Emergency Oxygen and Oxygen Toxicity

Q: When administering first aid oxygen to an injured diver, is there a risk of oxygen toxicity? I’ve heard about “air breaks” — are those necessary when providing first aid oxygen?

A: There are two forms of oxygen toxicity, and they are identified by the area of the body most affected: the central nervous system (CNS toxicity) and the lungs (pulmonary toxicity). Each results from a particular type of exposure to oxygen.

CNS toxicity occurs only in hyperbaric environments (those in which the pressure exceeds sea-level pressure) and can manifest as seizures. The risk of seizure due to CNS toxicity accounts for the generally accepted oxygen partial pressure limit in recreational diving of 1.4 ATA. CNS toxicity risk increases as the partial pressure of oxygen increases.

Within hyperbaric chambers, the maximum oxygen partial pressure allowed is 3 ATA. Most treatment protocols are performed at 2-2.8 ATA of oxygen. Exposure to these levels is appropriate in controlled clinical settings and is not harmful. In the event of acute oxygen toxicity, the controlled, dry environment is not associated with the risks divers face, like drowning. To further reduce the risk of oxygen seizure during hyperbaric treatment, some facilities also provide air breaks, which are thought to reduce oxygen seizure risk. Despite the high oxygen partial pressures experienced in hyperbaric chambers, seizures are very rare.
Pulmonary toxicity, on the other hand, results primarily from prolonged exposures, not just elevated oxygen partial pressures. However, the onset of pulmonary toxicity is accelerated in hyperbaric environments.

Pulmonary oxygen toxicity describes the irritation of lung tissue resulting from excess free radical production. The prolonged use of high concentrations of oxygen can overwhelm our cellular defenses. Symptoms may include substernal (behind the sternum) irritation, coughing, a burning sensation with inspiration and reduced pulmonary function. When breathing 100 percent oxygen at sea level, symptoms may occur after 12-16 hours of exposure. As such, pulmonary toxicity is generally not a concern in open-circuit recreational diving and other prehospital settings, and it does not require special prevention strategies or the use of air breaks.

From time to time, we hear about divers administering oxygen first aid and confusing it with chamber treatment protocols by giving air breaks to the injured diver. Air breaks are unnecessary and inappropriate for a diver breathing 100 percent oxygen at near-surface pressure. Giving air breaks while administering oxygen first aid diminishes the oxygen pressure gradient and reduces the oxygen window by introducing nitrogen into the diver’s breathing gas. This slows the elimination of nitrogen from the diver’s body.

If you participate in prolonged evacuations from a remote location, allowing occasional air breaks is acceptable, although these would happen naturally as the diver eats, drinks and goes to the bathroom. It isn’t necessary to plan these air breaks at regular intervals.
— Nicholas Bird, M.D., DAN CEO and chief medical officer, and Eric Douglas