Abdominal Aortic Aneurysm

In abdominal aneurysm, an abnormal dilation in the arterial wall generally occurs in the aorta between the renal arteries and iliac branches. Such aneurysms are four times more common in men than in women and are most prevalent in whites ages 50 to 80. Over 50% of all people with untreated abdominal aneurysms die within 2 years of diagnosis, primarily from aneurysmal rupture; over 85%, within 5 years.

Causes

About 95% of abdominal aortic aneurysms result from arteriosclerosis; the rest, from cystic medial necrosis, trauma, syphilis, and other infections. These aneurysms develop slowly.

First, a focal weakness in the muscular layer of the aorta (tunica media), due to degenerative changes, allows the inner layer (tunica intima) and outer layer (tunica adventitia) to stretch outward. Blood pressure within the aorta progressively weakens the vessel walls and enlarges the aneurysm.

Signs and symptoms

Although abdominal aneurysms usually don't produce symptoms. If an aneurysm expands rapidly, tears open (ruptured aneurysm), or blood leaks along the wall of the vessel (aortic dissection), symptoms may develop suddenly.

The symptoms of rupture include:

Pulsating sensation in the abdomen
Pain in the abdomen that is severe, sudden, persistent, or constant. The pain may radiate to groin, buttocks, or legs.
Abdominal rigidity
Pain in the lower back that is severe, sudden, and persistent. The pain may radiate to the buttocks, or legs.
Anxiety
Nausea and vomiting
Shock

Diagnosis

Because an abdominal aneurysm rarely produces symptoms, its often detected accidentally as the result of an X -ray or a routine physical examination. Several tests can confirm suspected abdominal aneurysm;

Serial ultrasonography allows accurate determination of aneurysm size, shape, and location.
Anteroposterior and lateral X-rays of the abdomen can detect aortic calcification, which outlines the mass, at least 75% of the time.
Aortography shows the condition of vessels proximal and distal to the aneurysm and the extent of the aneurysm but may underestimate the aneurysm's diameter because it visualizes only the flow channel and not the surrounding clot.

Treatment

Usually, an abdominal aneurysm requires resection of the aneurysm and replacement of the damaged aortic section with a Dacron graft. If the aneurysm is small and produces no symptoms, surgery may be delayed; however, small aneurysms may also rupture. Beta blockers may be administered to decrease the rate of growth of the aneurysm. Regular physical examinations and ultrasound checks are necessary to detect enlargement, which may presage a rupture. In asymptomatic patients, surgery is advised when the aneurysm is 2" to 2.3"(5 to 6 cm) in diameter. In symptomatic patients, repair is indicated regardless of size. In patients with poor distal runoff, external grafting may be done.

Special considerations

Monitor vital signs, and type and cross match blood.
Obtain kidney function tests (blood urea nitrogen, creatinine, electrolytes), blood samples (complete blood count with differential), an electrocardiogram and cardiac evaluation, baseline pulmonary function tests, and arterial blood gas (ABG) analysis.
Be alert for signs of rupture, which may be immediately fatal. Watch closely for any signs of acute blood loss (decreasing blood pressure; increasing pulse and respiratory rates; cool, clammy skin; restlessness; and decreased sensorium).
After surgery, closely monitor vital signs, intake and hourly output, neurologic status (level of consciousness, pupil size, sensation in arms and legs), and ABG levels.
Assess the depth, rate, and character of respirations and breath sounds at least every hour.
Watch for signs of bleeding (such as increased pulse and respiratory rates and hypotension), which may occur retro-peritoneally from the graft site. Check abdominal dressings for excessive bleeding or drainage.
Be alert for fever and other signs of infection.

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