Ascending and Arch Replacement Operation
The unique considerations in approaching aortic arch surgery concern cerebral protection. The question of how best to protect the brain while providing surgical access to the cerebral vessels is still a subject of controversy and of research. The issues of concern in brain protection involve both minimizing global ischaemia during the mandatory arrest of the circulation during aortic arch surgery and preventing embolisation of air and atheromatous debris from the often very diseased arch during the repair.
Ascending aortic replacement can be just ascending or root and ascending. With regard to arch replacement a number of variations exist, all of which need a different operative strategy:
Diagrams of the above procedures
All of the above procedures are achieved using:
Classic straight Dacron graft
Branched Dacron graft with perfusion side arm
Dumbo graft or flanged graft with perfusion side arm
Dumbo graft or flanged graft with branches and perfusion side arm
Arch aneurysm or dissection.
Nor fit enough for the operation.
A thorough medical history and routine laboratory studies are of extreme importance in evaluating possible symptoms due to the aneurysm and revealing other medical problems in these usually elderly patients. A family history of a ruptured aneurysm is not uncommon, and aids in the decision to recommend surgery. The discovery of other medical conditions may influence the operative approach, allow anticipation and possibly prevention of intraoperative or postoperative complications to which the patient is especially vulnerable, or may contraindicate operation altogether.
Evaluation of an aortic arch aneurysm itself requires a computed tomographic (CT) scan with contrast of the entire aorta. With new multidetector CT scans, the entire aorta can be imaged in tens of seconds with reduced contrast and 3-D reconstructions. However, with advances in MRI, equally detailed images can be obtained, and MRI is becoming the preferred modality for imaging in the view of some surgeons. Disadvantages of MRI are the duration of the examination and the cost, but there are definite indications for MRI in patients with renal dysfunction, since the contrast agents for MRI are not nephrotoxic. Angiograms are not required routinely to visualize the lesion, but if coronary angiography is indicated, an aortogram can be done with very little additional risk.
Cardiac Status and Management of Coronary Artery Disease
All patients being evaluated for aneurysm surgery require a preoperative echocardiogram. This is to assess left ventricular function and to rule out significant valvular heart disease. In patients with aneurysms of the ascending aorta in whom a Bentall procedure may be required, coronary arteriography is carried out to delineate the anatomy of the proximal coronary arteries. All patients over the age of 40 require routine coronary arteriography. Patients younger than 40 who have significant risk factors for coronary disease such as abnormal electrocardiogram, history of angina or smoking, or strong family history should also undergo coronary angiography.
If, on the basis of preoperative evaluation, insignificant coronary artery disease is found, then aneurysm surgery is performed as planned, with care taken to avoid undue cardiac stress. If significant coronary artery disease is present, coronary artery surgery or angioplasty is considered. If the lesions are amenable to angioplasty, this procedure is done two weeks before aneurysm surgery to prevent possible coronary thrombotic sequelae, since thrombotic complications have been observed when surgery involving administration of heparin and protamine is carried out sooner after angioplasty. If the aneurysm can be resected by a median sternotomy, or if the coronary arteries that require bypass are easily accessible through a left thoracotomy, coronary artery bypass grafting can be done at the time of aneurysm repair. If the aneurysm is very extensive, or if access to the relevant coronary arteries will be difficult through an incision that is optimal for aneurysm resection, coronary artery bypass surgery is undertaken in a separate procedure several weeks prior to aneurysm repair.
If severe pulmonary dysfunction is suspected on the basis of pulmonary function tests, or because of a history of severely limited exercise tolerance, pulmonary consultation is requested. Active pulmonary infection is treated prior to surgery. All patients are urged to stop smoking for at least a month before operation. Pulmonary dysfunction increases operative risk and prolongs recovery, but chronic lung disease is not necessarily a contraindication to operation unless oxygen dependence or significant carbon dioxide retention are present.
Cerebral Vessels and Prevention of Stroke
A history of transient ischemic attacks or of strokes, or the presence of carotid bruits on examination, prompts a noninvasive workup of extracranial cerebral vessels. Since emboli are likely to arise from the diseased aorta in the presence of an arch aneurysm, a history of a focal cerebral insult is not a contraindication to surgery. In patients with such a history, a CT scan of the brain is carried out preoperatively; this enables detection of silent fresh cerebral infarcts, which necessitate postponement of surgery in most instances. The preoperative CT scan is also invaluable for identification of old and new lesions, and may be helpful in prognosis if focal neurologic symptoms occur postoperatively. Rather than attempt to identify those patients most at risk for intraoperative and postoperative cerebral embolization because of extensive friable atherosclerotic debris in the ascending aorta and arch, we assume that all patients with arch aneurysms have a very high risk of embolization and take all possible steps to minimize their occurrence. Reasonably accurate preoperative identification of those patients at highest risk is possible using transesophageal echocardiography, and even better visualization of the ascending aorta and arch is possible using epiaortic ultrasound intraoperatively.
