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.

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.

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 10µg/kg alfentanil before etomidate appeared generalized muscle rigidity, bradycardia and hypotension.

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.