Is Oxygen Toxic in these High Doses?

OXYGEN TOXICITY

Oxygen for all practical purposes can be considered as a drug, and is capable of producing toxic effects. Just as in most other drugs, oxygen administration follows a dose response curve. Too little oxygen can be lethal, just as too much can be toxic and produce death. Unfortunately, the precise mechanisms involved in oxygen toxicity are not completely known. However, it is believed that the cause of oxygen toxicity is probably due to the increased formation of superoxide, H2O2 or other oxidizing free radicals. It is believed that the major elements attacked are sulfhydrl-containing proteins, lipoic acid and coenzyme A. The end result is damage by means of excessive oxidation of intracellular membranes and other essential cellular constituents.

Oxygen poisoning may also affect the central nervous system, causing muscle twitching and grand mal convulsions. Continued exposure after the onset of these symptoms can result in paralysis and even death. Untoward effects can also involve the eye, causing retinal damage and blindness. Other toxic effects have been described involving heart muscle, liver, and the endocrine organs.

One of the characteristics of oxygen poisoning is that the early effects are completely reversible. However, toxic effects of oxygen poisoning are generally the result of prolonged exposure at high pressures, generally greater than 3 ATA. This is one reason that most HBO treatments are given at 3 ATA or lower for periods of time not to exceed 2 hours. Under these conditions only the beneficial effects of HBO treatment are realized.

Further protection from hyperbaric oxygen toxicity is provided by maintaining adequate nutritional support of glutathione peroxidase, vitamin E (d-alpha- tocopherol), selenium, and vitamin C.


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