The Pharmacokinetics of Opioids and Sedative/Hypnotics During Selective Cerebral Perfusion

Overview

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.

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. A prior study that enrolled 6 patients has shown that the anesthetic administration is safe and feasible. Patients had no problems related to anesthesia or surgery. All patients left the hospital in stable condition.