Abstract Body: Introduction: Cerebral autoregulation (CAR) mechanisms, which maintain cerebral blood flow (CBF) over a range of mean arterial pressures (MAP), are impaired after cardiac arrest. Metrics of CAR impairment can be calculated from MAP and a CBF surrogate. Brain tissue oxygenation (StO₂) derived from near-infrared spectroscopy (NIRS) has been used, but its approximation of CBF is limited. Advanced optical imaging can directly estimate CBF and StO₂ with greater precision.
Aim: Compare CAR metrics derived from advanced optical modalities, including frequency-domain diffuse optical spectroscopy (FD-DOS) and diffuse correlation spectroscopy (DCS), with NIRS.
Hypothesis: CAR metrics derived from FD-DOS and DCS will not be significantly different from each other and NIRS.
Methods: We measured StO₂ and total hemoglobin concentration (HbT) via FD-DOS, blood flow index (BFI) via DCS, and StO₂ via NIRS for up to 8 h during the first 48 h after cardiac arrest. We identified 30-min epochs during which MAP changed more than 15% relative to the mean (Fig 1). Within each epoch, CAR was assessed using a moving-window Pearson correlation between MAP and each FD-DOS, DCS, and NIRS parameter. Pearson r values closer to 1 indicated impaired CAR and 0 to -1 indicated intact CAR. CAR metrics were compared by Kruskal-Wallis, and post-hoc pairwise comparisons with Bonferroni correction identified differences between metrics. Unfavorable outcomes were defined as hospital discharge PCPC score of 4-6.
Results: We identified 37 epochs of MAP change in 4 children (2 favorable, 2 unfavorable outcomes). We found significant differences between all 4 CAR metrics (p<0.001; Fig 2). In pairwise comparisons, StO₂ from FD-DOS and NIRS did not differ (p>0.05). The DCS BFI metric exhibited more severe CAR impairment than NIRS StO₂ across all subjects (p<0.05), with larger differences in unfavorable outcomes (0.62 [0.45,0.78] vs. 0.09 [-0.09,0.17], p<0.001) than in favorable outcomes (0.15 [0.05,0.31] vs. 0.15 [0.10,0.32], p>0.05).
Conclusion: CAR metrics derived from advanced optical modalities yielded variable results compared to NIRS in children after cardiac arrest. The DCS BFI metric demonstrated more severe CAR impairment than StO₂ from either NIRS or FD-DOS, particularly in patients with unfavorable outcomes, suggesting that a more direct measure of CBF may be more sensitive to CAR impairment in post-arrest patients with deficiencies in cerebral oxygen delivery or utilization.