Criteria for inclusion and exclusion
Patients were included if they (1) were 65-89 years old; (2) were American Society Anesthesiologists physical status (ASA) I to III; (3) had body mass index (BMI) 19–27 kg/m2.
Patients were excluded when they had (1) allergy to either esketamine or propofol; (2) alcohol abuse; (3) chronic use of sedative or analgesics; (4) neurological or pyschiatric disorders; (5) heart failure (ejection fraction <40%); (6) severe respiratory disease (vital capacity and/or forced expiratory volume <50%); (7) end stage liver or renal diseases or (8) uncontrolled hypertension, blood pressure is over 180/120mmHg.