Rocuronium-induced withdrawal movements can be harmful to patients during the induction period. Remifentanil has been reported to reduce these movements effectively. In this study, we determined the EC₅₀ of remifentanil for the prevention of rocuronium induced withdrawal movements in male, female, old and child group.

We included patients scheduled for general anesthesia and assigned them into 4 groups depending on their age and gender: male group (20-60 yr), female group (20-60 yr), old group (>65 yr) and child group (6-12 yr). Remifentanil was administered by target controlled infusion. Propofol 2 mg/kg was then administered after equilibration between the effect and plasma concentration of remifentanil was reached. After loss of consciousness, rocuronium 0.6 mg/kg was administered. Patient's response to the rocuronium was graded using a 4 point scale in a blinded manner. The EC₅₀ of remifentanil for preventing rocuronium induced withdrawal movements was determined using Dixon's up-and -down method.

The EC₅₀ of remifentanil for preventing rocuronium induced withdrawal movements was 1.8 ± 0.5 ng/ml [95% confidence interval 1.3-2.2] in the male group, 2.3 ± 1.0 ng/ml [1.3-3.2] in the female group, 0.5 ± 0.4 ng/ml [0.2-0.8] in the old group and 2.8 ± 0.8 ng/ml [2.1-3.5] in the child group.

The EC₅₀ of remifentanil for preventing rocuronium induced withdrawal movements was lowest in the elderly and higher in children than male adult patients. No difference in the EC₅₀ of remifentanil was seen between male and female adult patients.