Continuing Education Activity

An abdominal aortic aneurysm is a life-threatening condition that requires monitoring or treatment depending on the size of the aneurysm and/or symptomatology. An abdominal aortic aneurysm may be detected incidentally or at rupture time. An arterial aneurysm is defined as a permanent localized dilatation of the vessel by at least 150% compared to a relatively normal adjacent diameter of that artery. Risk factors for AAA include atherosclerosis (most common), smoking, advanced age, male gender, White race, family history of AAA, hypertension, hypercholesterolemia, and prior history of aortic dissection. This activity reviews the evaluation and management of abdominal aortic aneurysms and the need for an interprofessional team approach to improve the recognition of abdominal aortic aneurysms and enhance patient outcomes.

Objectives:

• Describe the histopathology of abdominal aortic aneurysms.
• Identify the location of most abdominal aortic aneurysms relative to the origin of the renal arteries.
• Outline some actions patients diagnosed with abdominal aortic aneurysms can take to lessen the risk of rupture.
• Summarize how interprofessional team strategies can improve the diagnosis and management of abdominal aortic aneurysms.

Introduction

Abdominal aortic aneurysm (AAA), abnormal focal dilation of the abdominal aorta, is a life-threatening condition that requires monitoring or treatment depending upon the size of the aneurysm and/or symptomatology. AAA may be detected incidentally or at the time of rupture. An arterial aneurysm is defined as a permanent localized dilatation of the vessel by at least 150% compared to a relatively normal adjacent diameter of that artery.[1]

Etiology

Risk factors for AAA include atherosclerosis (most common), smoking, advanced age, male gender, White race, family history of AAA, hypertension, hypercholesterolemia, and prior history of aortic dissection. Other causes include cystic medial necrosis, syphilis, HIV, and connective tissue diseases (Ehlers-Danlos, Marfan, Loeys-Dietz syndromes). Non-White race and diabetes are associated with a reduced risk for AAA.

Aneurysm enlargement can be step-wise with the stability of the size for some time and then a more rapid enlargement. The rate of enlargement for small AAA (3 to 5 cm) is 0.2 to 0.3 cm/year and 0.3 to 0.5 cm/year for those with a greater than 5 cm diameter.[2] The pressure on the aortic wall follows the Law of Laplace (wall stress is proportional to the radius of the aneurysm). Accordingly, larger aneurysms are at higher risk of rupture, and the presence of hypertension also increases this risk.

Epidemiology

Based on autopsy studies, the frequency of these aneurysms varies from 0.5% to 3%. The incidence of abdominal aortic aneurysms increases after age 60 and peaks in the seventh and eighth decades of life. White men have the highest risk of developing abdominal aortic aneurysms. They are uncommon in Asian, African American, and Hispanic individuals.[3] Data derived from Lifeline AAA screening and National Health and Nutrition Examination Survey (NHANES, 2003-2006) database reveals a prevalence of 1.4% or 1.1 million AAAs in those studied aged 50 to 84.[4] 

With the increased use of ultrasound, diagnosing abdominal aortic aneurysms is quite common. They tend to be more common in smokers and elderly white males. Although autopsy studies may under-represent the incidence of AAA, one study from Malmo, Sweden, found a prevalence of 4.3% in men and 2.1% in women detected on ultrasound.[5]

Pathophysiology

Abdominal aortic aneurysms tend to occur when there is a failure of the structural proteins of the aorta. What causes these proteins to fail is unknown, but it results in the gradual weakening of the aortic wall. The decrease in structural proteins of the aortic wall, such as elastin and collagen, has been identified.[6][7][8] The composition of the aortic wall is made of collagen lamellar units. The number of lamellar units is lower in the infrarenal aorta than in the thoracic aorta.[8][9][10] This is felt to contribute to the higher incidence of aneurysmal formation in the infrarenal aorta. A chronic inflammatory process in the wall of the aorta has been identified but is of unclear etiology.[11]

Other factors that may play a role in the development of these aneurysms include genetics, marked inflammation, and proteolytic degradation of the connective tissue in the aortic wall.[12][13][14]

Histopathology

Autopsy studies usually show marked degeneration of the media. Examination of resected abdominal aortic aneurysms usually reveals a state of chronic inflammation with an infiltrate of neutrophils, macrophages, and lymphocytes. The media is often thin, and there is evidence of degeneration of the connective tissue.

