The influence of age and gender on remifentanil EC50 for preventing rocuronium induced withdrawal movements

BACKGROUND 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 EC(50) of remifentanil for the prevention of rocuronium induced withdrawal movements in male, female, old and child group. METHODS 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 EC(50) of remifentanil for preventing rocuronium induced withdrawal movements was determined using Dixon's up-and -down method. RESULTS The EC(50) 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. CONCLUSIONS The EC(50) 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 EC(50) of remifentanil was seen between male and female adult patients.