An extended posterolateral thoracotomy is performed to expose the entire length of the thoracic aorta. The latissimus dorsi and a minimal portion of the serratus anterior muscles are divided. Left lung ventilation is terminated prior to entry into the pleural cavity. Aneurysms of the upper or middle thoracic aorta are accessed through a single intercostal space, which may be facilitated by division of one of the ribs posteriorly. We prefer two separate sites of entry through the fourth interspace and the seventh or eighth interspace for more extensive descending thoracoabdominal aneurysms. The fourth interspace is critical to proximal clamp application. Careful entry into the pleura allows anterior retraction of the lung under sponges to expose the aorta. The pleura over the aorta is divided. The intrathoracic course of the vagus nerve, recurrent laryngeal nerve, and proximal phrenic nerve at the aortic arch is identified. The aorta is then taped immediately proximal to or at the origin of the left subclavian artery where careful, sharp dissection allows for future application of the aortic cross-clamp. The thoracic duct and adjacent lymph vessels should be avoided. Intraoperative lymph leaks should be immediately repaired. The identification of the esophagus may be augmented by the direct palpation of the nasogastric tube or transesophageal echocardiography scope to avoid inadvertent injury.

Following achievement of the proximal aortic dissection, attention is directed to the aorta distal to the aneurysm. In the setting of extensive thoracic aortic involvement, a second pleural entry through the separate intercostal incision may be needed. Careful sharp dissection of the distal aorta is performed to achieve adequate control.
Importantly, no attempts are made in the dissection of the aneurysm along its entire length to avoid potentially hazardous bleeding; however, posterior mobilization of the aneurysmal segment may be necessary to support clip application to the intercostals prior to opening of the aorta.

Our standard incision is started posterolaterally over the ribs of the seventh, eighth, or ninth interspace dependent on the proximal extent of the aneurysm. The incision is then advanced across the ninth interspace at the costal margin to curve inferiorly to run parallel and left-lateral to the midline and rectus sheath. Single right lung ventilation is initiated and the left pleural space is entered. The abdominal muscles are divided and the peritoneum is preserved. Special care is needed at the lateral edge of the rectus abdominis muscle where the peritoneum and transversalis fascia are closely apposed to the abdominal wall. While the retroperitoneal approach is our preferred technique, we recognize that the intraperitoneal approach affords mobilization of the spleen and left colon, which may enable better access to the abdominal aorta in select patients. The diaphragm may be taken down with a curved incision along the costal margin with care to preserve a 3-cm rim along the posterior aspect of the rib. The tendinous center of the diaphragm is then conserved when anatomically feasible to improve postoperative respiratory recovery and weaning time. This limited phrenotomy technique allows passage of the graft through the natural hiatus of the diaphragm. The incision is continued down to the crura, and the left crus may be divided to expose the aorta beneath. A radial diaphragmatic incision may also be utilized and has become our preferred technique (Fig. 59.3).

Progressive retraction of the peritoneum and its contents will facilitate exposure of the retroperitoneum and a self-retaining retractor is necessary. The aorta is located medial to the iliopsoas muscle. Mobilization of the left kidney from the bed of the psoas muscle may provide additional exposure and is preferred at our institution. Importantly, this step is deferred in patients with a retroaortic left renal vein. Anterior visceral branches are identified and sharply dissected with attention to mobilization should reimplantation or bypass be required. Dissection is performed proximal and distal to the aneurysmal segment of aorta and each site is tapped in preparation for cross-clamping.

Proximal aortic cross-clamp application induces a significant increase in cardiac afterload. Sudden afterload reduction following clamp release is associated with an acute relative hypovolemia and systemic hypotension. These periods
of hemodynamic change are managed through the following intraoperative strategies.

Direct and cooperative communication between surgeon and anesthesiologist is imperative during periods of cross-clamp application and release. Our approach to cross-clamp application and distal aortic perfusion involves active distal aortic perfusion with femoral-to-femoral bypass for all but type IV and V aortic aneurysms, for which we minimize supraceliac clamp times with no active distal perfusion. This perfusion strategy maintains distal aortic perfusion with warm, oxygenated blood and provides the time necessary to safely perform the most complex of repairs. With this strategy, maintenance of distal aortic blood pressure is imperative and is achieved through the titration of pharmacologic agents and pump flow rates to maintain optimal perfusion. Infusion of nitroglycerine, trimethaphan, or sodium nitroprusside prior to the application of the aortic cross-clamp may be performed to lower systolic blood pressure to 70 to 80 mmHg. The anticipated acute rise in blood pressure with aortic cross-clamp application should necessitate aggressive blood pressure control until planned clamp release. Sodium bicarbonate, calcium, and rapid volume infusion may be initiated prior to unclamping to prevent acute hypotension. Vasopressor agents may also be utilized to augment these resuscitative measures to maintain blood pressure upon clamp release. Importantly, our principal focus is to carefully titrate both volume and pump flow rate to maintain target pressure, often eliminating the need for these additional interventions throughout the critical periods of clamp application and release.

Progressive clamp application and release over a period of 2 to 4 minutes may blunt the imposed physiologic insult and hemodynamic response. In assessment of end-organ ischemia, cross-clamp time is measured from the first click of clamp application until its complete release. Despite these preventative and resuscitative measures, hemodynamic instability may occur and should be anticipated with appropriate preparation.

Extracorporeal circulation support provides after load reduction and continuous end-organ perfusion during the aortic cross-clamp period. Techniques for the maintenance of extracorporeal circulation include passive aorto-aortic shunt, left atriofemoral bypass, and femorofemoral cardiopulmonary bypass.

The inherent threat of unavoidable temporary cord ischemia during repair and the potentially preventable lasting ischemia resulting from inadequate perioperative cord perfusion in patients with descending thoracic and thoracoabdominal aneurysms have supported significant technical advancements in spinal cord protection. Central to methods of cord protection is an understanding of the axial network and the supplying segmental, subclavian, and hypogastric arteries and the protective effect of permissive hypothermia on neural tissue. This collateral network may increase flow through alternative routes when another is reduced; however, this network may also result in steal that will result in decreased nutrient flow to the cord. Steal may occur secondary to the absence of visceral and iliac artery perfusion, during the cross-clamp period, or as a result of pharmacologically induced arteriovenous
shunting when bleeding intercostals into an excluded aortic segment. With these considerations, we have adopted the liberal use of multihead perfusion cannulae and pediatric coronary sinus catheters for the maintenance of perfusion to the visceral and subclavian aortic branches and dominant intercostal arteries, respectively (Fig. 59.4). The detection of potentially reversible delayed paraplegia may be achieved by MEP and SSEP monitoring with immediate assessment of function postoperatively. It is not our routine practice to perform MEP or SSEP monitoring. The adoption of the following provocative techniques for reduction of spinal cord ischemic-induced injury has resulted in a significant decrease in the incidence of paralysis following open repair that is dependent on the extent of repair: 15% for type I, 30% for type II, 7% for type III, and 4% for type IV. Additional predictors of delayed neurologic deficit for thoracoabdominal aneurysms include emergent operative status, prolonged aortic cross-clamp time, level of cross-clamp, hypogastric artery exclusion, aortic rupture, preoperative renal dysfunction, prior abdominal aortic aneurysm repair, acute dissection, and extent II involvement. These techniques and the avoidance of hemodynamic instability and significant blood volume loss have offset the influence of cross-clamp time on induced spinal cord injury.