There is a need to understand how long anesthetic drugs last in the brain during surgery on the ascending aorta or aortic arch. Drugs can have a prolonged effect when blood temperature is made cold therefore the influence of temperature needs to be studied. This type of surgery allows us to answer questions about how anesthetic drugs behave when they are given during a routine portion of surgery. Patients will be provided with anesthetic drugs during surgery while on a heart lung machine. After the drug is injected into the heart lung machine it will be delivered to the brain to provide more sleep and pain relief. Immediately after the injection of anesthetic drugs, blood samples will be taken from an existing intravenous line in the neck and plasma drug concentrations measured. This will help us to understand how long drugs last in the brain during this type of surgery.