Abdominal Aortic Aneurysm

Anatomy and Physiology

The main blood vessel exiting the heart is called the aorta. The ascending aorta receives blood from the heart in the chest then curves like a candy cane (aortic arch) down through the chest (descending thoracic aorta) and into the abdomen (abdominal aorta). The aorta gives off branches to the head, chest, arms, abdomen, kidney, and legs. At the level of the belly button, the aorta splits into two arteries. The left iliac artery and the right iliac artery carry blood down to the legs to the left and right legs respectively.

Atherosclerosis is a disease that describes the formation of plaque on blood vessels. Plaque which is composed of cholesterol, calcium, and fibrous tissue settles on the wall of the artery. With the burden of this plaque, the wall of the aorta can weaken and balloon outward causing an aneurysm. An aneurysm is similar in concept to a bubble on a tire or a bubble in a garden hose. The most common location of arterial aneurysm formation is the abdominal aorta below the kidneys (infrarenal aorta). About half of infrarenal abdominal aortic aneurysms (AAA) involve the iliac arteries. Aneurysm formation can occur in other portions of the aorta as well, including the portion of aorta above the renal arteries (suprarenal aorta) and as high as the thoracic aorta.

An aneurysm is a serious health problem because the weakened wall makes it prone to rupture once it reaches a certain size. Rupture of an aneurysm is life-threatening as it causes massive bleeding. Occasionally, debris (emboli) contained within the aneurysm can break off and travel to the legs or other organs blocking the blood flow to these tissues. If the blockage of blood flow is prolonged, death of that tissue can occur.

Who is at Risk?

Risks of developing an aneurysm include age, smoking, high cholesterol, high blood pressure, and diabetes mellitus. Aneurysms are more common in individuals over the age of 60 years. Approximately 6-9% of men over the age of 65 have an AAA. In addition, aortic aneurysms are four to five times more common in males than in females. Lastly, aneurysms tend to run in families.

How is it diagnosed?

Most aneurysms, approximately three-quarters, are detected by chance. They may be seen on a CAT scan of the abdomen performed for a completely different reason. They may also be detected on physical exam as an abnormal pulsation in your abdomen. If your physician suspects that you may have an aneurysm, he or she will send you for an ultrasound to measure the size of your abdominal aorta. If you are found to have an abdominal aortic aneurysm on ultrasound, the next step is to get a CAT scan or MRI to get a better sense of the physical characteristics of the aneurysm.

The most common symptom of an aneurysm is back pain. This is an ominous sign as it usually indicates a pending rupture or partial rupture.

How do I prepare for surgery?

Surgery is recommended for aneurysms greater than 5cm (2 inches). For aneurysms less than 5cm, the risk of rupture is small such that the risk of surgery outweigh the benefit of repair. The risks increase significantly when the aneurysm reaches 5cm and continue to increase thereafter. Surgery is also recommended for aneurysms <5cm, if the aneurysm grows greater than 0.5cm in 6 months or less.

Aortic surgery is a major operation. Your doctor will perform an extensive workup to make sure that you can withstand the operation safely. Since atherosclerosis affects the entire arterial system, patients with an abdominal aortic aneurysm often have other medical conditions such as heart disease, kidney disease, and are at high risk for stroke. Many patients with aneurysms smoked at one point in their life and may have concomitant lung disease. The tests your physicians may ask you to have include a cardiac stress test to test your heart function under exercise. Lung function tests particularly if you are or were a heavy smoker. Lastly, blood work will be obtained to test the function of your kidneys. If any noises (bruits) are heard in your neck during physical examination or if you ever had a stroke, an investigation of your carotid (neck) arteries will be done usually with an ultrasound study. If you are found to have major heart disease or carotid disease, you may be advised to have those conditions corrected before getting your aneurysm repaired.

You will be told not to eat or drink after midnight the night before surgery.

If you take any medications, ask your doctor which ones you should take before surgery. Generally, it is advised that you take all your blood pressure medications the morning before surgery with a very small sip of water.

How is the surgery performed?

Since aneurysm surgery involves making a long incision in your abdomen from your breastbone to down below your belly button, your anesthesiologist may recommend an epidural catheter for pain control after your operation. After the catheter has been placed, you will be put to sleep. A breathing tube will be inserted through your mouth into your windpipe and a machine will breathe for you. A catheter that goes into your blood vessel will be inserted into your neck to allow fluids and medications to be inserted directly into your vein. A catheter will also be placed into your bladder to drain it during the operation and to keep a record of your urinary output.

