The effect of tourniquet application on optic nerve sheath diameter and cerebral oxygenation during lower extremity...

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 <5 mm), and rSO2, EtCO2, and tourniquet times were compared between groups. Correlation analyses were conducted to assess the relationships among these variables. ONSD and EtCO2 values measured at 5 and 15 minutes after tourniquet deflation were significantly higher than pre-deflation values. Bilateral rSO2 values following tourniquet deflation were significantly higher compared with measurements obtained before anesthesia induction, tourniquet inflation, and immediately prior to deflation. At 5 minutes after tourniquet deflation, EtCO2 levels and tourniquet duration were significantly higher in patients with ONSD ≥5 mm compared with those with ONSD <5 mm. Moderate, positive, and statistically significant correlations were observed between EtCO2 and ONSD, EtCO2 and bilateral rSO2, and between ONSD and tourniquet duration at this time point. Tourniquet deflation during lower extremity surgery is associated with transient increases in EtCO2, ONSD, and cerebral oxygenation parameters. These findings suggest significant physiological associations between tourniquet duration, carbon dioxide levels, and surrogate markers of ICP and cerebral oxygenation; however, further studies incorporating direct ICP measurements and clinical neurological outcomes are required to determine their clinical significance.