Atlas of General Surgical Techniques (Courtney M. Townsend Jr., B. Mark Evers)

C H A P T E R 82

RESECTION OF ABDOMINAL

AORTIC ANEURYSM

Glenn C. Hunter

ELECTIVE ANEURYSM REPAIR

Most patients with asymptomatic abdominal aortic aneurysms are operated on electively once the aneurysm exceeds 5.5 cm in diameter. If the aneurysm has ruptured, immediate operative repair is indicated. Some steps appropriate to emergency aneurysmectomy will be included in the discussion of elective aneurysm repair.

STEP 1: SURGICAL ANATOMY

The aorta enters the abdomen between the crura of the diaphragm at the level of the 12th thoracic vertebra and bifurcates into the right and left common iliac arteries at the interspace between the fourth and fifth lumbar vertebrae. The aorta is crossed successively by the fourth portion of the duodenum, the left renal vein, and the root of the mesentery, and it is intimately related to the vena cava and iliac veins. The left common iliac vein runs posterior medial to the artery and is densely adherent to it (Figure 82-1).

In most patients with abdominal aortic aneurysm, dilation begins distal to the origins of renal arteries and extends to the aortic bifurcation and iliac arteries. The elongation accompanying the aortic dilation results in tortuosity displacing the aorta off the vertebral column anteriorly or off to one side of the midline. The tortuosity may also involve the iliac arteries, resulting in their displacement into the pelvis.

The inferior mesenteric vein is located in the mesentery anterior to the aneurysm. Care must be taken when ligating the inferior mesenteric vein to ensure that only the vein is ligated, because the collateral arterial supply to the colon often accompanies the vein in this location.

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STEP 2: PREOPERATIVE CONSIDERATIONS

A search for thoracic and iliac aneurysms and other associated anomalies, such as suprarenal extension, venous anomalies, horseshoe kidney, or aortocaval fistula, with computed tomography (CT) scanning, magnetic resonance imaging (MRI), or duplex ultrasound imaging should be made before repair of an abdominal aortic aneurysm. Assessment of cardiac, respiratory, and renal function should be undertaken and any abnormalities optimized before proceeding with aneurysm repair. A mechanical bowel preparation the night before surgery facilitates the operation. Prophylactic antibiotics are administered 1 hour before the incision.

Celiac trunk

Superior

mesenteric Left renal artery artery

Left kidney

Right kidney

Left renal vein

Inferior vena cava

Abdominal

aorta Inferior mesenteric artery

FIGURE 82–1

8 8 2 S E C T I O N X I I • VA S C U L A R

STEP 3: OPERATIVE STEPS

1.INCISION

For elective aneurysm repair, the operative field is prepped from the nipples to the knees after induction of general anesthesia and placement of central venous and arterial monitoring lines. In the setting of a ruptured abdominal aortic aneurysm, the chest, abdomen, and groins should be prepared and draped before the induction of general anesthesia. Additional large-bore catheters are inserted peripherally and centrally, with the latter connected to a rapid infusion device capable of delivering large volumes of blood and blood products.

Aortic aneurysm repair can be undertaken using either a transperitoneal or a retroperitoneal approach. With the transperitoneal approach, the patient is positioned supine on the operating table and in the right lateral decubitus position for retroperitoneal exposure of the aorta (Figure 82-2).

A midline incision extending from the xiphoid process to the pubic symphysis or a transverse incision extending from flank to flank above or below the umbilicus provides excellent exposure of the entire intra-abdominal aorta.

The retroperitoneal exposure is particularly helpful in patients with inflammatory aneurysms, horseshoe kidney, ostomies, or hostile abdomens. Although this approach allows exposure of the suprarenal aorta, exposure of the right iliac vessels may be limited and a counterincision required.

The patient is placed in the right lateral decubitus position over a kidney rest, with the hips allowed to rotate to the supine position after induction of anesthesia and placement of monitoring lines.

An oblique incision extending from the lateral border of the rectus sheath 2 cm below the umbilicus over the tip of the 12th rib is made. Dissection is continued through the external oblique, internal oblique, and transverse abdominis muscles. The retroperitoneal space is entered by incising the most lateral aspect of the posterior rectus sheath. Dissection is continued toward the midline anterior or posterior to the left kidney. The retroperitoneal structures are retracted to the right of the midline, and repair of the aneurysm is undertaken in the usual fashion.

