The goal of this observational study is to learn whether the brain's ability to use oxygen during surgery is associated with postoperative delirium in adults aged 65 years and older undergoing general anesthesia.

The main question it aims to answer is:

- Does reduced cerebral oxygen consumption responsiveness during surgery increase the risk of postoperative delirium in older patients?

Participants who are undergoing elective laparoscopic surgery under general anesthesia as part of their routine medical care will have brain oxygen levels measured during surgery using a non-invasive forehead sensor, and will be assessed for delirium for up to three days after surgery.

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

Participants will be recruited from patients scheduled for elective laparoscopic surgery at Seoul National University Bundang Hospital, a tertiary academic medical center in the Republic of Korea. Eligible patients will be identified during routine preoperative evaluation and approached for study participation prior to surgery.