[A comparative study of transcranial Doppler sonography and near-infrared spectroscopy for the assessment of cerebrovascular CO2 reactivity].

Simultaneous measurements of time averaged mean blood flow velocity in the right middle cerebral artery (Vmca) by transcranial Doppler sonography (TCD) and regional cerebral oxygen saturation (rSo2) by near-infrared spectroscopy (NIRS) were performed in 30 subjects under propofol /fentanyl/ oxygen anesthesia. End-tidal CO2 pressure (PetCO2) was controlled by adjusting minute ventilation. A paired measurements of Vmca and rSo2 was repeated at PetCO2 of 50, 45, 40, 35, 30, and 25 mmHg in each subject. Relative Vmca (rVmca) was also calculated as a relative expression of Vmca at PetCO2 of 40 mmHg. Linear regression analysis was applied to determine the individual best fit relationship of these, parameters. There were significant linear correlations between PetCO2 and Vmca (R > 0.94, P < 0.01), between PetCO2 and rVmca (R > 0.94, P < 0.01), between PetCO2 and rSo2 (R > 0.92, P < 0.01), and between rSo2 and Vmca (R > 0.88, P < 0.05) in each subject. Furthermore, there was a significant linear correlation between rVmca based CO2 reactivity and rSo2 based CO2 reactivity (R = 0.60, P < 0.001). These results indicate that measurements of rSo2 may be an alternative method for evaluating cerebrovascular CO2 reactivity when poor ultrasound window.