Decompression sickness
Encyclopedia
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization. DCS most commonly refers to a specific type of scuba diving hazard
but may be experienced in other depressurisation events such as caisson
working, flying in unpressurised aircraft, and extra-vehicular activity
from spacecraft.
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. 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 by its symptoms has evolved since its original description over a hundred years ago.
Although DCS is not a common event, its potential severity is such that much research has gone into preventing it, and scuba divers use dive tables or dive computers to set limits on their exposure to pressure and their ascent speed. Treatment is by hyperbaric oxygen therapy
in a recompression chamber. If treated early, there is a significantly higher chance of successful recovery.
, 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.
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 those from arterial gas embolism are generally more severe because they often arise from an infarction
(blockage of blood supply and tissue death).
and visual disturbances 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.
The distribution of symptoms of DCS observed by the U.S. Navy are as follows:
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 indicates onset of first symptoms. The table does not differentiate between types of DCS, or types of symptom.
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.
divers who have made a sequence of many deep dives with short surface intervals; and it 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 pearl
s.
Two principal factors control the risk of a diver suffering DCS:
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.
When a worker comes out of a pressurized caisson
or out of 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 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.
The original name for DCS was "caisson disease"; this term was used in the 19th century, in large engineering excavations below the water table
, such as bridge supports and tunnels, where caissons under pressure were used to keep water from flooding the excavations. Workers spending time in high-pressure atmospheric pressure conditions are at risk when they return to the lower pressure outside the caisson if the pressure surrounding them was 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
.
ascends to high altitude. Likewise, there is increased risk for divers flying in any aircraft shortly after diving, since even in a pressurized aircraft the cabin pressure is not maintained at sea-level pressure but may drop to as low as 73% of sea level pressure.
Altitude DCS became a common problem in the 1930s with the development of high-altitude balloon and aircraft flights. Today, cabin pressurization
systems maintain commercial aircraft cabin pressure at the equivalent altitude of 2400 m (7,874 ft) or less, allowing safe flights at 12000 m (39,370.1 ft) or more. DCS is very rare in healthy individuals who experience pressures equivalent to this altitude. However, since the pressure in the cabin is not actually maintained at sea-level pressure, there is still a risk of DCS in individuals having dived recently. Also, cabin pressurization systems still fail occasionally, and some people may be predisposed to the drop in pressure that occurs even in pressurized aircraft.
There is no specific altitude threshold that can be considered safe for everyone and below which no one will develop altitude DCS. Nevertheless, there is very little evidence of altitude DCS occurring among healthy individuals who have not been scuba diving at pressure altitude
s below 5500 m (18,044.6 ft). The higher the altitude of exposure the greater is the risk of developing altitude DCS. Although exposures to incremental altitudes above 5500 m (18,044.6 ft) show an incremental risk of altitude DCS, they do not show a direct relationship with the severity of the various types of DCS. Individual exposures to pressure altitudes between 5500 m (18,044.6 ft) and 7500 m (24,606.3 ft) have shown a low occurrence of altitude DCS. A US Air Force study of altitude DCS cases reported that 87% of incidents occurred at 7500 m (24,606.3 ft) or higher. High altitude parachutists performing a HALO jump may develop altitude DCS if they do not flush nitrogen from the body by pre-breathing pure oxygen.
The following individual factors have been identified as possibly contributing to increased risk of DCS:
Depressurisation causes inert gas
es, which were dissolved under higher pressure
, to come out of physical solution
and form gas bubble
s within the body. These bubbles produce the symptoms of decompression sickness. Bubbles may form whenever the body experiences a reduction in pressure, but not all bubbles result in DCS. The amount of gas dissolved in a liquid is described by Henry's Law
, which indicates that, when the pressure of a gas in contact with a liquid is decreased, the amount of that gas dissolved in the liquid will also decrease proportionately.
On ascent from a dive, inert gas comes out of solution in a process called "outgassing
" or "offgassing". Under normal conditions, most offgassing occurs by gas exchange
in the lung
s. If inert gas comes out of solution too quickly to allow outgassing in the lungs then bubbles may form in the blood or within the solid tissues of the body. The formation of bubbles in the skin or joints results in milder symptoms, while large numbers of bubbles in the venous blood can cause lung damage. The most severe types of DCS interrupt — and ultimately damage — spinal cord function, leading to paralysis
, sensory
dysfunction, or death. In the presence of a right-to-left shunt
of the heart, such as a patent foramen ovale, venous bubbles may enter the arterial system, resulting in an arterial gas embolism. A similar effect, known as ebullism
, may occur during explosive decompression
, when water vapour forms bubbles in body fluids due to a dramatic reduction in environmental pressure.
, but nitrogen is not the only gas that can cause DCS. Breathing gas
mixtures such as trimix and heliox
include helium
, which can also cause decompression sickness. Helium both enters and leaves the body faster than nitrogen, so different decompression schedules are required, but, since helium does not cause narcosis
, it is preferred over nitrogen in gas mixtures for deep diving.
There is some debate as to the decompression requirements for helium during short-duration dives. Most divers do longer decompressions, however some groups like the WKPP have been pioneering the use of shorter decompression times by including deep stops.
Any inert gas that is breathed under pressure can form bubbles when the ambient pressure decreases. Very deep dives have been made using hydrogen
-oxygen mixtures (hydrox
), but controlled decompression is still required to avoid DCS.
, and presents a problem for very deep dives. For example, after using a very helium-rich trimix at the deepest part of the dive, a diver will switch to mixtures containing progressively less helium and more oxygen and nitrogen during the ascent. Nitrogen diffuses into tissues 2.65 times slower than helium, but is about 4.5 times more soluble. Switching between gas mixtures that have very different fractions of nitrogen and helium can result in "fast" tissues (those tissues that have a good blood supply) actually increasing their total inert gas loading. This is often found to provoke inner ear decompression sickness, as the ear seems particularly sensitive to this effect.
had shown symptoms within 24 hours. An alternative diagnosis should be suspected if severe symptoms begin more than six hours following decompression without an altitude exposure or if any symptom occurs more than 24 hours after surfacing. The diagnosis is confirmed if the symptoms are relieved by recompression. Although MRI or CT
can frequently identify bubbles in DCS, they are not as good at determining the diagnosis as a proper history of the event and description of the symptoms.
