Abstract
INTRODUCTION: Near-infrared spectroscopy (NIRS) noninvasively measures peripheral tissue oxygen saturation (StO₂). NIRS may be utilized along with a vascular occlusion test, in which limb blood flow is temporarily occluded and released, to quantify a tissue bed's rate of oxygen exchange during ischemia and recovery. The objective of this study was to test the hypothesis that NIRS-derived StO₂ measures (StO₂ initial, StO₂ occlusion and StO₂ recovery) identify patients who are in shock and at increased risk of organ dysfunction (Sequential Organ Failure Assessment (SOFA) score ≥ 2 at 24 hours) and dying in the hospital. METHODS: This prospective, observational study comprised a convenience sample of three cohorts of adult patients (age > 17 years) at three urban university emergency departments: (1) a septic shock cohort (systolic blood pressure < 90 after fluid challenge; the "SHOCK" cohort, n = 58), (2) a sepsis without shock cohort (the "SEPSIS" cohort, n = 60) and emergency department patients without infection (n = 50). We measured the StO₂ initial, StO₂ occlusion and StO₂ recovery slopes for all patients. Outcomes were sepsis syndrome severity, organ dysfunction (SOFA score at 24 hours) and in-hospital mortality. RESULTS: Among the 168 patients enrolled, mean initial StO₂ was lower in the SHOCK cohort than in the SEPSIS cohort (76% vs 81%), with an impaired occlusion slope (-10.2 and 5.2%/minute vs -13.1 and 4.4%/minute) and an impaired recovery slope (2.4 and 1.6%/second vs 3.9 and 1.7%/second) (P < 0.001 for all). The recovery slope was well-correlated with SOFA score at 24 hours (-0.35; P < 0.001), with a promising area under the curve (AUC) for mortality of 0.81. The occlusion slope correlation with SOFA score at 24 hours was 0.21 (P < 0.02), with a fair mortality AUC of 0.70. The initial StO₂ was significantly but less strongly correlated with SOFA score at 24 hours (-0.18; P < 0.04), with a poor mortality AUC of 0.56. CONCLUSIONS: NIRS measurements for the StO₂ initial, StO₂ occlusion and StO₂ recovery slope were abnormal in patients with septic shock compared to sepsis patients. The recovery slope was most strongly associated with organ dysfunction and mortality. Further validation is warranted. TRIAL REGISTRATION: NCT01062685.