Low and 'supranormal' central venous oxygen saturation and markers of tissue hypoxia in cardiac surgery patients: a prospective observational study

To characterize incidence of low, normal and “supranormal” central venous oxygen saturation (ScvO2) and the relation to markers of tissue hypoxia, course and outcome in cardiac surgery patients. Prospective, observational study in a university multidisciplinary 50-bed intensive care unit including 205 consecutive patients undergoing elective cardiac surgery. Data were split into training and test data sets and subjected to 50 replications of fivefold cross-validation to estimate lower and upper bounds of ScvO2 indicative of impaired tissue oxygenation. Both low (≤60.8%) and supranormal (≥77.4%) ScvO2 were associated with an unfavorable course, while the logistic EuroSCORE for risk adjustment was comparable between groups. Incidences of abnormal ScvO2 were 13.2% low and 30.7% supranormal. Patients with low ScvO2 and an uneventful course initially presented with normal lactate levels, whereas patients with supranormal ScvO2 displayed consistently higher serum lactate levels. High ScvO2 values were associated with the use of β-mimetics and signs of systemic inflammation. Mortality rates were comparable for patient populations presenting either low (14.8%) or supranormal ScvO2 (7.9%) and higher than normals (0%, p