Effects of deliberate hypotension induced by labetalol on renal function

The effect of deliberate hypotension induced by labetalol on renal function, was studied in 25 patients undergoing middle-ear surgery. The patients were randomized into three groups, one enflurane (E) group and two isoflurane (I and F) groups. Group F received frusemide 0.5 mg kg-1 at the onset of hypotension. The mean arterial pressure was 50 mmHg (6.7 kPa) in Groups E and I, and 49 mmHg (6.5 kPa) in Group F during hypotension. During hypotension, urine flow rate, effective renal blood flow, endogenous creatinine clearance, and osmolar clearance decreased. Free-water clearance and fractional electrolyte excretions also indicated deterioration of renal function during hypotension, but it returned to normal after anaesthesia. The effects of frusemide appeared mainly after anaesthesia. Frusemide reduced the amount of labetalol and isoflurane needed to maintain hypotension. Serum fluoride concentration did not increase to a potentially nephrotoxic level.