The association of near-infrared spectroscopy-derived tissue oxygenation measurements with sepsis syndromes, organ dysfunction and mortality in emergency department patients with sepsis

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.