The decompression schedule may be derived from decompression tables, decompression software, or from dive computers, and these are commonly based upon a mathematical model of the body's uptake and release of inert gas as pressure changes. These models, such as the Bühlmann decompression algorithm, are designed to fit empirical data and provide a decompression schedule for a given depth and dive duration.
Since divers on the surface after a dive still have excess inert gas in their bodies, any subsequent dive before this excess is fully eliminated needs to modify the schedule to take account of the residual gas load from the previous dive. This will result in a shorter available time under water or an increased decompression
time during the subsequent dive. The total elimination of excess gas may take many hours, and tables will indicate the time at normal pressures that is required, which may be up to 18 hours.
Decompression time can be significantly shortened by breathing mixtures containing much less inert gas during the decompression phase of the dive (or pure oxygen
at stops in 6 metres (19.7 ft) of water or less). The reason is that the inert gas outgases at a rate proportional to the difference between the partial pressure
of inert gas in the diver's body and its partial pressure in the breathing gas; whereas the likelihood of bubble formation depends on the difference between the inert gas partial pressure in the diver's body and the ambient pressure. Reduction in decompression requirements can also be gained by breathing a nitrox mix during the dive, since less nitrogen will be taken into the body than during the same dive done on air.
Following a decompression schedule does not completely protect against DCS. The algorithms used are designed to reduce the probability of DCS to a very low level, but do not reduce it to zero.
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 currently used only by military flight crews and astronauts for protection during high-altitude and space operations. It is also used by flight test crews involved with certifying aircraft.
Astronauts aboard the International Space Station
preparing for extra-vehicular activity
(EVA) "camp out" at low atmospheric pressure, 10.2 psi (0.703265243886 bar), spending eight sleeping hours in the Quest airlock chamber before their spacewalk. During the EVA they breathe 100% oxygen in their spacesuits, which operate at 4.3 psi (0.296474563599 bar), although research has examined the possibility of using 100% O2 at 9.5 psi (0.655001942835 bar) in the suits to lessen the pressure reduction, and hence the risk of DCS.
(100% oxygen delivered in a high-pressure chamber) can be provided. Mild cases of the "bends" and some skin symptoms may disappear during descent from high altitude; however, it is recommended that these cases still be evaluated. Neurological symptoms, pulmonary symptoms, and mottled or marbled skin lesions should be treated with hyperbaric oxygen therapy if seen within 10 to 14 days of development.
Recompression on room air was shown to be an effective treatment for minor DCS symptoms by Keays in 1909. Evidence of the effectiveness of recompression therapy utilizing oxygen was first shown by Yarbrough and Behnke
, and has since become the standard of care for treatment of DCS. Recompression is normally carried out in a recompression chamber. At a dive site, a riskier alternative is in-water recompression
.
Oxygen first aid has been used as an emergency treatment for diving injuries for years. If given within the first four hours of surfacing, it increases the success of recompression therapy as well as a decrease the number of recompression treatments required. Most fully closed-circuit rebreather
s can deliver sustained high concentrations of oxygen-rich breathing gas
and could be used as a means of supplying oxygen if dedicated equipment is not available.
It is beneficial to give fluids, as this helps reduce dehydration
. It is no longer recommended to administer aspirin, unless advised to do so by medical personnel, as analgesics may mask symptoms. People should be made comfortable and placed in the supine position (horizontal), or the recovery position
if vomiting occurs. In the past, both the Trendelenburg position
and the left lateral decubitus position (Durant's maneuver) have been suggested as beneficial where air emboli are suspected, but are no longer recommended for extended periods, owing to concerns regarding cerebral edema
.
(DAN) created "Project Dive Exploration" to collect data on dive profiles and incidents. From 1998 to 2002, they recorded 50,150 dives, from which 28 recompressions were required — although these will almost certainly contain incidents of arterial gas embolism (AGE) — a rate of about 0.05%.
From 1870 to 1910, all prominent features were established. Explanations at the time included: cold or exhaustion causing reflex spinal cord damage; electricity cause by friction
on compression; or organ congestion
; and vascular stasis caused by decompression.
(DAN) offer medical insurance policies that specifically cover all aspects of treatment for decompression sickness at rates of less than $100 per year.
In the United Kingdom, treatment of DCS is provided by the National Health Service, either at a specialised facility or at a Hyperbaric Centre based within a general hospital.
Diving hazards and precautions
Divers face specific physical and health risks when they go underwater or use high pressure breathing gases. Some of these conditions also affect people who work in raised pressure environments out of water, e.g...
but may be experienced in other depressurisation events such as caisson
Caisson (engineering)
In geotechnical engineering, a caisson is a retaining, watertight structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships. These are constructed such that the water can be pumped out, keeping the working...
working, flying in unpressurised aircraft, and extra-vehicular activity
Extra-vehicular activity
Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...
from spacecraft.
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. 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 by its symptoms has evolved since its original description over a hundred years ago.
Although DCS is not a common event, its potential severity is such that much research has gone into preventing it, and scuba divers use dive tables or dive computers to set limits on their exposure to pressure and their ascent speed. Treatment is by hyperbaric oxygen therapy
Hyperbaric oxygen therapy
Hyperbaric medicine, also known as hyperbaric oxygen therapy , is the medical use of oxygen at a level higher than atmospheric pressure. The equipment required consists of a pressure chamber, which may be of rigid or flexible construction, and a means of delivering 100% oxygen...
in a recompression chamber. If treated early, there is 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 skinSkin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, musculoskeletal system
Musculoskeletal system
A musculoskeletal system is an organ system that gives animals the ability to move using the muscular and skeletal systems...
