Baseline patient characteristics will be collected in the pre-operative period and will include age, sex, weight, height, blood pressure, heart rate, temperature, comorbidities, type of aortic disease, and American Society of Anesthesiologists (ASA) grade. Prior to initiation of CPB, several factors will be recorded including arterial blood pressure, heart rate, cerebral oximetry, bispectral index score (BIS), latency & amplitude of SSEP, frequency of EEG background, cerebral blood flow assessed by middle cerebral artery (MCA) velocity on TCD, and nasopharyngeal temperature. During cooling, BIS scores, cerebral oximetry, and MCA velocity by TCD will be noted for each 0.5o C decrement in nasopharyngeal temperature; the duration from CPB initiation to 3 characteristic EEG changes (1. rhythmic delta, 2. Generalized periodic epileptiform discharge (GPED), 3. burst suppression) as defined by the neurophysiologist, the duration from CPB initiation to 2 characteristic SSEP changes (1. latency increase of >10%, 2. amplitude decrease of 50% from baseline), and hemodynamics at each 1o C nasopharyngeal temperature drop will also be recorded. At the time of HCA, several factors will be documented including nasopharyngeal temperature, duration from CPB initiation (the primary endpoint measure), total opioid doses, cerebral oximetry, BIS score, MCA velocity by TCD, hemodynamics. During rewarming, factors will be documented in the same fashion and at the same intervals as during cooling. At the first attempt at separation from CPB, documented factors will include BIS score, cerebral oximetry, MCA velocity by TCD, duration from CPB reinstitution to first attempt at separation, total dose of study drug, nasopharyngeal temperature, and hemodynamics. Finally, in addition to any Adverse Events (AEs) that may have occurred, data relating to length of ICU stay, length of hospital stay, in-hospital mortality, in-hospital acute kidney injury (defined as a 50% rise from baseline in serum creatinine, and of at least 0.3 mg/dl or need for dialysis), in-hospital stroke, in-hospital myocardial infarction, and discharge disposition from hospital (home, skilled nursing facility, other institution) will be recorded postoperatively.