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L~OE DOSES of intravenous morphine (0.5-4.0 mg/kg) and oxygen has recently become popular as a method of anaesthetizing critically ill patients for cardiac and other major operative procedures. 1,2 While the technique results in a minimum of cardiovascular depression, it has been suggested that a marked antidiuresis is associated with these doses of morphine. ' This study was conducted to determine the effects of morphine (2 mg/kg) and morphine plus 60 per cent nitrous oxide on the urinary output of patients scheduled for major abdominal operations. METHODSTen unpremedicated patients (ages 17-60) without known renal disease who were about to undergo vascular or gastro-intestinal surgery were studied approximately four to six hours before their operations were to begin. Informed written consent was obtained at the time of the preoperative visit. Before the experiments began each patient had two intravenous infusions started in the upper extremities, a central venous pressure catheter placed in the antecubital fossa and threaded to the right atrium, and a radial-artery catheter inserted. A catheter was also inserted into the urinary bladder and standard electrocardiograph leads were applied to the extremities. With the patients in a recumbent position, oxygen was then given by face mask and a diuresis was started by intravenous administration of lactated Ringer's solution at a rate of 25 ml/min. When urine output became more than 5 ml/min, the bladder catheter and collecting bag were emptied and the first of three 20-minute urine collections was begun. At the end of each collecting period complete emptying of the bladder was insured by suprapubic pressure. Urine collected was then measured and analyzed immediately for osmolarity and creatinine. At the end of each 20-minute collecting period a 10-ml blood sample was obtained for measurement of osmolarity and creatinine.

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