Osmolar output in the peri-operative period.

The hourly urine volume and urine concentration of seven patients undergoing major abdominal surgery were measured during the operative and postoperative periods. From these, the hourly osmolar output was calculated. The results show that the osmolar output, 700 mOsm/day, in the peri-operative period is less than that of a 70 kg man consuming a normal 2000 calorie diet. Calculation of the osmolar output might help in the differentiation of postoperative oliguria and renal dysfunction.