Heart Rate Variability Changes and Postoperative Delirium After Major Abdominal Surgery

This prospective observational cohort study aims to investigate whether early postoperative changes in heart rate variability (HRV) relative to baseline are associated with the development of postoperative delirium (POD) in older patients undergoing elective major abdominal surgery under general anesthesia. Patients aged 65-85 years will be enrolled. Resting HRV will be measured at 10:00 AM on the day of surgery before anesthesia induction and at the same time point on the first postoperative day using a validated heart rate monitoring device. HRV parameters will be derived from standardized 5-minute recordings. Changes in HRV parameters from baseline will be calculated, and their associations with POD occurrence will be evaluated. Postoperative delirium will be assessed daily from 24 hours after surgery to postoperative day 7, using the 3-Minute Diagnostic Interview for Confusion Assessment Method (3D-CAM). The study will also explore the potential utility of HRV-derived markers for early POD risk stratification. Approximately 500 participants will be enrolled.

Inclusion Criteria 1. Patients admitted to Jiangsu Provincial People's Hospital who are scheduled to undergo elective major abdominal surgery under general anesthesia. 2. Older patients aged 65 to 85 years. 3. Expected postoperative hospital stay of ≥7 days. 4. Body mass index (BMI) between 18.5 and 28.0 kg/m². 5. American Society of Anesthesiologists (ASA) physical status classification I-III. 6. Patients who are conscious, mentally competent, and able to cooperate with heart rate variability (HRV) measurements, questionnaire assessments, and follow-up evaluations. 7. Patients who voluntarily participate in the study and provide written informed consent. Exclusion Criteria 1. Patients with ASA physical status classification ≥IV or patients with end-stage cancer. 2. Patients with implanted cardiac pacemakers, implantable cardioverter-defibrillators, or other electronic devices that may interfere with ECG signal acquisition. 3. Patients with severe or unstable cardiovascular diseases, including but not limited to acute coronary syndrome, symptomatic bradycardia, sick sinus syndrome, second-degree or higher atrioventricular block, atrial fibrillation, atrial flutter, frequent premature beats, or other arrhythmias that may affect heart rate variability analysis. 4. Patients with diseases affecting autonomic nervous system function, including confirmed primary or secondary autonomic dysfunction, such as Parkinson's disease, multiple system atrophy, severe diabetic autonomic neuropathy, severe peripheral neuropathy, poorly controlled hyperthyroidism or hypothyroidism, and systemic amyloidosis. 5. Patients with a history of organic central nervous system diseases or psychiatric disorders, including major traumatic brain injury, stroke (ischemic or hemorrhagic), intracranial mass lesions, epilepsy, schizophrenia, bipolar disorder, major depressive disorder, or other severe psychiatric disorders. 6. Patients with severe baseline cognitive impairment or inability to complete cognitive assessments, including any of the following: (1) preoperative baseline Montreal Cognitive Assessment (MoCA) score \