An Approach to Point-Of-Care Ultrasound Evaluation of the Abdominal Aorta

Summary

This protocol reviews the steps to image the abdominal aorta with point-of-care ultrasound. We discuss image acquisition, troubleshooting imaging pitfalls and artifacts, and the recognition of life-threatening abdominal aortic pathology.

Abstract

Disorders of the abdominal aorta, including aneurysms and dissection, have potentially high rates of morbidity and mortality. While computed tomography (CT) is the current gold standard to image the abdominal aorta, the process of obtaining a CT may be time-consuming, requires the use of intravenous contrast dye, and involves exposure to ionizing radiation. Point-of-care Ultrasound (POCUS) can be performed at the bedside and has excellent sensitivity and specificity for the diagnosis of abdominal aortic aneurysm and excellent specificity for the diagnosis of abdominal aortic dissection. Additionally, POCUS is non-invasive, cost-effective, lacks ionizing radiation, requires no intravenous contrast dye, and can be performed without taking the patient from a critical care area. Screening for abdominal aortic aneurysm (AAA) can be done in primary care settings as well.

This article will review the approach to POCUS of the abdominal aorta to evaluate such critical pathology. In this paper, we will review the sonographic anatomy of the abdominal aorta as well as the choice of the ultrasound probe, description of POCUS image acquisition, and some pearls and pitfalls of using POCUS to aid in the diagnosis of potentially life-threatening abdominal aortic pathology.

Introduction

Point-of-care ultrasound (POCUS) has increased in use over the last several years and is being increasingly incorporated into various residency training programs^1,2. POCUS has great utility in critical care areas such as the emergency department and the intensive care unit, specifically to aid in the rapid diagnosis of life-threatening intraabdominal emergencies such as acute aortic dissection, as well as abdominal aortic aneurysms, especially those at risk for rupture and those that have ruptured into the peritoneum.

AAA rupture and acute aortic dissection are associated with high mortality. The mortality of ruptured aortic aneurysms ranges from 67% to 94%^3,4. The mortality associated with type A aortic dissection increases at a rate of 1% per hour after acute dissection and the mortality of type B aortic dissection ranges from 10% to 25% at 30 days⁵. Abdominal aortic dissection in isolation is rare and accounts for only 0.2% to 4% of all aortic dissections^6,7,8,9,10. Since most abdominal aortic dissections occur as an extension of thoracic aortic dissections, evaluation of the abdominal aorta for evidence of dissection may aid in the diagnosis of thoracic aortic dissection¹¹.

Computed tomography with angiography (CTA) is the gold standard for imaging pathology associated with the abdominal aorta; however, it has several drawbacks. It may be time-consuming, especially in an unstable patient, and requires a technician to perform and a radiologist or vascular surgeon to interpret the images. CTA uses ionizing radiation and requires the use of intravenous contrast dye for optimal detection of pathology. Furthermore, the performance of CTA requires potentially unstable patients to leave the critical care area. In contrast, POCUS is non-invasive, cost-effective, and lacks the ionizing radiation and contrast dye that CT requires. It can also be performed and interpreted by the same individual in real time and does not require the patient to leave the monitored area.

A systematic review of emergency department POCUS for diagnosing AAA by Rubano et al. revealed a sensitivity of 99% and specificity of 98%, with a positive likelihood ratio of 99 and a negative likelihood ratio of 0.01¹². This pooled analysis evaluated the test characteristics over a varied group of operators, including resident and attending physicians with a wide range of training in POCUS.

The test characteristics for the POCUS evaluation of abdominal aortic dissection are different from those of AAA and may vary depending on the origin of the dissection. Sonographic findings of an intimal flap separating the true and false lumens have a sensitivity of 67%-79% and a specificity of 99%-100% for aortic dissection^13,14. As most aortic dissections found in the abdomen are an extension of a thoracic aortic dissection, additional POCUS applications of the heart and lungs to evaluate for pericardial effusion, aortic root dilatation, and left pleural effusion may be performed, but will not be the focus of this paper¹³.

Finally, it is important to note that the United States Preventative Services task force provides a Grade B recommendation for a one-time ultrasound screening for AAA in men aged 65-75 who have ever smoked. This is particularly relevant to the primary care setting.

This review will describe a step-by-step protocol for the performance of POCUS in the bedside evaluation of the abdominal aorta, specifically to evaluate for AAA and abdominal aortic dissection. This protocol assumes a basic knowledge of diagnostic ultrasound, including physics, instrumentation, as well as medical knowledge of anatomy and pathologic states of the abdominal aorta and major branching arteries. Readers are advised to refer to other sources for prerequisite knowledge.

