Cannulation Strategy and setting up of cardiopulmonary bypass:
Our preference is antegrade perfusion if at all feasible. Due to the ease and relatively rapid initiation of cardiopulmonary bypass, we have of late preferred to use the direct ascending aorta true lumen cannulation over a guidewire under echocardiographic guidance. In patients who present with rupture or contained rupture of the ascending aorta/root, and/or are extremely unstable to even allow us to do a sternotomy, femoral artery cannulation can still be used. On occasions when the intimal flap has been found occluding the origin of arch vessels, double cannulation with axillary artery plus central or femoral artery cannulation has been performed to maintain both upper and lower body perfusion and achieve uniform systemic cooling.
For venous cannulation, we prefer the right atrium. Often times we cannulate the superior vena cava as well. This additional cannula can be used for retrograde cerebral perfusion during circulatory arrest. However, in an unstable patient with ruptured ascending aorta/root and cardiac tamponade, opening the pericardium can potentially lead to sudden hypertension and potential exsanguination of the patient. In such patients cannulating the femoral vein with a multistage venous cannula is an option. Once on pump and with ongoing systemic cooling, pericardium is opened to allow for controlled decompression. If then the drainage is believed to be inadequate, one can switch to right atrial cannulation.
Most often, Type-A dissection leads to significant aortic regurgitation due to loss of commissural support. This leads to left ventricular distension, especially as the heart fibrillates with systemic cooling. Hence venting of left ventricle is critical. A left ventricle vent advanced through the right superior pulmonary vein is the commonest approach.