All enrolled adult patients receive variable-dose intravenous tegileridine adjusted by biased-coin up-and-down sequential design plus fixed-dose propofol 2 mg/kg for sedation during painless gastroscopy. Patients are stratified into young (18-65 years) and elderly (≥65 years) subgroups for separate ED90 analysis.

All participants receive intravenous tegileridine with dose adjusted by biased-coin up-and-down sequential design, combined with fixed-dose propofol 2 mg/kg for anesthesia induction before painless gastroscopy. The initial dose of tegileridine is 5 μg/kg, with a 1 μg/kg step for dose increment or decrement according to gastroscopy insertion response. Subjects are stratified into young (18-65 years) and elderly (≥65 years) subgroups for separate ED90 calculation.

The 90% effective dose (ED90) of intravenous tegileridine combined with fixed-dose propofol 2 mg/kg to fully suppress positive responses during gastroscopy insertion, calculated via central ordinal regression with 95% confidence interval. Positive response is defined as body movement, cough, or blood pressure/heart rate elevation exceeding 20% compared with baseline within 3 minutes after gastroscopy placement. Subjects are divided into young (18-65 years) and elderly (≥65 years) subgroups for separate ED90 estimation.

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 gastroscopy insertion, The highest values within 3 minutes following insertion

The modified observer's assessment of alert/sedation scale (MOAA/S) is a commonly - used sedation evaluation tool in clinical practice. It classifies reactivity under different stimuli: Grade 5 means a sensitive response to calling the name in a normal tone of voice; Grade 4 indicates a sluggish response to calling the name in a normal tone of voice; Grade 3 requires a loud or repeated call of the name to elicit a response; Grade 2 shows a response to slight pushing and vibration; Grade 1 has a response to a painful stimulus (by squeezing the trapezius muscle area); Grade 0 means no response to a painful stimulus. Moreover, MOAA/S ≤ 2 indicates loss of consciousness, which can assist medical staff in judging the sedation level and consciousness state of patients.