The effect of tourniquet application on optic nerve sheath diameter and cerebral oxygenation during lower extremity surgery: A prospective observational study

Tourniquet deflation during lower extremity surgery is associated with abrupt physiological changes that may influence intracranial pressure (ICP) and cerebral oxygenation. This prospective observational study aimed to evaluate changes in ICP following tourniquet deflation using ultrasonographic optic nerve sheath diameter (ONSD) measurements and to investigate their association with cerebral oxygenation parameters. This prospective observational study included 43 adult patients undergoing lower extremity surgery with tourniquet application under standardized general anesthesia. In addition to routine hemodynamic monitoring, bilateral cerebral oxygen saturation (rSO2) was continuously monitored using near-infrared spectroscopy, and ONSD measurements were performed at predefined time points. End-tidal carbon dioxide (EtCO2) levels and tourniquet duration were recorded. Patients were stratified into 2 groups according to ONSD values (≥5 mm and