Midline incision

Transverse

incision Oblique incision for retroperitoneal exposure

FIGURE 82–2

The aorta is dissected between the aneurysm and the renal arteries; in 5% to 10% of patients, the suprarenal or pararenal aorta is involved. The surgeon should avoid injury to the left renal vein, which may be flattened over the proximal end of the aneurysm. Care should be taken to avoid injury to the iliac veins, which may be closely adherent to the arteriosclerotic arterial wall. This is best avoided by dissecting only the anterior and lateral surfaces of the common iliac arteries close to the arterial wall.

The anterior and lateral surfaces of the aneurysm are more completely freed of overlying tissue, care being taken not to interrupt the collateral arterial supply to the descending and sigmoid colon as it descends in the arcade on the left side of the aneurysm. After the systemic administration of heparin (100 U/kg) and mannitol (12.5 to 25 g), the aorta and iliac vessels are occluded with vascular clamps. The clamps are placed on the iliac vessels first and then on the aorta to minimize the risk of distal embolization. When the aorta and iliac arteries are heavily calcified, occlusion of the aorta at the diaphragmatic hiatus and balloon catheter occlusion of the iliac arteries may be necessary. The anterior wall of the aneurysm is incised with a no. 11 blade or electrocautery, and the arteriotomy is continued to the right of the origin of the inferior mesenteric artery to avoid injury to the hypogastric autonomic plexus on the left (Figure 82-4).

Left renal vein

Thrombus

FIGURE 82–4

Suturing the graft to the aorta is begun by passing the suture first through the graft and then through the aorta. Generous deep bites are taken through the aortic tissue to ensure a strong, blood-tight anastomosis. Several suturing techniques may be used. In this instance, a single 3-0 monofilament arterial suture is begun laterally at approximately the 3 o’clock position, sewing the posterior wall and continuing each end of the suture laterally and anteriorly where it is tied. Care must be taken to ensure that the suture is pulled tight before it is tied (Figure 82-7, A).

The graft should lie within the aortic lumen to allow better hemostasis and to prevent dissection beneath an atherosclerotic plaque at the suture line.

The integrity of the aortic anastomosis is assessed by temporarily releasing the aortic clamp while the graft is occluded digitally or with a shod clamp. This is the time to be certain that the posterior suture line is secure, because it is difficult to expose this area later in the operation. A shod clamp is placed across the aortic tube graft or each limb of a bifurcated graft.

Liquid blood, clots, and loose debris are aspirated from within the graft before proceeding with the distal aortic or iliac anastomosis. When a tube graft is used, the aorta above the bifurcation is partially divided transversely, leaving the posterior wall intact. The anastomosis is constructed using 3-0 polypropylene suture beginning at approximately the 3 o’clock position, taking deep bites of the posterior wall. Before placement of the final sutures, the graft and iliac arteries are flushed and the anastomosis completed (Figure 82-7, B).

Construction of proximal anastomosis using Creech technique

Aortic bifurcation

Completing distal anastomosis

A B

FIGURE 82–7

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When the distal anastomosis is to the iliac arteries, each iliac bifurcation is dissected, isolating the external and internal iliac arteries. The common iliac artery is divided 1 cm proximal to its bifurcation. If the common iliac artery is aneurysmal or otherwise unsuitable for anastomosis, the common iliac artery is oversewn or stapled and the external iliac or femoral arteries used for the distal anastomosis. The external iliac artery is allowed to back-bleed to ensure the absence of clot or debris and then flushed with heparinized saline. The limbs of the bifurcated graft are routed within the aneurysm bed to the iliac arteries.

The proximal clamp on the right limb is removed with the distal end occluded digitally to assess the appropriate length of the graft so that it is long enough to allow for a tension-free anastomosis but not so long that kinking occurs.

The distal anastomosis on the right is constructed first with a running 4-0 polypropylene suture. Before flow is reestablished, the iliac arteries are allowed to back-bleed, the iliac limb of the graft is flushed, and the remaining sutures are placed (Figure 82-8).

The order of clamp removal is important in preventing of air or atheromatous debris material from passing into the legs. The clamps on the right internal iliac artery, the right limb of the graft, and the external iliac artery are removed in sequence and flow is reestablished.

Left renal vein

Inferior vena cava

Aortic aneurysm

Completed aortoiliac bypass

Aortic wall

Iliac aneurysms

A B

FIGURE 82–8