Demystifying Venous Excess Ultrasound (VExUS): Image Acquisition and Interpretation

Summary

Point-of-care ultrasound (POCUS) is often used to assess the hemodynamic circuit and detect the presence of venous congestion. The Venous Excess Ultrasound (VExUS) scoring system was developed to aid clinicians in predicting the impact of venous congestion on organ dysfunction. This article aims to describe VExUS image acquisition and interpretation.

Abstract

Providers in many medical specialties must accurately assess the hemodynamic circuit to deliver appropriate patient care. Venous congestion is increasingly implicated in a range of multiorgan complications. However, hemodynamic assessment remains challenging because of the complex physiology involved and inconsistent diagnostic accuracy of conventional bedside tools and physical exam maneuvers. While right heart catheterization is regarded as the gold standard for measuring systemic venous pressure, it is invasive and not easily repeatable, and thus, there remains a need for non-invasive alternatives. Even point-of-care ultrasound examinations of the internal jugular vein or inferior vena cava have significant limitations in terms of accuracy of intravascular volume assessment and correlation with central venous pressure. To improve bedside clinicians' accuracy at assessing venous congestion, a protocol was developed and validated that utilizes pulsed-wave (PW) Doppler signals of veins in the liver and kidney to grade the degree of venous congestion present in patients. Although this scoring system, called Venous Excess Ultrasound (VExUS), is being increasingly adopted within certain subspecialties of medicine, such as nephrology and critical care, it remains underutilized in medicine as a whole. This is likely due, at least in part, to knowledge gaps and lack of training in this emerging modality. To address this educational gap, this article will describe VExUS image acquisition and interpretation.

Introduction

Assessment of the hemodynamic circuit at the bedside is fundamental to the daily care of acutely ill patients. The deleterious effects of fluid overload are increasingly recognized even outside of more obvious clinical syndromes such as heart failure, and there are now multiple studies showing that positive fluid balance is associated with increased mortality¹. There is a growing body of evidence that shows that even low levels of venous congestion are associated with organ dysfunction². Similarly, timely decongestion is associated with improved outcomes³. This multiorgan, dynamic circuit involves the right and left heart, systemic vascular resistance, pulmonary artery pressures, and sequential right-sided venous return, culminating in the vena cava. It is complex, and its accurate assessment remains challenging for bedside clinicians. Clinicians from a variety of specialties make decisions regularly based on this assessment. Conventional bedside tools and physical exam maneuvers, including assessment of jugular venous pressure, are almost always available but remain unreliable^4,5,6,7,8,9. Point of care ultrasound (POCUS) is a limited ultrasound examination performed at the bedside and is interpreted by the treating physician to answer focused clinical questions. It is integrated in real-time with the patient's history, physical examination, and other available data to aid in diagnosis and management. Over the last several years, ultrasound has solidified itself as an extension of the physical exam¹⁰, improving clinicians' ability to detect venous congestion^11,12. Additionally, POCUS can guide decongestive therapy, which can potentially positively affect patient outcomes^2,3.

One specific protocol using ultrasound that has been validated to help with hemodynamic assessment is the venous excess ultrasound score, or VExUS. First described by Beaubien-Souligny et al.¹³ in 2020, this scoring system was originally validated in post-cardiac surgery patients as a reliable predictor of acute kidney injury (AKI). Over the past several years, VExUS has also been shown to help with intravascular volume assessment in multiple other clinical contexts^14,15,16,17. VExUS evaluates multiple intra-abdominal veins to screen for sonographic signs associated with congestion. These sonographic signs of congestion appear and progress in incremental fashion as venous congestion worsens, allowing VExUS to both screen for congestion and potentially track its response to therapy over time.

While the individual components of the VExUS exam have long been in use^18,19,20, their combination, as well as their use to monitor therapy over time, remain underutilized, partly due to providers' lack of familiarity with how to perform the exam. We believe that this gap in knowledge is one major factor that has prevented wider-scale adoption of VExUS as the primary alternative to gold-standard invasive cardiac monitoring of venous pressures.

To attempt to address this knowledge gap, this article describes an instructional protocol for performing the VExUS exam, which can serve as a step-by-step guide for bedside clinicians. This protocol draws on the collective experience of a group of physicians representing multiple medical specialties (nephrology, critical care, internal medicine, and anesthesiology) from multiple academic medical centers to describe a standardized approach to VExUS image acquisition and interpretation.

Protocol

All procedures performed in studies involving human participants adhered to the ethical standards of the institutional research committee and the Declaration of Helsinki, including its later amendments or comparable ethical standards. Written informed consent was obtained from the human participants. The scanning technique encompassed transducer selection, machine settings, patient positioning, B-mode scanning, and image acquisition. Patients with unclear volume status, suspected venous congestion, heart failure, acute kidney injury (AKI), and/or chronic kidney disease (CKD) were included in the study, while those with end-stage kidney disease on dialysis, known cirrhosis or portal vein thrombosis, or any condition preventing safe probe usage over the abdomen were excluded. The details of the reagents and equipment used are listed in the Table of Materials.

