When scuba diving, additional oxygen and nitrogen dissolve in body tissues. The additional oxygen is consumed by the tissues, but the excess nitrogen must diffuse out by the blood during decompression.

During or after ascent this excess nitrogen gas can form bubbles in the tissues, analogous to the carbon dioxide bubbles that form when a carbonated drink container is opened.

These bubbles may then cause symptoms that are referred to as decompression sickness (“DCS” or “the bends”). Trapping of gas within the lungs during ascent, either because the lung is diseased or because of breath-holding, can cause bubbles to be forced into the bloodstream (“arterial gas embolism” or “AGE”), where they can block the flow of blood or damage the lining of blood vessels supplying critical organs such as the brain. AGE can also occur in non-divers, due to entry of air into the body, such as during medical, diagnostic or therapeutic procedures.

Symptoms of DCS or AGE can include joint pain, numbness, tingling, skin rash, extreme fatigue, weakness of arms or legs, dizziness, loss of hearing, and in serious cases, complete paralysis or unconsciousness. Emergency treatment of DCS or AGE includes administration of oxygen and measures to maintain adequate blood pressure, such as lying the patient down and fluid (either oral or intravenous, depending upon availability and severity of the illness).

Definitive treatment for DCS or AGE is administration of 100% oxygen at increased atmospheric pressure in a hyperbaric chamber (typically at a pressure 2-3 times greater than normal atmospheric pressure). While some delay in transporting a patient to a hyperbaric chamber is usually unavoidable, the success in relieving symptoms is greater if the treatment is administered within a few hours after the onset of symptoms. Some improvement might be expected, particularly in mild cases, even after a day or more of delay. The vast majority of cases respond satisfactorily to a single hyperbaric oxygen treatment. Sometimes, repetitive treatments are recommended until no further improvement can be observed.

A small minority of divers with severe neurological injury may require 15-20 repetitive treatments. The success of hyperbaric oxygen treatment for DCS or AGE over many decades has proven its value and continues to be the standard of care for the treatment of these disorders.

References:

1. Francis TJR, Gorman DF. Pathogenesis of the decompression disorders. In: Bennett PB, Elliott DH, eds. The Physiology and Medicine of Diving. Philadelphia: W.B. Saunders, 1993:454-480.
2. Elliott DH, Moon RE. Manifestations of the decompression disorders. In: Bennett PB, Elliott DH, eds. The Physiology and Medicine of Diving. Philadelphia, PA: WB Saunders, 1993:481-505.
3. Moon RE, Sheffield PJ. Guidelines for treatment of decompression illness. Aviat Space Environ Med 1997;68:234-243.
4. Navy Department. US Navy Diving Manual. Vol 1 Revision 3: Air Diving. NAVSEA 0994-LP-001-9110. Flagstaff, AZ: Best, 1993.
5. Ball R. Effect of severity, time to recompression with oxygen, and retreatment on outcome in forty-nine cases of spinal cord decompression sickness. Undersea Hyperbaric Med 1993;20:133-145.
6. Kizer KW. Delayed treatment of dysbarism: a retrospective review of 50 cases. JAMA 1982; 247: 2555-8.
7. Moon RE, Gorman D: Treatment of the Decompression Disorders. In: The Physiology and Medicine of Diving. Edited by Bennett PB, Elliott DH. Philadelphia, PA, Saunders, 1993, pp 506-541.