Open Abdominal Aortic Aneurysm Repair

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Table of Contents

Introduction
Considerations
Incisional Anatomy
Surgical Anatomy
Patient preparation
Surgical Procedure
Bibliography

Introduction

Great celebrities like Albert Einstein, General Charles de Gaulle, and Conway Twitty lost their lives as a consequence of Abdominal Aortic Aneurysm (AAA). AAA was first defined in the 16th century by Vesalius. Since then, a number of medical interventions have been introduced to treat the disease, but all of them proved unsuccessful. Various methods, including aortic ligation, cellophane wrapping, and aneurysmorraphy, were also used in earlier days, but they all had poor outcomes.

Effective treatment for aneurysms has just been introduced within the past 70-75 years. In 1951, the first AAA repair was performed by Charles Dubost using homograft. Later, homografts were replaced by nylon grafts and then finally by Dacron and Gore-Tex grafts. Silk sutures were replaced by Dacron, polyethylene, and PTFT sutures as they have higher tensile strength. The mortality rates for AAAs still remained high till the technique of endoaneurysmorrhaphy was introduced in 1962. Due to the introduction of this technique, the mortality rates dropped from more than 25% to 1.8-5%.

Nowadays, open AAA repair is considered to be a safe treatment option as better grafts have been introduced and preoperative assessment, intraoperative techniques, and postoperative care have improved. Recently, techniques of endovascular repair have also been introduced, and they further increase the safety of the procedure for high-risk individuals.

Considerations

Indications: There are many indications of this procedure. The indications are different for elective and emergency procedures. The main goal of repair is to prevent rupture and increase the life expectancy of patients.

For asymptomatic patients, the cutoff size of an aneurysm for an elective procedure is 5.0 cm. If the aneurysm is 5.0 cm or greater, and the surgical risk is acceptable, the aneurysm should be repaired as there are high chances of rupture. For women, a lower cutoff of 4.5 cm is used as they have shown to have a higher risk of rupture. Aneurysms can be repaired earlier in the disease course if the patients are young, have a low surgical risk, and have a higher life expectancy. Surgery can be delayed in high-risk patients up to the size of 6-7 cm.

Smaller aneurysms are monitored with ultrasound every six months. Repair should also be done if the aneurysm is growing at a rate of 1 cm/year. All symptomatic aneurysms and aneurysms leading to peripheral emboli formation should be repaired regardless of their size. Similarly, atypical aneurysms of all sizes, including dissecting, pseudoaneurysms, mycotic, saccular, and penetrating ulcers, should be surgically repaired. Emergency repair should be done in all cases of known or suspected rupture of the aneurysm.

Contraindications: The decision of surgery is based on the patient’s physical and functional condition. The procedure is contraindicated in patients who are considered to be at high risk. These include patients with unstable angina, serum creatinine >3 mg/dl, compromised pulmonary function (low oxygen saturation), and ejection fraction <25%. Thus, the contraindications of the procedure are severe COPD, severe cardiac disease, active infection, etc.

Tests: There are many different diagnostic tests that are used for the diagnosis of AAA. Plain radiograph shows a characteristic eggshell appearance of calcification of the abdominal aorta. This can detect aneurysm in 70% of the patients but is still an unreliable method as this does not detect the exact size of the aneurysm, and a negative result does not rule out the possibility of an aneurysm.

Diagnostic tests are usually done to determine the size of the aneurysm. Abdominal ultrasound is the most commonly used modality for diagnosis and determination of the size of the aneurysm. The advantages are that it is non-invasive, safe, cost-effective, and can detect the structural changes and size of the aneurysm accurately and in all dimensions. But it cannot clearly visualize other arteries and abnormalities present and is therefore not a good preoperative tool.

CT scan is a good diagnostic modality as it can accurately locate both the ends of the aneurysm and identify abnormalities in all the vessels. It can also identify surrounding abdominal structures. It can also clearly distinguish between the true and false lumen and can be used in the diagnosis of aortic dissection. The use of IV contrast helps in the investigation of aortic lumen, presence of hematoma, and mural thrombus. Nowadays, CT angiography has replaced traditional angiography techniques in the diagnosis of AAA.

MRI is another useful, non-invasive technique used in AAA. The advantages of MRI are that ionizing radiation is not used, and the contrasts used are not nephrotoxic. Therefore, it is the modality of choice in patients with renal disease. The disadvantages of MRI are that it is not easily available everywhere and is more expensive than ultrasound and CT.

