Postoperative Hypoventilation and Hypoxemia in Man after Hyperventilation

Abstract

In 13 patients, free of cardiopulmonary disease, who had been subjected to hyperventilation for an average of two and three-quarters hours during anesthesia and operation, spontaneous breathing began when arterial carbon dioxide tension rose from 18 to 38 mm of mercury. Thereafter the patients were allowed to breathe air. Tidal volume and minute volume increased progressively throughout the first postoperative hour while arterial carbon dioxide tension varied less than 2 mm of mercury. Twenty minutes after the onset of spontaneous breathing, arterial oxygen tension reached an average low value of 72 mm of mercury and then progressively increased toward normal, averaging 83 mm at 30 minutes and 88 mm at 60 minutes. Thus, in man the hypoventilation that follows a period of hyperventilation can result in a definite lowering of arterial oxygen tension if air is breathed after operation. Yet this hypoventilation was associated with a normal arterial carbon dioxide tension. Carbon dioxide tension is not a reliable index of adequate ventilation for the maintenance of normal arterial oxygen tension after hyperventilation and anesthesia.