, or lymphatic system
Lymphatic system
The lymphoid system is the part of the immune system comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph unidirectionally toward the heart. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated...
, and "Type II ('serious')" for symptoms where other organs (such as the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
) 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 dysbarismDysbarism
Dysbarism refers to medical conditions resulting from changes in ambient pressure. Various activities are associated with pressure changes. Scuba diving is the most frequently cited example, but pressure changes also affect people who work in other pressurized environments , and people who move...
encompasses decompression sickness, arterial gas embolism, and barotrauma
Barotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid...
, whereas decompression sickness and arterial gas embolism are commonly classified together as decompression illness
Decompression illness
Decompression Illness describes a collection of symptoms arising from decompression of the body.DCI is caused by two different mechanisms, which result in overlapping sets of symptoms. The two mechanisms are:...
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 those from arterial gas embolism are generally more severe because they often arise from an infarction
Infarction
In medicine, infarction refers to tissue death that is caused by a local lack of oxygen due to obstruction of the tissue's blood supply. The resulting lesion is referred to as an infarct.-Causes:...
(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. Neurological symptoms are present in 10% to 15% of DCS cases with headacheHeadache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
and visual disturbances 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.
| DCS type | Bubble location | Signs & symptoms (clinical manifestations) |
|---|---|---|
| Musculoskeletal | Mostly large joints (elbows, shoulders, hip, wrists, knees, ankles) |
|
| Cutaneous | Skin |
Formication Formication is the medical term for a sensation that resembles that of insects crawling on the skin. It is one specific form of a set of sensations known as paresthesia, which also include the more common prickling, tingling sensation of "pins and needles"... ) |
| Neurologic | Brain |
Paresthesia Paresthesia , spelled "paraesthesia" in British English, is a sensation of tingling, burning, pricking, or numbness of a person's skin with no apparent long-term physical effect. It is more generally known as the feeling of "pins and needles" or of a limb "falling asleep"... , increased sensitivity hyperesthesia Hyperesthesia Hyperesthesia is a condition that involves an abnormal increase in sensitivity to stimuli of the sense. "When a non-noxious stimulus causes the sensation of pain the area will be termed hyperaesthetic". Stimuli of the senses can include sound that one hears, foods that one tastes, textures that... Amnesia Amnesia is a condition in which one's memory is lost. The causes of amnesia have traditionally been divided into categories. Memory appears to be stored in several parts of the limbic system of the brain, and any condition that interferes with the function of this system can cause amnesia... ) |
| Neurologic | Spinal cord Spinal cord The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system... |
Paralysis Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed... in the legs Urinary incontinence Urinary incontinence is any involuntary leakage of urine. It is a common and distressing problem, which may have a profound impact on quality of life. Urinary incontinence almost always results from an underlying treatable medical condition but is under-reported to medical practitioners... and fecal incontinence Fecal incontinence Fecal incontinence is the loss of regular control of the bowels. Involuntary excretion and leaking are common occurrences for those affected. Subjects relating to defecation are often socially unacceptable, thus those affected may be beset by feelings of shame and humiliation... |
| Constitutional | Whole body |
|
| Audiovestibular | Inner ear |
Dizziness Dizziness refers to an impairment in spatial perception and stability. The term is somewhat imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness.... , vertigo Vertigo (medical) Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear... , nausea Nausea Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting... , vomiting |
| Pulmonary | Lungs |
|
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% |
The distribution of symptoms of DCS observed by the U.S. Navy are as follows:
Onset
| 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% |
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
Technical Diving International
Technical Diving International is the largest technical diving certification agency in the world. As one of the first agencies to provide training in mixed gas diving and rebreathers, TDI is seen as an innovator of new diving techniques and programs which previously were not available to the...
, a leading technical diver training organization, have published a table that indicates onset of first symptoms. The table does not differentiate between types of DCS, or types of symptom.
Causes
DCS is caused by a reduction in ambient pressureAmbient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object....
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.
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-holdingApnea
Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...
divers who have made a sequence of many deep dives with short surface intervals; and it may be the cause of the disease called taravana
Taravana
Taravana is a disease often found among Polynesian island natives who habitually dive deep without breathing apparatus many times in close succession, usually for food or pearls. These free-divers may make 40 to 60 dives a day, each of 30 or 40 metres .Taravana seems to be decompression sickness....
by South Pacific island natives who for centuries have dived by breath-holding for food and pearl
Pearl
A pearl is a hard object produced within the soft tissue of a living shelled mollusk. Just like the shell of a mollusk, a pearl is made up of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other...
s.
Two principal factors control the risk of a diver suffering 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 LawHenry's lawIn physics, Henry's law is one of the gas laws formulated by William Henry in 1803. It states that:An equivalent way of stating the law is that the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid...
); - 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
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
injury called dysbaric osteonecrosis
Dysbaric osteonecrosis
Dysbaric osteonecrosis or DON is a form of avascular necrosis where there is death of a portion of the bone that is thought to be caused by nitrogen embolism in divers...
(DON). DON can develop from a single exposure to rapid decompression.
Leaving a high-pressure environment
Caisson (engineering)
In geotechnical engineering, a caisson is a retaining, watertight structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships. These are constructed such that the water can be pumped out, keeping the working...
or out of a mine
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
that has been pressurized to keep water out, they will experience a significant reduction in ambient pressure
Ambient pressure
The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object....
. A similar pressure reduction occurs when an astronaut
Astronaut
An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....
exits a space vehicle to perform a space-walk or extra-vehicular activity
Extra-vehicular activity
Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...
, where the pressure in his spacesuit is lower than the pressure in the vehicle.
