Decompression Illness, or DCI, is a term used to describe illness that results from a reduction in the ambient pressure surrounding a body. A good example is what happens to a diver’s body after surfacing from a dive. DCI encompasses two diseases, Decompression Sickness (DCS) and Arterial Gas Embolism (AGE).
Decompression Sickness (DCS)
DCS is thought to result from bubbles growing in tissue and causing local damage which can lead to a variety of symptoms from joint pain and swelling to paralysis and even death, depending on the location of the bubbles involved.
Decompression sickness, also called the bends or caisson disease is the result of inadequate decompression following exposure to increased pressure. In some cases, the disease is mild and not an immediate threat. In other cases, serious injury does occur; when this happens, the quicker treatment begins, the better the chance for a full recovery.
During a dive, the body tissues absorb nitrogen from the breathing gas in proportion to the surrounding pressure. As long as the diver remains at pressure, the gas presents no problem. If the pressure is reduced too quickly, however, the nitrogen comes out of solution and forms bubbles in the tissues and bloodstream. This commonly occurs as a result of violating or approaching too closely the diving table limits, but it can also occur even when accepted guidelines have been followed.
Bubbles forming in or near joints are the presumed cause of the joint pain of a classical “bend.” When high levels of bubbles occur, complex reactions can take place in the body, often in the spinal cord or brain. Numbness, paralysis and disorders of higher cerebral function may result. If great amounts of decompression are missed and large numbers of bubbles enter the venous bloodstream, congestive symptoms in the lung and circulatory shock can then occur.
Arterial gas embolism (AGE)
Arterial gas embolism results from bubbles entering the lung circulation, traveling through the arteries and causing tissue damage at a distance by blocking blood flow at the small vessel level. AGE is a major cause of death in diving in which the initiating cause (pulmonary barotrauma) usually goes undetected. Caused most often by the expansion of respiratory gases during ascent, it may occur when the breath is held during ascent from a dive, when there is local pulmonary pathology, when there is dynamic airway collapse in the non-cartilaginous airways and if there is low pulmonary compliance, particularly if this is not distributed evenly throughout the lungs.
Hyperbaric oxygen therapy works by directly reducing the size of these bubbles and rapidly removing nitrogen from inside the bubble which further helps shrink the bubble’s size until it is eliminated. HBO may also have secondary benefits by reducing post-injury inflammation. The initial treatment of decompression illness varies in length from 5 to 12 hours, at pressures of 2.0 – 5.0 atmospheres. Sometimes, helium/oxygen mixtures are used as the treatment gas. Depending on the severity and the response to treatment a patient may require anywhere from 1- 5 (usually) or more treatments in severe of slow responding cases.
If treated in a timely fashion, a diver will typically have a complete recovery. Whether they can return to diving will depend on a host of factors and will be discussed with the treating physician.