Protocol

All ultrasounds in this protocol were performed on human subjects and were conducted following the ethical standards of the University of Illinois Hospital and the Declaration of Helsinki and its revisions. The imaging was performed on the authors themselves and patients in the emergency department as part of routine education and clinical care with preceding verbal consent as is the standard for the institution. Images collected illustrate both normal anatomy and physiology as well as abnormal findings collected at the University of Illinois Hospital. Images used to illustrate scanning techniques were performed on members of the writing team. All ultrasound images are free of any identifying information. The subsequent protocol was designed using sources from peer-reviewed journals and book chapters^{10,15,16,17,18,19}. For this review, the protocol will focus on obtaining US images of adults.

1. Safety

NOTE: POCUS studies can be performed with non-sterile gloves, either nitrile or latex, depending on patient allergies. Additional safety measures may be taken based on clinical context and institutional policies.

1. Examine the ultrasound system for cleanliness prior to use and clean the machine and probes in the appropriate manner after use. The cleaning material and process are dictated by the ultrasound unit manufacturer and institutional standards.

2. Selection of probe

1. For most adults, the abdominal aorta is best visualized with a 2.5-3.5 MHz curvilinear probe, which has a large footprint and a wide field of view with a convex beam shape. This probe will generally provide excellent resolution and measurement capabilities.
2. Alternatively, use the phased array probe (1-5 mHz), typically used for echocardiography and often informally referred to as the cardiac probe.
   ​NOTE: The phased array probe can be useful especially when attempting to visualize the proximal abdominal aorta as it exits through the diaphragmatic hiatus. This is especially true if the space just inferior to the xyphoid process is too narrow to accommodate the wider curvilinear probe. The phased array probe has a rectangular footprint and a triangular beam shape with a narrower field of view than the curvilinear probe but should be adequate to achieve the imaging goals.

3. Machine presets

1. Use the abdominal preset on the machine regardless of the probe used.
2. Set the mode to B mode or 2-dimensional grayscale.
3. Set the depth to 20 cm.
   NOTE: This is typically adequate to visualize the vertebral body which is an important landmark for the aorta.
4. Adjust the depth once the aorta is visualized to keep the aorta in the midfield of the screen.
5. Consider using harmonic imaging to provide better visualization if imaging is challenging due to excessive bowel gas.
   NOTE: Harmonics uses the resonance characteristics of tissue and creates a higher-resolution image with fewer artifacts.
6. Choose a lower frequency range for patients with a high body mass index to improve image acquisition.

