Abdominal Neoplasms

This prospective observational cohort study aims to investigate the relationship between perioperative endogenous melatonin levels and postoperative delirium in patients aged 65 years or older undergoing elective abdominal cancer surgery. The study will also evaluate serotonin, kynurenine, kynurenic acid, and vitamin B12 as potential biomarkers associated with postoperative delirium. Participants will undergo routine standardized general anesthesia and thoracic epidural analgesia. Venous blood samples will be obtained preoperatively and on postoperative day 3. In participants who develop delirium, an additional blood sample will be obtained as soon as possible after delirium is detected. Postoperative delirium will be assessed using the Confusion Assessment Method (CAM) on postoperative days 1, 3, and 5. No experimental drug or additional therapeutic intervention will be administered as part of the study.