, Kok Meng John Chan and John R. Pepper
(1)
Department of Cardiothoracic Surgery Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, UK
Introduction
Surgery on the ascending aorta and aortic root is indicated for aortic aneurysms, dissections and dilatation of the aorta with bicuspid aortic valves. The diseased aorta is replaced with a prosthetic graft, with or without replacement or repair of the aortic valve.
Cannulation Strategies
The site of cannulation for cardiopulmonary bypass is determined by the extent of the aorta which needs to be replaced. If only the proximal ascending aorta and root needs replacement, cannulation of the distal ascending aorta and right atrium is performed. More often, surgery involves the more distal ascending aorta and the proximal aortic arch. In such cases, cannulation of the axillary artery or femoral artery is necessary. Bicaval cannulation is performed if axillary artery cannulation is used. In some cases, it may be necessary to establish hypothermic circulatory arrest to perform an adequate distal anastomosis to healthy aortic tissue. Cannulation of the axillary artery allows for selective antegrade cerebral perfusion during the period of circulatory arrest. Cannulation of the left carotid artery can be performed, in addition, for complete cerebral perfusion. Cannulation of the left subclavian artery may well help to protect against spinal cord ischaemia.
Femoral Artery Cannulation
Cannulation of the common femoral artery is easily performed. However, this technique should be avoided in elderly patients with atherosclerotic aortas or in aortic dissections due to the risk of retrograde embolization and in patients with peripheral vascular disease due to the risk of limb ischaemia.
A 2–3 in. incision is made along the skin crease at the site of the femoral pulse. A vertical incision can also be performed. Dissection is continued until the femoral artery is exposed, both anteriorly and laterally. Care should be taken to ensure that the common femoral artery is exposed proximal to its bifurcation into the superficial femoral artery and the femoral profunda artery where it is of maximal size. Tapes are passed around the femoral artery proximally and distally to allow adequate control of the artery and a snugger passed through the proximal tape. A purse string suture is placed at the femoral artery at the site of the intended cannulation.
Cannulation of the femoral artery is performed by occluding the femoral artery proximally and distally with vascular clamps, incising the femoral artery horizontally with fine scissors and inserting an appropriately sized cannula directed superiorly. The proximal vascular clamp is released to allow passage of the cannula, followed by the distal vascular clamp. Tightening of the purse string suture and the snugger on the proximal tape to the femoral artery and tying this to the cannula secures it in position and prevents leakage. The cannula is then connected to the cardiopulmonary bypass circuit. Femoral artery cannulation can also be performed by the Seldinger technique, inserting a guidewire through a needle into the femoral artery, followed by dilation with a dilator and then, finally, insertion of an extended cannula.
Right Axillary Artery Cannulation
A horizontal incision is made about 1 cm below the middle third of the right clavicle. Dissection is continued to the pectoralis major muscle which is separated in the direction of its fibres. The axillary vein lies immediately anterior to the artery and needs to be retracted with tapes or slings inferiorly. The axillary artery is exposed, both anteriorly and either side of it, to allow passage of vascular loops or small tapes to gain control of it. If selective antegrade cerebral perfusion is planned, the innominate artery is mobilised proximal to its bifurcation with the subclavian and right common carotid arteries so that a cross-clamp can be applied here to maintain perfusion of the right carotid artery during the period of systemic circulatory arrest.
Purse string sutures are placed on the axillary artery at the site of the intended cannulation. The axillary artery is then occluded with vascular clamps or with a side biting clamp, proximally and distally to the site of the intended cannulation. A longitudinal incision is made on the artery with a pair of fine scissors. An 8 mm bevelled prosthetic graft is then sutured onto it in an end-to-side fashion, using a continuous 5/0 polypropylene suture. The prosthetic graft is then cut to about 3 in. in length. A 24 Fr elongated arterial cannula is inserted into it at one end for about 3–4 cm. This will fit snugly into the prosthetic graft. The cannula remains in the prosthetic graft and is not advanced into the axillary artery. The graft is then secured with thick ties onto the cannula, securing it in position and avoiding leakage and the cannula is connected to the cardiopulmonary bypass circuit. An extra limb for arterial perfusion in the cardiopulmonary bypass circuit is advisable in case inadequate flow is achieved through the 24 Fr cannula, in which case, additional cannulation of the aorta or the femoral artery can be performed.
Antegrade perfusion through this cannula achieves perfusion of the right arm and the systemic circulation through the aortic arch. A clamp is placed on the innominate artery during periods of hypothermic circulatory arrest to allow selective antegrade perfusion of the brain through the right common carotid artery. At the end of the operation, following removal of the cannula from the prosthetic graft, the side graft is trimmed close to its anastomosis with the axillary artery and oversewn with continuous 4/0 polypropylene.
Ascending Aortic Aneurysm Replacement
Replacement of an ascending aortic aneurysm limited to the proximal ascending aorta can be performed by placement of a cross-clamp in the proximal aortic arch and construction of the distal aortic anastomosis. If the aneurysm extends more distally, this anastomosis may need to be performed under hypothermic circulatory arrest without a cross-clamp in place. An aneurysm encroaching on the innominate artery may require a hemiarch replacement.
Cardiopulmonary bypass is commenced and a cross-clamp is applied to the distal ascending aorta. Cardioplegic arrest is achieved by cold blood cardioplegia, delivered retrogradely into the coronary sinus. The aneurysm is excised by transecting the aorta proximally about 1 cm above the sinotubular junction and distally about 1–2 cm below the aortic cross-clamp. Care should be taken to avoid injury to the right pulmonary artery, which lies behind the ascending aorta. Further cardioplegia is delivered antegradely directly into the coronary ostia and every 20 min. If necessary, hypothermic circulatory arrest can be performed. The patient is cooled to the desired temperature, depending on whether antegrade cerebral perfusion is used and the extent of surgery planned, and ice bags are placed around the head. Once the desired temperature is reached, the patient is placed in the Trendelenburg position, the circulation is stopped and allowed to drain and the cross-clamp is removed. If axillary artery cannulation is used, a cross-clamp is placed across the innominate artery and flow resumed, achieving selective antegrade cerebral perfusion through the right common carotid artery while maintaining systemic circulatory arrest. To achieve complete antegrade cerebral perfusion, the left common carotid artery can be cannulated, either intra-luminally with a balloon-tipped catheter or, in the standard fashion, with the placement of a purse string suture on the anterior carotid artery wall followed by cannulation with a fine-tipped, right-angled cannula.
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