4. Scanning technique

1. Apply ultrasound gel to the transducer.
2. Position the patient supine with the abdomen exposed. Hip flexion, if tolerated by the patient, will relax the abdominal muscles and may improve image acquisition.
   NOTE: Bowel gas can impede image acquisition. To improve image acquisition in the presence of bowel gas, the operator can apply firm, continuous pressure, known as graded compression, to the scanning area for a few minutes, displacing the bowel gas. Evaluation of the aorta in the coronal plane can also avoid bowel gas encountered in the transverse plane (see step 4.3.5).
3. For a thorough evaluation of the abdominal aorta, obtain the images listed below.
   1. Obtain images of the proximal aorta in the transverse plane.
      1. Orient the transducer in the transverse plane with the indicator toward the patient's right. Ensure that the indicator position matches the indicator on the screen (Figure 1A).
      2. Place the transducer just distal to the patient's xiphoid process and apply light pressure to visualize the anterior aspect of the vertebra with its hyperechoic shadow-casting arch (Figure 1B).
         NOTE: The liver will appear in the upper left corner of the screen and acts as an acoustic window. The aorta will appear just above the vertebral body as an anechoic circle on the right side of the screen, corresponding to the patient's left. The inferior vena cava (IVC) is on the left side of the screen, corresponding to the patient's right. The IVC has a thinner wall than the aorta and is often collapsible even with light pressure.
      3. Slide the transducer caudally until the celiac trunk is visualized. The celiac trunk is short and quickly bifurcates into the hepatic artery and splenic artery. When the two arteries are visualized together, this is called the seagull sign (Figure 2).
      4. Capture these images for later review by clicking the button on the system that records clips.
      5. Slide the transducer caudally to encounter the superior mesenteric artery (SMA), which comes off the anterior aorta and very quickly courses inferiorly, typically following a parallel path with the aorta. The splenic vein courses anterior to the SMA and the left renal vein courses between the SMA and the aorta (Figure 3).
      6. Capture these images for later review by clicking the button on the system that records clips.
      7. Measure the AP diameter of the suprarenal aorta by optimizing a live image of the aorta in this location and then pressing the system's freeze button.
      8. Press caliper or measure and move the track ball or touchpad of the system to the outer edge of the anterior wall, the adventitia, and click select.
      9. Move the trackball or touchpad again to the outer edge of the posterior wall and click Select. Wait for the system to generate a measurement (Figure 4).
      10. Save this image as a still image containing the measurement by clicking the button on the system that saves still images .
          NOTE: The upper limit of normal of the AP diameter of the aorta is 3.0 cm. Any measurement >3 cm is considered aneurysmal^15,16,20,21.
   2. Image the distal aorta in the transverse plane.
      NOTE: The distal aorta comprises two-thirds of the abdominal aorta and begins just distal of the renal arteries. The majority of AAAs occur in this distal segment.
      1. As with the proximal aorta, continue scanning in a transverse plane visualizing the entirety of the aorta through the bifurcation.
      2. Capture these images for later review by clicking the button on the system that records clips.
      3. When a live image of the distal aorta is optimized, measure the AP diameter of the infrarenal aorta.
      4. Press caliper or measure and move the trackball or touchpad of the system to the outer edge of the anterior wall, the adventitia, and click select.
      5. Move the trackball or touchpad again to the outer edge of the posterior wall and click Select. Wait for the system to generate a measurement.
      6. Save this image as a still image containing the measurement by clicking the button on the system that saves still images.
         NOTE: It is prudent to obtain at least two measurements of the distal aorta given its greater length and increased likelihood of having aneurysmal dilations.
      7. Adjust the depth as the abdominal aorta courses caudally through the abdomen, since it becomes more superficial and tapers slightly.
   3. Obtain a video clip of the aortic bifurcation into the left and right iliac arteries (Video 1-see Supplemental File 1: Supplemental Figure S1).
      1. Continue scanning caudally, adjusting the depth as necessary to maintain the aorta and vertebral body in the middle of the screen.
      2. Scan through the aortic bifurcation into the left and right iliac arteries.
      3. Capture images while scanning through the bifurcation.
   4. Obtain images and video clips of the aorta in the longitudinal plane.
      1. Place the probe in the proximal abdomen, starting again in the subxiphoid area.
      2. It is often easier to begin in the transverse plane with the indicator toward the patient's right. Once the transverse view of the aorta is optimized, rotate the probe clockwise, following the aorta as the image becomes longitudinal on the screen and the indicator is pointing toward the patient's head (Figure 5A).
      3. Acquire images while scanning caudally examining for aneurysmal dilatations.
      4. Capture these images for later review by clicking the button on the system that records clips.
         NOTE: The celiac trunk and SMA are easily visible projecting from the anterior aorta in long axis view (Figure 5B). It is advisable NOT to measure the diameter of the aorta in the longitudinal axis. If the US beam intersects the aorta tangentially, as opposed to in its midline, the measurement will be falsely smaller than if it were through the maximal AP diameter (Figure 6).
   5. Optional: Obtain a longitudinal view of the aorta in the coronal plane. This view is useful if obtaining views in the transverse or longitudinal planes is difficult.
      1. Begin with the transducer in the coronal plane at the midaxillary line on the patient's right with the indicator pointing cranially (Figure 7A).
      2. If the patient is able, position them in the left lateral decubitus position for better image acquisition.
      3. Scan the aorta in a coronal plane. The aorta will be visualized deep to the IVC if both vessels are imaged (Figure 7B).
      4. Capture these images for later review by clicking the button on the system that records clips.

Representative Results

Adequate exam
One of the biggest challenges in obtaining accurate results from an abdominal aortic ultrasound is the lack of consensus about measurement. As noted in protocol step 4.3.1.10, any diameter of the abdominal aorta greater than 3 cm is considered aneurysmal^15,16,22,23. There is, however, great variation in the methods used to measure the aorta's diameter, and no international consensus exists for measuring the abdominal aorta. There are three methods currently in use: (1) the outer wall to outer wall (OTO) measurement, (2) the inner wall to inner wall (ITI) measurement, and (3) the leading edge to leading edge (LELE) measurement, which measures the outer layer of the anterior wall and the inner layer of the posterior wall. There are benefits and drawbacks to using each method, the descriptions of which are beyond the scope of this protocol. We use the OTO method, which correlates best with CT-derived measurements. This is because the angle of the ultrasound beam relative to the aorta (angle of isonation) causes the AP measurement to be sharper than the transverse measurements^15,20. The OTO method also derives larger measurements than the other two methods. From a risk and screening standpoint, using the OTO method will capture more patients at risk who can be followed in an aneurysm surveillance program. Using the OTO measurement also reminds the operator to look for the vessel's adventitia rather than the lumen, since in aneurysmal dilatation, the lumen can be a fraction of the diameter of the aneurysm. The American Institute of Ultrasound in Medicine and the European Society of Cardiology recommend the use of the OTO method^15,16,17,23. With this in mind, however, it is important to note that most aneurysms expand asymmetrically and if the transverse measurement is obviously greater, it is recommended to take the larger measurement¹⁶.

