Comparison of Three Hypotensive Anaesthetic Methods for Middle Ear Microsurgery

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Abstract
Three hypotensive anesthetic methods were compared in 123 patients undergoing middle ear microsurgery. Hypotension was induced with halothane (1 vol%), nitroprusside (4.4 .mu.g/kg per min) or the combination of halothane (0.5 vol%) and nitroprusside (1.2 .mu.g/kg per min). The compensatory rise in the heart rate was controlled with a .beta.-adrenergic receptor blocking agent, practolol, the mean need for which was 0.03 mg/kg in the halothane group and 0.1 mg/kg in the other groups. The mean duration of the hypotensive period ranged from 79 to 107 min in the groups. During the hypotension, the average mean arterial pressure ranged from 55 to 60 mm Hg (7.33 to 8.00 kPa [Pascals]) and the mean heart rate from 67 to 79 beats/min in the groups. The PaO2 [O2 arterial partial pressure] value in the nitroprusside and halothane + nitroprusside groups, but not in the halothane group, decreased statistically and in some cases clinically significantly. The only preoperative side effects were ECG changes (mostly junctional rhythm), the incidence of which ranged from 16 to 24% in the groups. The mean values for the degree of hemostasis rated by the otologist on a visual analog scale between poor (0 mm) and excellent (100 mm) were 90, 73 and 89 mm in the halothane, nitroprusside and halothane + nitroprusside groups, respectively. Recovery in the halothane group was statistically highly significantly longer than in the other groups. No rebound hypertension occurred in any of the groups after discontinuation of the hypotension. The most common side effect was nausea + vomiting, the incidence of which ranged from 15 to 26% in the groups. Respiratory difficulties occurred in 7% of the patients in the halothane group but not in the other groups. Evidently the hypotension induced either with halothane or halothane + nitroprusside produced good and similar operating conditions. Nitroprusside hypotension was inferior to the other methods since it produced statistically significantly worse hemostasis than the other methods, and the PaO2 [O2 arterial partial pressure] value during hypotension decreased statistically significantly as also in the halothane + nitroprusside group. The disadvantage of halothane alone was long postanesthetic recovery.