EFFICIENCY OF TWO VARIABLE PERFORMANCE TECHNIQUES OF OXYGEN THERAPY IN RELIEVING POSTOPERATIVE HYPOXAEMIA

The efficiency of two patient-dependent, variable performance techniques of oxygen therapy in relieving hypoxaemia after upper abdominal surgery was compared. A high-flow system delivered a humidified mixture of oxygen 2 litre min"1 and air 13 litre min"1 through a cannula inserted into the anterior nares. The low-flow system delivered 2 litre min"1 of dry oxygen into the nasopharynx through a catheter. Thirteen otherwise healthy patients received either high-flow oxygen therapy for 30 min followed by low-flow oxygen therapy for a further 30 min after operation or the same therapy in reverse order. With the patients breathing room air, arterial hypoxaemia could be demonstrated with Paot inversely related to age. The increase of Pao, during either oxygen treat-ment was significantly greater with the low flow system. Impairment of arterial oxygenation in the period after operation is a common occurrence even in young patients without pre-existing respiratory or cardiovascular disease. The impairment is most profound and persistent after upper abdominal surgery and thoracotomy. However, arterial hyp-oxaemia seems an almost inevitable sequel to surgery requiring general anaesthesia for more than 20 min, despite normal Paco ^ cardiac output and oxygen consumption, and in absence of evident pulmonary complications. Extensive reviews on the subject have been presented (Sellery, 1968; Marshall and Wyche, 1972; Conway, 1975; Hewlett and Branthwaite, 1975). Although the beneficial effect of oxygen therapy in relieving hypoxaemia after operation has been well established, there are relatively few controlled clinical trials which have assessed the comparative efficiency of techniques available for the administra