ALTITUDE INDUCED DECOMPRESSION SICKNESS


One of the more dangerous problems aircrew may face is that of decompression sickness (possible nitrogen bubbles in body fluids and tissues) resulting from a high- altitude cabin depressurization.


Decompression sickness (DCS) describes a condition characterized by a variety of symptoms resulting from exposure to low pressures that cause inert gases (mainly nitrogen), normally dissolved in body fluids and tissues, to come out of physical solution and form bubbles. DCS can occur during exposure to altitude (altitude DCS) or during ascent from depth (mining or diving).


While at sea level, we are breathing air that is composed of 80% nitrogen. Because Nitrogen is a noble gas, it can not be metabolized in the human body. It is simply distributed throughout the body, via the circulatory system. When atmospheric pressure is reduced, as in a decompression nitrogen leaves the body too quickly and bubbles may form.


“The bends” (joint pain) account for about 60 to 70% of all altitude DCS cases with the shoulder being the most common site. Although bubbles can form anywhere in the body, the most frequently targeted anatomic locations are the shoulders, elbows, knees, and ankles.


Non-severe cases of “the bends” 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 should always be treated with hyperbaric oxygenation. These conditions are very serious and potentially fatal if untreated.


Responding to Rapid Depressurization


At a cruise altitude of 40,000 feet, the risk for DCS is very serious following a rapid decompression. Most cabin altitudes during routine flight are approximately 5,000 to 8,000 feet. So, imagine being exposed to a rapid decompression where you ascend from 8,000 feet to an altitude that is 10,000 feet higher than Mt. Everest within minutes or even seconds!


During the emergency descent that follows a rapid depressurization, everyone onboard should already have an oxygen mask on, but it is possible that some people may begin to experience symptoms of DCS. Anyone who is symptomatic during the descent should remain on 100 percent oxygen and first responders at the airport should be notified. The individual should not remove the mask at any time and should remain as still as possible until paramedics arrive. Movement in general will worsen the condition and result in increased pain.


Upon landing, the individual should be transported immediately to the nearest hospital for medical care. If the symptoms persist, the person will need a hyperbaric chamber treatment no different than what scuba divers receive. Anyone complaining of weakness or numbness of the legs or arms may be facing impending severe neurological damage and should receive immediate medical care.


Medical Assessment is Critical


With rapid decompressions it is common for people to minimize their symptoms and want to go home quickly, having been frightened by the emergency. It is crucial that these people are assessed by paramedics before being allowed to leave as DCS can develop slowly develop over 24 hours. It is also essential that everyone onboard be given instructions on what to look for over the following 24 hour period and told to report any symptoms they experience to their doctor or seek emergency treatment if appropriate. DCS can be insidious, and those at risk must remain vigilant for the next few days.


FLYING AFTER DIVING - Scuba Diving and DCS


Another time when DCS can be an issue is in the case of flying after scuba diving. In general, scuba divers should wait 24 hours before flying. This is due to the fact that excessive nitrogen gas that has accumulated while diving can take that long to equalize to ambient pressure. Exposing oneself to a cabin altitude of 8,000 feet soon after scuba diving dramatically increases the risk of developing DCS. If anyone onboard develops symptoms of DCS during the flight, this must be considered a medical emergency no different than that described above and handled in the same manner.


19 High Altitude Awareness Training


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