Study objective: We determine the utility of tissue oxygen saturation monitoring in diagnosing necrotizing fasciitis of the lower extremities.
Methods: We prospectively studied patients who met the criteria of soft tissue infection throughout the lower extremities by tissue oxygen saturation monitoring (with near-infrared spectroscopy) over the middle third of possible involved areas. Cases with evidence of chronic venous stasis, peripheral vascular disease, shock, and systemic hypoxia were excluded. Biceps and contralateral unaffected leg areas were measured as references. The tissue oxygen saturation reading for each area was compared with those finally diagnosed as necrotizing fasciitis and those with only simple soft tissue infection. The tissue oxygen saturation reading was presented as mean+/-SD. Receiver operating characteristic (ROC) curves were used to determine a cutoff value of tissue oxygen saturation reading for early diagnosis of necrotizing fasciitis.
Results: Two hundred thirty-four consecutive patients were enrolled. Nineteen patients (group N) were confirmed to have necrotizing fasciitis, whereas the remaining 215 patients (group C) had only cellulitis. The tissue oxygen saturation reading measured over the biceps muscle was 86%+/-11% in group N and 85%+/-12% in group C. In group N, the leg with necrotizing fasciitis had a tissue oxygen saturation reading of 52%+/-18% throughout the involved site, whereas the tissue oxygen saturation reading measured in the comparative values found in group C was 84%+/-7% (difference 95% confidence interval [CI] 22% to 29%). After fasciotomy, the tissue oxygen saturation reading of the leg with necrotizing fasciitis returned to 82%+/-17% (95% CI 23% to 28% compared with prefasciotomy value) in group N. At the cutoff value of a tissue oxygen saturation reading less than 70% (area under the curve 0.883; 95% CI 0.817 to 0.949) defined by ROC curve, the test revealed a sensitivity of 100% (95% CI 82% to 100%), a specificity of 97% (95% CI 94% to 99%), and an accuracy of 97% (95% CI 95% to 99%).
Conclusion: The low tissue oxygen saturation reading values measured by near-infrared spectroscopy throughout the involved areas of the lower extremities are of value in identifying necrotizing fasciitis. This method may offer a reliable noninvasive method of assessing lower extremities at risk for necrotizing fasciitis, at least for a selected patient population.