Cerebral Oxygen Consumption Response to Increased Oxygen Supply and Postoperative Delirium in Older Surgical Patients

• Intraoperative Cerebral Oxygen Utilization Assessment (Other): Cerebral oxygenation will be monitored intraoperatively using a non-invasive forehead sensor based on functional near-infrared spectroscopy technology. During general anesthesia, the fraction of inspired oxygen (FiO₂) may be temporarily adjusted within the standard clinical range used in routine anesthesia care to evaluate the brain's oxygen utilization response. No experimental oxygen levels or additional therapeutic interventions will be administered beyond standard clinical practice.

Primary outcomes

• Incidence of Postoperative Delirium [Up to 3 days after surgery]: Postoperative delirium diagnosed using 3D-CAM conducted in the post-anesthesia care unit and hospital ward. Delirium will be defined as at least one positive assessment during the first three postoperative days.

Secondary outcomes

• Intraoperative Cerebral Oxygen Utilization Response (ΔHbO-HbR) [During surgery]: Change in the difference between oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HbR), calculated as Δ(HbO-HbR), measured intraoperatively using functional near-infrared spectroscopy during variations in inspired oxygen concentration within the clinically applied range.

Other outcomes

• Predictive Performance of ΔHbO-HbR for Postoperative Delirium [Up to 3 days after surgery]: Predictive accuracy of intraoperative Δ(HbO-HbR) for postoperative delirium assessed using receiver operating characteristic (ROC) curve analysis. The area under the ROC curve (AUC) will be calculated to quantify discrimination.

Sex: All, ages: 65 Years to any

Inclusion Criteria:

* Patients undergoing elective laparoscopic surgery under general anesthesia
* Age 65 years or older

Exclusion Criteria:

* Diagnosis of dementia or presence of delirium before surgery
* Loss of capacity to provide informed consent
* Moderate or severe cerebrovascular stenosis diagnosed before surgery
* Moderate or severe obstructive or restrictive pulmonary dysfunction identified on preoperative pulmonary function testing
* Requirement for supplemental oxygen therapy before surgery
* History of neurological disorders (e.g., Parkinson's disease, stroke) or prior brain surgery
* Severe hepatic dysfunction (AST or ALT > 120 IU/L)
* Severe renal dysfunction (estimated GFR < 15 mL/min/1.73 m²)
* Persistent severe hemodynamic instability (mean arterial pressure < 60 mmHg)
* Skin conditions preventing placement of the forehead fNIRS sensor
* Combined surgical procedures performed concurrently
* Planned postoperative admission to the intensive care unit