Effect of Pre-pneumoperitoneum Reverse Trendelenburg Positioning on Optic Nerve Sheath Diameter During Bariatric Surgery: A Prospective Randomized Controlled Trial

Obesity is associated with physiological alterations that may affect intracranial dynamics during laparoscopic surgery. In bariatric procedures, the creation of pneumoperitoneum and the use of reverse Trendelenburg positioning are essential for optimal surgical exposure. However, pneumoperitoneum increases intra-abdominal pressure and may impair venous return from the brain, potentially leading to elevations in intracranial pressure (ICP). These effects may be particularly relevant in obese patients, who are more susceptible to hemodynamic and respiratory changes during surgery.

Direct measurement of ICP using intraventricular or intraparenchymal catheters remains the gold standard; however, these invasive techniques are not feasible in routine surgical practice because of the risks of hemorrhage, infection, and other complications. Ultrasonographic measurement of optic nerve sheath diameter (ONSD) has emerged as a reliable, noninvasive surrogate marker for assessing changes in ICP and has been widely used in perioperative and critical care settings.

Previous studies have demonstrated that pneumoperitoneum may increase ONSD during laparoscopic procedures. Reverse Trendelenburg positioning has been shown to facilitate cerebral venous drainage and may attenuate increases in intracranial pressure. However, the effect of the timing of reverse Trendelenburg positioning relative to pneumoperitoneum creation has not been adequately investigated, particularly in patients undergoing bariatric surgery.

This prospective randomized controlled trial aims to evaluate whether applying the reverse Trendelenburg position before pneumoperitoneum can reduce perioperative increases in ONSD during laparoscopic bariatric surgery. Eligible patients undergoing elective laparoscopic bariatric surgery will be randomly assigned to one of two groups. In the conventional group, pneumoperitoneum will be established before reverse Trendelenburg positioning. In the intervention group, reverse Trendelenburg positioning will be applied before pneumoperitoneum creation.

ONSD measurements will be performed using ocular ultrasonography at predefined perioperative time points. Hemodynamic parameters, including mean arterial pressure and heart rate, as well as respiratory variables including end-tidal carbon dioxide and peak airway pressure, will also be recorded.