All enrolled adult patients aged ≥18 years receive intravenous tegileridine followed by fixed-dose propofol 2 mg/kg for anesthesia induction. This single-group biased-coin sequential up-and-down design starts with an initial tegileridine dose of 10 μg/kg, with 1 μg/kg dose step for increment or decrement based on laryngeal mask airway insertion response. Patients are stratified into young subgroup (18-65 years) and elderly subgroup (≥65 years) for separate ED90 calculation. Intraoperative anesthesia maintenance and perioperative supportive treatments are consistent for all subjects.

Intravenous tegileridine with variable dose adjusted by biased-coin sequential design, combined with fixed-dose propofol 2 mg/kg for general anesthesia induction before laryngeal mask airway placement.

The 90% effective dose of intravenous tegileridine combined with fixed-dose propofol to completely inhibit positive responses during laryngeal mask airway insertion, calculated via central ordinal regression with 95% confidence interval. Positive response is defined as any body movement, frowning, tearing, cough, or blood pressure/heart rate increase over 20% compared with baseline within 3 minutes after LMA placement.

During anesthesia induction, intravenous injection of opioids may cause coughing. During the after laryngeal mask airway insertion process, coughing may occur due to airway stimulation.

Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) are recorded at:

Baseline (prior to tegileridine administration) ,2 minutes after tegileridine bolus, Immediately before laryngeal mask airway insertion, The highest values within 3 minutes following insertion