Cannulation for Cardiopulmonary Bypass—Be Careful Where You Point that Thing!
Jason Z. Qu MD
Edwin G. Avery IV MD
A 64-year-old female insulin-dependent diabetic with severe aortic atheromatous disease and peripheral vascular disease presents for coronary revascularization. Surgery is planned to include the use of cardiopulmonary bypass (CPB). Intraoperative pre-CPB transesophageal echocardiography exam reveals a “mine field” of an ascending aorta with multiple mobile elements and protruding atheromatous plaques. The surgeon requests your help to find an appropriate site for insertion of the arterial perfusion cannula. What is your move in this situation? An epiaortic scan will help better define the extent of atheromatous disease in the ascending aorta. The epiaortic scan did not suggest that it would be safe to place the cannula in the ascending aorta because the stroke risk would be as big as the state of Texas! The surgeon begins to prepare for cannulation of the left femoral artery. Is your left radial arterial line appropriate for systemic pressure monitoring? Yes, but given that the surgical plan involves femoral cannulation in a severely diseased aorta, the patient still has a high risk of stroke from retrograde emboli (e.g., like kicking your foot upstream in a brook where the bottom is covered with moss and loose sand, the upstream current stirs up a load of dirt and debris). The key to placing the cannula in this patient is to recognize that it is going to be difficult to minimize the stroke risk, and iatrogenic aortic dissection will also be of major concern.
Cannulation for more complex cardiac surgical operations is not quite as “cookbook” as it may be for coronary surgery. Although the ascending aorta is the most common site of arterial cannulation for CPB, the presence of ascending aortic aneurysms, dissections, severe atherosclerosis, or previous ascending aortic surgery may preclude safe cannulation in this region. In cannulating an ascending aorta that has severe atheromatous disease, one must ensure that the major force of the arterial cannula flow stream is not directed at a focus of aortic atheromatous disease (i.e., creating “the sand blasting effect”) in order to minimize the risk of stroke. Optimal selection of the aortic cannulation site is facilitated with epiaortic ultrasound assessment. Alternative sites for arterial cannulation include the femoral artery, axillary artery, innominate artery, common carotid artery, and cardiac apex. The different
cannulation sites will have unique implications for perfusion techniques and hemodynamic monitoring.
cannulation sites will have unique implications for perfusion techniques and hemodynamic monitoring.
FEMORAL ARTERY CANNULATION
The femoral artery is the most common alternative site for CPB cannulation. This vessel is readily accessible and is therefore often used for cannulation to emergently initiate CPB, or when the ascending aorta is not suitable for cannulation such as in an acute ascending aortic dissection. CPB can be initiated with cannulation of the femoral artery and femoral vein or vena cava. On initiation of CPB, the arterial blood flows retrograde through the aorta. In select emergent cases (e.g., massive pulmonary embolism), femoral cannulation can be accomplished under local anesthesia to avoid the potential hemodynamic collapse that may accompany induction of general anesthesia (related to the blunting of sympathetic outflow) and the initiation of positive-pressure ventilation.
In the case of aortic dissection or severe aortic atherosclerosis, the descending aorta and femoral artery are often involved. Retrograde perfusion via femoral cannulation may elevate the dissected intima, causing malperfusion with consequent neurologic injury or visceral organ ischemia, or it may cause retrograde embolization from the atherosclerotic aortic wall. Commonly, the right femoral artery is cannulated in preparation for CPB in patients with an aortic dissection that involves the descending thoracic aorta because it is more common for the dissection to extend into the left femoral artery.
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