Correlation Between Cerebral Tissue Oxygen Saturation and Oxygen Extraction Fraction During Anesthesia: Monitoring Cerebral Metabolic Demand-supply Balance During Vasopressor Administration

Background:The speculation that cerebral tissue oxygen saturation (SctO(2)) measured using tissue near-infrared spectroscopy reflects the balance between cerebral metabolic rate of oxygen and cerebral oxygen delivery has not been validated. Our objective was to correlate SctO(2) with cerebral oxygen extraction fraction (OEF) measured using positron emission tomography; OEF is the ratio between cerebral metabolic rate of oxygen and cerebral oxygen delivery and reflects the balance between these 2 variables. Materials and Methods:This cohort study was based on data collected in a previously published trial assessing phenylephrine versus ephedrine treatment in anesthetized patients undergoing brain tumor surgery. The variables of interest were measured twice over the healthy hemisphere before surgery: the first measurement performed after anesthesia induction and the second measurement performed after induction of a similar to 20% increase in blood pressure using either phenylephrine or ephedrine. Results:Data from 24 patients were analyzed. The overall vasopressor-induced relative changes in SctO(2) (Delta SctO(2)) and OEF (Delta OEF) were 3.16% [interquartile range, -0.73% to 6.04%] and -12.5% [interquartile range, -24.0% to -6.19%], respectively. Delta SctO(2) negatively correlated with Delta OEF after phenylephrine treatment (Spearman rank correlation coefficient [r(s)]=-0.76; P=0.007), ephedrine treatment (r(s)=-0.76; P=0.006), and any treatment (r(s)=-0.79; P<0.001). Delta SctO(2) significantly associated with Delta OEF based on multivariable analysis with Delta OEF, relative changes in mean arterial pressure, arterial blood oxygen tension, and the bispectral index as covariates (P=0.036). Conclusions:The negative correlation between changes in SctO(2) and OEF suggests that SctO(2) may reflect the cerebral metabolic demand-supply balance during vasopressor treatment. The generalizability of our findings in other clinical scenarios remains to be determined.