The original name for DCS was "caisson disease"; this term was used in the 19th century, in large engineering excavations below the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
, such as bridge supports and tunnels, where caissons under pressure were used to keep water from flooding the excavations. Workers spending time in high-pressure atmospheric pressure conditions are at risk when they return to the lower pressure outside the caisson if the pressure surrounding them was not reduced slowly. DCS was a major factor during construction of Eads Bridge
Eads Bridge
The Eads Bridge is a combined road and railway bridge over the Mississippi River at St. Louis, connecting St. Louis and East St. Louis, Illinois....
, when 15 workers died from what was then a mysterious illness, and later during construction of the Brooklyn Bridge
Brooklyn Bridge
The Brooklyn Bridge is one of the oldest suspension bridges in the United States. Completed in 1883, it connects the New York City boroughs of Manhattan and Brooklyn by spanning the East River...
, where it incapacitated the project leader Washington Roebling
Washington Roebling
Washington Augustus Roebling was an American civil engineer best known for his work on the Brooklyn Bridge, which was initially designed by his father John A. Roebling.-Education and military service:...
.
Ascent to altitude
Passengers may be at risk of DCS when an unpressurized aircraftAircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
ascends to high altitude. Likewise, there is increased risk for divers flying in any aircraft shortly after diving, since even in a pressurized aircraft the cabin pressure is not maintained at sea-level pressure but may drop to as low as 73% of sea level pressure.
Altitude DCS became a common problem in the 1930s with the development of high-altitude balloon and aircraft flights. Today, cabin pressurization
Cabin pressurization
Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...
systems maintain commercial aircraft cabin pressure at the equivalent altitude of 2400 m (7,874 ft) or less, allowing safe flights at 12000 m (39,370.1 ft) or more. DCS is very rare in healthy individuals who experience pressures equivalent to this altitude. However, since the pressure in the cabin is not actually maintained at sea-level pressure, there is still a risk of DCS in individuals having dived recently. Also, cabin pressurization systems still fail occasionally, and some people may be predisposed to the drop in pressure that occurs even in pressurized aircraft.
There is no specific altitude threshold that can be considered safe for everyone and below which no one will develop altitude DCS. Nevertheless, there is very little evidence of altitude DCS occurring among healthy individuals who have not been scuba diving at pressure altitude
Pressure altitude
In aviation, pressure altitude is the indicated altitude when an altimeter is set to an agreed baseline pressure setting. The baseline pressure is 1013.25 hPa, equivalent to 1013.25 millibar, or 29.92 inches of mercury. This setting is equivalent to the air pressure at mean sea level in the...
s below 5500 m (18,044.6 ft). The higher the altitude of exposure the greater is the risk of developing altitude DCS. Although exposures to incremental altitudes above 5500 m (18,044.6 ft) show an incremental risk of altitude DCS, they do not show a direct relationship with the severity of the various types of DCS. Individual exposures to pressure altitudes between 5500 m (18,044.6 ft) and 7500 m (24,606.3 ft) have shown a low occurrence of altitude DCS. A US Air Force study of altitude DCS cases reported that 87% of incidents occurred at 7500 m (24,606.3 ft) or higher. High altitude parachutists performing a HALO jump may develop altitude DCS if they do not flush nitrogen from the body by pre-breathing pure oxygen.
Predisposing factors
Although the occurrence of DCS is not easily predictable, many predisposing factors are known. They may be considered as either environmental or individual.Environmental
The following environmental factors have been shown to increase the risk of DCS:- the magnitude of the pressure reduction ratio – a large pressure reduction ratio is more likely to cause DCS than a small one.
- repetitive exposures – repetitive dives within a short period of time (a few hours) increase the risk of developing DCS. Repetitive ascents to altitudes above 5500 metres (18,044.6 ft) within similar short periods increase the risk of developing altitude DCS.
- the rate of ascent – the faster the ascent the greater the risk of developing DCS. The US Navy Dive Manual indicates that ascent rates greater than about 20 m/min when diving increase the chance of DCS, while recreational dive tables such as the Bühlmann tablesBühlmann tablesThe Bühlmann decompression algorithm is a mathematical model of the way in which inert gases enter and leave the body as the ambient pressure changes. It is used to create Bühlmann tables. These are decompression tables which allow divers to plan the depth and duration for dives and show...
require an ascent rate of 10 m/min with the last 6 m (19.7 ft) taking at least one minute. An individual exposed to a rapid decompression (high rate of ascent) above 5500 metres (18,044.6 ft) has a greater risk of altitude DCS than being exposed to the same altitude but at a lower rate of ascent. - the duration of exposure – the longer the duration of the dive, the greater is the risk of DCS. Longer flights, especially to altitudes of 5500 m (18,044.6 ft) and above, carry a greater risk of altitude DCS.
- scuba diving before flying – divers who ascend to altitude soon after a dive increase their risk of developing DCS even if the dive itself was within the dive table safe limits. Dive tables make provisions for post-dive time at surface level before flying to allow any residual excess nitrogen to outgas. However, the pressure maintained inside even a pressurized aircraft may be as low as the pressure equivalent to an altitude of 2400 m (7,874 ft) above sea level. Therefore, the assumption that the dive table surface interval occurs at normal atmospheric pressure is invalidated by flying during that surface interval, and an otherwise-safe dive may then exceed the dive table limits.
- diving before travelling to altitude – DCS can occur without flying if the person moves to a high-altitude location on land immediately after scuba diving, for example, scuba divers in EritreaEritreaEritrea , officially the State of Eritrea, is a country in the Horn of Africa. Eritrea derives it's name from the Greek word Erethria, meaning 'red land'. The capital is Asmara. It is bordered by Sudan in the west, Ethiopia in the south, and Djibouti in the southeast...
who drive from the coast to the AsmaraAsmaraAsmara is the capital city and largest settlement in Eritrea, home to a population of around 579,000 people...
plateau at 2400 m (7,874 ft) increase their risk of DCS. - diving at altitudeAltitude divingAltitude diving is scuba diving where the surface is 300 meters or more above sea level . The U.S. Navy tables recommend that no alteration be made for dives at altitudes lower than 91 meters and dives between 91 meters and 300 meters correction is required for dives over 44 meters sea water...
