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

Abstract

Purpose: To characterize incidence of low, normal and "supranormal" central venous oxygen saturation (ScvO(2)) and the relation to markers of tissue hypoxia, course and outcome in cardiac surgery patients.

Methods: 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 ScvO(2) indicative of impaired tissue oxygenation.

Results: Both low (≤ 60.8%) and supranormal (≥ 77.4%) ScvO(2) were associated with an unfavorable course, while the logistic EuroSCORE for risk adjustment was comparable between groups. Incidences of abnormal ScvO(2) were 13.2% low and 30.7% supranormal. Patients with low ScvO(2) and an uneventful course initially presented with normal lactate levels, whereas patients with supranormal ScvO(2) displayed consistently higher serum lactate levels. High ScvO(2) 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 ScvO(2) (7.9%) and higher than normals (0%, p < 0.001). Lactate was comparably increased in patients that ultimately died, irrespective whether they had low or supranormal ScvO(2) values. In contrast, neither low nor supranormal ScvO(2) was associated with altered gastric pCO(2.)

Conclusions: High ScvO(2) is an under-recognized warning sign for impaired tissue oxygenation in the peri-operative period. Including values ≥ 77.4% as 'normal' impaired performance of ScvO(2) monitoring to predict a complicated perioperative course.