Value of combined lactate and central venous oxygen saturation measurement in patients with sepsis: a retrospective cohort study

Introduction. Lactate and central venous oxygen saturation (ScvO2) reflect tissue hypoperfusion but each measure is confounded by many additional factors. These confounding factors differ between lactate and ScvO2. Objectives. We postulated that combined assessment of lactate and ScvO2 may yield information beyond that of each measure alone. Specifically we sought to determine whether lactate has different characteristics and predictive value at different levels of ScvO2. Material and methods. We conducted a retrospective analysis of a Derivation cohort and a Validation Cohort of sepsis patients with lactate and ScvO2 measured within the first 4 hours of intensive care unit admission and 12 hours after resuscitation. Patients were grouped according to: 1) ScvO2 < 60 %; 2) 60 % < ScvO2 < 80 %; 3) ScvO2 > 80 %. Results. Lactate was negatively correlated with ScvO2 in the ScvO2 < 60 % group in both cohorts but was not correlated with ScvO2 in the other ScvO2 groups. Using receiver operator characteristic analysis in the Derivation Cohort, in the ScvO2 > 80 % group lactate was predictive of 28-day mortality with an area under the ROC curve (AUC) of 0.94 and an optimal threshold lactate of 3.0 mmol/L. Using this threshold in the ScvO2 > 80 % groups, 28-day mortality was 32.7 %. Conclusions. Lactate has different characteristics and predictive value at different levels of ScvO2. When ScvO2 < 60 % correlation between lactate and ScvO2 is consistent with a degree of oxygen supply limitation. When ScvO2 > 80 % lactate > 3.0 mmol/L is predictive of mortality.