Chapter 5

Abdominal aortic aneurysm (AAA) has an adult incidence of 2%–4%, with approximately 10% of these cases occurring in people over the age of 65. The prevalence increases with risk factors for vascular disease, particularly smoking and hypertension. AAA has a male to female preponderance of 8:1 and may be present in as many as 10% of elderly male patients with at least one risk factor.

The rapid and accurate diagnosis of AAA at the bedside is important in decreasing the morbidity and mortality that may be associated with this disease entity. Bedside ultrasound has been shown to be a quick and reliable method to diagnose AAA in the critical care setting. Sensitivity and specificity of ultrasound are high when the aorta is visualized completely.

AAA rupture is among the top leading causes of death in the United States. When aneurysms rupture, they are highly lethal, with a mortality rate exceeding 50%. Ultrasound is not sensitive for rupture, as most ruptures occur into the retroperitoneum, which is a difficult area to visualize with ultrasound. In a stable patient, computed tomography (CT) still represents the best method for defining the extent of the aneurysm and the presence of leak or rupture. Although ultrasound does not detect rupture well, it has been shown to expedite care in patients who are hemodynamically unstable. In hemodynamically unstable symptomatic patients (abdominal pain, flank pain, back pain), the presence of an aneurysm is likely to mean leak or rupture and should prompt immediate preparation for operative intervention.

Ultrasound may also visualize aortic dissection. While ultrasound should not be used to rule out dissection (sensitivity is not good), specificity is high when a flap or false lumen is visualized. In particular, thoracic aneurysm and dissection are emergent, deadly diseases that may also be seen using bedside cardiac ultrasound, and may be a cause of pericardial effusion or tamponade. Contrast-enhanced CT, magnetic resonance imaging (MRI), and transesophageal echocardiography (TEE) remain the modalities of choice for thoracic aortic pathology.

Bedside ultrasound evaluation of the abdominal aorta should be performed in:

• The patient with undifferentiated hypotension, shock, or syncope
• The elderly patient with undifferentiated abdominal, flank, or back pain

### Curvilinear Probe with a Frequency of 3.5–5.0 MHz

Lower frequencies, which provide better penetration, may be helpful in obese patients or when significant bowel gas is present.

### Tissue Harmonic Imaging

Tissue harmonics may help to sharpen the image and improve visualization of the aorta and associated deep vessels.

### Focal Zone

The focal zone should be adjusted and placed at the depth of the aorta. This improves the lateral resolution of the image.

### Color-Flow Doppler

Color-flow Doppler detects blood flow and therefore is helpful in identifying a blood vessel and distinguishing it from other artifacts that may be ...

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