Near-infrared spectroscopy versus compartment pressure for the diagnosis of lower extremity compartmental syndrome using electromyography-determined measurements of neuromuscular function

Background: Compartmental syndrome (CS) is difficult to diagnose in intensive care unit patients. Compartment perfusion pressure (CPP) is an invasive, indirect measure of ischemia. Near-infrared spectroscopy is noninvasive, and directly measures ischemia by transmitting light through tissues at wavelengths that react with hemoglobin to provide percent tissue oxygen saturation (StO₂). Animal studies demonstrate that StO₂ is superior to CPP for detecting CS. However, there are no studies in humans comparing StO₂ with CPP. We hypothesized that StO₂ can reliably detect CS, and is superior to CPP. Methods: CS was induced in 15 human volunteers using a standard calf compression model. At 30-minute intervals, compression was increased to reduce StO₂ from baseline (86% ± 4%) to 60%, 40%, 20%, and < 10%, with simultaneous recording of CPP. Outcome variables included deep peroneal nerve conduction assessed by electromyography, cutaneous peroneal nerve sensitivity using Semmes-Weinstein monofilanients, and pain (visual analog scale). Results: Both StO₂ and CPP significantly correlated with all ischemia outcome variables (p < 0.001). Receiver operating characteristic curves of deep peroneal nerve conduction demonstrated that StO₂ had higher sensitivity than CPP for detecting > 50% block. For example, when specificity was 83% for StO₂ and 84% for CPP, sensitivity was 85% versus 56%, respectively (p = 0.02). When specificity for both was 72%, sensitivity was 94% for StO₂ versus 76% for CPP (p = 0.04). Conclusion: In intensive care unit patients who cannot alert physicians to symptoms, near-infrared spectroscopy may help clinicians to avoid delayed or unnecessary prophylactic fasciotomy, and provides the benefits of a continuous, non-invasive monitoring technique.