History and Physical

Most abdominal aortic aneurysms are identified incidentally during an examination for another unrelated pathology. Most individuals are asymptomatic. Palpation of the abdomen usually reveals a non-tender, pulsatile abdominal mass. Enlarging aneurysms can cause symptoms of abdominal, flank, or back pain. Compression of adjacent viscera can cause gastrointestinal (GI) or renal manifestations.

The rupture of an abdominal aortic aneurysm is life-threatening. These patients may present in shock, often with diffuse abdominal pain and distension. However, the presentation of patients with this type of ruptured aneurysm can vary from subtle to quite dramatic. Most patients with a ruptured abdominal aortic aneurysm die before hospital arrival. On physical exam, the patient may have tenderness over the aneurysm or demonstrate signs of embolization. The aneurysm may rupture into adjacent viscera or vessels, presenting with GI bleeding or congestive heart failure due to the aortocaval fistula. A physical exam should also look for other associated aneurysms. The most common associated aneurysm is an iliac artery aneurysm. Peripheral aneurysms are also associated with approximately 5 % of patients, of which popliteal artery aneurysms are the most common.

Evaluation

The diagnosis of an abdominal aortic aneurysm is usually made with ultrasound (US). Still, a CT scan is needed to determine the exact location, size, and involvement of other vessels and the imaging of choice in symptomatic patients. The US can be used for screening purposes but is less accurate for aneurysms above the renal arteries because of the overlying air-containing lung and viscera. CTA requires the use of ionizing radiation and intravenous contrast. Magnetic resonance angiography can be used as well to delineate the anatomy and does not require ionizing radiation.

Most of these aneurysms are located below the origin of the renal arteries. They may be classified as saccular (localized) or fusiform (circumferential). More than 90% of abdominal aortic aneurysms are fusiform. Some people may develop an inflammatory abdominal aortic aneurysm characterized by intense inflammation, a thickened peel, and adhesions to adjacent structures. Angiography is now rarely done to make the diagnosis because of the superior images obtained with CT scans.[15]

For those patients with allergies to contrast media, MRA is an option. An echocardiogram is recommended as many patients also tend to have associated heart disease.

All patients need routine blood work, including a cross-match if surgery is necessary. Patients with comorbidity like diabetes, COPD, or heart disease should be seen by the relevant specialist and cleared for surgery.

Treatment / Management

The treatment of unruptured abdominal aortic aneurysms has changed over time. Treatment is recommended when the aneurysm diameter reaches 5 to 5.5 cm, is demonstrated as rapidly enlarging for greater than 0.5 cm over six months, or becomes symptomatic. Open surgical repair via transabdominal or retroperitoneal approach has been the gold standard. Endovascular repair from a femoral arterial approach is now applied for most repairs, especially in older and higher-risk patients. Endovascular therapy is recommended in patients who are not candidates for open surgery. This includes patients with severe heart disease and/or other comorbidities that preclude open repair. A ruptured abdominal aortic aneurysm warrants emergency repair. The endovascular approach for ruptured AAA has demonstrated superior results and survival compared to open repair if the anatomy is suitable, but the mortality rates remain high. The risk of surgery is influenced by the patient's age, the presence of renal failure, and the status of the cardiopulmonary system.[16][17]

Data show that for unruptured abdominal aortic aneurysms, endovascular repair has no long-term differences in outcomes compared to open repair. However, data indicates that expansion of the neck of the aorta continues despite endovascular therapy, which is of concern. The need to take beta-blockers cannot be understated in these patients. An open repair has been the gold standard for AAA repair for many decades. It involves a long midline incision followed by replaced of the diseased aorta with a graft. Postoperatively, these patients do need close monitoring in the ICU for 24 to 48 hours.

