The administration of esmolol decreases the propofol blood concentration, preventing movement after skin incision during propofol/morphine/nitrous oxide anesthesia. However, interaction with esmolol has not been tested when propofol is infused alone. Accordingly, we tested the hypothesis that esmolol decreases the propofol blood concentration, preventing response to command (CP50awake) when propofol is infused alone in healthy patients presenting for minor surgery. With approval and consent, we

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... studied 30 healthy patients, who were randomized to esmolol bolus (1 mg/kg) and then infusion (250 g · kg Ϫ1 · min Ϫ1 ) or placebo. Five minutes later, a targetcontrolled infusion of propofol was commenced. Ten minutes later, responsiveness was assessed by a blinded observer. Oxygen saturation, heart rate, and noninvasive arterial blood pressure were recorded every 2 min. Arterial blood samples were taken at 5 and 10 min of propofol infusion for propofol assay. Results were analyzed with a generalized linear regression model: P Ͻ0.05 was considered statistically significant. The probability of response to command decreased with increasing propofol blood concentration (CP50-awake ϭ 3.42 g/mL). Esmolol did not alter the relative risk of response to command. We conclude that the previously observed effect of esmolol on propofol CP50 was not caused by an interaction between these two drugs. (Anesth Analg 2002;93:112-6) E smolol is used in anesthesia to attenuate stress responses to tracheal intubation, control postoperative hypertension, and manage unstable coronary syndromes and tachyarrhythmias (1). Because of its potential for drug interactions via central nervous system depression (2,3) and for acute hemodynamic effects (4), esmolol has been investigated for possible interactions with anesthetics (5-8). Johansen et al. (6) initially reported that esmolol decreased propofol blood concentrations, preventing movement after skin incision (CP50) during propofol/ morphine/nitrous oxide anesthesia. Subsequently, they reported that esmolol increased the anestheticsparing effect of alfentanil during isoflurane anesthesia but had no effect on isoflurane requirements for skin incision on its own (7). However, interaction with esmolol has not been tested for propofol infused alone. Accordingly, we tested the hypothesis that esmolol decreases the propofol blood concentration, preventing response to command (CP50-awake) when propofol is infused alone in healthy patients presenting for minor surgery. Methods With approval from the Institutional Ethics Committees and informed consent, 30 patients, aged 18 -60 yr and of ASA physical status I or II, scheduled for minor orthopedic and general surgical procedures, were studied. Exclusion criteria included: 1) Ͼ150% of ideal body weight; 2) significant coexisting illness, including asthma or hypertension; 3) coincidental prescribed or nonprescribed drugs affecting anesthetic requirement; and 4) risk of gastroesophageal reflux during sedation. By using random number tables, patients were randomized to receive an esmolol bolus (1 mg/kg) and then infusion (250 g · kg Ϫ1 · min Ϫ1 ) or a placebo (normal saline) bolus and infusion. In addition, patients were randomized to receive target propofol blood concentrations (1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0