Check out that image! Wow!
As we all know, a ruptured AAA or aortic dissection is a true vascular emergency and the ability to rapidly diagnose these 2 entities is critical…this is where bedside emergency ultrasound combined with clinical correlation can SHINE!
Our definitive ED question for the evaluation of the aorta is "does the aorta measure more than 3cm or the iliacs more than 1.5cm?"
Any patient with abdominal pain, back pain, flank pain (and even hematuria on UA) who may have diminished lower extremity pulses or feeling lower extremity weakness should be considered to have a AAA. If they are hypotensive, then consider it ruptured. On ultrasound, make sure to avoid the common error of visualizing only one section of the aorta and being reassured. As 90% of AAA are infrarenal, it is essential to scan the entire abdominal aorta (from proximal aorta down to the bifurcation). You should slide the transducer down the abdomen seeing the aorta in transverse axis the entire way (indicator toward the patient's right and using the vertebral body spine shadow as your landmark). Make sure not to mistake the IVC for the aorta (ensure your indicator is pointed in the correct direction matching the dot on the screen being on your left. You can also use doppler to differentiate venous from arterial waveforms). If you are fighting bowel gas or habitus, apply steady pressure to help to push the gas away. You can also consider bending the patient's knees to relax abdominal wall musculature or even ask the patient to take a deep breath which allows the diaphragm to push lower structures better into view. You should also include a clip of the long axis. Always measure from outer wall to outer wall (intraluminal clot can cause a false negative result if you measure from inner to inner).
Even though the large majority of AAAs rupture in the retroperitoneum (and your FAST will thus be negative)– it is still prudent to check for intraperitoneal fluid with a quick RUQ view. You may even see the kidney laterally displaced on the side of rupture.