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to avoid the bends.]] INTRODUCTION Decompression sickness can happen in any of the following situations:
This causes inert gases (mainly Nitrogen ), normally dissolved in body fluids and tissues, to come out of physical Solution and form gaseous Bubble s. According to Henry's Law , when the Pressure of a Gas over a Liquid is decreased, the amount of gas dissolved in that liquid will also decrease. One of the best practical demonstrations of this law is offered by opening a Soft Drink . When the cap is removed from the bottle, gas is heard escaping, and bubbles can be seen forming in the soda. This is Carbon Dioxide gas coming out of solution as a result of the pressure inside the container reducing to Atmospheric Pressure . Similarly, nitrogen is an Inert Gas normally stored throughout the human body, such as tissues and fluids, in physical Solution . When the body is exposed to decreased pressures, such as when flying an un-pressurised aircraft to altitude, or during a Scuba ascent through water, the nitrogen dissolved in the body comes out of solution. If nitrogen is forced to come out of solution too quickly, bubbles form in parts of the body, causing signs and Symptom s ranging from itching and Rash es, to Joint pain, which is known as "the bends," to Sensory failure, Paralysis and Death . Air Embolism , caused by other processes, can have many of the same symptoms as DCS. The two conditions are grouped together under the name Decompression Illness or DCI. HISTORY The first documented cases of DCS were reported in 1841 by a mining engineer who observed the occurrence of pain and muscle cramps among coal miners exposed to air-pressurized mine shafts designed to keep water out. The first description of a case resulting from diving activities while wearing an Air-pumped Helmet was reported in 1869. PREDISPOSING FACTORS
SIGNS AND SYMPTOMS Bubbles can form anywhere in the body, but symptomatic sensation is most frequently observed in the shoulders, elbows, knees, and ankles. This table gives symptoms for the different DCS types. "The bends" (joint pain) accounts for about 60 to 70% of all altitude DCS cases, with the shoulder being the most common site. Neurological symptoms are present in 10% to 15% of all DCS cases with headache and visual disturbances the most common. "The chokes" are rare and occur in less than 2% of all DCS cases. Skin manifestations are present in about 10 to 15% of all DCS cases. Signs and symptoms of DCS can be skin rashes, extreme fatigue, joint pain, visual disturbances, balance disturbances, breathing difficulties, lack of strength, numbness, paralysis, unconsciousness and death. Symptoms associated with impairment of the Central Nervous System indicate a serious injury. There can be joint pain, typically in the Elbow or Knee . There are other terms describing other symptoms, such as the "chokes", the "niggles", and the "staggers". TREATMENT Recompression is the only effective treatment for severe DCS, although rest and oxygen (increasing the percentage of oxygen in the air being breathed via a tight fitting Oxygen Mask ) applied to lighter cases can be effective. Normally this is carried out in a Recompression Chamber . In diving, a high-risk alternative is In-water Recompression . Oxygen First Aid treatment is useful for suspected DCS casualties or divers who have made fast ascents or missed decompression stops. Most fully closed-circuit Rebreather s can deliver sustained high concentrations of oxygen-rich Breathing Gas and could be used as an alternative to pure Open-circuit oxygen Resuscitator s. COMMON PRESSURE REDUCTIONS THAT CAUSE DCS The main cause of DCS is a reduction in the pressure surrounding the body. Common ways in which the required reduction in pressure occur are:
Leaving a high pressure environment The original name for DCS was Caisson Disease ; this term was used in the 19th century, when large engineering excavations below the Water Table , such as with the Pier s of Bridge s and with Tunnel s, had to be done in Caisson s under pressure to keep water from flooding the excavations. Workers who spend time in high pressure atmospheric pressure conditions are at risk if they leave that environment and reduce the pressure surrounding them. DCS was a major factor during construction of Eads Bridge , when 13 workers died from what was then a mysterious illness, and later during construction of the Brooklyn Bridge , where it incapacitated the project leader Washington Roebling . Ascent during a dive DCS is most well known as an Injury that affects Divers . The pressure of the surrounding water increases as the diver descends and reduces as the diver ascends. The risk of DCS increases by diving long or deep without slowly ascending and making the Decompression Stops needed to eliminate the inert gases normally, although the specific risk factors are not well understood. Some divers seem more susceptible than others under identical conditions. There have been known cases of bends in Snorkeller s who have made many deep dives in succession. DCS may be the cause of the disease Taravana which affects South Pacific island natives who for centuries have dived without equipment for food and Pearl s. Two linked factors contribute to divers' DCS, although the complete relationship of causes is not fully understood:
The physiologist simply reduce the volume and number of the bubbles to a level at which there is no injury to the diver. Severe cases of decompression sickness can lead to death. Large bubbles of gas impede the flow of oxygen-rich blood to the Brain , Central Nervous System and other vital organs. Even when the change in pressure causes no immediate symptoms, rapid pressure change can cause permanent Bone injury called Dysbaric Osteonecrosis (DON) "bone cell death from bad pressure". DON can develop from a single exposure to rapid decompression. DON is diagnosed from lesions visible in X-ray images of the bones. Unfortunately, X-rays appear normal for at least 3 months after the permanent damage has occurred; it may take 4 years after the damage has occurred for its effects to become visible in the X-ray images. {Link without Title} Avoidance Decompression Tables and Dive Computer s have been developed that help the diver choose depth and duration of Decompression Stops for a particular dive ''profile'' at depth. Avoiding ''decompression sickness'' is not an exact science. Accidents can occur after relatively shallow and short dives. To reduce the risks, divers should avoid long