Measurements should be done in a transverse view of the aorta for best wall to wall measurement
Avoid oblique measurements which can be falsely large
IVC can be differentiated by aorta as it is on the patient’s right, thin-walled, nonpulsatile, and compressible (depending on habitus)
Constant gentle pressure and jiggling the probe can help to move bowel gas to visualize the aorta
In the setting of ruptured AAA, blood may not show up in a fast exam if the bleeding is retroperitoneal
AAA vs Dissection
Dissections will continue while AAA typically are located in single area
Dissections can be a normal diameter
Mural thrombus can cause falsely small measurements<unk>  generally cannot differentiate ruptured from an intact AAA. The distinction is made based on clinical context.
Avoid oblique measurements which can be falsely large
Dissections will continue while AAA typically are located in single area
Dissections can be a normal diameter
Aortic ultrasound
Cardiac ultrasound
Age adjusted D-dimer
Bubble study
NEXUS Chest CT Rule
IVC ultrasound
ECG 
D-dimer