Reading
Aorta Supporting Literature:
Emergent Question: Is the aorta enlarged?
Probe Type: Cardiac (phased array) or abdominal (curvilinear) probe; 2-5 MhZ
Critical Care Scenario: Patients who are hypotensive should be evaluated for aortic aneurysm and possible dissection. If an abnormally high aorta size is found in a patient who is hypotensive, the clinician should consider aortic dissection as a possible cause of the hypotension. The ability for limited exam to detect aortic dissection is not accurate, and the limited exam must be used to help provide guidance for further definitive imaging or treatment in case the patient is unstable for transfer to radiological suite.
Scanning technique: The patient should be in the supine position. The probe marker is towards the patient’s right side for obtaining transverse views of the aorta and towards the patient’s head for the longitudinal views. Gentle pressure is applied in the epigastric region to push bowel gas out of the way [Figure 4]. The aorta should be imaged from the proximal celiac trunk to the distal bifurcation. Its usually visualized as the circular vessel immediately anterior to the vertebral body [Figure 1]. Both transverse and longitudinal planes should be measured at its maximal diameter from outside wall to outside wall. A measurement should be made near the celiac trunk and another measurement distal to the iliac bifurcation. The transverse measurement is preferred due to ‘cylinder’ effect and underestimation of aortic size in the longitudinal measurements [Figure 2]. Abdominal aorta size greater than 3 cm and iliac arteries size greater than 1.5 cm are an indication of abnormal size [Figure 3]. Another common challenge is ensuring the aorta is imaged and not the inferior vena cava. The inferior vena cava has both sides bordered by the liver, whereas the aorta does not. Other landmarks such as the spinal shadow and celiac takeoffs should be used to confirm appropriate vessel is evaluated.
Supporting Literature: Imaging of the aorta is becoming for applicable for many situations. A class B recommendation was given by the US Preventive Services Task Force for one time ultrasound screening for abdominal aortic aneurysms in men between ages of 65-75 who had ever smoked. This led to the addition of screening for abdominal aortic aneurysms into Medicare reimbursement [1-2]. Also there have been many studies that have shown that emergency physicians are able to obtain these views comparable to computed tomography scans [3-5].
Figure 1 – 1a. Aorta in transverse view 1b. Aorta in longitudinal view
Figure 2 – Cylinder effect showing underestimation of size in longitudinal view
Figure 3 – Aortic aneurysm
Figure 4 – Probe location-transverse view
[1]. U.S. Preventive Services Task Force. Screening for abdominal aortic aneurysm: recommendation statement. Ann Intern Med 2005;142:198-202.
[2]. Thompson SG, Ashton HA, Gao L, Scott RA. Screening men for abdominal aortic aneurysm: 10 year mortality and cost effectiveness results from the ran- domised Multicentre Aneurysm Screening Study. BMJ 2009;338:2307-18.
[3]. Knaut, A. L., Kendall, J. L., Patten, R., & Ray, C. (2005). Ultrasonographic measurement of aortic diameter by emergency physicians approximates results obtained by computed tomography. The Journal of emergency medicine, 28(2), 119-126.
[4]. Tayal, V. S., Graf, C. D., & Gibbs, M. A. (2003). Prospective study of accuracy and outcome of emergency ultrasound for abdominal aortic aneurysm over two years. Academic emergency medicine, 10(8), 867-871.
[5]. Dent, B., Kendall, R. J., Boyle, A. A., & Atkinson, P. R. T. (2007). Emergency ultrasound of the abdominal aorta by UK emergency physicians: a prospective cohort study. Emergency Medicine Journal, 24(8), 547-549.
Figure 1 – 1a. Aorta in transverse view 1b. Aorta in longitudinal view
Figure 2 – Cylinder effect showing underestimation of size in longitudinal view
Figure 3 – Aortic aneurysm
Figure 4 – Probe location-transverse view