Contrast aortography is another modality used for the diagnosis. The quality of pictures obtained is excellent, but it is not very reliable. This is because the presence of mural thrombus reduces the size of the aortic lumen and therefore does not reflect the true diameter of the aneurysm. Aortography can accurately identify the extent of disease and indicate if other vessels like iliac arteries, renal arteries, and femoral arteries are involved. The side effects of aortography are that the contrast used is nephrotoxic, and there is a risk of distal embolization, hemorrhage, and pseudoaneurysm formation. Due to all these disadvantages, aortography is not as commonly used as other diagnostic modalities discussed previously.

Incisions: There are two main types of incisions or approaches used in the open repair of AAA. These are a long midline incision for the transperitoneal approach and an oblique flank incision for the retroperitoneal approach. The third type of incision used is the upper abdominal transverse incision, and it can be used for both approaches.

Both the approaches have their own advantages and disadvantages. The transperitoneal approach is most commonly used. It provides the greatest amount of flexibility during surgery and the greatest amount of exposure of aortic aneurysm and renal, iliac and femoral arteries. But this approach is difficult when the patient has a history of abdominal surgery or there is a suprarenal extension of the disease. It cannot be used in the case of horseshoe kidneys, ascites, and peritoneal dialysis.

The retroperitoneal approach can completely avoid intraperitoneal structures and can be used when there are peritoneal adhesions and severe pulmonary disease and intestinal stoma are present. This can also be used when greater suprarenal exposure is required. There are also fewer complications associated with the retroperitoneal approach. Patients have a shorter postoperative stay in the hospital, duration of postoperative ileus is less, pulmonary complications are less frequent, and the stay in ICU is also shorter. The disadvantage of the retroperitoneal approach is that it leads to difficulty in the accessibility of the right iliac and renal arteries.

Other considerations: Sometimes, comorbid conditions can complicate the repair of AAA. These include hepatobiliary, gastrointestinal, pancreatic, gynecological, and genitourinary problems. Therefore, careful preoperative evaluation should be done, and more life-threatening conditions should be treated first.

A number of anatomical variants can also occur in many patients. These include venous anomalies, accessory renal arteries, and horseshoe kidneys.

Usually, there are 3-5 renal arteries in patients with horseshoe kidneys, and in order to maintain kidney function, it is necessary to reimplant renal arteries arising from the aneurysm. The presence of horseshoe kidneys also creates difficulties in the transperitoneal approach. Thus, in such cases, the left retroperitoneal approach is used.

The common venous anomalies seen are circumaortic venous rings, retroaortic left renal vein, azygous continuation of inferior vena cava, and bilateral inferior vena cava. All these anomalies lead to unnecessary bleeding and require careful dissection.

Inflammatory AAA leads to extensive involvement of surrounding structures and makes the repair difficult. Thus, the retroperitoneal approach is used to overcome intraoperative difficulties.

Incisional Anatomy

The incision for this procedure is made in the abdominal wall. Thus, many different layers of the abdominal wall are cut in order to make the incision. In order to understand the incisional anatomy, it is important to have good knowledge about the anatomy of the abdominal wall. There are nine layers in the abdominal wall: skin, subcutaneous tissue, superficial fascia, external oblique muscle, internal oblique muscle, transversus abdominis muscle, transversalis fascia, preperitoneal adipose and areolar tissue, and peritoneum.

The subcutaneous tissue comprises Camper’s fascia and Scarpa’s fascia. Camper’s fascia is the outer layer and contains subcutaneous fat; Scarpa’s fascia is the inner, dense layer of fibrous connective tissue. Scarpa’s fascia helps in the alignment of the skin after the abdominal incision.

The external oblique muscle is the most superficial muscle of the abdominal wall. It arises from the lower eight ribs and runs transversely in a superolateral to inferomedial direction to insert into the anterior half of iliac crests. The muscles form the aponeurosis (a strong tendinous sheath) in the midclavicular line that passes anteriorly to the rectus sheath to attach medially into the linea alba.