– diving in water whose surface altitude is above 300 m (984.3 ft) — for example, Lake TiticacaLake TiticacaLake Titicaca is a lake located on the border of Peru and Bolivia. It sits 3,811 m above sea level, making it the highest commercially navigable lake in the world...
is at 3800 m (12,467.2 ft) — without using versions of decompression tables or dive computerDive computerA dive computer or decompression meter is a device used by a scuba diver to measure the time and depth of a dive so that a safe ascent profile can be calculated and displayed so that the diver can avoid decompression sickness.- Purpose :...
s that are modified for high-altitude.
Individual
- a person's 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 decompression-related bubbles.
- ambient temperature – there is some evidence suggesting that individual exposure to very cold ambient temperatures may increase the risk of altitude DCS. Decompression sickness risk can be reduced by increased ambient temperature during decompression following dives in cold water.
- body type – typically, a person who has a high body fat content is at greater risk of DCS. This is due to nitrogen's five times greater solubility in fat than in water, leading to greater amounts of total body dissolved nitrogen during time at pressure. Fat represents about 15–25 percent of a healthy adult's body, but stores about half of the total amount of nitrogen (about 1 litre) at normal pressures.
- alcohol consumption and dehydration – although alcoholAlcoholIn chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
consumption increases dehydration and therefore may increase susceptibility to DCS, a 2005 study concluded that alcohol consumption did not increase the risk of DCS. Studies by Walder concluded that decompression sickness could be reduced in aviators when the serum surface tension was raised by drinking isotonic saline, and the high surface tension of water is generally regarded as helpful in controlling bubble size. Maintaining proper hydration is recommended. - patent foramen ovale – a hole between the atrial chambers of the heartHeartThe heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
in the fetusFetusA fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
is normally closed by a flap with the first breaths at birth. In about 20% of adults the flap does not completely seal, however, allowing blood through the hole when coughing or during activities that raise chest pressure. In diving, this can allow venous blood with microbubbles of inert gas to bypass the lungs, where the bubbles would otherwise be filtered out by the lung capillary system, and return directly to the arterial system (including arteries to the brain, spinal cord and heart). In the arterial system, bubbles (arterial gas embolism) are far more dangerous because they block circulation and cause infarctionInfarctionIn medicine, infarction refers to tissue death that is caused by a local lack of oxygen due to obstruction of the tissue's blood supply. The resulting lesion is referred to as an infarct.-Causes:...
(tissue death, due to local loss of blood flow). In the brain, infarction results in strokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
, and in the spinal cord it may result in paralysisParalysisParalysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
.
Mechanism
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
es, which were dissolved under higher pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
, to come out of physical solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
and form gas bubble
Liquid bubble
A bubble is a globule of one substance in another, usually gas in a liquid.Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.-Common examples:...
s within the body. These bubbles produce the symptoms of decompression sickness. Bubbles may form whenever the body experiences a reduction in pressure, but not all bubbles result in DCS. The amount of gas dissolved in a liquid is described by Henry's Law
Henry's law
In physics, Henry's law is one of the gas laws formulated by William Henry in 1803. It states that:An equivalent way of stating the law is that the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid...
, which indicates that, when the pressure of a gas in contact with a liquid is decreased, the amount of that gas dissolved in the liquid will also decrease proportionately.
On ascent from a dive, inert gas comes out of solution in a process called "outgassing
Outgassing
Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in some material. As an example, research has shown how the concentration of carbon dioxide in the Earth's atmosphere has sometimes been linked to ocean outgassing...
" or "offgassing". Under normal conditions, most offgassing occurs by gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
in the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s. If inert gas comes out of solution too quickly to allow outgassing in the lungs then bubbles may form in the blood or within the solid tissues of the body. The formation of bubbles in the skin or joints results in milder symptoms, while large numbers of bubbles in the venous blood can cause lung damage. The most severe types of DCS interrupt — and ultimately damage — spinal cord function, leading to paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
, sensory
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...
dysfunction, or death. In the presence of a right-to-left shunt
Right-to-left shunt
A right-to-left shunt is a cardiac shunt which allows blood to flow from the right heart to the left heart. This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptiles...
of the heart, such as a patent foramen ovale, venous bubbles may enter the arterial system, resulting in an arterial gas embolism. A similar effect, known as ebullism
Ebullism
Ebullism is the formation of gas bubbles in bodily fluids due to reduced environmental pressure, for example at high altitude. It occurs because a system of liquid and gas at equilibrium will see a net conversion of liquid to gas as pressure lowers, for example, liquids reach their boiling point...
, may occur during explosive decompression
Explosive decompression
Uncontrolled decompression refers to an unplanned drop in the pressure of a sealed system, such as an aircraft cabin and typically results from human error, material fatigue, engineering failure or impact causing a pressure vessel to vent into its lower-pressure surroundings or fail to pressurize...
, when water vapour forms bubbles in body fluids due to a dramatic reduction in environmental pressure.
Inert gases
The main inert gas in air is nitrogenNitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, but nitrogen is not the only gas that can cause DCS. Breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
mixtures such as trimix and heliox
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...
include helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
, which can also cause decompression sickness. Helium both enters and leaves the body faster than nitrogen, so different decompression schedules are required, but, since helium does not cause narcosis
Nitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...
, it is preferred over nitrogen in gas mixtures for deep diving.
There is some debate as to the decompression requirements for helium during short-duration dives. Most divers do longer decompressions, however some groups like the WKPP have been pioneering the use of shorter decompression times by including deep stops.
