Butorphanol pre-treatment prevents myoclonus induced by etomidate

QUESTIONS UNDER STUDY: Myoclonic movements are common problems during induction of anaesthesia with etomidate. The myoclonus occurring after etomidate administration may represent a form of seizure. Agonistic modulation of the kappa opiate receptor may reduce seizures, and butorphanol acts in such a manner. The aim of this randomised, double-blind, placebo-controlled clinical trial was to test our hypothesis that pre-treatment with butorphanol might reduce the incidence and severity of myoclonus induced by etomidate. METHODS: Patients (108) with American Society of Anaesthesiologists physical status I or II were randomly assigned to one of two groups to receive either 0.015 mg/kg of butorphanol (n = 54) or saline (n = 54) intravenously. At two minutes after infusion of butorphanol or saline, 0.3 mg/kg etomidate was given. The occurrence and severity (observational score of 0-3) of myoclonus was assessed during 2 minutes after administration of etomidate. For each patient, blood pressure (BP), saturation of peripheral oxygen (SpO(2)), and heart rate (HR) were measured. RESULTS: The incidence of myoclonus was significantly lower in Group Butorphanol than in Group Saline (13.0% vs 79.6%; RR = 0.163, 95%CI: 0.081-0.329; chi(2) = 48.265, p <0.0001). The severity levels of myoclonic movement were also significantly lower in Group Butorphanol than in Group Saline (p <0.0001). Throughout the procedure, changes of BP, SpO(2), and HR did not differ between the groups. There were no problems with bradycardia or hypotension. CONCLUSIONS: Infusion of 0.015 mg/kg butorphanol 2 minutes before etomidate administration is effective for suppressing myoclonus induced by etomidate during induction of general anaesthesia.