Assessment of ??-Adrenoceptor Blockade during Anesthesia in Humans

Patients with hypertension or ischemic heart disease are often treated with β-adrenoceptor antagonists, yet the degree of β-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 β-adrenoceptor antagonists; group III, 15 hypertensive patients receiving nonselective β-adrenoceptor antagonists; group IV, 13 patients receiving an infusion of labetalol at 0.15 mg-kg −1-hr−1. Geometric mean CD25, the dose of isoproterenol required to increase the heart rate by 25 beats/min was 4.4 μg (3.5–5.6, 95% confidence interval (CI) of the mean) in group I, and 27 μg (19–38, 95% CI), 39 μg (29–52, 95% CI), and 95 μg g (62–147, 95% CI) in groups II, III, and IV, respectively. All differences were significant (P < 0.01), except those between groups II and III (P < 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 β-adrenoceptor blockade during anesthesia and the postoperative period.