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

Abstract

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 [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). 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.