Any inert gas that is breathed under pressure can form bubbles when the ambient pressure decreases. Very deep dives have been made using hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
-oxygen mixtures (hydrox
Hydrox (breathing gas)
Hydrox, a gas mixture of hydrogen and oxygen, is used as a breathing gas in very deep diving. It allows divers to descend several hundred metres....
), but controlled decompression is still required to avoid DCS.
Isobaric counterdiffusion
DCS can also be caused at a constant ambient pressure when switching between gas mixtures containing different proportions of inert gas. This is known as isobaric counterdiffusionIsobaric counterdiffusion
Isobaric Counterdiffusion, Inert Gas Counterdiffusion , or ICD is the term used to describe the physiologic effect when the diffusion of different gases occurs in opposite directions while under a constant ambient pressure.- Background :...
, and presents a problem for very deep dives. For example, after using a very helium-rich trimix at the deepest part of the dive, a diver will switch to mixtures containing progressively less helium and more oxygen and nitrogen during the ascent. Nitrogen diffuses into tissues 2.65 times slower than helium, but is about 4.5 times more soluble. Switching between gas mixtures that have very different fractions of nitrogen and helium can result in "fast" tissues (those tissues that have a good blood supply) actually increasing their total inert gas loading. This is often found to provoke inner ear decompression sickness, as the ear seems particularly sensitive to this effect.
Diagnosis
Decompression sickness should be suspected if any of the symptoms associated with the condition occurs following a drop in pressure, in particular, within 24 hours of diving. In 1995, 95% of all cases reported to Divers Alert NetworkDivers Alert Network
The Divers Alert Network is a non-profit 501 organization devoted to assisting divers in need. The Research department conducts significant medical research on recreational scuba diving safety...
had shown symptoms within 24 hours. An alternative diagnosis should be suspected if severe symptoms begin more than six hours following decompression without an altitude exposure or if any symptom occurs more than 24 hours after surfacing. The diagnosis is confirmed if the symptoms are relieved by recompression. Although MRI or CT
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
can frequently identify bubbles in DCS, they are not as good at determining the diagnosis as a proper history of the event and description of the symptoms.
Underwater diving
To prevent the excess formation of bubbles that can lead to decompression sickness, divers limit their ascent rate to about 10 metres (32.8 ft) per minute, and carry out a decompression schedule as necessary. This schedule requires the diver to ascend to a particular depth, and remain at that depth until sufficient gas has been eliminated from the body to allow further ascent. Each of these is termed a "decompression stop", and a schedule for a given bottom time and depth may contain one or more stops, or none at all. Dives that contain no decompression stops are called "no-stop dives", but divers usually schedule a short "safety stop" at 3 metres (10 ft), 4.6 metres (15.1 ft), or 6 metres (19.7 ft), depending on the training agency.The decompression schedule may be derived from decompression tables, decompression software, or from dive computers, and these are commonly based upon a mathematical model of the body's uptake and release of inert gas as pressure changes. These models, such as the Bühlmann decompression algorithm, are designed to fit empirical data and provide a decompression schedule for a given depth and dive duration.
Since divers on the surface after a dive still have excess inert gas in their bodies, any subsequent dive before this excess is fully eliminated needs to modify the schedule to take account of the residual gas load from the previous dive. This will result in a shorter available time under water or an increased decompression
Decompression
Decompression has several meanings:* Decompression , the release of pressure and the opposition of physical compression* Decompression sickness, a condition arising from the precipitation of dissolved gases into bubbles inside the body on depressurization* Decompression , a procedure used to treat...
time during the subsequent dive. The total elimination of excess gas may take many hours, and tables will indicate the time at normal pressures that is required, which may be up to 18 hours.
Decompression time can be significantly shortened by breathing mixtures containing much less inert gas during the decompression phase of the dive (or pure oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
at stops in 6 metres (19.7 ft) of water or less). The reason is that the inert gas outgases at a rate proportional to the difference between the partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
of inert gas in the diver's body and its partial pressure in the breathing gas; whereas the likelihood of bubble formation depends on the difference between the inert gas partial pressure in the diver's body and the ambient pressure. Reduction in decompression requirements can also be gained by breathing a nitrox mix during the dive, since less nitrogen will be taken into the body than during the same dive done on air.
Following a decompression schedule does not completely protect against DCS. The algorithms used are designed to reduce the probability of DCS to a very low level, but do not reduce it to zero.
Exposure to altitude
One of the most significant breakthroughs in the prevention of altitude DCS is oxygen pre-breathing. Breathing pure oxygen significantly reduces the nitrogen loads in body tissues and, if continued without interruption, provides effective protection upon exposure to low-barometric pressure environments. However, breathing pure oxygen during flight alone (ascent, en route, descent) does not decrease the risk of altitude DCS.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 currently used only by military flight crews and astronauts for protection during high-altitude and space operations. It is also used by flight test crews involved with certifying aircraft.
Astronauts aboard the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
preparing for extra-vehicular activity
Extra-vehicular activity
Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...
(EVA) "camp out" at low atmospheric pressure, 10.2 psi (0.703265243886 bar), spending eight sleeping hours in the Quest airlock chamber before their spacewalk. During the EVA they breathe 100% oxygen in their spacesuits, which operate at 4.3 psi (0.296474563599 bar), although research has examined the possibility of using 100% O2 at 9.5 psi (0.655001942835 bar) in the suits to lessen the pressure reduction, and hence the risk of DCS.
Treatment
All cases of decompression sickness should be treated initially with 100% oxygen until hyperbaric oxygen therapyHyperbaric oxygen therapy
Hyperbaric medicine, also known as hyperbaric oxygen therapy , is the medical use of oxygen at a level higher than atmospheric pressure. The equipment required consists of a pressure chamber, which may be of rigid or flexible construction, and a means of delivering 100% oxygen...
(100% oxygen delivered in a high-pressure chamber) can be provided. Mild cases of the "bends" and some skin symptoms may disappear during descent from high altitude; however, it is recommended that these cases still be evaluated. Neurological symptoms, pulmonary symptoms, and mottled or marbled skin lesions should be treated with hyperbaric oxygen therapy if seen within 10 to 14 days of development.
