Remifentanil requirements during remimazolam induction for videolaryngoscopic endotracheal intubation: a prospective dose-finding study

Endotracheal intubation often induces rapid increases in blood pressure and heart rate due to sympathetic stimulation. Remimazolam has recently emerged as an alternative induction agent with a lower incidence of postinduction hypotension than propofol; however, the optimal remifentanil effect-site concentration ( Ce ) required to suppress intubation-induced hemodynamic responses during remimazolam induction remains unknown. This prospective, double-blinded clinical trial aimed to estimate the Ce of remifentanil required to inhibit hemodynamic responses to intubation during remimazolam anesthesia. Thirty-four adult patients undergoing elective surgery were enrolled. All patients received remimazolam and target-controlled infusion of remifentanil, and tracheal intubation was performed using a videolaryngoscope. The Ce was determined using Dixon’s up-and-down sequential allocation method. A positive response was defined as a > 20% increase in mean arterial pressure (MAP) or heart rate (HR) at 1 min after intubation compared with baseline. EC 50 and EC 95 values were estimated using isotonic regression and the pooled-adjacent violators algorithm. Based on the responses of the 30 patients included in the primary analysis, the EC 50 and EC 95 of remifentanil were estimated as 5.70 ng/mL (83% CI, 5.50–6.00) and 6.40 ng/mL (95% CI, 6.00–6.50), respectively. No patient experienced bradycardia or hypotension requiring treatment. These findings provide preliminary estimates of the remifentanil EC 50 and EC 95 during remimazolam induction; however, the EC 95 should be interpreted cautiously and prospectively validated. Clinical Research Information Service (CRIS), KCT0008697. Registered 10 August 2023. Retrospectively registered.