Dexmedetomidine-Esketamine Combination and Sleep Disturbances After Major Noncardiac Surgery

Inclusion Criteria: 1. Aged ≥18 years. 2. Scheduled for major noncardiac surgery (≥60 minutes) under general anesthesia with an expected end of surgery no later than 18:00 pm. 3. Required patient-controlled intravenous analgesia after surgery. Exclusion Criteria: 1. Emergency surgery, transurethral surgery, organ transplantation. 2. Pregnant or lactating women. 3. Patients who need hypnotics for sleep disturbance or antidepressants for depression prior to surgery. 4. History of schizophrenia, epilepsy, Parkinson's disease, or myasthenia gravis. 5. Inability to communicate due to coma, severe dementia, or speech disorders, endured hypoxic encephalopathy or traumatic brain injury, or after neurosurgery. 6. Comorbid with hyperthyroidism and pheochromocytoma. 7. Preoperative left ventricular ejection fraction \<30%, sick sinus syndrome, severe sinus bradycardia (heart rate \<50 beats/min), atrioventricular block of degree II or higher without pacemaker implantation, or systolic blood pressure below 90 mmHg despite use of vasopressors. 8. Diagnosed as sleep apnea, or judged to be at high risk of moderate-to-severe sleep apnea as assessed by STOP-Bang. 9. Severe hepatic dysfunction (Child-Pugh class C), severe renal dysfunction (on dialysis), or ASA classification ≥IV. 10. Hypersensitive to dexmedetomidine and/or esketamine. 11. Other conditions that are deemed unsuitable for study participation.