Recompression on room air was shown to be an effective treatment for minor DCS symptoms by Keays in 1909. Evidence of the effectiveness of recompression therapy utilizing oxygen was first shown by Yarbrough and Behnke
Albert R. Behnke
Captain Albert Richard Behnke Jr. USN was an American physician, who was principally responsible for developing the U.S. Naval Medical Research Institute...
, and has since become the standard of care for treatment of DCS. Recompression is normally carried out in a recompression chamber. At a dive site, a riskier alternative is in-water recompression
In-water recompression
In-water recompression or underwater oxygen treatment is the emergency treatment of decompression sickness of sending the diver back underwater to allow the gas bubbles in the tissues, which are causing the symptoms, to resolve...
.
Oxygen first aid has been used as an emergency treatment for diving injuries for years. If given within the first four hours of surfacing, it increases the success of recompression therapy as well as a decrease the number of recompression treatments required. Most fully closed-circuit rebreather
Rebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
s can deliver sustained high concentrations of oxygen-rich breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
and could be used as a means of supplying oxygen if dedicated equipment is not available.
It is beneficial to give fluids, as this helps reduce dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
. It is no longer recommended to administer aspirin, unless advised to do so by medical personnel, as analgesics may mask symptoms. People should be made comfortable and placed in the supine position (horizontal), or the recovery position
Recovery position
The recovery position refers to one of a series of variations on a lateral recumbent or three-quarters prone position of the body, in to which an unconscious but breathing casualty can be placed as part of first aid treatment.An unconscious person The recovery position refers to one of a series of...
if vomiting occurs. In the past, both the Trendelenburg position
Trendelenburg position
In the Trendelenburg position the body is laid flat on the back with the feet higher than the head by 15-30 degrees, in contrast to the reverse Trendelenburg position, where the body is tilted in the opposite direction. This is a standard position used in abdominal and gynecological surgery...
and the left lateral decubitus position (Durant's maneuver) have been suggested as beneficial where air emboli are suspected, but are no longer recommended for extended periods, owing to concerns regarding cerebral edema
Cerebral edema
Cerebral edema or cerebral œdema is an excess accumulation of water in the intracellular or extracellular spaces of the brain.-Vasogenic:Due to a breakdown of tight endothelial junctions which make up the blood-brain barrier...
.
Prognosis
Immediate treatment with 100% oxygen, followed by recompression in a hyperbaric chamber, will in most cases result in no long term effects. However, permanent long-term injury from DCS is possible. Three-month follow-ups on diving accidents reported to DAN in 1987 showed 14.3% of the 268 divers surveyed "still had residual signs and symptoms from Type II DCS and 7% from Type I DCS". Long-term follow-ups showed similar results, with 16% having permanent neurological sequelae.Epidemiology
The incidence of decompression sickness is rare, estimated at 2.8 cases per 10,000 dives, with the risk 2.6 times greater for males than females. DCS affects approximately 1,000 U.S. scuba divers per year. In 1999, the Divers Alert NetworkDivers Alert Network
The Divers Alert Network is a non-profit 501 organization devoted to assisting divers in need. The Research department conducts significant medical research on recreational scuba diving safety...
(DAN) created "Project Dive Exploration" to collect data on dive profiles and incidents. From 1998 to 2002, they recorded 50,150 dives, from which 28 recompressions were required — although these will almost certainly contain incidents of arterial gas embolism (AGE) — a rate of about 0.05%.
History
- 1670: Robert BoyleRobert BoyleRobert Boyle FRS was a 17th century natural philosopher, chemist, physicist, and inventor, also noted for his writings in theology. He has been variously described as English, Irish, or Anglo-Irish, his father having come to Ireland from England during the time of the English plantations of...
demonstrated that a reduction in ambient pressure could lead to bubble formation in living tissue. This description of a viperViperidaeThe Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four...
in a vacuumVacuumIn everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
was the first recorded description of decompression sickness. - 1769: Giovanni MorgagniGiovanni Battista MorgagniGiovanni Battista Morgagni was an Italian anatomist, celebrated as the father of modern anatomical pathology.-Education:...
described the post mortem findings of air in cerebral circulationCirculatory systemThe circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
and surmised that this was the cause of death. - 1840: Charles PasleyCharles PasleyGeneral Sir Charles William Pasley KCB was a British soldier and military engineer who wrote the defining text on the role of the post-American revolution British Empire: An Essay on the Military Policy and Institutions of the British Empire, published in 1810. This text changed how Britons...
, who was involved in the recovery of the sunken warship HMS Royal GeorgeHMS Royal George (1756)HMS Royal George was a 100-gun first-rate ship of the line of the Royal Navy, built at Woolwich Dockyard and launched on 18 February 1756...
, commented that, of those having made frequent dives, "not a man escaped the repeated attacks of rheumatism and cold". - 1841: First documented case of decompression sickness, reported by a mining engineer who observed pain and muscle cramps among coal miners working in mine shafts air-pressurized to keep water out.
- 1870: Bauer published outcomes of 25 paralyzed caissonCaisson (engineering)In geotechnical engineering, a caisson is a retaining, watertight structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships. These are constructed such that the water can be pumped out, keeping the working...
workers.
From 1870 to 1910, all prominent features were established. Explanations at the time included: cold or exhaustion causing reflex spinal cord damage; electricity cause by friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
on compression; or organ congestion
Congestion
Congestion generally means excessive crowding.Congestion may refer to:* congestion in heart failure, a term to describe low cardiac output seen in heart failure.* Nasal congestion, the blockage of nasal passages due to swollen membranes...
; and vascular stasis caused by decompression.
