The effect-site concentration of remifentanil blunting endotracheal intubation responses in elderly patients during anesthesia induction with etomidate: a dose-exploration study.

Purpose: Laryngoscopy and endotracheal intubation are known to increase activity of the sympathetic nervous system, and are usually associated with perioperative hypertension, cardiac arrhythmia, and tachycardia. The aim of this study was to determine the effect-site concentrations of remifentanil to inhibit the tracheal intubation response during etomidate anesthesia in elderly patients.

Methods: American Society of Anesthesiologists physical status I-III patients aged 65 or older and scheduled for general anesthesia for elective surgery were enrolled in the study. Anesthesia induction was applied with etomidate 0.3 mg/kg, rocuronium 0.6 mg/kg, and target controlled infusion of remifentanil under the Minto pharmacokinetic model. Invasive continuous arterial blood pressure monitoring was used throughout the operation. A positive response was defined if the maximal mean arterial pressure (MAP) or heart rate (HR) within 3 min after tracheal intubation was 20% higher than the baseline value. The Dixon sequential method was used for the test, and the initial effect-site concentrations of remifentanil was 6 ng/ml. The EC₅₀ and EC₉₅ for the suppression of endotracheal intubation response by remifentanil were calculated by the probit method.

Results: The EC₅₀ for inhibiting tracheal intubation response by remifentanil in elderly patients was 6.53 ng/ml (95% CI:6.01-7.05 ng/ml) and EC₉₅ was 8.05 ng/ml (95% CI:7.32-8.78 ng/ml) when combined with etomidate anesthesia. The changes of MAP, HR and BIS in positive group were significantly higher than those of negative group (P < 0.05). There were no episodes of hypoxemia, muscular tremor, chest wall rigidity or choking cough in both groups.

Conclusions: Target controlled infusion of remifentanil in combination with etomidate is effective preventing hemodynamic instability in elderly patients during the anesthesia induction and endotracheal intubation.

Clinical trial registration: This article was registered at Chinese Clinical Trial Registry ( www.chictr.org.cn registration number: ChiCTR2300076261, date of registration: 28/09/2023).