Ultrasound of the Month | September 2019

Bedside US has revolutionized the practice of medicine and allows EM physicians to more quickly and accurately diagnose life threatening illness at the bedside and also perform risky procedures more safely and efficiently. Here we will take some space to briefly review common point-of-care ultrasound (POCUS) procedures utilized at our hospital or a just a BAFERD POCUS finding with tips and tricks for optimizing your probe skills.

Point-of-Care Ultrasound for AAA: A Quick Bedside Review

• Abdominal aortic aneurysm (AAA) rupture has an extremely high mortality rate and needs to be a differential diagnosis for hypotensive patients and/or patients with abdominal/flank/back pain

• Overall mortality of AAA may exceed 90%

• Risk Factors for AAA: males over age 60 who have a smoking or hypertensive history

• Rapid diagnosis of AAA rupture is essential and can be expedited with utilization of point-of-care ultrasound (POCUS)

• POCUS is highly sensitive for presence of AAA, but has low sensitivity for acute rupture because majority of AAA ruptures occur retroperitoneal, which is difficult to visualize with POCUS

• AAA POCUS Review:

• Curvilinear probe

• Transverse/longitudinal views of high, low, and mid abdominal aorta from xiphoid process through iliac bifurcation (which occurs roughly at level of umbilicus)

• Transverse views will allow you to more easily see majority of AAA in their entirety

• Steady pressure downwards toward bed to scan through bowel gas

• Normal POCUS aorta findings:

• ALWAYS measure outer wall to outer wall in transverse view

• Normal aorta diameter is less than 3 cm

• Mural thrombus or plaque may underestimate diameter

• Remember: distinguish aorta from IVC

• When probe is oriented correctly, aorta is to left of IVC

• Aorta will have anterior branches caudal to liver, IVC does not

• Abnormal POCUS aorta findings:

• Aorta diameter greater than 3cm, failure of aorta to taper distally

• REMEMBER: 3 letters in AAA = abnormal POCUS if aorta measures > 3cm

• Of note, majority of AAA are infrarenal, so scan thoroughly

• Two types of AAA:

• Fusiform - more common, involve circumferential dilation of aorta

• Saccular - less common, an asymmetric outpouching of aorta

• Additional findings during aorta POCUS:

• Modified FAST exam should be performed to look for free fluid from intraperitoneal ruptured AAA in LUQ, RUQ, and around the bladder

• Free fluid seen is an ominous finding

• REMEMBER: absence of free fluid does NOT rule out acutely ruptured AAA (will not see free fluid with retroperitoneal bleeding which is more common)

• Aortic dissection, a floating intimal flap, may also be noted during aorta POCUS

• Take to the Bedside Points:

• Consider AAA rupture in the hypotensive patient with abdominal/back/flank pain, especially if they are a >60 year old male who smokes

• Assess the aorta with POCUS to quickly look for AAA, aorta measuring greater than 3cm outer wall to outer wall in transverse view

• REMEMBER: 3 letters in AAA = abnormal POCUS if aorta measures > 3cm

• AAA outer wall to outer wall measuring > 5cm is very abnormal and very likely to have ruptured

• Perform a modified FAST POCUS exam to assess for any free fluid (blood) if the AAA rupture is intraperitoneal (this is a very ominous finding)

• But remember, a negative modified FAST exam does NOT rule out acute AAA rupture as the majority of AAA ruptures occur retroperitoneal which is difficult to visualize with POCUS

• Call Vascular Surgery early in cases where you suspect AAA rupture and see AAA on POCUS

Resources:

Dawson, Matthew and Mike Mallin. “Chapter 3: Aorta.” Introduction to Bedside Ultrasound:

Volume 1, Lexington, KY, Emergency Ultrasound Solutions, 2012.

EM:RAP Productions. “Ultrasound of Abdominal Aorta Aneurysm (AAA).” Youtube, narrated by Dr. Jacob Avila, 28 Nov. 2016, https://www.youtube.com/watch?v=4JTq2gyW5Nw.

Author: Megan Gillespie, PGY4 EM/FM

Residency: Jefferson Northeast