Low-dose Droperidol for Prevention of Postoperative Delirium in Elderly Patients After Non-cardiac Surgery

Inclusion Criteria: * Age≥65 years * American Society of Anesthesiologists (ASA): I-III * Planning to undergo elective non-cardiac surgery under general anesthesia with endotracheal intubation, including digestive, orthopedic, urologic and gynecological surgery * Estimated operation time more than 2 hours * Not expected to be admitted to ICU postoperatively * Proficient in Chinese * Informed consent Exclusion Criteria: * Morbid obesity with BMI \>35 kg/m2; * History of psychological and neurological diseases, such as depression, schizophrenia, epilepsy, severe central nervous system depression, Parkinson's disease, Alzheimer's disease, myasthenia gravis, basal ganglia disease, etc; * Corrected QT (QTc) of electrocardiogram\> 500ms; * Preoperative liver insufficiency (Child Pugh grade C); * End-stage renal disease requiring dialysis; * Severe heart failure \[Metablic equivalent (METs)\<4\]; * Allergic to droperidol; * Inability to communicate due to coma or dementia in preoperative period; * Preoperative delirium, assessed by 3D-CAM; * More than three standard alcoholic drinks per day (≈10 g alcohol , equivalent to 50 g of strong Chinese spirits); * Participating in conflicting clinical trials; * Expected to have an additional operation within 7 days after the index operation.