Effect-site concentration of remifentanil inhibiting hemodynamic response following endotracheal intubation during remimazolam induction

Endotracheal intubation often induces rapid increases in blood pressure and heart rate due to sympathetic stimulation. Remifentanil is commonly used to attenuate these responses, yet its optimal effect-site concentration ( Ce ) during remimazolam induction remains unclear. This prospective, double-blinded clinical trial aimed to determine the Ce of remifentanil required to inhibit hemodynamic response to intubation under remimazolam anesthesia. Thirty-four adult patients undergoing elective surgery were enrolled. All patients received remimazolam and target-controlled infusion of remifentanil, with the Ce 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) within 1 minute after intubation compared to baseline. Based on the responses of 30 patients included in the final analysis, the EC₅₀ and EC₉₅ 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, using isotonic regression and the pooled-adjacent violators algorithm. No patient experienced bradycardia or hypotension requiring treatment. These findings suggest that a remifentanil Ce of 6.40 ng/mL is effective in blunting the hemodynamic response to intubation in 95% of patients during remimazolam-based induction.