Decompression illness

Decompression Illness (DCI) is a term generally used to describe illness after a decrease in the ambient pressure that a body is exposed to. Decompression Illness is usually experienced by divers, but it is not limited to diving in water. Any person exposed to great pressure changes (such as scuba divers, aviators, astronauts and compressed-air workers) may be at risk of decompression illness.

DCI is one of two main types of barotrauma-- specifically it is illness of barotrauma caused by untolerated release of pressure. The other type of barotrauma is caused directly by increase in pressure.

DCI is caused by two different mechanisms: decompression sickness (DCS) and Arterial Gas Embolism (AGE), which result in overlapping sets of symptoms. DCS usually results from bubbles forming in tissues, causing direct damage to the tissues by several mechanisms, including pressure occlusion, clotting, and immune response. AGE results from bubbles entering the blood vessels and moving with the blood flow, eventually lodging in an artery as the artery narrows, and causing ischemic tissue damage by blocking blood flow to a region of tissue normally dependent on flow from the artery.

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Decompression sickness

Main article: Decompression sickness

Decompression sickness is usually the result of inadequate decompression following exposure to increased pressure. The disease is usually mild and not an immediate threat. However, it must be noted that serious injury can occur. As a general rule, the sooner treatment is initiated, the better the chance for a full recovery.

Decompression sickness is also known as "the bends" or Caisson Disease.

Mechanism of injury

At sea level, air is composed of about 79% nitrogen. The pressure exerted by the water on the air in the tank and your body compresses the air and makes it more dense (concentrated per square inch) so that the deeper you go and take the same deep breath, you will get more and more nitrogen. There is only so much your lungs can eliminate, so it starts to accumulate in your blood after certain depths (like adding carbon dioxide to soft drinks and sealing the can).

During a dive, the body tissues absorb nitrogen in proportion to the surrounding pressure. As long as the diver remains at pressure the excess nitrogen is exhaled by the lungs (like a can being closed). However, if the body is subjected to a rapid loss of pressure (such as rapid ascent - like opening a can of soda) the nitrogen will expand into bubbles (come out of solution) faster than it can be exhaled by the lungs (notice how you can see the bubbles form when you open a bottle of pressurized softdrinks).

If the bubbles form in or near joints, this will cause joint pains which contributed to the nickname of the "bends" because you can't stand up due to the pain and are "bent" over. The bubbles in the blood may form in any part of the body, as the nitrogen is absorbed in different tissues at different concentrations. For example, fatty tissue absorbs nitrogen at a much faster rate than muscle or bone tissue, but that fatty tissue also off-gasses the nitrogen at a much faster rate. The different concentrations of nitrogen in the different tissues explain why symptoms may not occur until the diver has been on the surface for quite a while. The most important complication occurs when the bubbles travel to the heart and then are shot into the blood vessels in the lungs and clog off the blood flow as if they were clots. Suddenly the blood flow into the lungs is not enough and shortness of breath and eventually, death ensue. If you have a patent foramen ovale in the heart (embriological communication between the right and left sides that normally closes at birth) the bubbles may cross over and be shot into the brain or extremities leading to strokes or black fingers/toes respectively.

Numbness, pain, shortness of breath, paralysis and disorders of higher cerebral function may also occur as the bubble from the various tissues increase in size.

If suspected you should suspend the dive, lay the person on their left side down (to keep the bubbles in the right side and not go to the lungs or brain) give them 100% oxygen (to help push out the nitrogen from the blood), call a decompression chamber as soon as possible to place the person within it and push the bubbles back into solution until the lungs can clear it out.

Symptoms

• Fatigue
• Skin itch
• Pain in joints or muscles
• Dizziness, vertigo, ringing in the ears
• Numbness, tingling and paralysis
• Shortness of breath

Signs

• Skin rash
• Paralysis, muscle weakness
• Difficulty in urinating
• Confusion, personality changes, bizarre behavior
• Loss of memory, tremors
• Staggering
• Bloody, frothy sputum
• Collapse or unconsciousness

Signs and symptoms can appear immediately after surfacing, but may take up to a day or two to appear. Delayed onset is rare, but does happen.

Arterial Gas Embolism

Main article: Air embolism

Arterial gas embolism (AGE) is usually the result of some injury to the lungs causing air bubbles to "leak" into the bloodstream.

Mechanism of injury

If a diver ascends without exhaling, the gas in the lungs will expand due to the reduced pressure surrounding the lungs and may rupture lung tissue. This is pulmonary barotrauma which releases gas bubbles into the arterial circulation. This will cause the bubbles to be circulated through the body via the bloodstream. If the bubbles reach the brain and damage it, this is a particularly serious type of arterial gas embolism termed CAGE (Cerebral Arterial Gas Embolism). The symptoms of CAGE are those of stroke.

A person suffering from AGE may surface unconscious. This does not mean that any person who is conscious on surfacing is excluded from the possibility of AGE.

Symptoms

• Dizziness
• Blurring of Vision
• Areas of decreased sensation
• Chest pain
• Disorientation

Signs

• Bloody froth from mouth or nose
• Paralysis or weakness
• Convulsions
• Unconsciousness
• No breathing
• Death

First aid

First aid for DCI is administered by:

• Monitoring the victim for responsiveness, airway, breathing and circulation, to resuscitate if necessary. The victim should be laid on his or her back or (for drowsy, unconscious, or nauseated victims) on their side.
• Administration of 100% oxygen as soon as possible.
• Seeking of immediate medical aid and consultation with a diving medical specialist.

Details of recent dives and responses to first aid treatment should be recorded and provided to the treating medical specialist. The diving details should include depth and time profiles, breathing gases used and surface intervals.

The victim may be allowed to drink water or isotonic fluids only if they are responsive, stable, and not suffering from nausea or stomach pain. Administration of saline via intravenous drip is preferable.

Entonox should not be given.

Treatment

Very often hyperbaric oxygen therapy in a recompression chamber is needed. With some types of lung barotrauma, surgery is required.

References

• Diving First Aid Manual, John Lippmann and Stan Bugg, DAN SEAP Membership Edition
• The Diving Emergency Handbook, John Lippmann and Stan Bugg, ISBN 0-946020-18-3