For arterial cannulation in the management of arch aneurysms, we use the right axillary artery almost exclusively. The axillary artery is usually soft and rarely involved in the generalized atherosclerotic process. Its use avoids retrograde perfusion through a diseased abdominal and descending thoracic aorta and the turbulent flow patterns in the arch associated with ascending aortic cannulation, which we—as well as others—believe reduces the risk of atheroembolism. Another advantage of axillary artery cannulation is its usefulness for selective antegrade cerebral perfusion during arch reconstruction.
Many surgeons still use the femoral vessels for cannulation. However, these are often calcified and atherosclerotic, and associated with the inherent risk of local dissection, retrograde dissection, and cerebral embolisation. Cannulation can also be carried out in the ascending aorta using intraoperative epiaortic ultrasound to select a site free of atheroma in a segment of aorta adjacent to or even included in the anticipated resection; the perfusion cannula can subsequently be moved to the graft during the procedure. Despite the accuracy of epiaortic ultrasound, we are still concerned about using the aorta as a cannulation site and prefer to use the right axillary artery.
These operations are so variable it is probably better to see the aortic cases section of this disk.
In 80% to 90% of aortic arch cases, an extended median sternotomy is used. This incision gives access to the ascending aorta, the arch, and the proximal descending thoracic aorta as far as 5 cm beyond the origin of the left subclavian artery. The conventional median sternotomy can be extended along the border of the sternocleidomastoid muscle on the left side of the neck if necessary. The strap muscles of the left side of the neck can be incised, and the left innominate vein temporarily ligated and divided.
If the anticipated surgical procedure involves both intracardiac pathology and/or extensive resection of the ascending aorta and the arch as well as resection of aorta beyond the proximal descending thoracic aorta, some surgeons advocate a thoracosternotomy incision. This incision is a bilateral anterior thoracotomy in the 3rd or 4th intercostal space joined by dividing the sternum. It gives excellent exposure to the entire ascending aorta, arch, and most of the descending aorta. However, it may have a deleterious effect on pulmonary function, and puts both phrenic nerves at risk. Another option in this situation is the two stage approach using the elephant trunk procedure, and to reserve the thoracosternotomy incision for reoperations. In patients with a lesion primarily in the descending aorta that extends no farther proximally than the distal arch, a left lateral thoracotomy in the 4th or 5th intercostal space is the incision of choice; this can be extended inferiorly across the costochondral site if necessary.
Cooling and Rewarming
Cooling the perfusate to~10°C, and monitor both bladder and esophageal temperatures. After HCA, a period of hypothermic reperfusion can be used as this has been shown this may be beneficial. During rewarming, never raise blood temperature above 37°C, and avoid creating a gradient exceeding 10°C between blood and esophagus. Some discontinue warming when the patient reaches an esophageal temperature higher than 35°C, and a bladder temperature of 30°C to 32°C. Some prefer the patient to rewarm gradually in the ICU following closure. Others rewarm to 37°C.
Prevention of Paraplegia
Although the possible development of paraplegia is not a major concern with most operations involving the aortic arch, it is a consideration with procedures involving the descending thoracic and thoracoabdominal aorta. In these patients, some protection of the spinal cord is afforded by the use of total body hypothermia, but additional safeguards are warranted. During operations for resection of the distal arch plus a significant portion of the descending aorta, some routinely monitor somatosensory evoked potentials (SSEPs). Motor evoked potentials (MEPs) have recently been introduced and may provide superior monitoring of anterior cord integrity. Intercostal vessels are sacrificed gradually prior to institution of cardiopulmonary bypass: each vessel is clamped initially, and the vessel is sacrificed only if no change in SSEPs is seen for more than 10 minutes after its temporary occlusion. Postoperatively, SSEP monitoring is continued until the patient awakens. Thereafter, function of the lower extremities is assessed clinically on an hourly basis, for a total of 72 hours of postoperative monitoring. If a change in SSEPs or deterioration in motor function of the lower extremities is seen, blood pressure is increased, and intrathecal pressure is decreased by withdrawal of cerebral spinal fluid via an intrathecal catheter. These maneuvers to increase spinal cord perfusion pressure have proven successful in reversing the manifestations of late onset paraparesis.
Cerebral and Organ Protection
Anterograde, Retrograde and Integrated Perfusion of the brain
Ascending and Arch Replacement
Graft sizing and length can cause dog ears or kinks.
Routine with annual CT or MRI