Abdominal Aortic Aneurysm

Well you guessed it, huge AAA. Here's her CT scan: watch quickly, it comes in fast!

The patient underwent sucessful repair, but sustained a very rocky course based on her comorbidities. She coded once in the MICU requiring electrical cardioversion, and is currently in critical but stable condition. Her final dispostion has not been arranged as of yet, and she remains on a ventilator.

To finish, here are a few pearls regarding the disease and ultrasonography of the abdominal aorta...

AAA Tidbits

-AAA's present with variable presentations, from catastrophic hemodynamic status and symptoms, to completely asymptomatic.

-Risk factors include HTN, smoking, age, atherosclerotic vascular disease and genetic predispostition.

-Dilation of the abdominal aorta is considered aneurysmal when the external diameter is >1.5 times normal size (usually any aorta measuring >3 cm is abnormal. Risk of rupture is directly related to the size of the aneurysm.

-The incidence of AAA is 11% in men over age 65! Male:female ratio is 7:1.

-Prior to rupture, most AAA's are asymptomatic.

-The familiar triad of pulsatile mass, back pain and hypotension is seen in less than a third of patients.

Ultrasound Techniques

Use a 2.5 MHz curvilinear transducer

Obtain OUTSIDE WALL to OUTSIDE WALL measurements of the aorta proximally (subxiphoid) and distally (just before the bifurcation into the iliacs near the umbilicus).

Obtain longitudinal views in the same fashion.

Be sure you are completely perpendicular with your measurements as "cylinder tangent error" may occur if you are not, and you will overestimate the diameter of the vessel.

Be careful not to measure the IVC; it frequentlly will be pulsatile as well. Use pulse wave doppler to differentiate.

Bowel gas is the enemy; you may need to lay the patient in the left lateral decubitus position and use the liver as a window to visualize the aorta. Gentle pressure and using the larger abdominal probe may also help in the supine patient.

Good luck, and grab me at any time for help.

Hunter

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