Abstract Body (Do not enter title and authors here): Introduction
In patients undergoing cardiac surgery on the aortic arch, hypothermic circulatory arrest (HCA) is utilized to reduce metabolic demand and reduce ischemic neurologic injury. However, the deleterious effects of hypothermia limit the safe arrest time. The use of antegrade cerebral perfusion (ACP) may allow for safe longer arrest times and warmer temperatures. No randomized controlled trial has definitively determined optimal operative strategy, and no gold standard technique exists. Operative techniques and processes vary among practices, and up to 29% of patients do not receive cerebral perfusion during HCA.

Hypothesis
We hypothesize that an ideal ACP flow rate exists that is beneficial for neurocognitive protection during HCA.

Aims
In a canine model of HCA, we evaluated neuroprotection using three ACP flow rates and compared them to Ketamine alone (a potentially beneficial pharmacologic intervention that has been demonstrated to be beneficial during HCA).

Methods
Eighteen animals underwent HCA (90 min) and unilateral cerebral perfusion via the carotid artery at either 2.5, 5, or 10 cc/kg/min. Postoperative neurobehavioral deficit scores and Novel Object Recognition (NOR) testing (a unique methodology to measure memory, executive function, and cognition in the most impacted area of injury) were obtained. Regional brain mitochondrial function and histopathologic injury were compared at 72 hours.

Results
All ACP groups had better neurobehavioral scoring on the Finnish assessment on postoperative day 1 compared to Ketamine alone (p<0.01), and the highest flow (10 cc/kg/min) demonstrated a return to baseline behavior on NOR at 72 hours. Maximal respiration, a measure of mitochondrial function, was better in 10 cc/kg/min compared to Ketamine in the cortex, hippocampus, basal ganglia, and cerebellum (p<0.05). However, only the cortex demonstrated better spare respiratory capacity at 2.5 and 10 cc/kg/min compared to Ketamine alone (p<0.05). On histopathological scoring (n=14), Ketamine resulted in severe global neuronal injury that was statistically different than the 2.5 cc/kg/min group (p < 0.05). No between-group regional brain differences were identified.

Conclusion
Our findings support the incorporation of ACP during cardiac surgery as a reliable neuroprotection strategy in patients undergoing HCA.