Labetalol as a hypotensive agent for middle ear microsurgery

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Abstract
Labetalol, an α‐ and β‐adrenergic receptor‐blocking agent, was studied as a hypotensive agent during halothane (mostly 0.5 vol.%)‐N2O‐fentanyl‐d‐tuhocurarine anaesthesia with a head‐up tilt of 5 degrees in 41 patients undergoing middle ear microsurgery. After the mean initial dose of 0.3 mg/kg, the mean need for labetalol ranged from 0.05 to 0.07 mg/kg at 30 ± 5‐min intervals. The mean duration of the hypotensive period was 102 min. During the hypotension, the average mean arterial pressure ranged from 59 to 62 mmHg (7.9‐8.3 kPa) and the mean heart rate from 61 to 66 b.p.m. After labetalol the maximum cardiac output decrease was 7%. Before labetalol the mean Pao2 value was 158 mmHg (21.1 kPa) and during hypotension it ranged from 145 to 149 mmHg (19.3–19.9 kPa) when Fio2 was 40%. The only peroperative side effects were ECG changes (middle junctional rhythm and sinus bradycardia) which occurred in 10% of the patients. The mean value for the degree of haemostasis rated by the otologist on a visual analogue scale between poor (0 mm) and excellent (100 mm) was 91 mm. The patients were able to open their eyes and to give their names 8–9 min after the end of anaesthesia. After extubation the patients were normotensive and there were no clinically significant changes in the cardiovascular parameters during the 4‐h recovery room period. Acid‐base status showed slight metabolic acidosis. The most common postoperative side effects were nausea only and nausea + vomiting, which occurred in 39% and 20% of the patients, respectively. It is concluded that labetalol produced stable, easily controllable hypotension without a compensatory rise in the heart rate, with minimal effect on peroperative Pao2 value or cardiac output, as well as good operating conditions. The postoperative course was uneventful with the exception of a high incidence of nausea and vomiting, most probably due to the operation rather than to the anaesthesia.