RecruitingProcedureComparing Hypothermic Temperatures During Hemiarch SurgeryHypothermic circulatory arrest is an important surgical technique, allowing complex aortic surgeries to be performed safely. Hypothermic circulatory arrest provides protection to cerebral and visceral organs, but may result in longer cardiopulmonary bypass times during surgery, increased risks of bleeding, inflammation, and neuronal injury. To manage these consequences, a trend towards warmer core body temperatures during circulatory arrest has emerged. This trial will randomize patients to either mild (32°C) or moderate (26°C) hypothermia during aortic hemiarch surgery to determine if mild hypothermia reduces the length of cardiopulmonary bypass time and other key measures of morbidity and mortality.