This study investigates the effects of low-flow desflurane anesthesia in adult patients undergoing major abdominal surgery. The researchers will examine whether different low-flow strategies:

Cause differences in the Bispectral Index (BIS), which measures brain activity during anesthesia, Affect postoperative cognitive functions such as memory and attention.

Participants will:

Receive desflurane anesthesia during surgery, Have anesthesia delivered at different low-flow rates, Have their BIS values monitored throughout the operation, Complete tests after surgery to evaluate their cognitive functions.

This research will help determine the safety of different low-flow strategies and their impact on patients' cognitive recovery after surgery.

This prospective observational study is designed to evaluate the effects of different low-flow desflurane anesthesia strategies on intraoperative anesthetic depth, measured by the Bispectral Index (BIS), and on postoperative cognitive functions in patients undergoing major abdominal surgery.

Patients will receive desflurane anesthesia delivered at different low-flow rates. Throughout surgery, BIS values will be continuously monitored to assess the depth of anesthesia. Postoperatively, standardized cognitive function tests will be performed at predetermined time points to evaluate potential cognitive impairment or recovery. The study aims to clarify whether the choice of low-flow strategy influences short-term postoperative neurocognitive outcomes.

Quality assurance and data management procedures:

Data collection will be conducted using standardized electronic case report forms (eCRFs).

All collected data will undergo range and consistency checks against predefined rules.

Source data verification will be performed through comparison with medical records and anesthetic monitoring logs.

A data dictionary will be maintained, documenting each variable, coding standards (e.g., MedDRA where applicable), and reference ranges.

Missing data will be handled according to a predefined plan, with cases flagged as missing, unusable, or inconsistent.

Sample size and statistical plan:

The sample size has been estimated to ensure sufficient statistical power to detect clinically meaningful differences in BIS and postoperative cognitive function scores between different low-flow strategies. Statistical analyses will include descriptive statistics, group comparisons using parametric or non-parametric tests, and regression models where appropriate. A detailed statistical analysis plan has been developed to address both primary and secondary endpoints.

This study will provide evidence regarding the safety and neurocognitive impact of different low-flow desflurane strategies. Findings are expected to support clinical decision-making in optimizing anesthetic management for patients undergoing major abdominal procedures.

Inclusion Criteria:

Patients aged 18-75 years

ASA physical status I-III

Scheduled for elective major abdominal surgery

Provided written informed consent

Normal preoperative neurocognitive function

Exclusion Criteria:

History of neurological or psychiatric disorders

History of cognitive impairment

Diagnosed hepatic or renal insufficiency

Presence of other systemic diseases contraindicating anesthesia

The study population will be recruited from patients undergoing elective major abdominal surgery at the Department of Anesthesiology and Reanimation, Ankara Dr Abdurrahman Yurtaslan Onkology Training and Research Hospital.