The purpose of this study is to compare brain function after surgical circulatory arrest using either antegrade perfusion or retrograde perfusion.

The purpose of this study is to compare brain function after surgical circulatory arrest (surgeon stops the heart-lung machine to work on the heart) in antegrade perfusion versus retrograde perfusion. There are 2 ways to supply blood to the brain, antegrade and retrograde perfusion. In antegrade perfusion, the surgeon accesses one of two arteries that branch off from the aorta (the artery that delivers blood to the rest of the body) to provide blood to the brain. In retrograde perfusion, the surgeon accesses the superior vena cava (large vein bringing blood back to the heart) to supply blood to the brain.

It is standard practice to cool the patient down during this type of surgery to help protect the brain. Despite measures to safeguard brain health, some patients still experience postoperative cognitive decline such as confusion, delirium and agitation. The investigators are conducting this study to see which method of perfusing the brain is superior and decreases the symptoms of confusion, delirium and agitation.

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

The neuroimaging personnel will be blinded to the assignment of the subject.