The aim of this study was to compare the effect-site target concentration (including EC₅₀ and EC₉₀) of remifentanil required to suppress cardiovascular responses to tracheal intubation during anesthesia induction with etomidate combined with either lidocaine or sufentanil.

This study is a single-center, randomized controlled trial utilizing a modified sequential method to determine the effect site target concentration of remifentanil, including the median effective concentration (EC₅₀) and the 90% effective concentration (EC₉₀). The study population consists of ASA class I-II patients undergoing general anesthesia with endotracheal intubation. Patients will be randomly assigned to one of three groups: placebo group, lidocaine group, and sufentanil group. Patients in each group will receive anesthesia induction with a combination of either saline, lidocaine, or sufentanil along with etomidate, followed by target-controlled infusion of remifentanil. The primary outcome measure is the median effective target concentration of remifentanil in the effect site (EC₅₀) for suppressing the intubation response. Secondary outcomes include the 90% effective target concentration of remifentanil (EC₉₀), changes in mean arterial pressure (MAP), heart rate (HR), and bispectral index (BIS) before and after intubation. Each group is expected to enroll 33 patients, totaling 99 patients across all three groups.

Inclusion Criteria:

• Patients scheduled for elective surgery under general anesthesia with endotracheal intubation;
• Classified as ASA physical status I-II.

Exclusion Criteria:

• Age <18 years or >65 years;
• Body mass index (BMI) >30 kg/m² or <18.5 kg/m²;
• Diagnosis of hypertension or severe cardiovascular diseases (including myocardial infarction, heart failure, atrial fibrillation, atrioventricular block, moderate-to-severe valvular diseases) or respiratory diseases (including acute exacerbation of chronic obstructive pulmonary disease, acute respiratory distress syndrome, acute asthma attack, moderate-to-severe pulmonary hypertension, severe pneumonia);
• Diagnosis of obstructive sleep apnea syndrome or history of difficult intubation or preoperatively anticipated difficult airway;
• Renal, hepatic or hematologic diseases;
• High risk of aspiration or reflux;
• Current use of analgesics for chronic pain or β-blockers for cardiovascular diseases;
• Current use of psychotropic medications;
• Contraindications to remifentanil or sufentanil, including: known hypersensitivity to any component of these drugs or other fentanyl analogues, current use of monoamine oxidase inhibitors, myasthenia gravis or conditions predisposing to respiratory depression, bronchial asthma or related disorders;
• Contraindications to lidocaine, including: known allergy to local anesthetics, concurrent Adams-Stokes syndrome, Wolff-Parkinson-White syndrome, or severe cardiac conduction block.