Retrograde Versus Antegrade Perfusion in Low-Moderate Hypothermia for Aortic Arch Surgery

Inclusion Criteria: 1. \> 18 years of age 2. Participant's that are scheduled for elective proximal aortic reconstructive surgery (ascending aorta + aortic valve or root) with concomitant proximal hemi-arch replacement via median sternotomy Exclusion Criteria: 1. \< 18 years of age 2. history of symptomatic cerebrovascular disease, e.g., prior stroke with residual deficit 3. current alcoholism (\> 2 drinks/day) 4. current psychiatric illness requiring pharmacotherapy 5. current drug abuse (any illicit drug use in the past 3 months) 6. hepatic insufficiency (liver function tests \> 1.5 times the upper limit of normal) 7. severe pulmonary insufficiency (requiring home oxygen therapy) 8. renal failure (serum creatinine \> 2.0 mg/dL) 9. claustrophobic fear 10. unable to read and thus unable to complete the cognitive testing 11. pregnant women 12. patients who score \<19 om the Montreal Cognitive Assessment (MoCA) or ≥27 on the baseline Center for Epidemiological Studies Depression (CES-D) scale 13. patients who have pre-existing unsafe implants for 3 Tesla magnetic resonance imaging (MRI) 14. Patients who have received chemotherapy in the last 12 months or radiation to the brain