Quantifying the cerebral metabolic rate of oxygen by combining diffuse correlation spectroscopy and time-resolved near-infrared spectroscopy

Abstract.  Preterm infants are highly susceptible to ischemic brain injury; consequently, continuous bedside monitoring to detect ischemia before irreversible damage occurs would improve patient outcome. In addition to monitoring cerebral blood flow (CBF), assessing the cerebral metabolic rate of oxygen ($CMRO2$) would be beneficial considering that metabolic thresholds can be used to evaluate tissue viability. The purpose of this study was to demonstrate that changes in absolute $CMRO2$ could be measured by combining diffuse correlation spectroscopy (DCS) with time-resolved near-infrared spectroscopy (TR-NIRS). Absolute CBF was determined using bolus-tracking TR-NIRS to calibrate the DCS measurements. Cerebral venous blood oxygenation ($SvO2$) was determined by multiwavelength TR-NIRS measurements, the accuracy of which was assessed by directly measuring the oxygenation of sagittal sinus blood. In eight newborn piglets, $CMRO2$ was manipulated by varying the anesthetics and by injecting sodium cyanide. No significant differences were found between the two sets of $SvO2$ measurements obtained by TR-NIRS or sagittal sinus blood samples and the corresponding $CMRO2$ measurements. Bland–Altman analysis showed a mean $CMRO2$ difference of $0.0268±0.8340mL$$O2/100g/min$ between the two techniques over a range from 0.3 to 4 mL $O2/100g/min$.