Abdominal aneurysm

Abdominal aneurysm, an abnormal dilation in the arterial wall, generally occurs in the aorta between the renal arteries and iliac branches. Rupture — in which the aneurysm breaks open, resulting in profuse bleeding — is a common complication that occurs in larger aneurysms. Dissection occurs when the artery’s lining tears, and blood leaks into the walls.

Causes and incidence

Abdominal aortic aneurysms result from arteriosclerosis, hypertension, congenital weakening, cystic medial necrosis, trauma, syphilis, and other infections. In children, this disorder can result from blunt abdominal injury or Marfan syndrome. 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.

This disorder is four times more common in men than in women and is most prevalent in whites ages 40 to 70. Less than 50% of people with a ruptured abdominal aortic aneurysm survive.

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.

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 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 stable for hours before shock and death occur, although 20% die immediately.

Diagnosis

Because abdominal aneurysms seldom produce symptoms, they’re commonly detected accidentally as the result of an X-ray or a routine physical examination.

Confirming diagnosis  

Several tests can confirm a suspected abdominal aneurysm. Serial ultrasound (sonography) can accurately determine the aneurysm’s 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 aneurysm’s extent but may underestimate aneurysm diameter because it visualizes only the flow channel and not the surrounding clot. Computed tomography scan is used to diagnose and size the aneurysm. Magnetic resonance imaging can be used as an alternative to aortography.

Treatment

Usually, abdominal aneurysm requires resection of the aneurysm and replacement of the damaged aortic section with a Dacron graft. (See Abdominal aneurysms: Before and after surgery. Also see Endovascular grafting for repair of an abdominal aortic aneurysm, page 1140.) If the aneurysm is small and asymptomatic, surgery may be delayed and the aneurysm may be followed and allowed to expand to a certain size because of possible surgical complications; however, small aneurysms may also rupture. Because of this risk, surgical repair or replacement is recommended for symptomatic patients or for patients with aneurysms greater than 5 cm in diameter.

Stenting is also a treatment option. It can be performed without an abdominal incision by introducing the catheters through arteries in the groin. However, not all patients with abdominal aortic aneurysms are candidates for this treatment.

Regular physical examination and ultrasound checks are necessary to detect enlargement, which may forewarn rupture. Large aneurysms or those that produce symptoms pose a significant risk of rupture and necessitate immediate repair. In patients with poor distal runoff, external grafting may be done.

Risk factor modification is fundamental in the medical management of abdominal aneurysm, including control of hypocholesterolemia and hypertension. Beta-adrenergic blockers are commonly prescribed to reduce the risk of aneurysm expansion and rupture.

Special considerations

Abdominal aneurysm requires meticulous preoperative and postoperative care, psychological support, and comprehensive patient teaching. Following diagnosis, if rupture isn’t imminent, elective surgery allows time for additional preoperative tests to evaluate the patient’s clinical status.

❑ Monitor vital signs, and type and crossmatch blood.

❑ Use only gentle abdominal palpation.

❑ As ordered, obtain renal function tests (blood urea nitrogen, creatinine, and electrolyte levels), blood samples (complete blood count with differential), 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 signs of acute blood loss (decreasing blood pressure; increasing pulse and respiratory rate; 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 caused by 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 pulmonary artery catheter to monitor fluid and hemodynamic balance. Give prophylactic antibiotics as ordered.

❑ Explain the surgical procedure and the expected postoperative care in the intensive care unit (ICU) for patients undergoing complex abdominal surgery (I.V. lines, endotracheal [ET] and nasogastric [NG] intubation, and mechanical ventilation).

❑ After surgery, in the ICU, closely monitor vital signs, intake and hourly output, neurologic status (level of consciousness, pupil size, and sensation in arms and legs), and ABG values. Assess the depth, rate, and character of respirations and breath sounds at least every hour.

❑ Watch for signs of bleeding (increased pulse and respiratory rates and hypotension) and back pain, which may indicate the graft is tearing. Check abdominal dressings for excessive bleeding or drainage. Be alert for temperature elevations 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 values, tidal volume, and vital capacity 24 hours after surgery, he will be extubated and will require oxygen by mask.

❑ Weigh the patient daily to evaluate fluid balance.

❑ Help the patient walk as soon as he’s able (generally the second day after surgery).

❑ Provide psychological support for the patient and his family. Help ease their fears about the ICU, the threat of impending rupture, and surgery by providing appropriate explanations and answering all questions.

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Book Source Details

• Book Title: Professional Guide to Diseases (Eighth Edition)
• Author(s): Springhouse
• Year of Publication: 2005
• Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.

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Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2008 Williams & Wilkins.

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More About This Book: Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X

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