- 1871: The Eads BridgeEads BridgeThe Eads Bridge is a combined road and railway bridge over the Mississippi River at St. Louis, connecting St. Louis and East St. Louis, Illinois....
in St Louis employed 352 compressed air workers including Dr. Alphonse Jaminet as the physician in charge. There were 30 seriously injured and 12 fatalities. Dr. Jaminet developed decompression sickness and his personal description was the first such recorded. - 1872: The similarity between decompression sickness and iatrogenic air embolism as well as the relationship between inadequate decompression and decompression sickness was noted by Friedburg. He suggested that intravascular gas was released by rapid decompression and recommended: slow compression and decompression; four-hour working shifts; limit to maximum depth 44.1 psigPounds per square inchThe pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
(4 ATAAtmosphere (unit)The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...
); using only healthy workers; and recompression treatment for severe cases. - 1873: Dr. Andrew Smith first utilized the term "caisson disease" describing 110 cases of decompression sickness as the physician in charge during construction of the Brooklyn BridgeBrooklyn BridgeThe Brooklyn Bridge is one of the oldest suspension bridges in the United States. Completed in 1883, it connects the New York City boroughs of Manhattan and Brooklyn by spanning the East River...
. The project employed 600 compressed air workers. Recompression treatment was not used. The project chief engineer Washington RoeblingWashington RoeblingWashington Augustus Roebling was an American civil engineer best known for his work on the Brooklyn Bridge, which was initially designed by his father John A. Roebling.-Education and military service:...
suffered from caisson disease. (He took charge after his father John Augustus Roebling died of tetanusTetanusTetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...
.) Washington's wife, Emily, helped manage the construction of the bridge after his sickness confined him to his home in BrooklynBrooklynBrooklyn is the most populous of New York City's five boroughs, with nearly 2.6 million residents, and the second-largest in area. Since 1896, Brooklyn has had the same boundaries as Kings County, which is now the most populous county in New York State and the second-most densely populated...
. He battled the after-effects of the disease for the rest of his life. During this project, decompression sickness became known as "The [Grecian] Bends" because afflicted individuals characteristically arched their backs: this is possibly reminiscent of a then fashionable women's dance maneuver known as the Grecian BendGrecian bendThe Grecian Bend was a dance move introduced to polite society in America just before the American Civil War. The "Bend" was considered very daring at the time....
, or as historian David McCullough asserts in The Great Bridge it was a crude reference to "Greek" or anal sex. - 1900: Leonard HillLeonard Erskine HillSir Leonard Erskine Hill was a British physiologist. He was elected a Fellow of the Royal Society in 1900 and was knighted in 1930. One of his sons was the epidemiologist and statistician Austin Bradford Hill...
used a frog model to prove that decompression causes bubbles and that recompression resolves them. Hill advocated linear or uniform decompression profilesDive profileA dive profile is a two dimensional graphical representation of a dive showing depth and time.It is useful as an indication of the risks of decompression sickness and oxygen toxicity and also the volume of open-circuit breathing gas needed for a planned dive as these depend in part upon the depth...
. This type of decompression is used today by saturation diversSaturation divingSaturation diving is a diving technique that allows divers to reduce the risk of decompression sickness when they work at great depth for long periods of time....
. His work was financed by Augustus SiebeAugustus SiebeAugustus Siebe was a German-born British engineer chiefly known for his contributions to diving equipment.- Contribution to diving :...
and the Siebe Gorman CompanySiebe GormanSiebe Gorman & Company Ltd was a British company which developed diving equipment and breathing equipment and worked on commercial diving and marine salvage projects...
.
- 1908: "The Prevention of Compressed Air Illness" was published by JS Haldane, Boycott and Damant recommending staged decompression. These tables were accepted for use by the Royal Navy.
- 1916: The decompression chamber was invented by the Italian engineer Alberto GianniAlberto GianniAlberto Gianni was an Italian underwater diver and inventor.He invented the decompression chamber in 1916.-References:...
. - 1924: The US Navy published the first standardized recompression procedure.
- 1930s: Albert R Behnke separated the symptoms of Arterial Gas Embolism (AGE) from those of DCS.
- 1935: Behnke et al. experimented with oxygen for recompression therapy.
- 1937: Behnke introduced the “no-stop” decompression tables.
- 1941: Altitude DCS is treated with hyperbaric oxygen for the first time.
- 1957: Robert Workman established a new method for calculation of decompression requirements (M-values).
- 1959: The "SOS Decompression Meter", a submersible mechanical device that simulated nitrogen uptake and release, was introduced.
- 1960: FC Golding et al. split the classification of DCS into Type 1 and 2.
- 1982: Paul K Weathersby, Louis D Homer and Edward T Flynn introduce survival analysisSurvival analysisSurvival analysis is a branch of statistics which deals with death in biological organisms and failure in mechanical systems. This topic is called reliability theory or reliability analysis in engineering, and duration analysis or duration modeling in economics or sociology...
into the study of decompression sickness. - 1983: Orca produced the "EDGE", a personal dive computer, using a microprocessorMicroprocessorA microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
to calculate nitrogen absorption for twelve tissue compartments. - 1984: Albert A Bühlmann released his book "Decompression-Decompression Sickness," which detailed his deterministic model for calculation of decompression schedules.
Economics
In the United States, it is common for medical insurance not to cover treatment for the bends that is the result of recreational diving. This is because scuba diving is considered an elective and "high-risk" activity and treatment for decompression sickness is expensive. A typical stay in a recompression chamber will easily cost several thousand dollars, even before emergency transportation is included. As a result, groups such as Divers Alert NetworkDivers Alert Network
The Divers Alert Network is a non-profit 501 organization devoted to assisting divers in need. The Research department conducts significant medical research on recreational scuba diving safety...
(DAN) offer medical insurance policies that specifically cover all aspects of treatment for decompression sickness at rates of less than $100 per year.
In the United Kingdom, treatment of DCS is provided by the National Health Service, either at a specialised facility or at a Hyperbaric Centre based within a general hospital.