Inclusion Criteria | Exclusion Criteria |
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1. 18–65 years old 2. Scheduled for orthopedic, urologic, and thoracic elective surgery under general anesthesia with tracheal intubation 3. Physical status I or II of American Society of Anesthesia 4. BMI (kg/m2) ≥ 18 and ≤ 30 5. Estimated anesthesia time 1–4 h 6. Use narcotic analgesics (sufentanil or remifentanil) intraoperatively 7. Use electronic intravenous analgesia pump after surgery 8. Informed consent | 1. Refused to participate in this study 2. Refused to receive intravenous analgesia 3. A medical or family history of cognitive disorders, delirium, epilepsy, alienation, anxiety, or depression 4. Recently used anticholinergic drugs, antidepressants, anxiolytics, or anticonvulsants 5. A medical history of organic brain diseases or craniovascular diseases 6. A history of allergy to any drug used in this study 7. A history of drug addiction, alcoholism, or drug abuse 8. Comorbid conditions of severe heart and lung disease; active heart disease; severe hepatic dysfunction ( Child–Pugh class C); severe renal dysfunction ( undergoing dialysis) before surgery; or critical illness (preoperative physical status classification ≥ 3 of American Society of Anesthesia) 9. Participated in other clinical trials within 4 weeks 10. Intraoperative complications, such as cerebrovascular accident, heart failure, or pneumothorax, or transfer to the intensive care unit during hospitalization 11. Unable to communicate in the preoperative period because of coma, profound dementia, language barrier, or incapacity from severe disease 12. Anesthesia time < 1 or > 4 h 13. Chronic pain, which is defined as unsatisfied pain control for at least one month |