Sex differences in remifentanil requirements for preventing cough during anesthetic emergence

Abstract

Purpose: Target-controlled infusion (TCI) of remifentanil can suppress coughing during emergence from general anesthesia, but previous studies under different clinical conditions have recommended significantly different effective effect-site concentrations (effective Ce) of remifentanil for 50% of patients (EC50). The differences among these studies include type of surgery and patient sex. In recent years, there has been a growing interest in studying sex differences in anesthetic pharmacology. Therefore, we determined the effective Ce of remifentanil for each sex under the same clinical conditions.

Materials and Methods: Twenty female and twenty-five male ASA I–II grade patients between the ages of 20 and 46 who were undergoing thyroidectomy were enrolled in this study. The effective Ce of remifentanil for preventing cough was determined for each sex using the isotonic regression method with a bootstrapping approach following Dixon’s up-and-down method.

Results: Isotonic regression with a bootstrapping approach showed that the estimated EC50 of remifentanil for preventing coughing during emergence was significantly lower in females [1.30 ng/ml (83% confidence interval, 1.20–1.47 ng/ml)] than in males [2.57 ng/ml (83% CI, 2.45–2.70 ng/ml)]. Mean EC50 in females was also significantly lower than in males (1.23 ± 0.21 ng/ml vs. 2.43 ± 0.21 ng/ml, P<0.001). MAP, HR and RR over time were not significantly different between the sexes.

Conclusion: When using remifentanil TCI for cough prevention during anesthetic emergence, patient sex should be a considered for appropriate dosing.