A further distinction can be made between routine exposure and exposure required for emergency treatment, where a higher risk of oxygen toxicity may be justified to achieve a reduction of a more critical injury, particularly when in a relatively safe controlled and monitored environment. The Repex (repetitive exposure) method, developed in 1988, allows oxygen toxicity dosage to be calculated using a single dose value equivalent to 1 minute at atmospheric pressure called an Oxygen Tolerance Unit (OTU), is used to avoid toxic effects over several days of operetional exposure. Some dive computers will automatically track the dosage bases on depth and selected gas mixture. The limits allow a greater exposure when the person has not been exposed recently, and daily allowable dose decreases with an increase in consecutive days with exposure. These values may not be fully supported by current data. A more recent proposal uses a simple power equation, Toxicity Index (TI) = t2 × PO2c, where t is time and c is the power term. This was derived from the chemical reactions producing reactive oxygen or nitrogen species, and has been shown to give good predictions for CNS toxicity with c = 6.8 and for pulmonary toxicity for c = 4.57.For pulmonary toxicity, time is in hours, and PO2 in atmospheres absolute, TI should be limited to 250. For CNS toxicity, time is in minutes, PO2 in atmospheres absolute, and a TI of 26,108 indicates a 1% risk.
This has led to the current recommendation by the Diving Committee of the Undersea and Hyperbaric Medical Society that a diver should be raised during the seizures clonic (convulsive) phase if the regulator is not in the divers mouth—as the danger of drowning is then greater than that of AGE—but the ascent should be delayed until the end of the clonic phase otherwise. Rescuers ensure that their own safety is not compromised during the convulsive phase. They then ensure that where the victims air supply is established it is maintained, and carry out a controlled buoyant lift. Lifting an unconscious body is taught by most recreational diver training agencies as an advanced skill, and for professional divers it is a basic skill, as it is one of the primary functions of the standby diver. Upon reaching the surface, emergency services are always contacted as there is a possibility of further complications requiring medical attention. The U.S. Navy has procedures for completing the decompression stops where a recompression chamber is not immediately available.The occurrence of symptoms of bronchopulmonary dysplasia or acute respiratory distress syndrome is treated by lowering the fraction of oxygen administered, along with a reduction in the periods of exposure and an increase in the break periods where normal air is supplied. Where supplemental oxygen is required for treatment of another disease (particularly in infants), a ventilator may be needed to ensure that the lung tissue remains inflated.