Direct Surgical Repair of Aneurysms of the Thoracic and Thoracoabdominal Aorta

Historical Background

The first surgeon to repair a thoracoabdominal aortic aneurysm (TAAA) was Etheredge in 1955 in a patient with a Type IV TAAA using a homograft. In 1956 DeBakey and associates reported the surgical treatment of four patients with TAAA by resection and homograft replacement. A Dacron graft was used as a shunt between the descending thoracic aorta and infrarenal abdominal aorta. Sequentially, the celiac axis, superior mesenteric artery, and both renal arteries were revascularized, limiting ischemic time for the liver, stomach, bowels, and kidneys to 10 to 15 minutes. Subsequent reports utilized Dacron grafts instead of homografts for primary reconstruction of the aorta with Dacron side arms to each visceral vessel, as the primary approach for repair from the 1950s to the late 1970s.

In 1965 Crawford ushered in the modern era of TAAA and descending thoracic aortic aneurysm (DTAA) repair. Three principles of repair were formulated: (1) the inclusion technique, as originally described by Matas, Javid, and Creech, in which the aneurysm wall is not excised, thus avoiding damage to surrounding structures; (2) the reattachment of the renal arteries, superior mesenteric artery, and the celiac axis into the larger graft, by either creating an orifice in the body of the graft or beveling the anastomosis, as described by Carrel ; and (3) reattachment of the intercostal arteries to prevent paraplegia, as initially described by Spencer in a canine model. From the 1970s until the 1990s, the “clamp and sew” technique was the primary surgical approach for treatment.

Beginning in the 1960s, multiple approaches to prevent paraplegia were introduced. As an early adjunct, cerebrospinal fluid drainage (CSFD) was described by Miyamoto and colleagues in 1960, as well as by Blaisdell and Cooley in 1962. Although the benefit of reduced cerebrospinal fluid (CSF) pressure during TAAA repair was demonstrated in a canine model, CSFD did not gain clinical popularity until the 1980s. The use of perfusion catheters from the descending aorta to both renal arteries, the celiac axis, and the superior mesenteric artery was first described by Korompai and Hayward in 1975.

Although Hollier and co-workers confirmed the benefits of CSFD, Crawford and associates initially reported that CSFD did not improve outcomes. Despite this early controversy, subsequent studies have demonstrated the benefit of CSFD during TAAA repair.

The use of distal aortic perfusion (DAP) or partial bypass was first reported in 1956 by DeBakey and associates and later by Connolly and colleagues to reduce distal ischemia and cardiac afterload. The benefit of DAP was confirmed in multiple studies conducted in the 1980s and 1990s.

Preoperative Preparation

• Cardiac evaluation. Echocardiography is obtained to determine ventricular function and the presence of valvular abnormalities. Normal ventricular function is a predictor of good outcome after TAAA repair. Severe valvular dysfunction should be treated before aortic repair if repair is not urgent. Cardiac evaluation should include a physical examination and determination of exercise tolerance. If coronary artery disease is identified, then the extent and location of disease and associated symptoms determine the order of repair. Drug-eluting stents should be avoided as TAAA repair mandates discontinuation of clopidogrel. If required, coronary artery bypass grafting should be performed at least 6 weeks before repair.

• Pulmonary function. Pulmonary function tests and arterial blood gases are obtained as a routine. Patients with severe chronic obstructive pulmonary disease, as suggested by a forced expiratory volume in 1 second (FEV1) of less than 0.8 L/min, should be evaluated by a pulmonologist and receive bronchodilators as well as pulmonary rehabilitation before repair.

• Nutritional and gastrointestinal status. Large aneurysms may cause “aortic dysphagia” as a result of intrinsic compression of the lower esophagus leading to a nutritionally depleted state that may benefit from preoperative enteral alimentation.

• Renal function. Preoperative renal function is a strong predictor of postoperative mortality after TAAA repair, and glomerular filtration rate (GFR) is more sensitive than serum creatinine in predicting postoperative outcome. Patients with renal dysfunction may benefit from admission before surgery for intravenous hydration. Advanced, irreversible renal failure constitutes a relative contraindication to surgery.

Operative Strategy

A classification for thoracoabdominal aortic aneurysm describes five anatomic types: Type I extends from the left subclavian artery to just above the renal arteries; Type II from the left subclavian to the aortic bifurcation; Type III from the sixth intercostal space to the aortic bifurcation; Type IV from the twelfth intercostal space to the aortic bifurcation; and Type V from the sixth intercostal space to just above the renal arteries ( Fig. 18-1 ). This classification has been used in the prediction of complications, especially the risk of spinal cord ischemia, which is highest for Type II TAAA.

A separate classification scheme has been devised for those aneurysms confined to the descending thoracic aorta. Type A extends distal to the left subclavian artery to the sixth intercostal space; Type B arises between the sixth and twelfth intercostal spaces, above the diaphragm; and Type C extends distal to the left subclavian artery to the twelfth intercostal space.

Avoiding Diaphragmatic Paralysis

Radial division of the diaphragm to the aorta has traditionally provided good exposure but rendered most of the diaphragm paralyzed, adversely affecting respiratory function. As an alternative, partial division of the anterior muscular portion of the diaphragm can be performed, avoiding injury to the phrenic nerve, followed by division of the crus of the diaphragm to create an aortic hiatus for the graft ( Fig. 18-2 ). This approach has reduced the incidence of diaphragmatic paralysis and has aided expeditious extubation.

Avoiding Injuries to the Esophagus

The esophagus is located directly behind the thoracic aorta. When performing the proximal anastomosis in patients with DTAA and TAAA, the aorta is circumferentially divided and lifted off the esophagus to prevent an inadvertent esophagograft fistula ( Fig. 18-3 ).

Operative Considerations