Measurement of anesthetic depth has long been a subject of investigation, aiming to titrate anesthetic agents appropriately and to prevent intraoperative awareness and consciousness. Many patients undergoing surgery experience fear and anxiety regarding the possibility of remaining conscious, perceiving pain, and being unable to move during anesthesia. Intraoperative awareness-defined as consciousness during anesthesia with explicit recall afterward-is a distressing condition that can lead to post-traumatic stress disorder.

However, aiming for excessively deep anesthesia to avoid the possibility of awareness during surgery is not recommended, as it may result in hemodynamic instability due to the effects of anesthetic agents and may impair postoperative cognitive functions, particularly in the elderly population.

Common methods used in monitoring anesthetic depth include observing sweating, lacrimation, pupillary dilation, heart rate variability, and blood pressure. However, some of these are subjective and may not always be reliable indicators.

Electroencephalogram (EEG)-based monitors such as the Bispectral Index (BIS) and the Patient State Index (PSI) offer more reliable and objective means of monitoring anesthetic depth. These monitors provide numerical values between 0 (indicating unconsciousness) and 100 (indicating full alertness) based on proprietary algorithms, offering valuable insight into the patient's anesthetic state.

"Our aim is to examine BIS and PSI values and to investigate the factors that influence these parameters."

Inclusion Criteria:

• "Patients aged 18 to 65 years,
• Classified as ASA (American Society of Anesthesiologists) physical status II-III,
• scheduled for elective open-heart surgery via median sternotomy

Exclusion Criteria:

• "Patients with an ejection fraction below 35%,
• Those with pre-existing central nervous system disorders (e.g., history of epileptic seizures or intracranial space-occupying lesions),
• A history of prior open cranial surgery,
• Known allergies to anesthetic agents, alcohol or substance abuse,
• Any other conditions deemed to negatively affect the BIS profile (e.g., patients with preoperative intra-aortic balloon pump insertion, those undergoing surgery under inotropic support, or receiving preoperative sedative infusions),
• As well as patients scheduled to undergo antegrade or retrograde cerebral perfusion or total circulatory arrest

"This study will be conducted with the approval of the Ethics Committee of Kocaeli University Faculty of Medicine Hospital and after obtaining written informed consent from all participants. The aim of our study is to investigate the factors influencing the BIS (Bispectral Index) and PSI (Patient State Index) methods, which are used to assess the depth of anesthesia in patients undergoing open-heart surgery with the use of a cardiopulmonary bypass (CPB) machine at Kocaeli University Faculty of Medicine Hospital."