The purpose of this study is to understand the disposition of sufentanil, midazolam and morphine when the drugs are introduced into the arterial circulation of the brain. Patients undergoing surgery on the ascending aorta or aortic arch often require cessation of blood flow to the organs of the body, while maintaining some degree of blood flow to the brain. In order to achieve organ protection during the circulatory arrest phase of surgery, the body is cooled to a core temperature of 28°C. Various techniques including deep hypothermic circulatory arrest, retrograde cerebral perfusion through the superior vena cava, and partial or bilateral antegrade selective cerebral perfusion have been proposed as means to protect the brain from ischemic injury during surgery on the aortic arch. At our institution selective cerebral perfusion has found success for major aortic surgery. This technique was devised and first employed by DeBakey and associates, to protect the brain during aortic arch surgery with bilateral carotid perfusion [1]. Selective cerebral perfusion requires the surgical construction and placement of a Dacron graft onto the right axillary artery that when connected to a cardiopulmonary bypass machine it will provide 10 ml/kg/min antegrade flow for brain perfusion [2]. Cerebral cooling will also decrease the oxygen demand of the brain. In such a way brain ischemia may be minimized. The nature of major aortic arch surgery requires independent cerebral circulation or selective cerebral perfusion for a finite period of time. The cardiopulmonary bypass machine is allowed to perfuse the brain indirectly by serial flow through the right axillary artery to the innominate artery and finally to the right carotid artery. Any anesthetic drug that is introduced into the cardiopulmonary bypass circuit will be delivered the same way. We will take advantage of this independent circuit to safely deliver anesthetic drugs to the brain via the right carotid artery during surgery.