The internal oblique muscle arises from the upper surface of the inguinal ligament, the iliac crest, and the thoracolumbar fascia and is at a right angle to the external oblique muscle. The fibers run in inferolateral to superomedial direction. The aponeurosis of the internal oblique split near the rectus muscle and covered the rectus muscles. The anterior layer combines with the aponeurosis of the external oblique muscle to form the anterior rectus sheath, and the posterior layer combines with the aponeurosis of the transversus abdominis to form the posterior rectus sheath. The lowermost fibers of the internal oblique muscle run inferomedially and accompany the spermatic cord into the scrotum as the cremasteric muscle.

Transversus abdominis is the innermost muscle layer of the abdominal wall. This muscle arises from the inguinal ligament, the iliac crest, the thoracolumbar fascia, and the lower costal cartilages. It runs transversely through the midline and forms aponeurosis, which passes posterior to the rectus sheath above the semicircular line and anteriorly below it. The inferior fibers of the muscle run inferomedially and form the aponeurotic arch, which is a major surgical landmark.

The transversalis fascia lies beneath the transversus abdominis muscle and forms a complete fascial envelope around the abdominal cavity. This fascia binds together all the muscles and aponeurosis and increases the strength and structural integrity of the abdominal wall.

The rectus muscle runs in the midline from the xiphoid process to the pubic crest. The rectus muscle is surrounded by the rectus sheath, which consists of the aponeuroses of the oblique muscles and the transversus abdominis muscle. Pyramidalis is a small, triangular-shaped muscle that marks the midline and assists in the identification of the medial borders of the rectus muscle.

The linea alba consists of a band of dense, crisscross fibers of the aponeuroses of the abdominal muscles. It extends from the xiphoid to the pubic symphysis.

The retroperitoneum is bounded anteriorly by the peritoneum and cranially by the diaphragm. The posterior border of the retroperitoneum is the abdominal wall which consists of the lumbodorsal fascia and sacrospinalis, and quadratus lumborum muscles. The lateral boundary of the retroperitoneum is the preperitoneal fat and transversus abdominis musculature of the lateral abdominal wall. Caudally the retroperitoneum is continuous with the extraperitoneal pelvic structures.

Thus, the layers encountered in a midline incision from superficial to deep are skin, subcutaneous tissue, superficial fascia, linea alba, transversalis fascia, extraperitoneal fat, and peritoneum. The midline incision is easy and allows quick entry into the abdominal cavity, but there is an increased risk of wound dehiscence and hernia formation. On the other hand, oblique incision involves all the nine layers of the abdominal wall, including skin, subcutaneous tissue, superficial fascia, external oblique muscle, internal oblique muscle, transversus abdominis muscle, transversalis fascia, preperitoneal adipose and areolar tissue, and peritoneum.

Surgical Anatomy

Aorta: Abdominal aorta has three layers: tunica intima, tunica media, and tunica adventitia. An aortic aneurysm leads to the dilatation of all three layers.

The aorta pierces the diaphragm and enters the abdominal cavity at the level of T12. after entering the abdominal cavity, the aorta divides into two branches at the level of L4 or fourth lumbar vertebra. The two branches of the abdominal aorta are the iliac arteries. Aorta is anterior to the vertebral bodies. The inferior vena cava is situated on the right side of the aorta, whereas a sympathetic trunk is present on its left side. Cisterna chyli lies between the aorta and inferior vena cava. Anteriorly, the aorta is covered by many structures. These include the peritoneum of the lesser sac, pancreas, splenic vein, left renal vein, part of the duodenum, and small intestine.

There are numerous branches of the abdominal aorta. These include anterior vessel branches (celiac axis, superior and inferior mesenteric arteries), lateral vessel branches (suprarenal, renal, gonadal arteries), parietal branches (phrenic, paired lumbar arteries), and three-terminal branches (median sacral, two common iliac arteries, which further divide into internal and external iliac arteries).

Related structures of importance: There are many important structures related to the abdominal aorta. These include renal, iliac, and visceral arteries, as these can be involved in the disease process. Location of the hypogastric artery is very important as the loss of blood from this artery can lead to impotence in men and ischemia of the sigmoid colon. During the repair, inferior vena cava and other numerous surrounding vessels can be damaged. As the aorta is covered by many gastrointestinal structures like the duodenum and pancreas, they can be damaged if precautions are not taken.

Patient preparation

Before the surgery, all cardiac, renal, and pulmonary functions of a patient are thoroughly evaluated. There are some general preoperative interventions that are used in all patients. These include bowel preparation with cathartic to reduce colon caliber and luminal flora (modified Condon-Nichol bowel preparation). Beta-adrenergic antagonists are also administered. Prophylactic antibiotics are also given. If the patient has ventricular dysfunction, a Swan-Ganz catheter is inserted, and cardiac functions are optimized.

