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

Abstract

BackgroundWe hypothesized that previously reported contradictory results regarding the equivalence of mixed venous () and cerebral (rScO 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 with relative (INVOS®) and absolute (Foresight®) rScO2 measurements.MethodsForty-two consenting patients undergoing elective off-pump coronary artery bypass grafting were included. Two INVOS and two Foresight sensors continuously registered rScO2. was measured continuously via a pulmonary artery catheter. Data were assessed by within- and between-group comparisons and correlation analysis.ResultsA similar time delay of 19 (4) and 18 (4) s was found for compared with rScO2 measurements by Foresight and INVOS, respectively, during haemodynamic changes. After adjusting for this time delay, the correlation between and rS cO2 increased from r=0.25 to 0.75 (P<0.001) for Foresight, and from r=0.28 to 0.73 (P<0.001) for INVOS. Comparison of Foresight and INVOS revealed significant differences in absolute rS cO2 values (range 58-89% for Foresight and 28-95% for INVOS). Changes in rScO2 in response to acute haemodynamic alterations were significantly more pronounced with INVOS compared with Foresight (P<0.001).ConclusionsConsidering the important time delay with, 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 rS cO2 measurements demonstrated significant differences in measured rScO2 values and in the magnitude of rS cO2 changes during haemodynamic alterations. © 2012 © The Author [2012]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved.