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 (SctO2) 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 SctO2 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 ∼20% increase in blood pressure using either phenylephrine or ephedrine. RESULTS Data from 24 patients were analyzed. The overall vasopressor-induced relative changes in SctO2 (ΔSctO2) and OEF (ΔOEF) were 3.16% [interquartile range, -0.73% to 6.04%] and -12.5% [interquartile range, -24.0% to -6.19%], respectively. ΔSctO2 negatively correlated with ΔOEF after phenylephrine treatment (Spearman rank correlation coefficient [rs]=-0.76; P=0.007), ephedrine treatment (rs=-0.76; P=0.006), and any treatment (rs=-0.79; P<0.001). ΔSctO2 significantly associated with ΔOEF based on multivariable analysis with ΔOEF, 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 SctO2 and OEF suggests that SctO2 may reflect the cerebral metabolic demand-supply balance during vasopressor treatment. The generalizability of our findings in other clinical scenarios remains to be determined.