The surgery is done under general anesthesia. After giving general anesthesia, a urinary catheter, radial arterial line, and nasogastric tube are inserted. An epidural catheter is also placed for postoperative pain management.

For the transperitoneal approach, the patient is put in a supine position with both arms abducted at 90 degrees. The patient is scrubbed and prepped from the level of nipples to the knees and draped widely for access to the entire abdominal cavity and femoral arteries. All these procedures are carried out in a sterile manner.

For the retroperitoneal approach, the patient is put in a 40-60 degrees right decubitus position, and the left arm is supported with arm support. After this, the kidney rest of the bed is elevated, and the bean bag is inflated to maintain the proper position of the patient. In order to increase the space between the iliac crest and costal margin, further flexion of the table can be done.

Surgical Procedure

Incision: In the transperitoneal approach, a midline abdominal incision is made, and it extends from the level of the xiphoid process to the pubis.

In the retroperitoneal approach, the incision is made infraumbilically. It starts at the lateral border of the rectus sheath and goes up to the 11th or 12th rib.

Surgery: As defined earlier, there are two main surgical approaches that are used: transperitoneal and retroperitoneal approaches. There are differences in both approaches, and therefore, these procedures are explained separately.

Transperitoneal approach: After the midline incision is made, the abdomen is explored carefully, and all the abdominal contents are inspected. The confirmation of proper insertion of urinary catheter and a nasogastric tube is done. The omentum and transverse colon are retracted superiorly, whereas the small intestine is eviscerated to the right of the patient. This helps in the visualization of mesenteries and the left colon. Small intestines are not manipulated vigorously and are not taken out of the abdominal cavity. This reduces the occurrence of postoperative ileus.

After this, the effort is made to expose the infrarenal abdominal aorta. This is done by incising the posterior peritoneum from the ligament of Treitz to the aortic bifurcation. The posterior peritoneum is located between the inferior mesenteric vein and the fourth portion of the duodenum. It is important to dissect on the right side of the inferior mesenteric vein, and this should be done cautiously. This is because there are chances of damaging the inferior mesenteric artery at its origin from the left anterolateral aspect of the aorta halfway between the renal arteries and the aortic bifurcation. The dissection of this area becomes difficult in inflammatory AAA. Ureteral stents can also be placed to avoid ureteral damage in inflammatory AAA or in the presence of pelvic infection.

Then an abdominal, self-retaining retractor is placed on maintaining and facilitating the exposure which has been created. Increasing the exposure superiorly helps in the identification of the left renal vein. The left renal vein crosses the neck of the aneurysm anteriorly. It is extremely necessary to mobilize the left renal vein and ligate its branches (left adrenal vein, left gonadal vein, and lumbar vein) to get proper exposure to the suprarenal aorta. Next, the infrarenal neck of the aneurysm is dissected and mobilized after the identification of renal arteries. The purpose of this is to make space for placing an infrarenal clamp. If there is a need for suprarenal clamping, then both the renal arteries are dissected, and renal arteries are occluded with soft bulldog clamps or fine vessel loops to prevent embolization. As far as inferior dissection is concerned, it is carried down to the level of the aortic bifurcation to expose both common iliac arteries. It is important to avoid excessive dissection of the aortic bifurcation and the proximal common iliac arteries, especially on the left side, to prevent damage to the parasympathetic nerve plexus, which is important in males to maintain normal erectile and ejaculatory function. The ureters are located near the iliac bifurcations, coursing along the anterior surface of the iliac arteries, and care should be taken to avoid injury during dissection and clamping. Circumferential dissection of the iliac arteries can cause injury to the iliac veins, which can result in extensive hemorrhage.

Before clamping, the anesthesia team is informed, and IV heparin is administered (60-70 U/kg), and mannitol (12.5 mg) is given to force diuresis. First, the iliac clamps are placed, and this is followed by the placement of the aortic clamp. This technique reduces the risk of distal embolization. The aortic clamp is placed at a position where the chance of loose thrombus leading to renal embolization is less. If the infrarenal aorta appears “shaggy” on the CT scan or the proximal aortic neck is short, suprarenal clamping is also required. Kidney perfusion with iced heparin is done if suprarenal aortic clamping is done and renal perfusion is interrupted for more than 30 minutes. If the aorta is friable, anastomosis can be supported by Teflo-felt pledges.

