The Effect-site Concentration of Remifentanil Blunting Endotracheal Intubation Responses During Anesthesia Induction With Lidocaine or Sufentanil Combined With Etomidate: A Randomized Controlled Study

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.