The optimal dosage of alfentanil pretreatment for prevention of myoclonus after injection of etomidate

Abstract

Background: Myoclonus is a common problem during induction of general anesthesia with etomidate. We investigated the optimal dosage of alfentanil pretreatment for prevention of myoclonus after injection of etomidate. Methods: In a double blinded fashion, 76 patients scheduled for outpatient elective surgery were randomized into 4 groups according to pretreatment drug: alfentanil 2.5μg/kg, alfentanil 5μg/kg, alfentanil 10μg/kg, or normal saline. The pretreatment was followed by etomidate 0.3 mg/kg IV. Laryngeal mask airway (LMA) was inserted at 5 minutes after the induction. The patients were observed for any myoclonic movement. Onset time, duration and intensity of myoclonus, side effects of alfentanil, mean arterial pressure and heart rate were measured during the study period. Results: There were significant differences in the incidence and intensity of myoclonus. An injection of 5, and 10μg/kg alfentanil before etomidate prevented increase of mean arterial pressure and heart rate after LMA insertion. But injection of 10 μg/kg alfentanil before etomidate appeared generalized muscle rigidity, bradycardia and hypotension. Conclusions: An injection of 2.5, 5, and 10μg/kg alfentanil before etomidate decreases the incidence and intensity of myoclonus. But injection of 10μg/kg alfentanil before etomidate appeared side effects. Therefore the optimal dosage of alfentanil pretreatment for prevention of myoclonus after injection of etomidate is 5μg/kg.