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ANESTHETIC PHARMACOLOGY

Esmolol and Anesthetic Requirement for Loss of Responsiveness During Propofol Anesthesia

Ruari Orme, MBBS^*, Kate Leslie, MD FANZCA, Abhay Umranikar, MBBS FANZCA^*, and Antony Ugoni, BSc(Hons), MSciStat

*Department of Anaesthesia, Ballarat Base Hospital, Ballarat, Victoria, Australia; Outcomes Research^TM Group, Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Parkville, Victoria, Australia; and University of Melbourne, Victoria, Australia

Address correspondence and reprint requests to Kate Leslie, MD, FANZCA, Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Parkville, VIC, 3050, Australia. Address e-mail to kate.leslie{at}mh.org.au

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 (CP50-awake) when propofol is infused alone in healthy patients presenting for minor surgery. With approval and consent, we studied 30 healthy patients, who were randomized to esmolol bolus (1 mg/kg) and then infusion (250 µg · kg^-1 · min^-1) or placebo. Five minutes later, a target-controlled 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 <0.05 was considered statistically significant. The probability of response to command decreased with increasing propofol blood concentration (CP50-awake = 3.42 µg/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.

IMPLICATIONS: There is no evidence to suggest that esmolol, an ultra-short-acting cardioselective ß-blocker, affects anesthetic requirement for loss of responsiveness during propofol anesthesia.