Effect of lithotomy position on optic nerve sheath diameter in patients undergoing retrograde intrarenal surgery

Background: The lithotomy position is frequently used in perineal examinations, childbirth, and various surgical procedures. This position alters venous return, intra-abdominal pressure, and intrathoracic pressure, which may influence intracranial pressure (ICP). This study evaluated the effect of the lithotomy position on ICP by measuring optic nerve sheath diameter (ONSD) using ultrasonography (USG) in patients undergoing retrograde intrarenal surgery (RIRS). Methods: Fifty-two patients scheduled for elective RIRS were included. Bilateral ONSD measurements were performed by a single operator using USG at seven predefined time points spanning the preoperative, intraoperative, and postoperative periods (T0–T6). Statistical analysis was performed using repeated-measures ANOVA with post hoc testing. Results: ONSD values increased significantly compared with baseline (T0) at all subsequent time points (p < 0.05). The peak value was observed before position correction (T5), corresponding to a 12.5 % increase relative to baseline. After emergence from anesthesia (T6), ONSD decreased but remained 6.3 % above baseline. Conclusion: Both general anesthesia and lithotomy positioning were associated with significant increases in ONSD, suggesting transient ICP elevation. Although partial recovery occurred after position correction and emergence, ONSD values did not fully return to baseline. These findings highlight the potential of ONSD ultrasonography as a noninvasive method for perioperative ICP monitoring. Further studies are needed to clarify the clinical relevance of these changes.