and deep dives and should ascend slowly. Also, dives requiring Decompression Stops and dives with less than a 16 hour interval since the previous dive increase the risk of DCS. There are many additional risk factors, such as age, obesity, fatigue, use of alcohol, dehydration and a Patent Foramen Ovale . In addition, flying at high altitude less than 24 hours after a deep dive can be a precipitating factor for decompression illness. Helium Nitrogen is not the only Breathing Gas that causes DCS. Gas mixtures such as Trimix and Heliox include Helium , which can also be implicated in decompression sickness. Helium both enters and leaves the body faster than nitrogen and for long dives, of around 3 hours or more, the body almost reaches saturation of helium. For such dives, the decompression is shorter than for nitrogen based breathing gases such as air. There is some debate as to the decompression effects of helium for shorter dives. Most divers do longer decompressions, whereas some groups like the WKPP have been pioneering the use of shorter decompression times by including Deep Stops . Decompression time can be significantly shortened by breathing Nitrox (or pure Oxygen if in very shallow water), during the decompression phase of the dive. The reason is that the nitrogen comes out of solution at a rate proportional to difference between the ppN2 ( Partial Pressure of nitrogen) in the diver's body and the ppN2 in the gas that he is breathing; but the likelihood of bubbles is proportionate to the difference between the ppN2 in the diver's body and the total surrounding air or water pressure. Ascent to altitude People flying in un-pressurised Aircraft at High Altitude , such as stowaways, passengers after Explosive Decompression of the cabin Pressure Vessel or pilots in an open cockpit, can suffer from decompression sickness. Divers who dive and then travel in aircraft are at risk even in pressurised aircraft because the cabin air pressure is less than the air pressure at sea level. The same applies to going onto very high land after diving. Altitude DCS became a commonly observed problem associated with high-altitude balloon and aircraft flights in the 1930s. In present-day aviation, technology allows civilian aircraft (commercial and private) to fly higher and faster than ever before. Though modern aircraft are safer and more reliable, occupants are still subject to the stresses of high altitude flight and the unique problems that go with these lofty heights. A century and a half after the first DCS case was described, our understanding of DCS has improved, and a body of knowledge has accumulated; however, this problem is far from being solved. Altitude DCS is still a risk to the occupants of modern aircraft. There is no specific altitude that can be considered an absolute altitude exposure threshold, below which it can be assured that no one will develop altitude DCS. However, there is very little evidence of altitude DCS occurring among healthy individuals at altitudes below 18,000 feet who have not been SCUBA Diving . Individual exposures to altitudes between 18,000 feet and 25,000 feet have shown a low occurrence of altitude DCS. Most cases of altitude DCS occur among individuals exposed to altitudes of 25,000 feet or higher. A US Air Force study of altitude DCS cases reported that only 13% occurred below 25,000 feet The higher the altitude of exposure, the greater the risk of developing altitude DCS. It is important to clarify that although exposures to incremental altitudes above 18,000 feet show an incremental risk of altitude DCS, they do not show a direct relationship with the severity of the various types of DCS (see Table 1). Arterial Gas Embolism and DCS have very similar symptoms and treatment because they are both the result of gas bubbles in the body. In a diving context, the two are often called Decompression Illness . Another term, Dysbarism , encompasses decompression sickness, arterial gas embolism, and Barotrauma . Medical treatment Mild cases of "the bends" and skin bends (excluding mottled or marbled skin appearance) may disappear during descent from high altitude, but still require medical evaluation. If the signs and symptoms persist during descent or reappear at ground level, it is necessary to provide Hyperbaric Oxygen Treatment immediately (100% oxygen delivered in a high-pressure chamber). Neurological DCS, "the chokes," and skin bends with mottled or marbled skin lesions (see Table 1) should always be treated with hyperbaric oxygenation. These conditions are very serious and potentially fatal if untreated. Effects of breathing pure oxygen One of the most significant breakthroughs in altitude DCS research was oxygen pre-breathing. Breathing pure oxygen before exposure to a low barometric pressure decreases the risk of developing altitude DCS. Oxygen pre-breathing promotes the elimination or washout of nitrogen from body tissues. Pre-breathing pure oxygen for 30 minutes before starting ascent to altitude reduces the risk of altitude DCS for short exposures (10-30 minutes only) to altitudes between 18,000 and 43,000 feet. However, oxygen pre-breathing has to be continued without interruption with in-flight, pure oxygen to provide effective protection against altitude DCS. Furthermore, it is very important to understand that breathing pure oxygen only during flight (ascent, en route, descent) does not decrease the risk of altitude DCS, and should not be used instead of oxygen pre-breathing. Although pure oxygen pre-breathing is an effective method to protect against altitude DCS, it is logistically complicated and expensive for the protection of civil aviation flyers, either commercial or private. Therefore, it is only used now by military flight crews and astronauts for their protection during high altitude and space operations. Scuba diving before flying A SCUBA Diver breathes air under pressure higher than sea level atmospheric. This makes more nitrogen dissolve in the body (body nitrogen saturation). The deeper the SCUBA dive, the greater the rate of body nitrogen saturation. After SCUBA diving, if not enough time is allowed to eliminate the excess nitrogen stored in the body, altitude DCS can occur during exposure to altitudes as low as 5,000 feet or less. The same applies to going to high altitudes on land: e.g. if you scuba dive in Eritrea and then go onto the Asmara plateau (''where the airport is''), which is about 8000 feet or 2400 meters above sea level. What to do if altitude DCS occurs
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