm symptoms 70% leg symptoms 30% dizziness 5.3% paralysis 2.3% shortness of breath 1.6% extreme fatigue 1.3% collapse/unconsciousness 0.5% onset although onset of dcs can occur rapidly after a dive, in more than half of all cases symptoms do not begin to appear for at least an hour. in extreme cases, symptoms may occur before the dive has been completed. the u.s. navy and technical diving international, a leading technical diver training organization, have published a table that documents time to onset of first symptoms. the table does not differentiate between types of dcs, or types of symptom. onset of dcs symptoms time to onset percentage of cases within 1 hour 42% within 3 hours 60% within 8 hours 83% within 24 hours 98% within 48 hours 100% causes dcs is caused by a reduction in ambient pressure that results in the formation of bubbles of inert gases within tissues of the body. it may happen when leaving a high-pressure environment, ascending from depth, or ascending to altitude. a closely related condition of bubble formation in body tissues due to isobaric counterdiffusion can occur with no change of pressure. ascent from depth dcs is best known as a diving disorder that affects divers having breathed gas that is at a higher pressure than the surface pressure, owing to the pressure of the surrounding water. the risk of dcs increases when diving for extended periods or at greater depth, without ascending gradually and making the decompression stops needed to slowly reduce the excess pressure of inert gases dissolved in the body. the specific risk factors are not well understood and some divers may be more susceptible than others under identical conditions. dcs has been confirmed in rare cases of breath-holding divers who have made a sequence of many deep dives with short surface intervals, and may be the cause of the disease called taravana by south pacific island natives who for centuries have dived by breath-holding for food and pearls. two principal factors control the risk of a diver developing dcs: the rate and duration of gas absorption under pressure – the deeper or longer the dive the more gas is absorbed into body tissue in higher concentrations than normal (henry's law); the rate and duration of outgassing on depressurization – the faster the ascent and the shorter the interval between dives the less time there is for absorbed gas to be offloaded safely through the lungs, causing these gases to come out of solution and form "micro bubbles" in the blood. even when the change in pressure causes no immediate symptoms, rapid pressure change can cause permanent bone injury called dysbaric osteonecrosis (don). don can develop from a single exposure to rapid decompression. leaving a high-pressure environment the principal features of a caisson are the workspace, pressurised by an external air supply, and the access tube with an airlock when workers leave a pressurized caisson or a mine that has been pressurized to keep water out, they will experience a significant reduction in ambient pressure. a similar pressure reduction occurs when astronauts exit a space vehicle to perform a space-walk or extra-vehicular activity, where the pressure in their spacesuit is lower than the pressure in the vehicle. the original name for dcs was "caisson disease". this term was introduced in the 19th century, when caissons under pressure were used to keep water from flooding large engineering excavations below the water table, such as bridge supports and tunnels. workers spending time in high ambient pressure conditions are at risk when they return to the lower pressure outside the caisson if the pressure is not reduced slowly. 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. on the other side of the manhattan island during construction of the hudson river tunnel contractor's agent ernest william moir noted in 1889 that workers were dying due to decompression sickness and pioneered the use of an airlock chamber for treatment. ascent to altitude the most common health risk on ascent to altitude is not decompression sickness but altitude sickness, or acute mountain sickness (ams), which has an entirely different and unrelated set of causes and symptoms. ams results not from the formation of bubbles from dissolved gasses in the body but from exposure to a low partial pressure of oxygen and alkalosis. however, passengers in unpressurized aircraft at high altitude may also be at some risk of dcs. altitude dcs became a problem in the 1930s with the development of high-altitude balloon and aircraft flights but not as great a problem as ams, which drove the development of pressurized cabins, which coincidentally controlled dcs. commercial aircraft are now required to maintain the cabin at or below a pressure altitude of 2,400 m (7,900 ft) even when flying above 12,000 m (39,000 ft). symptoms of dcs in healthy individuals are subsequently very rare unless there is a loss of pressurization or the individual has been diving recently. divers who drive up a mountain or fly shortly after diving are at particular risk even in a pressurized aircraft because the regulatory cabin altitude of 2,400 m (7,900 ft) represents only 73% of sea level pressure. generally, the higher the altitude the greater the risk of altitude dcs but there is no specific, maximum, safe altitude below which it never occurs. there are very few symptoms at or below 5,500 m (18,000 ft) unless patients had predisposing medical conditions or had dived recently. there is a correlation between increased altitudes above 5,500 m (18,000 ft) and the frequency of altitude dcs but there is no direct relationship with the severity of the various types of dcs. a us air force study reports that there are few occurrences between 5,500 m (18,000 ft) and 7,500 m (24,600 ft) and 87% of incidents occurred at or above 7,500 m (24,600 ft). high-altitude parachutists may reduce the risk of altitude dcs if they flush nitrogen from the body by pre-breathing pure oxygen. predisposing factors