Postoperative Delirium and Analgesia in Elderly Patients

Inclusion Criteria: * Patients undergoing elective unilateral total knee arthroplasty under spinal anesthesia * ASA physical status I-III * Age ≥60 years * Body mass index (BMI) between 18-30 kg/m² * Preoperative fasting duration of approximately 8 hours Exclusion Criteria: * Refusal to participate in the study or inability to provide written informed consent * American Society of Anesthesiologists (ASA) physical status IV or higher * Obese patients (BMI \>30 kg/m²) or cachectic patients (BMI \<18 kg/m²) * Patients requiring general anesthesia or in whom spinal anesthesia could not be achieved * Contraindications to spinal anesthesia * Emergency surgeries * Psychiatric or neurological disorders causing cognitive dysfunction (e.g., epilepsy, schizophrenia, dementia, Alzheimer's disease) * Use of psychotropic or opioid medications, or a history of alcohol abuse or withdrawal within the last 6 months * Mini-Mental State Examination (MMSE) score ≤24 * Stage III-IV hepatic encephalopathy * Severe impairments preventing cognitive assessment, such as blindness or severe hearing loss * Patients meeting delirium criteria according to baseline 3D-CAM assessment or unable to complete the test * History of cranio-cerebral surgery * Acute myocardial infarction within the previous 12 months before surgery * Requirement for postoperative intensive care unit admission