Holding the breath on ascent is the main cause of an air embolism. As the diver moves from high pressure at depth to a lower pressure at a shallower depth, the air in the lungs expands. If this air doesn’t escape out the windpipe, the only release is via the delicate air membranes in the lungs, called alveoli, and into the blood stream.
To illustrate this in numbers; if a diver’s lungs holds 5 litres of air at 10 metres depth, this will expand to 10 litres on the surface. With the average male's lungs having a capacity of 5.8 litres there is an obvious problem if this expanded air is not released.
The result is similar to the Bends, as both result in air bubbles in the blood stream and the myriad of problems this can cause.
Symptoms Of Air Embolism
Some, but not all symptoms of an air embolism are:
- Bloody froth or mucous at the mouth
- Tightness in the centre of the chest
- Numbness at the extremities
- Dizziness
- Unconsciousness
Possible Causes Of An Air Embolism
An air embolism usually occurs from breaking scuba diving’s number one rule: “never hold the breath on scuba”.
Though it sounds easy to observe, the following are some scenarios where holding the breath on ascent can occur:
- Stress. When the diver is under stress and panics, the natural reaction is to head for the surface - fast. An experienced diver might feel a growing tightness in the chest as the air expands while ascending, while the stressed diver may not recognize this as a sign of an imminent lung rupture.
- Snorkler using Alternate air supply. A scuba diver might offer a snorkler to duck down a few metres and enjoy a few breaths off the scuba diver’s alternate air supply. While this may seem tempting, the risk is if the snorklers is unaware of the dangers of breathing air at depth and holds their breath on ascent. In this situation, the scuba diver should know better, as they have done the course and should understand the theory.
- Emergency ascent. When suddenly no air is flowing through the regulator (equipment failure or running out of air) and the buddy has their head in a crevice coaxing out a crayfish, the only option is a controlled emergency ascent. If this is not done properly, and the air is not released from the lungs slowly, an air embolism can result. Again, anxiety and panic could come into the equation as an emergency ascent is a stressful time.
- Asthma. An asthma attack while scuba diving can result in an air embolism, as the air trapped in the lungs from the swelling and possible mucous buildup as a result of the asthma will expand on ascent. It needs to go somewhere, so will be forced into the bloodstream.
The treatment for an air embolism is generally the same as the Bends. The patient needs to be placed in a decompression, or hyperbaric, chamber in which the pressure is increased, then decreased gradually back to atmospheric. This forces the bubbles in the blood back into solution.
Further treatment may be required for damaged lungs from the over expansion.
Preventing An Air Embolism
The rule of “never hold the breath on scuba” should not be broken. In some situations the breath can be held while rising slightly; such as when using the lungs to fine tune buoyancy control. But this should be done when the diver is fully aware of what they are doing.
Disclaimer
This article contains general advice, not specific medical advice. For specific medical advice, consult a physician.
Bruce Iliff - Hello from an Australian freelancer! I’ve been scratching articles together in Australia in a range of subjects for a number of ...
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