Relation Between Mixed Venous Oxygen Saturation and Cerebral Oxygen Saturation Measured by Absolute and Relative Near-Infrared Spectroscopy During Off-pump Coronary Artery Bypass Grafting

Background We hypothesized that previously reported contradictory results regarding the equivalence of mixed venous (SmvO2) and cerebral (rScO2) oxygen saturation might be related to time delay issues and to measurement technology. In order to explore these two factors, we designed a prospective clinical study comparing SmvO2 with relative (INVOS®) and absolute (Foresight®) rScO2 measurements. Methods Forty-two consenting patients undergoing elective off-pump coronary artery bypass grafting were included. Two INVOS and two Foresight sensors continuously registered rScO2. SmvO2 was measured continuously via a pulmonary artery catheter. Data were assessed by within- and between-group comparisons and correlation analysis. Results A similar time delay of 19 (4) and 18 (4) s was found for SmvO2 compared with rScO2 measurements by Foresight and INVOS, respectively, during haemodynamic changes. After adjusting for this time delay, the correlation between SmvO2 and rScO2 increased from r=0.25 to 0.75 (P Conclusions Considering the important time delay with SmvO2, rScO2 seems to reflect more appropriately acute haemodynamic alterations. This might suggest its use as a valid alternative to invasive monitoring of tissue oxygen saturation. Relative and absolute rScO2 measurements demonstrated significant differences in measured rScO2 values and in the magnitude of rScO2 changes during haemodynamic alterations.