Background: Local anesthetics can cause vasoconstriction and disrupt neuronal impulses, reducing regional\r\nblood flow and increasing tissue oxygen consumption. This could alter regional oxygen supply and demand. Because\r\nmicrocirculation modifies during development and oxygen consumption kinetics differ between children and adults,\r\nwe aimed to assess effects of ropivacaine Peripheral Nerve Block (PNB) on regional tissue saturation in children and\r\nyoung adults using Near-Infrared Spectroscopy (NIRS).\r\nMethods: Following Institutional Review Board approval and informed consent, 20 patients undergoing PNB\r\nfor various orthopedic surgeries were studied. NIRS sensors were placed on the operative limb, contralateral limb,\r\nand forehead. Tissue saturations (rSO2) were recorded at baseline and every 5 minutes for 60 minutes following\r\nropivacaine PNB. Mean rSO2 was assessed with repeated measures ANOVA. Correlation of tissue rSO2 with cerebral\r\noximetry was calculated and significance determined with student�s t-test.\r\nResults: In all patients, blocked limb rSO2 decreased significantly compared to control limb 20 minutes after\r\ninjection and remained lower. Control limb rSO2 and cerebral oximetry did not change over time. Non-blocked limb\r\nrSO2 demonstrated weak but significant correlation with cerebral oximetry while blocked limb rSO2 showed no\r\ncorrelation. Mean change in blocked limb rSO2 from baseline was significantly negative compared to a net positive\r\nmean change in the non-blocked limb.\r\nConclusions: Decreased rSO2 following PNB suggests reduced local blood flow due to vasoconstriction,\r\nincreased tissue oxygen consumption, or both. Changes in rSO2 provide an opportunity to develop NIRS as a\r\nnon-invasive tool to identify successful PNB. Local anesthetic-induced decline in rSO2 could have implications in\r\noperative settings with ischemia or low-flow.
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