BACKGROUND: The induced hypotensive anesthesia may produce serious complications related to central nervous system, heart, liver, kidney and eyes. In this study, the blood loss during and after operation were compared to evaluate the delayed effect of hypotension on postoperative bleeding and also, the urine output was measured in control group and furosemide treated group, to investigate the effect of furosemide on the protection of kidney function. METHODS: Forty patients undergoing spinal surgery were evaluated and the hypotension was induced by the combination of hydralazine, esmolol and propranolol under enflurane anesthesia. During hypotensive anesthesia, the systolic arterial blood pressure was maintained between 65 to 75 mmHg. I compared the arterial blood gas analysis, plasma protein, albumin and calcium level, blood urea nitrogen (BUN), creatinine and complete blood count (CBC) before, durng and after hypotensive anesthesia. And also, the volume of blood loss and the units of transfused blood were measured intraoperatively and postoperatively. To investigate the effect of furosemide on the protection of kidney function, patients were randomly divided to contol group (n=20) and furosemide group (n=20). In furosemide goup, 0.1 mg/kg was administered intravenously and the urine output was measured during and after hypotensive anesthesia in both groups. RESULTS: The systolic arterial blood pressure during hypotensive anesthesia was maintained between 65 to 75 mmHg as planned in all forty patients. The average blood loss during and after operation were 769+/-541 and 786+/-397 ml, respectively and the average total blood loss was 1555+/-784 ml. The average units of transfused packed red cell during and after operation were 2.6+/-0.8 and 1.9+/-0.4 units, respectively, and the average total transfused units were 2.3+/-0.8 units. In both control and furosemide treated groups, all forty patients showed oliguria during first two hours after starting hypotensive anesthesia but urine outputs were recovered after the end of hypotensive anesthesia in both groups. During and after hypotensive anesthesia, pH was slightly but significantly decreased. Plasma protein, albumin, calcium and BUN were decreased during and after hypotensive anesthesia compared with before hypotensive anesthesia values. During and after hypotensive anesthesia, platelet count was decreased significantly but white cell count was increased. Severe oliguria was noted during hypotensive anesthesia in both groups and no serious complication related to hypotensive anesthesia was found. CONCLUSIONS: In this study, the volume of blood loss after anesthesia was almost same as that during anesthesia. And the administration of furosemide 0.1 mg/kg did not prevent oliguria during hypotensive anesthesia.