Madtown Sono

Elderly female with nausea and vomiting

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By Amy Hummel, MD
Edited by Hani I. Kuttab, MD and Leah Anderson, MD

Clinical Case

An elderly female with a past medical history significant for hypertension, hyperlipidemia, chronic obstructive pulmonary disease, bladder cancer, and infrarenal abdominal aortic aneurysm (AAA) presented to the emergency department with several hours of nausea, vomiting, and abdominal pain. She denied chest pain, shortness of breath, syncope, hematemesis, or melena, though she did report two episodes of diarrhea. Her vital signs on arrival were: blood pressure 144/79, heart rate 95, respiratory rate 18, and oxygen saturation 98% on room air. Shortly after arrival to the ED, bedside point of care ultrasound (POCUS) of the aorta was obtained (Figures 1, 2, 3).

Figure 1
Figure 1: Transverse view of the proximal abdominal aorta showing a diameter of 4.57 cm.
Figure 2
Figure 2: Transverse view of the mid abdominal aorta showing a diameter of 5.66 cm.
Figure 3
Figure 3: Transverse view of the distal abdominal aorta showing a diameter of 5.28 cm.

Diagnosis

AAA with Rupture. The diameter of her abdominal aorta was measured in three segments, with a maximum diameter of 5.6 cm. A focused assessment with sonography in trauma (FAST) scan was also completed and did not identify any intraperitoneal free fluid. The patient was taken emergently for a CT angiography of the abdomen and pelvis. This demonstrated a ruptured infrarenal abdominal aortic aneurysm with 12 cm retroperitoneal hematoma. The patient was placed on a labetalol drip and Vascular Surgery was consulted for operative repair.

Point of Care Ultrasound (POCUS) in AAA

Emergency providers are able to identify AAA with about 99% sensitivity and specificity, sufficient to rule a diagnosis of AAA in or out. While ultrasound cannot reliably identify whether a AAA has ruptured, it is a rapid, easily accessible tool to help guide further workup of patients suspected of having a AAA, which can ultimately expedite patient workup and care.

Scanning the Aorta

Approach the aorta scan systematically to avoid these common pitfalls:

  • Mistaking the IVC for the aorta (especially in the sagittal plane)
  • Missing saccular aneurysms
  • Not including mural thrombus when measuring aortic diameter

Follow These Steps

  1. Use the curvilinear probe for optimal depth.
  2. With the probe in the transverse orientation, identify the aorta in the upper abdomen/subxiphoid region (proximal aorta).
    • The aorta will lay anterior to the vertebral bodies, which appear as a hyperechoic structure with a posterior acoustic shadow.
  3. Measure the diameter of the aorta, from outer-wall to outer-wall. Save a still image. This measurement is the measurement for the proximal aorta.
    • Annual risk of AAA rupture increases as diameter increases from 0.5-5% for a 4-5 cm AAA to 30-50% for a >8 cm AAA, so measuring the maximal outer wall to outer wall diameter of the transverse aorta is important for risk stratification.
  4. Repeat these steps and obtain measurements of the mid-aorta (just distal to the renal artery takeoffs) and distal-aorta (just above the bifurcation of the aorta to the iliac arteries, above the umbilicus).
  5. Lastly, obtain a measurement of the aorta in the sagittal plane. Aim the indicator up towards the patient head, rocking the probe upwards. Slightly fan the probe towards the liver to identify the IVC entering the right atrium. Fan the probe towards the patient’s left to visualize the aorta. Save a 6-second clip.
  6. Slide the probe inferiorly (towards the patients feet), visualizing the aorta from proximal aorta down to the distal aorta. This is to evaluate for a potential saccular aneurysm (Figure 5).

Tips

  1. Press hard! Get that bowel gas out of the way. Hold constant, downward pressure to help displace bowel gas. Maintain that pressure while saving clips and taking measurements. Sometimes, gently ‘wiggling’ the ultrasound probe for 20-30 seconds also assists with displacement of bowel gas, making the aorta more easily visible. Lastly, you may try to position the patient in the reverse trendelenburg position, this sometimes helps to displace bowels inferiorly and makes the aorta more easily visible.
  2. Always include any mural thrombus in your measurements of diameter (Figure 4). It is acceptable to over-estimate measurements (being overly sensitive as to not miss it).
  3. Can’t remember the normal measurement? <3cm. Remember there are three ‘A’s in ‘AAA’, so anything <3 cm is considered normal.
Figure 4: Abdominal aortic aneurysm with mural thrombus.

Teaching Points

  1. Ultrasound can be an extremely useful tool in the assessment of patients with abdominal pain and hypotension.
  2. When using ultrasound to evaluate the aorta, make sure to measure from outer wall to outer wall.
  3. Normal diameter of aorta is <3 cm, anything above that is abnormal.

References

  1. Rubano E, Mehta N, Caputo W, Paladino L, Sinert R. Systematic review: emergency department bedside ultrasonography for diagnosing suspected abdominal aortic aneurysm. Acad Emerg Med. 2013 Feb;20(2):128-38. doi: 10.1111/acem.12080. PMID: 23406071.
  2. Emory University School of Medicine, Department of Emergency Medicine. (n.d.). Ultrasound Images – Aorta. photograph. Retrieved from https://med.emory.edu/departments/emergency-medicine/sections/ultrasound/case-of-the-month/gallery/aorta.html.