Validation of a stand-alone near-infrared spectroscopy system for monitoring cerebral autoregulation during cardiac surgery

BACKGROUND:: Individualizing arterial blood pressure (ABP) targets during cardiopulmonary bypass (CPB) based on cerebral blood flow (CBF) autoregulation monitoring may provide a more effective means for preventing cerebral hypoperfusion than the current standard of care. Autoregulation can be monitored in real time with transcranial Doppler (TCD). We have previously demonstrated that near-infrared spectroscopy (NIRS)-derived regional cerebral oxygen saturation (rScO2) provides a clinically suitable surrogate of CBF for autoregulation monitoring. The purpose of this study was to determine the accuracy of a stand-alone "plug-and-play" investigational system for autoregulation monitoring that uses a commercially available NIRS monitor with TCD methods. METHODS:: TCD monitoring of middle cerebral artery CBF velocity and NIRS monitoring were performed in 70 patients during CPB. Indices of autoregulation were computed by both a personal computer-based system and an investigational prototype NIRS-based monitor. A moving linear correlation coefficient between slow waves of ABP and CBF velocity (mean velocity index [Mx]) and between ABP and rScO2 (cerebral oximetry index [COx]) were calculated. When CBF is autoregulated, there is no correlation between CBF and ABP; when CBF is dysregulated, Mx and COx approach 1 (i.e., CBF and ABP are correlated). Linear regression and bias analysis were performed between time-averaged values of Mx and COx derived from the personal computer-based system and from COx measured with the prototype monitor. Values for Mx and COx were categorized in 5 mm Hg bins of ABP for each patient. The lower limit of CBF autoregulation was defined as the ABP where Mx incrementally increased to 0.4. RESULTS:: There was correlation and good agreement between COx derived from the prototype monitor and Mx (r = 0.510; 95% confidence interval, 0.414-0.595; P < 0.001; bias, -0.07 ± 0.19). The correlation and bias between the personal computer-based COx and the COx from the prototype NIRS monitor were r = 0.957 (95% confidence interval, 0.945-0.966; P < 0.001 and 0.06 ± 0.06, respectively). The average ABP at the lower limit of autoregulation was 63 ± 11 mm Hg (95% prediction interval, 52-74 mm Hg). Although the mean ABP at the COx-determined lower limit of autoregulation determined with the prototype monitor was statistically different from that determined by Mx (59 ± 9 mm Hg; 95% prediction interval, 50-68 mm Hg; P = 0.026), the difference was not likely clinically meaningful. CONCLUSIONS:: Monitoring CBF autoregulation with an investigational stand-alone NIRS monitor is correlated and in good agreement with TCD-based methods. The availability of such a device would allow widespread autoregulation monitoring as a means of individualizing ABP targets during CPB.