Postoperative hypoxaemia and oxygen therapy.

Arterial blood and expired gas samples were taken from 20 patients before operation and on the first day after upper abdominal surgery. After operation the patients were studied breathing air and also breathing 35% oxygen from a venturi-type mask. Preoperative Pao2 with age was exaggerated by operation. Pao2 after operation was closely related to, and lower than, the preoperative value. The postoperative Pao2 during oxygen therapy correlated well with the postoperative Pao2 breathing air. Severely hypoxaemic patients show less improvement of oxygen tension during 35% oxygen therapy.