ABDOMINAL AORTIC ANEURYSM
Abdominal aortic aneurysm (AAA) is defined by an abdominal aortic diameter greater than or equal to 3 cm. Aortic aneurysms occur as the elastic connective tissue of the aortic wall weakens, resulting in aortic dilatation. Risk factors include male gender, hypertension, smoking, advancing age, and family history. As the aortic diameter increases, the risk of rupture rises. Current recommendations call for elective repair of AAA ≥ 5.5 cm. Rupture of an aortic aneurysm can lead to immediate and catastrophic hemorrhagic shock. Clinical signs and symptoms of AAA rupture can include syncope or cardiac arrest, abdominal and/or back pain, lightheadedness, and hypotension. Classically, a pulsatile mass is present on exam, but the absence of this finding does not rule out the disease. More subtle presentations can include extremity or groin pain as well as neurologic symptoms related to spinal cord hypoperfusion.
In the United States, AAA rupture is among the top 15 causes of death in patients older than 60 years of age. Early mortality in AAA rupture is around 90% (including out of hospital deaths), and 20% to 30% with operative repair. Without repair, one in eight patients dies within 2 hours of arrival to the hospital.
Emergency Care and Disposition
When AAA rupture is suspected, immediate resuscitative steps should include large bore intravenous (IV) access, preoperative laboratory studies including type and cross-match for massive blood transfusion, and surgical consultation based on suspicion alone. Unstable patients should be considered for operative care before definitive diagnosis.
Bedside ultrasound can be used to assess the presence of AAA. Because ultrasound is relatively insensitive for rupture, the presence of AAA in a symptomatic patient should be considered a strong surrogate for rupture. When ultrasound is used, the entire abdominal aorta (from xiphoid process to the iliac bifurcation at the level of the umbilicus) and the proximal iliac arteries should be screened. The majority of AAAs are infrarenal. Care should be taken to identify intravascular mural thrombus, which should be included in the measurement of aortic diameter. If mural thrombus is not recognized in the lumen and the thrombus is mistaken as part of the aortic wall, aortic size may be underestimated and the diagnosis missed.
(A) Ultrasound imaging of this acute aortic aneurysm (AAA) correctly measures the complete diameter (including mural thrombus) of the aorta at about 6 cm. (B) This ultrasound image underestimates the diameter of the aorta at about 4 cm because the patent lumen alone is measured.
Hemodynamically stable patients can be considered for rapid computer tomographic (CT) assessment. CT without contrast media can detect the presence of AAA and AAA ...