Continuous mixed venous and central venous oxygen saturation in cardiac surgery with cardiopulmonary bypass

Replacing mixed venous oxygen saturation (SvO2) monitoring by central venous oxygen saturation (ScvO2) monitoring in order to avoid the use of a pulmonary artery catheter and its related complications is still controversial in the setting of cardiac surgery. The influence of surgery, cardiopulmonary bypass and anaesthesia drugs on the relationship between SvO2 and ScvO2 has never been studied.

Fifteen patients scheduled for cardiac surgery with cardiopulmonary bypass were included in the study. SvO2 (from the pulmonary artery) and ScvO2 (from the superior vena cava) were continuously measured with fibre-optic catheters from induction of anaesthesia to 24 h postoperatively.

A total of 9267 pairs of measurements were recorded. Mean bias between SvO2 and ScvO2 was 4.4% with limits of agreement of -13.6 and +22.5%, respectively. Trends of SvO2 and ScvO2 values followed very different patterns for some patients. Surgery, cardiopulmonary bypass and anaesthesia drugs did not influence the relationship between the two methods.

Because of the large interindividual variability in the difference between SvO2 and ScvO2, the measure of ScvO2 should not replace the measure of SvO2 with a pulmonary artery catheter for the management of patients undergoing cardiac surgery with cardiopulmonary bypass.