The goal of this observational study is to evaluate whether hypothermia affects the relationship between electroencephalography-derived indices during cardiac surgery in adult patients undergoing cardiopulmonary bypass.

The main questions it aims to answer are:

Does the correlation between Bispectral Index (BIS) and Patient State Index (PSI) change between normothermic and hypothermic phases during cardiopulmonary bypass? How do BIS and PSI values change in response to decreasing body temperature?

Participants will:

Undergo standard general anesthesia for elective on-pump coronary artery bypass surgery Be monitored simultaneously with BIS and PSI devices during surgery Have data recorded at predefined temperature-based time points during cardiopulmonary bypass

Hypothermia during cardiopulmonary bypass (CPB) is known to influence cerebral metabolism and electroencephalographic activity. Processed electroencephalography-derived indices such as the Bispectral Index (BIS) and Patient State Index (PSI) are commonly used to monitor anesthetic depth; however, these indices are generated using different proprietary algorithms. While previous studies have demonstrated moderate to high correlation between BIS and PSI under normothermic conditions, it remains unclear whether this relationship is preserved during hypothermic CPB.

This prospective observational study aims to evaluate the effect of hypothermia on the relationship between BIS and PSI in adult patients undergoing elective on-pump coronary artery bypass grafting. Both indices will be monitored simultaneously throughout the intraoperative period using standard sensor placement.

Data will be collected at predefined time points representing normothermic, hypothermic, and rewarming phases of CPB. The primary analysis will focus on comparing the correlation between BIS and PSI at a normothermic reference point (36°C) and a hypothermic reference point (32°C).

To minimize confounding effects, anesthetic management and physiological parameters will be maintained within routine clinical target ranges, and relevant variables will be recorded throughout the procedure. Secondary analyses will explore temperature-dependent changes in each index and agreement between clinically relevant depth-of-anesthesia categories.

This study is designed to clarify whether hypothermia alters the relationship between commonly used processed EEG indices, which may have implications for intraoperative neuromonitoring and anesthetic management during cardiac surgery.

Inclusion Criteria:

• Age ≥18 years
• Elective on-pump Coronary Artery Bypass Grafting (CABG) surgery
• Planned use of general anesthesia
• Written informed consent

Exclusion Criteria:

• Preexisting neurological disease
• Use of medications affecting Electroencephalography (e.g., antiepileptics)
• Severe hepatic dysfunction
• Emergency surgery
• Inadequate signal quality for anesthesia depth monitoring

Adult patients undergoing elective on-pump coronary artery bypass grafting (CABG) with cardiopulmonary bypass at a single tertiary care center will be included. All participants will receive standard general anesthesia and perioperative management according to institutional protocols. Patients will be monitored intraoperatively with both Bispectral Index (BIS) and Patient State Index (PSI) devices, and data will be collected at predefined time points during normothermic, hypothermic, and rewarming phases of cardiopulmonary bypass.

Individual participant data may be shared upon reasonable request, subject to approval by the institutional ethics committee and in accordance with applicable data protection regulations. At the time of registration, a definitive data sharing plan has not been finalized.