Abdominal Aneurysm

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. More than 50% of all people with untreated abdominal aneurysms die within 2 years of diagnosis, primarily from rupture of the aneurysm; more than 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, most are evident (unless the patient is obese) as a pulsating mass in the periumbilical area, accompanied by a systolic bruit over the aorta. Some tenderness may be present on deep palpation. A large aneurysm may produce symptoms that mimic renal calculi, lumbar disk disease, and duodenal compression. Abdominal aneurysms rarely cause diminished peripheral pulses or claudication unless embolization occurs.
• Pain, rupture, and hemorrhage
• Lumbar pain that radiates to the flank and groin from pressure on lumbar nerves may signify enlargement and imminent rupture. If the aneurysm ruptures into the peritoneal cavity, it causes severe, persistent abdominal and back pain, mimicking renal or ureteral colic.
• Signs and symptoms of hemorrhage—such as weakness, sweating, tachycardia, and hypotension—may be subtle because rupture into the retroperitoneal space produces a tamponade effect that prevents continued hemorrhage. Patients with such rupture may remain in stable condition for hours before shock and death occur, although 20% die immediately.

Diagnosis
Because an abdominal aneurysm rarely produces symptoms, it’s usually 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 aneu-rysm 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 rupture. A beta-adrenergic blocker 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 prestage a rupture.

In asymptomatic patients, surgery is advised when the aneurysm is 5 to 6 cm (2? to 2¼ ?) in diameter. In symptomatic patients, repair is indicated regardless of size. In patients with poor distal runoff, external grafting may be done. (See Endovascular grafting for repair of an abdominal aortic aneurysm.)

Special considerations

• Monitor vital signs and type and crossmatch blood.
• Obtain kidney function tests (blood urea nitrogen, creatinine, and electrolyte levels), 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).
• If rupture does occur, the first priority is to get the patient to surgery immediately. A pneumatic antishock garment may be used while transporting him to surgery. Surgery allows direct compression of the aorta to control hemorrhage. Large amounts of blood may be needed during the resuscitative period to replace blood loss. In such a patient, renal failure due to ischemia is a major postoperative complication, possibly requiring hemodialysis.
• Before elective surgery, weigh the patient, insert an indwelling urinary catheter and an I.V. line, and assist with insertion of an arterial line and a pulmonary artery catheter to monitor fluid and hemodynamic balance. Also, give him a prophylactic antibiotic.
• If the patient is undergoing complex abdominal surgery (that is, with I.V. lines, endotracheal [ET] and nasogastric [NG] intubation, and mechanical ventilation), explain the surgical procedure and the expected postoperative care in the intensive care unit (ICU).
• After surgery, closely monitor vital signs, intake and hourly output, neurologic status (level of consciousness, pupil size, and 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 retroperitoneally from the graft site. Check abdominal dressings for excessive bleeding or drainage.
• Be alert for fever and other signs of infection.
• After NG intubation for intestinal decompression, irrigate the tube frequently to ensure patency. Record the amount and type of drainage.
• Suction the ET tube often. If the patient can breathe unassisted and has good breath sounds and adequate ABG levels, tidal volume, and vital capacity 24 hours after surgery, he’ll be extubated and require oxygen by mask. Weigh the patient daily to evaluate fluid balance.
• Help the patient walk as soon as he’s able (generally the 2nd day after surgery).
• Provide psychological support for the patient and family. Help ease their fears about the ICU, the threat of impending rupture, and surgery by providing appropriate explanations and answering all questions.