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 damage to red blood cells (haemolysis),  the liver, heart, endocrine glands (adrenal glands, gonads, and thyroid), or kidneys, 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 has a partial pressure of oxygen of 0.21 bar (21 kPa) whereas toxicity does not occur below 0.3 bar (30 kPa). Signs and symptoms
Central nervous system
Central nervous system oxygen toxicity manifests as symptoms such as visual changes (especially tunnel vision), ringing in the ears (tinnitus), nausea, twitching (especially of the face), behavioural changes (irritability, anxiety, confusion), and dizziness. This may be followed by a tonic–clonic seizure consisting of two phases: intense muscle contraction occurs for several seconds (tonic phase); followed by rapid spasms of alternate muscle relaxation and contraction producing convulsive jerking (clonic phase). The seizure ends with a period of unconsciousness (the postictal state).
Hypobaric setting
In low-pressure environments oxygen toxicity may be avoided since the toxicity is caused by high partial pressure of oxygen, not merely by high oxygen fraction. This is illustrated by modern pure oxygen use in spacesuits, which must operate at low pressure (also historically, very high percentage oxygen and lower than normal atmospheric pressure was used in early spacecraft, for example, the Gemini and Apollo spacecraft). In such applications as extra-vehicular activity, high-fraction oxygen is non-toxic, even at breathing mixture fractions approaching 100%, because the oxygen partial pressure is not allowed to chronically exceed 0.3 bar (4.4 psi). Management
During hyperbaric oxygen therapy, the patient will usually breathe 100% oxygen from a mask while inside a hyperbaric chamber pressurised with air to about 2.8 bar (280 kPa). Seizures during the therapy are managed by removing the mask from the patient, thereby dropping the partial pressure of oxygen inspired below 0.6 bar (60 kPa).A seizure underwater requires that the diver be brought to the surface as soon as practicable. Although for many years the recommendation has been not to raise the diver during the seizure itself, owing to the danger of arterial gas embolism (AGE), there is some evidence that the glottis does not fully obstruct the airway.