The aneurysmal sac is opened longitudinally after clamping using electrocautery, and laminated mural thrombus is removed. Bleeding from the lumbar arteries is controlled with polypropylene suture ligature, and bleeding from the inferior mesenteric artery is controlled with a vessel loop or clamp. If the iliac arteries are not aneurysmal, straight collagen or gelatin-coated zero porosity polyester (Dacron) graft is used for repair. It is sutured with 2-0 or 3-0 polypropylene sutures to the neck of the aneurysm and aortic bifurcation. When the common iliac arteries are involved, a 16- or 18-mm bifurcated graft is used and sutured to the distal common iliac arteries in an end-to-end fashion, using 4-0 polypropylene running sutures. If the internal iliac aneurysm is present, one of the limbs of the graft is connected to the external iliac artery, and the internal iliac artery is reconstructed with an 8-mm interposition graft from the iliac limb to the distal internal iliac artery. Associated external iliac artery occlusive disease is treated with aortofemoral bypass. In all these situations, control of iliac arteries is maintained by mobilization of internal and external arteries and clamping them individually.

Before declamping, both the proximal and distal anastomoses are flushed to remove any loose plaque or thrombus, and suture lines are completed. This also confirms the patency. Then the graft is filled with dilute heparinized saline solution, and the anesthesia team is informed that the aorta will be declamped soon. This allows time for stopping vasodilator infusion and adequate volume replacement. The aortic clamp is removed with caution to minimize hypotension and allow anesthesia for adequate volume replacement.

The inferior mesenteric artery is again reassessed for back bleeding. If there is strong back bleeding, the inferior mesenteric artery is ligated close to the aorta. If the back bleeding is minimal, the inferior mesenteric artery is reimplanted by using the Carrel patch technique.

Once all the clamps have been released, topical hemostatic agents, such as Gelfoam and thrombin, are placed around the anastomosis to promote hemostasis secondary to needle puncture leaks. Any brisk bleeding is controlled with simple reinforcing sutures using 3-0 polypropylene. A side-biting Satinsky clamp is used for the aortic graft, and the anastomosis is performed by running a 4-0 polypropylene suture. At the end of the procedure, two ampules of fluorescein dye IV are injected, and the perfusion pattern of the bowels is assessed with a Woods lamp.

Retroperitoneal Approach: After the incision, lateral abdominal wall muscles, including the external oblique muscle, the internal oblique, and transversus abdominis muscles, are divided with electrocautery. The dissection is usually lateral in the left lower quadrant, and effort is made to enter the retroperitoneum at the lateral border of the rectus sheath. This is done to minimize the risk of entering the peritoneal cavity. The inferior epigastric vessels are usually preserved or ligated if an extension of the incision is required.

Blunt digital dissection is used to free the peritoneum laterally and posteriorly from the overlying muscle fascia, and muscle fascia is divided along the incision. The peritoneum is retracted medially and superiorly to identify the psoas muscle. The dissection is continued, and the left ureter is identified. The ureter is then retracted laterally, and dissection is extended to the left common iliac artery and renal pelvis. This helps in the identification of the gonadal vein. Care is taken to maintain the blood supply to the ureter and avoid excessive dissection of this structure. Injury to the descending colon is also avoided during dissection of the plane over Gerota’s fascia. The dissection is continued further till the left renal vein is identified, and the gonadal vein is ligated at this level to expose the neck of the aorta. The aortic neck and the iliac arteries are then clamped, and the repair and sac closure is carried out the same way as described for the transperitoneal approach. In patients with horseshoe kidney or inflammatory aneurysm and in those who likely need a suprarenal or supra celiac clamp, the ureter and the left kidney are retracted medially with the peritoneal cavity.

Wound Closure: Absorbable 2-0 sutures are used for the approximation of the wall of the aneurysm. Then the peritoneum is reapproximated over the aorta, and the small bowel is returned to the abdominal cavity. The duodenum and surrounding structures are carefully inspected, and the peritoneum is placed between the graft and the duodenum to avoid the formation of aortoduodenal fistulas. The linea alba is closed with 1-0 polydioxanone. If an aortobifemoral bypass has been performed, the groin incisions are closed in layers using 2-0 absorbable sutures. The skin is closed with skin staples.

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