Sex-Related Differences in the Effect-Site Concentration of Remifentanil for Preventing QTc Interval Prolongation Following Intubation in Elderly Patients with a Normal QTc Interval

Background Female sex and age more than 65 years are common risk factors for the development of torsades de pointes in association with heart rate-corrected QT (QTc) interval prolongation, which can be induced by tracheal intubation during general anaesthesia. However, the administration of remifentanil can prevent intubation-induced QTc interval prolongation. We compared sex-related differences in the effect-site concentration (Ce) of remifentanil for preventing QTc interval prolongation among elderly patients. Methods Twenty-two female and 22 male patients older than 65 years were enrolled. Anaesthesia was induced with remifentanil and propofol using a target-controlled infusion. The Ce of remifentanil for maintaining a QTc interval prolongation <15 ms following intubation was determined for each sex using the isotonic regression method and a bootstrapping approach following Dixon's up-and-down method. Results The Ce of remifentanil for preventing QTc interval prolongation following intubation in 50 % of the population (EC50) and 95 % of the population (EC95) were significantly lower in females than in males. Isotonic regression revealed that the EC50 (83 % confidence interval) of remifentanil was 3.50 (2.95-4.08) ng/mL in females and 4.38 (4.08-4.63) ng/mL in males. The EC95 (95 % confidence interval) of remifentanil was 4.43 (4.25-4.48) ng/mL in females and 4.94 (4.78-4.98) ng/mL in males. Conclusions Target-controlled infusion of remifentanil is effective in attenuating QTc interval prolongation after intubation among elderly patients and the Ce of remifentanil is lower in females than in males.