Assessment of beta-adrenoceptor blockade during anesthesia in humans: use of isoproterenol dose-response curves.

Patients with hypertension or ischemic heart disease are often treated with beta-adrenoceptor antagonists, yet the degree of beta-adrenoceptor blockade has rarely been studied in relation to anesthesia. We have constructed isoproterenol dose-response curves in four groups of patients under general anesthesia: group I, 27 elderly normotensive patients not receiving drugs; group II, 14 hypertensive patients treated with cardioselective beta-adrenoceptor antagonists; group III, 15 hypertensive patients receiving nonselective beta-adrenoceptor antagonists; group IV, 13 patients receiving an infusion of labetalol at 0.15 mg X kg-1 X hr-1. Geometric mean CD25, the dose of isoproterenol required to increase the heart rate by 25 beats/min was 4.4 micrograms (3.5-5.6, 95% confidence interval (CI) of the mean) in group I, and 27 micrograms (19-38, 95% CI), 39 micrograms (29-52, 95% CI), and 95 micrograms (62-147, 95% CI) in groups II, III, and IV, respectively. All differences were significant (P less than 0.01), except those between groups II and III (P less than 0.1). No signs of myocardial ischemia and only a few transient arrhythmias were observed. Isoproterenol dose-response curves are a safe means to assess the degree of beta-adrenoceptor blockade during anesthesia and the postoperative period.