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

Background and objective Replacing mixed venous oxygen saturation (SvO 2 ) monitoring by central venous oxygen saturation (ScvO 2 ) 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 SvO 2 and ScvO 2 has never been studied. Methods Fifteen patients scheduled for cardiac surgery with cardiopulmonary bypass were included in the study. SvO 2 (from the pulmonary artery) and ScvO 2 (from the superior vena cava) were continuously measured with fibre-optic catheters from induction of anaesthesia to 24 h postoperatively. Results A total of 9267 pairs of measurements were recorded. Mean bias between SvO 2 and ScvO 2 was 4.4% with limits of agreement of ―13.6 and +22.5%, respectively. Trends of SvO 2 and ScvO 2 values followed very different patterns for some patients. Surgery, cardiopulmonary bypass and anaesthesia drugs did not influence the relationship between the two methods. Conclusion Because of the large interindividual variability in the difference between SvO 2 and ScvO 2 , the measure of ScvO 2 should not replace the measure of SvO 2 with a pulmonary artery catheter for the management of patients undergoing cardiac surgery with cardiopulmonary bypass.