Oxygen Toxicity - Classification

Classification

The effects of oxygen toxicity may be classified by the organs affected, producing three principal forms:

• Central nervous system, characterised by convulsions followed by unconsciousness, occurring under hyperbaric conditions;
• Pulmonary (lungs), characterised by difficulty in breathing and pain within the chest, occurring when breathing elevated pressures of oxygen for extended periods;
• Ocular (retinopathic conditions), characterised by alterations to the eyes, occurring when breathing elevated pressures of oxygen for extended periods.

Central nervous system oxygen toxicity can cause seizures, brief periods of rigidity followed by convulsions and unconsciousness, and is of concern to divers who encounter greater than atmospheric pressures. Pulmonary oxygen toxicity results in damage to the lungs, causing pain and difficulty in breathing. Oxidative damage to the eye may lead to myopia or partial detachment of the retina. Pulmonary and ocular damage are most likely to occur when supplemental oxygen is administered as part of a treatment, particularly to newborn infants, but are also a concern during hyperbaric oxygen therapy.

Oxidative damage may occur in any cell in the body but the effects on the three most susceptible organs will be the primary concern. It may also be implicated in red blood cell destruction (haemolysis), damage to liver (hepatic), heart (myocardial), endocrine glands (adrenal, gonads, and thyroid), or kidneys (renal), and general damage to cells.

In unusual circumstances, effects on other tissues may be observed: it is suspected that during spaceflight, high oxygen concentrations may contribute to bone damage. Hyperoxia can also indirectly cause carbon dioxide narcosis in patients with lung ailments such as chronic obstructive pulmonary disease or with central respiratory depression. Hyperventilation of atmospheric air at atmospheric pressures does not cause oxygen toxicity, because sea-level air a has a partial pressure of oxygen (ppO₂) of 0.21 bar (21 kPa) and the lower limit for toxicity is more than 0.3 bar (30 kPa).