Patients undergoing thoracic aortic surgery at Duke University Medical Center (DUMC) requiring hypothermic circulatory arrest (HCA) and neurophysiologic monitoring (NIOM) will give written informed consent and be enrolled into the study. Exclusion criteria will include previously documented allergy to nicardipine and age less than 18 years. Patients will then be randomized to one of two study groups: general anesthesia with or without nicardipine. Pre-operatively they will undergo clinical evaluation determined by the attending surgeon and anesthesiologist. During the pre-induction time period, all usual monitors and intravenous devices will be placed at the discretion of the attending anesthesiologist. In addition to the standard anesthetic monitors (Bispectral Index [BIS] and cerebral oximetry), transcranial Doppler (TCD) will be placed. Furthermore, the neurophysiology technician will place both standard EEG and somatosensory evoked potential (SSEP) electrode configurations. During the pre-induction time period, midazolam use will be at the discretion of the anesthesiologist but will be limited to a maximum dose of 0.1 mg/kg; other benzodiazepines will not be allowed. Opioid (fentanyl) administration will be at the discretion of the anesthesiologist. Total benzodiazepine and opioid doses will be recorded and converted to midazolam and fentanyl equivalents for subsequent analysis.