The Effects of Subanesthetic S-ketamine on Postoperative Delirium and Cognitive Function in the Elderly Undergoing Non-cardiac Thoracic Surgery

Inclusion Criteria: * Aged 60 years or over * Both genders * American anesthesiologist association (ASA) physical status classificationⅠ-Ⅲ * Diagnosed with lung, esophagus, or mediastinum disorders * Undergoing open or video-assisted thoracic surgery including lobectomy, segmentectomy, pneumonectomy, esophagectomy, or resection of mediastinal tumor * General anesthesia with one-lung ventilation (OLV) or bronchial blocker. * An expected operation duration of 2 hours or more. * Voluntarily participate in the trial and sign informed consent. Exclusion Criteria: * History of psychiatric disease or severe depression * History of glaucoma or hyperthyroidism * History of severe hepatic (Child-Pugh grade C) or renal (requirement for renal replacement therapy) disorder. * Body mass index (BMI) greater 35 kg/m2 * Dementia history or baseline Mini-Mental State Examination (MMSE) score less than 23 * Severe audio-visual impairments, or inability to speak Mandarin or Cantonese precluding communication * Sinus bradycardia (heart rate \< 50 beats per minutes, bpm), sick sinus or Wolff- Parkinson-White syndromes, or Ⅱ degree atrioventricular block and over * Poorly controlled hypertension (resting systolic blood pressure over 180 mm Hg, or resting diastolic blood pressure over 100 mm Hg) * Allergic to dexmedetomidine, S-ketamine or any of their formulation ingredients; * Taking sedatives, antidepressants or glucocorticoids * Alcohol or drug abuser * Life expectancy of less than 2 months d…