An adequate normal exam should have at least two still images with measurements of the maximal diameter of the abdominal aorta. The images should be taken from the suprarenal aorta and the infrarenal aorta. It is preferable to capture two measurements from the infrarenal aorta because of its greater length compared to the suprarenal aorta and higher rate of aneurysms in the infrarenal segment. Additionally, scanning the entire length of the abdominal aorta from the diaphragmatic hiatus to the bifurcation in both the transverse and longitudinal planes will capture even small variations in diameter. If image acquisition in the transverse and longitudinal planes is challenging, scanning in the coronal plane may be useful.

POCUS can reveal many abnormalities in the abdominal aorta. For this protocol, we will describe ultrasound findings of abdominal aortic aneurysm and dissection. Approximately 85% of AAAs are infrarenal²⁴. When imaging the abdominal aorta in the transverse plane, any measurement of the aorta greater than 3.0 cm is considered aneurysmal. The aneurysm may also contain a hematoma, which can fill most of the lumen. Video 2 (see Supplemental File 1: Supplemental Figure S2) and Video 3 (see Supplemental File 1: Supplemental Figure S3) illustrate an aneurysm with significant hematoma. Figure 8 is a still image illustrating the aneurysm size via the ruler on the screen. The value of the longitudinal plane is especially useful in determining whether the aneurysm is fusiform or saccular. While both are pathologic, saccular aneurysms are more likely to rupture²².

Aortic dissection is a tear in the intima of the aorta that propagates within the media of the aortic wall. Aortic dissections may originate anywhere in the aorta and extend through the abdominal aorta and into the iliac arteries. It is important to consider thoracic aortic dissection when an intimal flap is visualized in the abdominal aorta. Isolated abdominal aortic dissections comprise only 0.2-4% of all aortic dissections and are typically infrarenal^6,7,8,9,10. On POCUS, the key finding is an intimal flap within the lumen of the aorta, separating the true from the false lumen. Depending on the chronicity of the dissection, the flap may be thin and move with the pulsations of the aorta (Video 4 and Supplemental File 1: Supplemental Figure S4) or may be thickened and have an adjacent hematoma (Figure 9). Video 5 (see Supplemental File 1: Supplemental Figure S5) shows an acute thoracic aortic dissection with extension through the abdominal aorta and into the right iliac artery. Color doppler may be used to aid in the diagnosis of aortic dissection. Color flow can be seen on either side of an intimal flap if there is flow through the true and false lumen. Flow through only part of the lumen can raise concern for an intimal flap even if a flap is not well seen. Additionally, with increasing use of endovascular aneurysm repair (EVAR), patients can present with complications of the endograft such as endoleaks, stent migration, and increasing aneurysmal sac diameter^15,16. A detailed discussion of the evaluation of an endograft in a patient who has undergone EVAR is out of the scope of this paper.

Inadequate exams: pearls and pitfalls
There are several common pitfalls and limitations when evaluating the abdominal aorta as well as some important artifacts to discuss. One of the most common pitfalls when evaluating the abdominal aorta is mistaking the IVC for the aorta. The IVC is thin-walled and is more easily compressible than the aorta. The IVC also runs along the patient's right in the transverse plane. In the coronal plane from the patient's right, the aorta is "underneath" the IVC. Another common pitfall is mistaking the celiac trunk, SMA, or SMV for the aorta due to inadequate depth and failure to identify the vertebral body as a landmark. Other advanced sonographic techniques can be employed such as color doppler or pulse wave doppler to differentiate arterial from venous flow.

Imaging the entirety of the abdominal aorta may be challenging and some aneurysms may be impossible to locate due to body habitus, the presence of bowel gas, ascites, tachypnea, and guarding¹⁹. Controlling a patient's pain can improve image acquisition and quality.

