Hyperbaric Oxygen in Relation to Circulatory and Respiratory Emergencies.

A patient is placed in a pressure chamber and breathes oxygen in order to increase the oxygenation of an organ or tissue which has been rendered anoxic or ischaemic by disease or accident. The theory is simple; successful practical application depends on the appreciation of certain difficulties. Table I shows the "ideal" alveolar oxygen partial pressures which are attainable with oxygen at 1 and 2 atmospheres absolute. To reach these levels, however, the inspired gas must consist of 100 per cent oxygen and this is not easy in a patient breathing oxygen from a mask. McDowall et al. (1964) have shown that the commonly used B.L.B. mask when applied to an adult with a fresh gas flow of 8 litres a minute produces an alveolar oxygen partial pressure which is only 60 per cent of the maximum possible. This problem arises only in the larger pressure chambers which are pressurized with air; smaller chambers, such as that described by Hopkinson and Williams (1963) are usually pressurized with 100 per cent oxygen so that this particular difficulty is avoided. Very high alveolar partial pres-