Abstract Body (Do not enter title and authors here): Background: Although neurologic injury commonly occurs following neonatal aortic arch reconstruction, the mechanism(s) are poorly understood. A decrease or inter-hemispheric difference in the electroencephalogram (EEG) Alpha:Delta ratio (A:D) precedes cerebral ischemia during antegrade cerebral perfusion (ACP). However, it is unknown if A:D changes precede neurologic injury during deep hypothermic circulatory arrest (DHCA). We hypothesized during DHCA, the A:D would decrease and that a significant A:D inter-hemispheric difference would precede neurologic injury.

Methods: Neonates requiring aortic arch reconstruction underwent simultaneous quantitative EEG monitoring. Left vs. right hemispheric, anterior, and posterior A:Ds were recorded at baseline, arterial cannulation, cooling, ACP vs. DHCA, and the rewarming phases of the operation. Left vs. right A:D differences > 25% were considered significant for ischemia and the cumulative duration of a significant A:D inter-hemispheric difference was calculated. Post-operative neurologic injury was defined as either stroke or seizure.

Results: From 86 neonates, 16.2 % (14) required DHCA and 83.8 % (72) ACP. There were no significant differences in the pre-operative demographics or baseline A:Ds between groups. Although the A:Ds remained similar during ACP, after 15 minutes the hemispheric A:Ds decreased significantly during DHCA (Figure 1). Eleven neonates (ACP-7 vs. DHCA-4) developed neurologic injury. The duration of an anterior A:D inter-hemispheric difference > 25% was significantly greater within neonates that developed neurologic injury (25 {IQR:0,65 minutes} vs. 5 {IQR: 0, 15 minutes}; p<0.001). Multivariate analysis demonstrated that the duration of an anterior A:D difference > 25% was independently associated with neurologic injury using either ACP or DHCA (Odds Ratio:1.081, 95% CI: 1.025, 1.141; p-value=0.004).

Conclusion: Unlike ACP, the A:D decreased significantly during DHCA. During either DHCA or ACP, a significant anterior inter-hemispheric A:D difference was independently associated with neurologic injury and suggests the importance of quantifying the A:D during neonatal arch reconstruction.