Ketamine reduces the dose of remifentanil required during prolonged head and neck surgery: a propensity-matched analysis.

High-dose opioids induce hyperalgesia and tolerance, which negatively affects postoperative recovery. Prolonged surgery inevitably requires higher opioid doses. Ketamine reduces perioperative opioid consumption and prevents opioid-induced tolerance. However, its effects in cases of prolonged surgery remain unknown. This study aimed to evaluate the dose of intraoperative remifentanil, an ultrashort-acting µ-opioid agonist, administered after an intravenous ketamine bolus during prolonged head and neck surgery. This single-center, retrospective, observational study included 251 patients who underwent head and neck surgery (operation time ≥8 h) between January 2015 and December 2019. The participants were stratified into two groups: those who received an intravenous bolus of ketamine and those who did not (ketamine group and non-ketamine group, respectively). Propensity score-matching was used to match patients in a 1:1 ratio between the two groups, based on their covariates. The difference in intraoperative remifentanil dose administered between the two groups was assessed. After 1:1 propensity score-matching, 89 matched patients were selected from each group. The mean ± standard deviation dose of remifentanil administered was significantly lower in the ketamine group than in the non-ketamine group before (0.15±0.05 vs 0.17±0.05 µg/kg/min;