All patients with small abdominal aortic aneurysms who do not undergo repair need periodic follow-ups with an ultrasound every 6 to 12 months to ensure the aneurysm is not expanding.[18]

Traditionally, the anatomic eligibility for endovascular aortic aneurysm repair was mainly based on three major indexes, 1. the proximal aortic neck, 2. common iliac arteries, and 3. external iliac and common femoral arteries. The mentioned index areas characterize the proximal and distal landing zones. In the proximal aortic neck of less than 15 mm, an endovascular approach is not indicated.[19] However, the endovascular approach to managing complex aortic aneurysms has been widely approved. The endovascular approach might be utilized in managing thoracoabdominal, pararenal, and juxtarenal aneurysms.[20]

Fenestrated and branched endovascular aneurysm repair (F/B-EVAR) application in managing aortic aneurysms elucidated obvious advantages, including fewer perioperative complications. The advantage was specifically significant in high-volume vascular centers.

The selected stent graft and the characteristics of the stent durability identify the long-term efficacy of the (F/B-EVAR) procedures. F-EVAR and B-EVAR procedures are frequently reported together, and the separate effects of the procedures have not been discussed thoroughly. However, the stent selection, either balloon-expandable (B-EXP) versus self-expandable (S-EXP) stent-graft, is mainly affected by the surgeon's preferences.[21]

Institutional algorithms for juxtarenal aortic aneurysm (JRA) repair have discussed the factors affecting decision-making for the (F/B-EVAR) procedures. However, absolute indications or contraindications criteria in the patient selection are lacking.[22] Accordingly, high-surgical risk and appropriate morphology would mainly affect the decision-making toward the fenestrated endovascular repair. The aneurysm morphology characteristics to be reviewed include 1. visceral and renal artery localization, 2. number of arteries, 3. iliac access, and 4. shaggy aorta.[22] 

Considering the complications with Fenestrated endovascular graft and fenestration stent repair, in-stent stenosis of bare metal renal stents is regarded as the most common indication for secondary intervention. The low rate of type IA endoleak, sac enlargement, and device migration favor the use of fenestrated endovascular repair in patients with juxtarenal AAAs.[23]

SVS Guidelines on Management of Patients With Abdominal Aortic Aneurysms

The Society for Vascular Surgery (SVS) issued updated guidelines on the care of patients with abdominal aortic aneurysms that include the following:

• Yearly surveillance imaging in patients with an AAA of 4.0 to 4.9 cm in diameter
• Assessment of distal leg pulses at each clinic visit
• For unruptured AAA, endovascular aneurysm repair (EVAR) is recommended
• The endovascular procedure should only be done in a hospital that has performed at least 10 cases every year and has a conversion rate to open of less than 2%
• Elective AAA open surgery should be done in hospitals with a mortality of less than 5%, and that perform at least ten open cases a year.
• For ruptured AAA, a facility with a door-to-intervention time of fewer than 90 minutes is preferred.
• Recommend treatment of type I and III endoleaks and type II endoleaks with aneurysm expansion.
• Antibiotic prophylaxis is not recommended before respiratory tract procedures, genitourinary, dermatologic, gastrointestinal, or orthopedic procedures unless there is a potential for infection in an immunocompromised patient.
• Color duplex ultrasonography should be used for postoperative surveillance after endovascular surgery.
• A preoperative 12-lead electrocardiogram is recommended in all patients undergoing EVAR or open surgical repair within four weeks of the elective surgery.
• If the patient just had a drug-eluting stent placed, open aneurysm surgery should be delayed for at least six months, or one can perform endovascular surgery while the patient is on dual antiplatelet therapy.
• Only transfuse blood perioperatively if hemoglobin is less than 7 g/dL
• Elective repair should be recommended in low-risk patients when the AAA is 5.5 cm
• The open surgery should be done under general anesthesia[24]

Differential Diagnosis

The differential diagnosis for AAA includes the following:

