The purpose of this study is to compare the effects of the standard Trendelenburg position and the modified Z-Trendelenburg position on cerebral oxygenation and optic nerve sheath diameter (ONSD) in patients undergoing laparoscopic surgery. The prolonged use of the standard Trendelenburg position combined with pneumoperitoneum can increase intracranial pressure and affect cerebral blood flow. In this study, researchers will use non-invasive methods, including Near-Infrared Spectroscopy (NIRS) to monitor regional cerebral oxygenation, and ocular ultrasonography to measure ONSD as an indicator of intracranial pressure changes. The main goal is to determine whether the modified Z-Trendelenburg position serves as a safer physiological alternative by reducing these potential adverse effects compared to the standard position.

Laparoscopic surgeries frequently require patients to be placed in a steep Trendelenburg position with pneumoperitoneum to provide optimal surgical exposure. However, this combination induces significant physiological alterations, most notably an increase in intracranial pressure (ICP) and a potential compromise in cerebral venous drainage and regional cerebral oxygen saturation (rSO2). Non-invasive monitoring techniques, such as measuring the optic nerve sheath diameter (ONSD) via ultrasonography, provide reliable, real-time estimates of ICP changes. Additionally, Near-Infrared Spectroscopy (NIRS) allows for the continuous monitoring of cerebral oxygenation.

This prospective clinical study is designed to evaluate and compare the cerebral and hemodynamic impacts of the standard straight Trendelenburg position versus a modified Z-Trendelenburg position. Participants scheduled for elective laparoscopic procedures will be divided into specific positioning groups. Hemodynamic parameters, NIRS values, and ONSD measurements will be recorded at predefined time points throughout the surgery: at baseline, post-induction, after the establishment of pneumoperitoneum and positioning, at specific intervals during the surgery, and post-operatively in the recovery room. The primary hypothesis is that the modified Z-Trendelenburg position will attenuate the rise in ICP (reflected by a smaller increase in ONSD) and provide better cerebral oxygenation stability compared to the traditional standard position.

Inclusion Criteria:

Patients aged between 18 and 70 years

American Society of Anesthesiologists (ASA) physical status I or II

Scheduled for elective laparoscopic surgery requiring Trendelenburg position

Provided written informed consent

Exclusion Criteria:

Patient refusal to participate

History of severe cerebrovascular disease

Known increased intracranial pressure

Pre-existing ocular pathology that could affect optic nerve sheath diameter (ONSD) measurements (e.g., glaucoma, optic neuritis, ocular trauma)

Severe cardiovascular or pulmonary disease Body Mass Index (BMI) greater than 35 kg/m^2 Pregnancy

The study population consists of adult patients up to 80 years of age who [are admitted to the intensive care unit / are undergoing elective surgery / present to the emergency department]. The population excludes patients with known increased intracranial pressure, severe cerebrovascular, cardiovascular, or pulmonary diseases, morbid obesity (BMI > 35 kg/m^2), pregnancy, and any pre-existing ocular pathologies that could affect optic nerve sheath diameter (ONSD)

The study population consists of adult female patients, aged 18 to 80 years, classified with an American Society of Anesthesiologists (ASA) physical status of I or II, who are scheduled to undergo elective laparoscopic gynecological surgery under general anesthesia at Ankara Etlik City Hospital. Eligible participants must have a Body Mass Index (BMI) between 18 and 30 kg/m2 and require the Trendelenburg position during surgery. Patients are excluded from the study population if they have a history of intracranial pathology, neurological disorders, severe ophthalmologic conditions (such as glaucoma), cerebrovascular diseases, severe cardiac or pulmonary diseases, profound anemia (Hb < 10 g/dL), or if they are pregnant.