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

Aim: This study aimed to investigate the effect of tourniquet application on optic nerve sheath diameter (ONSD) and cerebral oxygenation during lower extremity surgery. Materials and Methods: Forty-three ASA I-II patients aged >18 years scheduled for lower extremity surgery using tourniquet application under general anesthesia were included in the study. Cerebral oxygen saturation (rSO2) was measured using near-infrared spectroscopy in addition to routine hemodynamic monitoring. Bilateral basal ONSDs were measured by ultrasonography. Anesthesia was maintained using sevoflurane and remifentanil after routine anesthesia induction. Before initiating the surgery, the tourniquet was inflated to a pressure of 300 mmHg. Intraoperatively monitored parameters and ONSD measurements were recorded at regular intervals. Tourniquet application time was recorded. All the monitored data of the patients were evaluated according to the time intervals. Standardized mini-mental state examination (MMSE) was also applied pre-and postoperatively to the patients. Patients were divided into groups according to ONSD values (≥5 mm and <5 mm) and medical history of hypertension (HT). These groups were then compared in terms of rSO2, end-tidal carbon dioxide (EtCO2), tourniquet duration, and MMSE scores. Results: The heart rate and mean arterial pressure (MAP) values of the patients at all time intervals were found to be lower than those before anesthesia induction (p < 0.001). The MAP values, which were measured after tourniquet inflation, were higher than those before tourniquet application (p < 0.05). However, a decrease in the MAP values was observed after the tourniquet deflation (p < 0.001). It was found that the EtCO2 and ONSD values, which were measured 5 and 15 minutes after tourniquet deflation, were higher than those before tourniquet deflation (p < 0.001). All intraoperative ONSD values of the patients were higher than the pre-induction values (p < 0.001). The bilateral rSO2 values after tourniquet deflation were higher than those before anesthesia induction and before tourniquet inflation and deflation (p < 0.05). At 5 minutes after tourniquet deflation (T9), EtCO2 values and tourniquet time were higher in the ONSD ≥5 mm group compared with the ONSD <5 mm group (p < 0.05). In the ONSD <5 mm group, the postoperative MMSE score at 1. month was higher than that on preoperative and postoperative days 1 (p < 0.05). Basal MAP values of the patients with HT were higher than those of the patients without HT. Additionally, right sided rSO2 and MAP values at T9 were low, and ONSD values at T9 were high (p < 0.05). There was a moderate, positive, and significant relationship between EtCO2 value at T9 and both ONSD and right/left rScO2 values at T9 (p < 0.05). A moderate, positive, and significant relationship was also found between ONSD and tourniquet duration at T9 (p = 0.038). Conclusion: This study evaluated the effect of tourniquet application on ONSD and cerebral oxygenation during lower extremity surgery. It was observed that there was a significant increase in ONSD and rSO2 values with tourniquet deflation, and this increase was associated with the EtCO2 value and the length of tourniquet duration. MAP and rSO2 values following tourniquet removal in patients with a history of HT were lower, but ONSD values were higher. There was no decrease in MMSE score suggesting cognitive dysfunction due to tourniquet application. We believe that possible complications in surgeries using tourniquet can be prevented by keeping the tourniquet usage time short, preventing an increase in EtCO2 after tourniquet deflation, and providing sufficient monitoring for cerebral oxygenation and ONSD. Key Words: Tourniquet, Optic Nerve Sheath Diameter, Cerebral Oxygenation