The 2008 ACEP Policy Statement on Emergency Ultrasound Guidelines recommends measuring the maximal aortic diameter in both longitudinal and transverse planes when measuring the aorta and iliacs.

When scanning in the longitudinal plane, avoid inadvertently sweeping the beam into a right parasagittal plane, which may result in visualization of the IVC. Inaccurate measurements can occur when the longitudinal beam is directed at a tangent, resulting in a smaller AP diameter.

To avoid this operator error, measure the aorta in both longitudinal and transverse planes; verifying measurements in two planes ensures dimensions are consistent with the true size of the aorta.

Identifying Abdominal Aorta Pathology

An aorta measuring between 3.0 cm and 4.0 cm is suspicious for an abdominal aortic aneurysm.

In addition, the aorta tapers and becomes more superficial as it moves distally. An aorta that increases in size as it courses through the body, even if within the normal measurement range, may still be aneurysmal.

A common iliac artery measuring greater than 1.5 cm is concerning for an iliac aneurysm.

If an aneurysm is identified, evaluate the peritoneal cavity for free fluid using views similar to the FAST (Focused Assessment by Sonography in Trauma) exam.

Signs of rupture include peritoneal free fluid, retroperitoneal hematoma, and/or lateral displacement of the kidney on the side where the aorta is ruptured.

Most aneurysms that do rupture will leak into the retroperitoneum, which may contain the leak by tamponade and local clotting.

A saccular aneurysm can arise from an aorta with a normal sized lumen and may be missed if the aorta is visualized only in the median plane longitudinally or in intermittent areas transversely.

The major complication of AAA is rupture. Rupture leads to rapid hemodynamic deterioration and death from hemorrhagic shock.

The risk of rupture increases with female sex and increased AAA diameter. Other risk factors include tobacco smoking and hypertension.

The Difficult Aorta: Limitations to Visualization

The most common impediments to visualization of the aorta are bowel gas, obese habitus, and an uncooperative patient in pain. Remember that a focused exam is a rapid evaluation, and minimizing time spent scanning will help to limit the patient’s pain.

In the subxiphoid area, the liver can be used as an acoustic window to view the proximal aorta. In addition, using respiratory variation by asking the patient to take a deep inhalation will lower the diaphragm and liver margin, allowing better visualization of structures beneath.