Impact of Reverse Trendelenburg on ONSD in Obesity Surgery

This prospective randomized controlled trial aims to investigate the effect of reverse Trendelenburg positioning applied before pneumoperitoneum on optic nerve sheath diameter (ONSD) and, consequently, intracranial pressure during laparoscopic bariatric surgery. Patients will be randomly assigned to two groups, and perioperative changes in ONSD will be compared between the groups. The primary hypothesis of the study is that applying the reverse Trendelenburg position before pneumoperitoneum may attenuate ONSD enlargement and thereby help prevent increases in intracranial pressure.

Inclusion Criteria: * Age between 18 and 65 years. * American Society of Anesthesiologists (ASA) physical status I-III. * Body mass index (BMI) ≥ 40 kg/m² and scheduled for elective laparoscopic bariatric surgery. * Ability to provide written informed consent. * Willingness to participate in the study and comply with study procedures. Exclusion Criteria: * Age younger than 18 years or older than 65 years. * Refusal or inability to provide written informed consent. * History of ophthalmologic disease that may affect optic nerve sheath diameter (ONSD) measurements (e.g., glaucoma, optic neuritis, optic nerve tumors, severe ocular trauma, previous ocular surgery). * Known intracranial pathology, including intracranial hypertension, hydrocephalus, intracranial mass lesions, or cerebrovascular disease. * Neurological disorders that may influence intracranial pressure measurements. * Emergency surgery. * Pregnancy. * Severe cardiopulmonary disease (e.g., decompensated heart failure, severe pulmonary hypertension, severe chronic obstructive pulmonary disease). * Inability to obtain adequate ocular ultrasonography images for ONSD measurement. * Conversion from laparoscopic to open surgery. Intraoperative events requiring deviation from the study protocol.