Postoperative hypoxemia after nonabdominal surgery: a frequent event not caused by nitrous oxide. We tested whether anesthesia that includes nitrous oxide (N2O) results in the development of intraoperative and postoperative pulmonary complications, including hypoxemia. We also tested whether aging contributes to the development of such complications, particularly when anesthesia includes N2O. We randomly allocated patients having total hip replacements, carotid endarterectomies, or transsphenoidal hypophysectomies (total n = 270) to an anesthetic regimen with and without N2O (stratified within surgical group). A heat-and-moisture exchanger was included in the anesthetic circuit of all patients. Patients were monitored perioperatively and for 1 wk after surgery using intermittent and continuous pulse oximetry to determine oxyhemoglobin saturation. Intraoperatively, mean oxygen (O2) saturations were lower in patients given N2O, particularly older patients. Hypoxemia (O2 saturation less than 86%) developed in five patients receiving N2O and in one receiving O2. This difference was not significant. Administration of N2O did not decrease postoperative O2 saturation, nor did it alter the incidence of postoperative hypoxemia, cough, or sputum production. 