A tortuous aorta may be very difficult to track, and measurement may need to be performed from an atypical angle as transducer malalignment may overestimate the diameter (Figure 10). While POCUS has excellent sensitivity and specificity in the detection of AAA, it cannot reliably detect AAA rupture as most ruptures occur in the retroperitoneal space, an area not well visualized by ultrasound^19,21. Detection of free fluid in the abdomen is concerning for intraperitoneal rupture in a patient with AAA. Other signs of free rupture include focal discontinuity of AAA wall, irregular aneurysm shape, and/or floating thrombus²².

Finally, there are a few artifacts that are important to mention. The first is abdominal aortic pseudothrombus, which is typically located at the level of the SMA when scanning in the longitudinal plane. The pseudothrombus (Figure 11) is a reverberation artifact resulting from the reflection of the ultrasound beam between the anterior and posterior walls of the SMA. The wall of the SMA is displayed as a hyperechoic linear structure within the lumen of the abdominal aorta at an equal distance from the posterior wall. Changing the transducer position by rocking or fanning the probe usually leads to the resolution of this artifact^15,25. Another artifact is duplication of the aorta, most commonly seen in transverse and longitudinal planes. This occurs more often with transducers with a larger radius of curvature (i.e., curvilinear more than a phased array). This is due to prismatic fat tissue of the anterior abdominal wall and is more common in young athletic individuals. This artifact is typically resolved by slight lateral movement of the transducer in the transverse plane^15,26.

Figure 1: Imaging of the transverse orientation of the probe. (A) Red dot indicates probe indicator. (B) Imaging of proximal aorta in the transverse plane. Abbreviations: VB = Vertebral body; A = Transverse proximal aorta; IVC = Inferior vena cava. Please click here to view a larger version of this figure.

Figure 2: Imaging of the proximal aorta with celiac trunk in the transverse plane. The branches of the hepatic artery [white arrow] and the splenic artery [red arrow] from the celiac trunk make up the "seagull sign". Abbreviations: A = Aorta; C = Celiac trunk. Please click here to view a larger version of this figure.

Figure 3: Imaging of the proximal aorta with superior mesenteric artery in the transverse plane. The splenic vein courses anterior to the SMA and the left renal vein [white arrow] courses between the SMA and the aorta. Note the partially collapsed inferior vena cava. Abbreviations: A = aorta; SMA = superior mesenteric artery; SV = splenic vein; IVC = inferior vena cava. Please click here to view a larger version of this figure.

Figure 4: Measuring of the proximal aorta using the outer-to-outer wall convention. Please click here to view a larger version of this figure.

Figure 5: Imaging of the longitudinal orientation of the probe. (A) Red dot indicates probe indicator. (B) Longitudinal axis view of the proximal aorta showing the celiac trunk and the superior mesenteric artery. Abbreviations: C = celiac trunk; S = superior mesenteric artery. Please click here to view a larger version of this figure.

Figure 6: Illustration of the pitfalls of measuring the diameter of the aorta in long axis. The figure on the left shows the US beam directly through the aorta, while the figure on the right shows shortening of the true diameter. Please click here to view a larger version of this figure.

Figure 7: Imaging of the coronal view of the abdominal aorta. (A) Coronal orientation of the probe; red dot indicates probe indicator. (B) Imaging of the abdominal aorta in the coronal plane. Note the aorta runs "beneath" the inferior vena cava. For reference the left side of the US screen is cranial, and the right side of the screen is caudal. The area closest to the probe (near field) is the right flank and the area furthest from the probe (far field) where the IVC and aorta are visualized is deep to the body surface. Please click here to view a larger version of this figure.

Figure 8: Imaging of the transverse view of a large abdominal aortic aneurysm with hematoma. Aneurysm size is measured using the ruler on the screen. Please click here to view a larger version of this figure.

Figure 9: Chronic abdominal aortic dissection with thickened dissection flap between the true lumen and the false lumen. Abbreviations: DF = dissection flap; TL = true lumen; FL = false lumen. Please click here to view a larger version of this figure.

Figure 10: Tortuous aorta. The solid line represents the transducer angled perpendicular to the midline of the body but in misalignment with the tortuosity of the aorta. The dashed line more accurately represents the true diameter of the aorta, despite not being perpendicular to the midline. Please click here to view a larger version of this figure.

Figure 11: Imaging of the aorta in long axis. A pseudothrombus [red arrow] is a commonly seen artifact beneath the superior mesenteric artery. The celiac trunk is just proximal to the SMA. Abbreviations: SMA = superior mesenteric artery; C =celiac trunk. Please click here to view a larger version of this figure.

