DECOMPRESSION ILLNESS

What is decompression illness?

Decompression illness (DCI) is an all-inclusive term that comprises dysbaric injuries, arterial gas embolism (AGE), and decompression sickness (DCS).

Because the two diseases are considered to result from separate causes, they are described separately. However, from a clinical and practical standpoint, distinguishing them in the field may be impossible and unnecessary, since the initial treatment is the same for both.

DCI can occur even in divers who have carefully followed the standard decompression tables and the principles of safe diving.

Arterial Gas Embolism

Overinflation of the lungs can result as a scuba diver ascends toward the surface without exhaling. During ascent, compressed gas trapped in the lung increases in volume until the expansion exceeds the elastic limit of lung tissue, causing damage and allowing gas bubbles to escape into the spaces around the lung. Air entering the pleural space causes lung collapse or pneumothorax.

Air can also enter the mediastinum (space around the heart, trachea and oesophagus), causing mediastinal emphysema. Air in the mediastinum frequently tracks under the skin (subcutaneous emphysema) or into the tissue around the larynx, precipitating a change in the voice characteristics.

While mediastinal or subcutaneous emphysema usually resolves spontaneously, pneumothorax may require specific treatment to remove the air and reinflate the lung.

Air can also enter the arterial blood, where bubbles distribute into the body tissues, including the heart and brain, where they disrupt circulation. AGE may cause minimal neurologic symptoms or symptoms may be dramatic and require immediate attention.

These signs and symptoms include numbness, weakness, tingling, dizziness; visual blurring; chest pain; personality change; bloody froth from mouth or nose; paralysis or seizures; loss of consciousness; or death.

In general, any scuba diver who surfaces unconscious or loses consciousness within 10 minutes after surfacing should be assumed to have AGE. Institution of basic life support, including the administration of 100% oxygen, is indicated, followed by rapid evacuation to a hyperbaric treatment facility.

Decompression Sickness

Breathing air under pressure causes inert gas (nitrogen) to diffuse into the body's tissues. This diffusion occurs at different rates in various tissues and continues as long as the partial pressure of inspired gas is greater than the absorbed gas in the tissues. Thus, the amount of inert gas absorbed is dependent on the depth and time spent at depth. As the diver ascends to the surface, this process is reversed as the partial pressure of residual gas exceeds that in the circulatory and respiratory systems. Ascent from a dive can cause supersaturation of inert gas (tissue partial pressure exceeding ambient pressure), allowing dissolved gas to form bubbles in tissues and causing signs and symptoms of decompression sickness.

These symptoms include joint aches or pain; numbness, tingling, mottling or marbling of skin; coughing spasms, shortness of breath; itching; unusual fatigue; dizziness, weakness; personality changes; loss of bowel or bladder function; staggering, loss of coordination, tremors; or paralysis; and collapse or unconsciousness.

Serious permanent injury may result from both decompression sickness and arterial gas embolism.