1. Transducer selection

1. Select a low-frequency transducer: the sector array (aka "phased array"; 1-5 MHz) transducer can be selected for its smaller footprint²¹; the curvilinear transducer (2-5 MHz) can serve as a substitute.
   NOTE: On some machines, the curvilinear probe will de-activate EKG gating, whereas the sector array probe will permit EKG gating. But if EKG gating is available with either the curvilinear or sector array probe, it is preferable to use the curvilinear to maximize visualization of the color Doppler signal.

2. Machine settings

1. For all views, set the depth such that the target of the scan will appear in the middle third of the ultrasound screen (the typical setting is between 16-20 cm).
2. For all views, set the gain such that the lumen of blood vessels appears anechoic (black), the vessel walls appear hyperechoic (bright), and the surrounding structures appear intermediate between these extremes.

3. Patient and sonographer positioning

1. For most of the exam, position the patient supine.
   1. When imaging the inferior vena cava (IVC), ask the patient to lift their feet onto the bed (i.e., flex their hips) to relax their abdominal muscles and allow for image optimization.
   2. When imaging the right kidney, reposition the patient in the left lateral recumbent position for better visualization of the right kidney.
2. Before scanning, expose the patient's lower chest and abdomen.
3. Position the ultrasound machine so that the sonographer's dominant hand can hold the ultrasound probe. This allows for finer manipulation of the ultrasound probe and frees up the non-dominant hand for operating the ultrasound machine. For example, right-handed sonographers should position themselves with the patient on their right side and vice versa.

4. Mode, presets, and setup

1. Select two-dimensional (2-D) mode, also called brightness mode (B-mode).
2. Select the Cardiac preset.
3. Set up EKG gating by plugging the leads into the ultrasound machine and placing the leads in the standard orientation on the patient's skin.
   NOTE: The VExUS exam can be performed in either the Cardiac or Abdominal preset, but on many machines, the Abdominal preset will de-activate EKG gating, whereas the Cardiac preset will permit EKG gating. So, if EKG gating is available on a given machine, it is preferable to use whichever preset permits EKG gating.

5. Inferior vena cava (IVC) imaging

1. Gel
   1. Apply gel to the ultrasound probe directly to maximize scanning efficiency prior to acquiring each image.
2. Subxiphoid view
   1. Place the probe beneath the xiphoid process with the indicator pointing cranially (Figure 1).
   2. Adjust the probe position until the IVC is seen in its maximal anteroposterior diameter (Figure 2).
   3. While keeping the IVC in the center of the screen, rotate the probe 90 degrees counterclockwise to obtain a short-axis view of the IVC (Figure 3).
   4. Cine clip acquisition: For machines configured for retrospective image acquisition, click on acquire after step 5.2.3. For machines configured for prospective image acquisition, click on acquire before step 5.2.3.
3. Right flank view
   1. In patients with contraindications to subxiphoid imaging, place the probe along the right anterior axillary line in the body's coronal plane with the probe indicator pointing cranially (Figure 4).
   2. Adjust the probe position until the IVC is seen in its maximal anteroposterior diameter.
   3. While keeping the IVC in the center of the screen, rotate the probe 90 degrees counterclockwise to obtain a short-axis view of the IVC.
   4. Cine clip acquisition: For machines configured for retrospective image acquisition, click on acquire after step 5.3.3. For machines configured for prospective image acquisition, click on acquire before step 5.3.3.
4. IVC assessment
   1. If IVC is >2 cm in anterior-to-posterior maximal diameter (Figure 5), proceed to step 6.
   2. If IVC is <= 2 cm (Figure 3), VExUS is not indicated. Use clinical judgment or other tools to assess volume status.

6. Hepatic vein Doppler

1. Gel
   1. Apply gel to the ultrasound probe directly to maximize scanning efficiency prior to acquiring each image.
2. Right flank view
   1. Place the probe along the right anterior axillary line in the body's coronal plane with the probe indicator pointing cranially (Figure 4).
   2. Adjust the probe position until the hepatic vein is visualized emptying into the IVC near the cavo-atrial junction (Figure 6).
   3. Select the color Doppler mode on the ultrasound machine.
   4. Move the color box so that the majority of the vessel is within its borders.
   5. Select PW Doppler mode on the ultrasound machine.
   6. Move the Doppler gate so that it is located within the lumen of the hepatic vein.
   7. Activate PW Doppler.
   8. Ask the patient to hold their breath at end-expiration.
   9. Allow a full screen of PW Doppler tracing to occur, and then click on Freeze (or equivalent) (Figure 7).
   10. Click on Acquire (or equivalent) to save still images of flow tracing.