Once all the anesthesia preparations are performed, your surgeon will start your operation. An incision will be made from the base of your breastbone to below your bellybutton. To reach the aorta which is located just above your spine, your bowels will be moved to the side. Just like a plumber turns off the water valve before working on your pipes, a clamp will be placed onto your aorta just above the aneurysm shutting off blood flow to the area. A second clamp will be placed just below the aneurysm. The aneurysm will be opened, a graft will be sewn to the normal aorta above and below where the aneurysm was. Once the aneurysm is repaired, the clamps will be removed. The abdomen will be closed and you will be taken to the recovery room. Some blood loss is expected and you may receive a blood transfusion during the surgery or afterwards.

An alternative approach to aneurysm repair is via endovascular means. While proving to be a promising, minimally invasive method to fix aneurysms, its long-term durability is not yet proven. Endovascular repair of AAA is achieved by making small 3-inch incisions in your groin on both sides to reveal the common femoral artery. The stent graft device is introduced into the common femoral artery and brought up into the aorta. The stent graft is seated just below the arteries to your kidneys into your aorta and often extends to the common iliac artery on both sides. The incisions are then closed, usually with absorbable suture. This approach avoids the large abdominal incision that must be made in the open approach. In addition, it is shorter and reduces the required time under general anesthesia. In some cases, surgery is done under local or regional anesthesia.

Complications of Surgery

As with every surgery, bleeding is always a risk. The risk of bleeding is higher with surgeries involving repair of blood vessels. More than half of all patients undergoing aneurysm repair will need a blood transfusion. Bleeding after surgery may require a second trip back to the operating room to wash out all the blood clots. Infection of the surgical wound is also a potential risk. More often than not, this can be managed with antibiotics.

Open Repair

The risks of surgery tend to relate to decreased blood flow to various tissues and organs of the body. Cardiovascular complications such as heart attack and stroke, while rare, are the most common. Lung complications including the need for supplemental oxygen, dependence on a ventilator or breathing machine, and pneumonia are the second most common. Other serious complications that happen less frequently include temporary kidney failure, rarely permanent renal failure requiring dialysis. This complication tends to occur in patients who already have some degree of kidney disease. Decreased blood flow to the bowels leading to an operation to remove dead bowel is another rare but serious complication. Paraplegia could also result from decreased blood flow to the spinal cord.

Infection of the aortic graft is a complication that tends to occur many years after the operation. A serious and potentially deadly complication, it requires removal of the graft and performance of a bypass to restore blood flow to the legs.

Endovascular Repair

The complications of endovascular repair mimic some of the same complications seen with open repair but to a lesser extent. There are few other complications unique to endovascular repair that are worth mentioning. Endovascular repair is still relatively new and its long-term durability has not yet been proven. Hence surveillance with regular, yearly abdominal CAT scans is needed. The CT scans may reveal an endoleak which is a persistent leak of blood around the aortic repair. A continual leak of blood prevents the aneurysm from shrinking and the risk of rupture remains. Some types of endoleaks can be watched, others require a number of interventions usually endovascular to seal the leak. Ultimately, if the leak cannot be fixed endovascularly, an open operation may be necessary to definitively fix the aneurysm. Other graft-related problems can include kinking of the graft cutting off blood flow to the legs or migration of the graft. An attempt to fix the problem via endovascular means is always made first. Finally, CT scans require the use of a contrast agent to visualize the arteries. This contrast can be toxic to the kidneys. In patients with a history of kidney disease, this could lead to worsening kidney function.

What to expect after surgery?

You will likely stay in the ICU for 24-48 hours to monitor your blood pressure and obtain respiratory therapy. You can help to minimize complications by coughing and doing breathing exercises. Since your bowels are moved out of the way to identify the aorta, a tube will be inserted through your nose into the stomach. When the bowels are manipulated, they become stunned and do not contract normally. If you eat too soon after surgery, you may vomit. Clear liquids and then eventually regular food will be started about two to three days after surgery. You will be encouraged to get out of bed as early as day one to a chair followed by walking in the halls. Patients are generally discharged from the hospital between five and ten days after an open repair and one to three days after an endovascular repair. Discharge is mostly dependent upon being able to eat without being nauseous or vomiting, having a bowel movement, being off oxygen, and being able to walk around enough to perform your activities of daily living.

At home, you should avoid lifting anything greater than a yellow pages phone book. Driving is not allowed while you are on pain medication as the pain medication can make you confused and lightheaded. In general, before driving, you should simulate driving maneuvers and making rapid turns in your car on your driveway before you take the road. There are no dietary restrictions, although you should attend to a low-fat, heart-healthy diet. All efforts should be made to quit smoking. Your surgeon will generally want to see you back anywhere from 2 to 4 weeks.