Esmolol Potentiates Reduction of Minimum Alveolar Isoflurane Concentration by Alfentanil

Abstract

Esmolol, a short-acting beta1-receptor antagonist, decreases anesthetic requirements during propofol/N2 O/morphine anesthesia. This study was designed to determine whether esmolol affects the volatile anesthetic (isoflurane) required to prevent movement to skin incision in 50% patients (minimum alveolar anesthetic concentration [MAC]) with or without an additional opioid (alfentanil). One hundred consenting adult patients were randomly divided into five treatment groups: isoflurane alone (I), I with continuous large-dose (250 [micro sign]g [center dot] kg-1 [center dot] min-1) esmolol (E), I with alfentanil (effect site target of 50 ng/mL) via a continuous computer-controlled infusion (A), A plus continuous small-dose (50 [micro sign]g [center dot] kg-1 [center dot] min-1) esmolol (A1), or A plus large-dose esmolol (A2). Anesthesia was induced via a face mask, and steady-state target end-tidal isoflurane concentrations were maintained before incision. The MAC of isoflurane alone was 1.28% +/- 0.13%. Large-dose esmolol did not significantly alter the isoflurane MAC (1.23% +/- 0.14%). Alfentanil alone significantly decreased isoflurane MAC by 25% (0.96% +/- 0.09%). Adding small-dose esmolol did not further decrease MAC with alfentanil (0.96% +/- 0.13%). However, large-dose esmolol significantly decreased isoflurane MAC with alfentanil (0.74% +/- 0.09%). Esmolol and alfentanil both significantly reduced the increases in heart rate and mean arterial pressure associated with endotracheal intubation and incision. The mechanism of this effect is unknown. Implications: Most anesthetic techniques rely on a balance of several highly selective medications. The current results define a new anesthetic-sparing effect when volatile anesthetic, analgesic, and beta-adrenergic blocking drugs are combined. (Anesth Analg 1998;87:671-6)