7. Portal vein Doppler

1. Gel
   1. Apply gel to the ultrasound probe directly to maximize scanning efficiency prior to acquiring each image.
2. Right flank view
   1. Place the probe along the right anterior axillary line in the body's coronal plane with the probe indicator pointing cranially (Figure 4).
   2. Adjust the probe position until the portal vein is visualized (Figure 8).
   3. Select the color Doppler mode on the ultrasound machine.
   4. Move the color box so that most of the vessel is within its borders.
   5. Select PW Doppler mode on the ultrasound machine.
   6. Move the Doppler gate so that it is located within the lumen of the portal vein.
   7. Activate PW Doppler.
   8. Ask the patient to hold their breath at end-expiration.
   9. Allow a full screen of PW Doppler tracing to occur, and then click on Freeze (or equivalent) (Figure 9).
   10. Click on Acquire (or equivalent) to save still images of flow tracing.

8. Imaging of renal parenchymal veins

1. Gel
   1. Apply gel to the ultrasound probe directly to maximize scanning efficiency prior to acquiring each image.
2. Right flank view
   1. Place the probe along the right anterior axillary line in the body's coronal plane with the probe indicator pointing cranially (Figure 4).
   2. Adjust the probe position until the right kidney is seen in the long-axis view.
   3. Select the color Doppler mode on the ultrasound machine.
   4. Enlarge the color Doppler box to contain most of the renal cortex (Figure 10).
   5. Select PW Doppler mode on the ultrasound machine.
   6. Move the Doppler gate to a location within the renal cortex that has a color Doppler reading.
   7. Activate PW Doppler.
   8. Ask the patient to hold their breath at end-expiration.
   9. Allow a full screen of PW Doppler tracing to occur, and then click on Freeze (or equivalent) (Figure 11).
   10. Click on Acquire (or equivalent) to save still images of flow tracing.

Results

The first step to the VExUS exam involves imaging the inferior vena cava (IVC) to determine if there are signs of elevated right atrial pressures that would qualify the patient for the remainder of the exam. When imaging the IVC, it is important to view it from both the longitudinal and transverse perspectives to see the vessel in its maximal dimension. If the IVC is greater than 2 cm in its maximal anteroposterior diameter, then the remainder of the examination can be performed.

The next step...

Discussion

Critical steps
VExUS was developed in post-cardiac surgery patients to quantify venous congestion non-invasively, but the utility has expanded for its use to assist in the evaluation of venous congestion and assessment of fluid status in multiple clinical contexts. To perform the exam properly, several critical steps must be considered. First, to maximize the diagnostic yield of the exam, one must consider the requirements of the VExUS exam when selecting a transducer and preset²³. ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
5500P Ultrasound System	Philips	HC795143	Used to obtain a subset of the Figures and Videos
Affiniti 70 Ultrasound System	Philips	HC795210	Used to obtain a subset of the Figures and Videos
Curvilinear Transducer (C1-5-D)	GE	5409287-R	1-5 MHz, also called the abdominal probe
Curvilinear Transducer (C5-1)	Philips	HC989605412041	2-5 MHz, also called the abdominal probe
Curvilinear Transducer (C5-1)	SonoSite	https://www.sonosite.com/products/ultrasound-transducers/c5-1	1-5 MHz, also called the abdominal probe
Curvilinear Transducer (C5-2s)	Mindray	https://lysis.cc/products/mindray-c5-2s	1-5 MHz, also called the abdominal probe
Edge 1 Ultrasound Machine	SonoSite		Used to obtain a subset of the Figures and Videos
Handheld Probe (Butterfly iQ3)	Butterfly	https://www.butterflynetwork.com/iq3?srsltid=AfmBOorvY6WqHGbdeWW gtefztEJa8pt_xbwSOc6hQuB2s-Kb0wRlsCLR	Used to obtain a subset of the Figures and Videos
LOGIQ P9 Ultrasound System	GE	H42752LS	Used to obtain a subset of the Figures and Videos
Lumify Handheld Ultrasound	Philips		Used to obtain a subset of the Figures and Videos
Phased-Array Transducer (3Sc-D)	GE	https://services.gehealthcare.in/gehcstorefront/p/5863286	1-5 MHz, also called the cardiac probe
Phased-Array Transducer (P4-2s)	Mindray	https://lysis.cc/products/mindray-p4-2s	1-5 MHz, also called the cardiac probe
Phased-Array Transducer (P5-1)	SonoSite	https://www.sonosite.com/in/products/ultrasound-transducers/p5-1	1-5 MHz, also called the cardiac probe
Phased-Array Transducer (S4-1)	Philips	HC989605389271	1-5 MHz, also called the cardiac probe
TE7 Max Ultrasound System	Mindray	https://www.mindray.com/na/products/ultrasound/point-of-care/te-series/te-7-max-portable-ultrasound-machine/	Used to obtain a subset of the Figures and Videos