Video 1: Video clip of the bifurcation of the abdominal aorta into the iliac arteries. This clip was obtained with the probe perpendicular to the distal aorta, scanning inferior to the umbilicus as the abdominal aorta bifurcates into the iliac arteries. Please click here to download this Video.

Video 2: Imaging of a large abdominal aortic aneurysm in the transverse plane with echogenic swirling of blood and hematoma within the lumen of the aorta. Please click here to download this Video.

Video 3: Imaging of a large abdominal aortic aneurysm in the transverse plane more distal than video 2. Please click here to download this Video.

Video 4: Imaging of proximal abdominal aorta in the transverse plane with an acute dissection. Note a thin dissection flap moving with aortic pulsations. Please click here to download this Video.

Video 5: Imaging of the distal abdominal aorta in the transverse plane with an acute dissection and extension into the right iliac artery. Please click here to download this Video.

Supplemental File 1: Still images corresponding to Video 1-5.   Please click here to download this File.

Discussion

Timely diagnosis of AAA and aortic dissection is key in the treatment of these high-morbidity conditions. POCUS used in the diagnosis of AAA leads to improved outcomes and significantly decreases the time to diagnosis and operative intervention when compared with traditional imaging²⁷. POCUS has high sensitivity and specificity for AAA and high specificity for aortic dissection^{12,13,19,21,28,29}. It is useful across specialties and for physicians at various levels of training. In medical settings without access to vascular surgery, cardiopulmonary bypass, and even CT imaging, early bedside ultrasound to evaluate an unstable patient with chest, abdominal, back, flank, pelvic, or groin pain for an abdominal aortic emergency can expedite transfer to definitive care. Furthermore, evaluation of the abdominal aorta in a patient with undifferentiated shock can be key in guiding resuscitation and management.

This protocol for the detection of AAA and abdominal aortic dissection is both simple and comprehensive, and there are some critical steps to be noted. Scanning the entire abdominal aorta from the diaphragmatic hiatus to the aortic bifurcation into the iliac vessels must be done in a transverse orientation. Scanning the entire abdominal aorta from the diaphragmatic hiatus to the aortic bifurcation into the iliac vessels must be done in the longitudinal orientation. Scanning in the coronal plane may be performed if the longitudinal plane imaging is suboptimal. Still measurements of an optimized image, measuring the outer anterior wall to the outer posterior wall of the aorta in the transverse plane must be taken at the suprarenal abdominal aorta and two levels of the infrarenal abdominal aorta.

It is important to differentiate between the aorta and the IVC as this is a common error. Bowel gas and body habitus are the most challenging and common pitfalls to obtaining good images. Using graded compression allows for improved images when bowel gas is obscuring the view.

POCUS of the abdominal aorta has some important limitations. First, ultrasound is operator-dependent and while even novice physicians can perform this study with accuracy, it is important to have training and practice^30,31. The sensitivity and specificity of POCUS for the detection of AAA are both greater than 98%^{12,19,21,28,29,30}. While the specificity of an intimal flap as seen on POCUS in abdominal aortic dissection is 99%, the sensitivity for abdominal aortic dissection is poor and highly variable^13,14,32. Finally, POCUS is not the ideal imaging modality for the evaluation of ruptured AAA, as most will rupture in the retroperitoneum, a location POCUS does not evaluate well.

With practice, this protocol can be performed in under five minutes allowing for one to two minutes to perform graded compression if bowel gas is present. As far as how long it takes to achieve competency in this protocol, this is variable. The literature in emergency medicine resident education and many training programs' procedural competency suggests that a total of 150 reviewed exams in the major POCUS applications including abdominal aorta should be performed prior to graduation. However, the number of completed exams may not confer competency and evaluative tools such as observed structured clinical exams using standardized direct observation tools may provide a more robust competency assessment³³. For those who have already completed training and/or trained in an era prior to the advent of POCUS, the ultrasound director should have a credentialing plan for providers who would like to perform this exam.

We believe strongly that practicing physicians, especially those working primarily in emergent, critical care, primary care, or other settings with an at-risk population should be comfortable using POCUS to evaluate the abdominal aorta for life-threatening pathology. POCUS is a life- and time-saving tool that can provide data in real time and with few additional resources.

Materials

Name	Company	Catalog Number	Comments
M9 Ultrasound Machine	Mindray	n/a	Used to obtain all adequate and inadequate images/clips