• Mesenteric ischemia
• Peptic ulcer disease
• Diverticulitis
• Pyelonephritis
• Myocardial infarction
• Ureteric colic[25]

Prognosis

Once an abdominal aortic aneurysm ruptures, the prognosis is grim. More than 50% of patients die before they reach the emergency room. Those who survive have very high morbidity. Predictors of mortality include preoperative cardiac arrest, age >80, female gender, massive blood loss, and ongoing transfusion.[26] In a patient with a ruptured abdominal aortic aneurysm, the one factor determining mortality is the ability to get proximal control. For those undergoing elective repair, the prognosis is good to excellent. However, long-term survival depends on other comorbidities like chronic obstructive pulmonary disease, heart disease, and peripheral vascular disease. It is estimated that 70% of patients will survive for five years after repair.

Complications

• Bleeding
• Limb ischemia
• Delayed rupture secondary to endoleak
• Abdominal compartment syndrome
• Myocardial infarction
• Pneumonia
• Graft infection
• Colon ischemia
• Renal failure
• Bowel obstruction
• Blue toe syndrome
• Amputation
• Impotence
• Lymphocele
• Death

Postoperative and Rehabilitation Care

After repair, it is essential that the patient discontinue smoking, eat a healthy diet, and maintain a healthy weight. Physical and/or occupational therapy may be necessary. Obtaining computed tomography five years following the open repair management to exclude the late aortic dilation or pseudoaneurysm is recommended.

Consultations

Once an abdominal aortic aneurysm is diagnosed, the patient should be referred to a vascular surgeon. Surveillance imaging at 12-month intervals is recommended for patients with an AAA of 4.0 to 4.9 cm in diameter.[27]

To ensure that the patient is fit for surgery, cardiology and pulmonology, as indicated, are recommended.

Deterrence and Patient Education

Many patients with abdominal aortic aneurysms (AAAs) can live healthy, symptom-free lives. The decision to have surgery involves weighing the risk of aneurysmal rupture against the risks and benefits of the surgical procedure. While the aneurysm size and the rate at which it enlarges are included in some general guidelines, each treatment decision should be made individually. Clinicians should discuss the surgical risks with their patients so they can make informed decisions.

Pearls and Other Issues

• Patients with abdominal aortic aneurysms should quit smoking to reduce the risk of enlargement.
• Medical optimization of hypertension, hyperlipidemia, diabetes, and other atherosclerotic risk factors should be assessed.
• Moderate exercise does not cause a rupture of AAA expansion.[28]
• The Society for Vascular Surgery Guidelines recommends ultrasound screening for all men and women 65 years or older who have smoked or have a family history of AAA(20).
• Surveillance Guidelines for AAA per the Society for Vascular Surgery using duplex US are the following:
  • 3-year intervals for patients with an AAA between 3.0 and 3.9 cm
  • 12-month intervals for patients with an AAA of 4.0 to 4.9 cm in diameter.
  • 6-month intervals for patients with an AAA between 5.0 and 5.4 cm in diameter
• Those patients with an initial aortic diameter <3 cm has a low risk of rupture. At this time, there are no recommendations for surveillance; however, it should be noted that gradual expansion in these patients has been noted over time.
• Patients presenting with symptomatic AAA should be considered for urgent repair.
• Asymptomatic patients with AAA demonstrating an aortic diameter > 5.4 cm or those with the rapid expansion of small AAA should be evaluated for repair.
• The goal of AAA repair is to increase survival. Consideration of quality of life after the repair is essential, particularly in those with shortened life expectancy due to medical comorbidities or cancer.
• Endovascular repair may offer fewer complications and better quality of life in those at high risk for open repair up to 1-year post-intervention.[29]

Factors that increase the operative risk for abdominal aortic aneurysm repair include:

• Severe heart disease.
• Severe chronic obstructive pulmonary disease.
• Poor renal function
• Comorbidities such as stroke, diabetes, hypertension, and advanced age can increase open surgical risk. If the aortic anatomy permits, these individuals should be considered for endovascular stenting of the aneurysm.

