Effects of smoking on the optimal effect-site concentration of remifentanil required for preventing cough during anesthetic emergence in male patients undergoing laparoscopic or robotic cholecystectomy

Target-controlled infusion of remifentanil is known to reduce cough effectively during emergence from general anesthesia. The effect of smoking on emergence cough remains controversial. Therefore, we aimed to investigate the effect-site concentration (Ce) of remifentanil in the male patients undergoing laparoscopic or robotic cholecystectomy for suppressing emergence cough in smokers and non-smokers. Twenty smokers and 24 non-smokers (sex, male; age range, 20-65 years) were enrolled in this study. Anesthesia was maintained using sevoflurane and remifentanil. The Ce of remifentanil in 50% (EC50) and 95% (EC95) of the patients required for suppressing emergence cough were determined for each group (smokers and non-smokers) using Dixon up-and-down method and isotonic regression method with a bootstrapping approach. Dixon up-and-down method revealed that the EC50 value was significantly higher in smokers (3.51 +/- 0.60 ng/mL) than in non-smokers (2.71 +/- 0.30 ng/mL) (P < 0.001). In smokers and non-smokers, isotonic regression revealed EC50 to be 4.40 (83% CI, 4.17-4.58) ng/mL and 2.58 (83% CI, 2.31-2.87) ng/mL, respectively, and EC95 to be 4.76 (95% CI, 4.73-4.78) ng/mL and 3.15 (95% CI, 3.04-3.18) ng/mL, respectively. The Ces of remifentanil required to prevent cough during emergence were significantly higher in smokers than in non-smokers. Therefore, clinicians should pay attention to the smoking history of a patient to prevent cough during emergence.