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 (Smv O 2 ) and cerebral (rS c O 2 ) 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 Smv O 2 with relative (INVOS ® ) and absolute (Foresight ® ) rS c O 2 measurements. Methods Forty-two consenting patients undergoing elective off-pump coronary artery bypass grafting were included. Two INVOS and two Foresight sensors continuously registered rS c O 2 . Smv O 2 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 Smv O 2 compared with rS c O 2 measurements by Foresight and INVOS, respectively, during haemodynamic changes. After adjusting for this time delay, the correlation between Smv O 2 and rS c O 2 increased from r =0.25 to 0.75 ( P r =0.28 to 0.73 ( P c O 2 values (range 58–89% for Foresight and 28–95% for INVOS). Changes in rS c O 2 in response to acute haemodynamic alterations were significantly more pronounced with INVOS compared with Foresight ( P Conclusions Considering the important time delay with Smv O 2 , rS c O 2 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 rS c O 2 measurements demonstrated significant differences in measured rS c O 2 values and in the magnitude of rS c O 2 changes during haemodynamic alterations.