In patients with aortic dissection, the disease often extends distally, sometimes down to the femoral vessels; therefore, care must be exercised not to cannulate and perfuse through the false lumen of the femoral artery in a retrograde manner.

In elderly patients with severe atherosclerosis, the femoral and iliac arteries are markedly diseased and cannulation may be hazardous. Cannulas are available which can be introduced into these vessels percutaneously or under direct vision with a needle and wire technique (Fig. 8-2). The flow through a size 20 cannula is adequate for all but very large patients. Alternatively, the axillary artery may be used.

A dual-stage atriocaval cannula is usually used for venous drainage.

If the ascending aorta is large, preventing adequate exposure of the right atrium for venous cannulation, femoral vein cannulation is performed.

If the procedure is a reoperation, it is preferable to achieve cardiopulmonary bypass through a femoral
artery and femoral vein before opening the sternum (see Chapter 2).

It is prudent to initiate cardiopulmonary bypass promptly by means of the femoral vessels before the administration of general anesthesia in patients with unstable hemodynamics to prevent circulatory collapse. This is especially important if pericardial tamponade is apparent or suspected.

Femoral vein cannulation can be achieved by introducing a long cannula with multiple side holes for excellent venous return. The important characteristic of this device is that it comes with a guidewire and contains a tapered, dilated sheath inside the cannula. The guidewire allows easy, comfortable, and safe passage of the cannula over the pelvic rim. The cannula has multiple side holes and may be advanced into the right atrium, providing superior drainage.

Venous cannulas that lack guidewires often hang up at the pelvic rim, resulting in inadequate venous return. If an attempt is made to push the cannula further into the inferior vena cava, perforation of the iliac vein with catastrophic consequences may ensue. It is usually easier to pass the cannula through the right femoral vein because of its straighter course compared with the left femoral vein.

After completion of a median sternotomy, an additional venous cannula is placed in the right atrium if required. A left ventricular vent through the right superior pulmonary vein (see Chapter 4) decompresses the heart and expedites the procedure. Venting is especially important if aortic valve insufficiency is present.

Whenever deep circulatory arrest is contemplated, the patient is generally cooled down to bladder temperature of 18°C to 24°C. Moderate hypothermia (bladder temperature of 26°C to 28°C) is safe if the anticipated period of circulatory arrest is less than 15 to 20 minutes. Ice is packed around the patient’s head. A tape is passed around the superior vena cava (see Chapter 2). A purse-string suture of 4-0 Prolene is applied to the adventitia of the superior vena cava at its junction with the pericardium. The adventitial tissue within the purse-string suture is cleaned off the superior vena cava, and an incision is made on the vein. The opening is enlarged with the tip of a clamp or scissors, and a long right-angled cannula is introduced into the superior vena cava and guided upward past the innominate vein (Fig. 8-3). This cannula is then connected to an arm of the cardioplegia delivery system or to the arterial line to perfuse cold blood into the superior vena cava whenever circulatory arrest is initiated. The tape around the superior vena cava is snugged down on the cannula to prevent perfusate from flowing back into the right atrium.

An alternative to retrograde cerebral perfusion is selective antegrade cerebral perfusion through the right axillary artery. In conjunction with innominate artery occlusion, this method can provide effective cerebral protection during circulatory arrest by allowing antegrade right carotid artery perfusion. Right axillary perfusion is also used for systemic perfusion during cardiopulmonary bypass.

Before sternotomy, the right axillary artery is exposed through an 8 to 10 cm incision below and parallel to the lateral two-thirds of the clavicle. The pectoralis major muscle is divided in the direction of its fibers. The clavipectoral fascia is incised and the pectoralis minor muscle is retracted laterally. The axillary artery is located superior to the axillary vein. Using sharp dissection, the first part of the axillary artery is isolated. After administration of intravenous heparin, a small side-biting vascular clamp is applied to the artery. A longitudinal arteriotomy incision of approximately 1 cm is made and an 8-mm Hemashield Dacron tube graft (Medox Medical, Oakland, NJ) is sewn to the axillary artery in an end-to-side manner using 5-0 Prolene suture (Fig. 8-4). A 24-F arterial cannula is inserted into the graft and secured. Perfusion through a graft is safer than direct cannulation of the axillary artery and allows more accurate cerebral perfusion by monitoring the right radial artery pressure. During hypothermic circulatory arrest, axillary arterial blood flow is adjusted to maintain a radial artery pressure of 50 to 60 mm Hg.

On cardiopulmonary bypass with the heart decompressed, preliminary evaluation is made. The need for any concomitant additional procedures, such as coronary artery bypass grafting, must be noted. The conduct of the surgery should be choreographed precisely at this time.

When the nasopharyngeal temperature reaches 18°C to 24°C, the patient is placed in the Trendelenburg position. The heart-lung machine is halted, and retrograde cerebral perfusion or selective antegrade axillary perfusion is started. A transverse or longitudinal aortotomy is made on the anterior aspect of the aortic wall (Fig. 8-5). When dissection is present, the false lumen may be entered first. This necessitates opening of the true lumen.