Infrarenal Aortic Aneurysm Repair

Consideration for repair is appropriate for all symptomatic aneurysms. Aortic anatomy and device availability can dictate the approach. Open aneurysm repair had been the gold standard but carried increased risk and potential complications, which may be acceptable in a younger, good surgical-risk patient. This is still a more durable procedure. Endovascular repair is now an established technique for repairing an abdominal aortic aneurysm. This minimally invasive procedure can also be offered but has better outcomes and durability when the anatomy meets device-specific recommendations. This is the preferred approach in rupture cases and patients with multiple risk factors or shortened life expectancy. Intervention or surgical treatment risks versus benefits of repair in patients at increased risk for open surgery should be considered, and no intervention may be appropriate in some cases. 

Patients should be well informed regarding their options, risks of repair, and potential postoperative complications. Endovascular repair requires life-long follow-up with imaging as early or late endoleaks may develop, causing aortic sac pressurization and rupture. Secondary interventions may be necessary, the majority of which are minimally invasive. Still, there is a small chance that an open conversation with the stent-graft removal may be required when these secondary endovascular interventions fail.

Enhancing Healthcare Team Outcomes

Infrarenal abdominal aortic aneurysms are the most common aneurysms of the aorta. Screening ultrasound has helped detect AAA and allows for surveillance in asymptomatic patients with a diameter < 5 cm. In females, the repair should be considered at 5 cm, and in males, at 5.5 cm. If rapid enlargement is demonstrated (>5 mm over six months), repair should be considered. Education of first responders, including the nurse practitioner, triage nurse, primary care physicians, physician assistants, and emergency department physicians, can facilitate diagnosis and reduce delays in treatment.

An interprofessional team approach of emergency nurses, emergency physicians, intensivists, radiologists, and a vascular surgeon will facilitate rapid evaluation and treatment and improve outcomes. The vast majority of patients with AAA initially present to the emergency department with vague abdominal pain and/or a pulsatile mass. Thus, the triage nurse must be familiar with the presentation of an AAA and initiate a rapid admission with direct communication to the emergency department physician and the rest of the interprofessional team about the patient. Once admitted, if stable, these patients need an urgent ultrasound, so the radiologist needs to be notified. If the patient is unstable, the nurse should obtain vitals, attach monitoring equipment, and assist with resuscitation if the patient is hemodynamically unstable.

Referral to a vascular center that can provide a standard of care management is appropriate. Once the decision for repair has been made, cardiology workup and clearance and optimization of other medical co-morbidities can improve outcomes. If the aneurysm is small, the patient and family should be educated by the interprofessional team regarding compliance with blood pressure control, a healthy diet, exercise, cessation of smoking, and follow-up.

During postoperative care, the nurse has to be familiar with potential complications of the surgery and notify the interprofessional team if the patient has abdominal or back pain, wound discharge, fever, oliguria, or hypotension. The nurse should also ensure that the patient has prophylaxis for deep vein thrombosis prevention. The respiratory therapist has to encourage deep breathing and coughing, and the physical therapist has to encourage ambulation. The nurse should also auscultate for bowel sounds and convey the results to the interprofessional team so that feeding can be initiated. Before discharge, the pharmacist and nurse should educate the patient on the importance of medication compliance, the need to control blood pressure, and avoiding tobacco. The nurse should also ensure that the appropriate consulting physician/dietitian/social workers have seen the patient and the surgeon notified prior to discharge. Open communication between the interprofessional team is vital to ensure good outcomes. [Level 5]

Outcomes

For elective AAA repair, the outcomes are good, with minimal morbidity. However, if a rupture has occurred, the mortality rates can exceed 50%. Current guidelines suggest that patients with AAA should have the surgery in hospitals with an interprofessional team approach to dealing with this pathology. To improve outcomes, it is vital that the patient stop smoking, maintain a healthy body weight, control their blood pressure, and remain compliant with medications.