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Ultrasound Zoom: The VExUS Score: Fluid Status, Reconsidered By Ernesto H. Weisson, Dr. Joshua Goldstein, Duyen Vo, MS; edited by Dr. Leila Posaw
The VExUS Score: Fluid Status, Reconsidered
By Ernesto H. Weisson, BS
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UM Miller School of Medicine
By Joshua Goldstein, MD
UM Miller School of Medicine
By Duyen Vo, BS
UM Miller School of Medicine
Edited by Leila Posaw, MD, MPH
Emergency Ultrasound Faculty, Jackson Memorial
CLINICAL PROBLEM
Proper evaluation of fluid status is imperative to the management and outcome of patients in the emergency department (ED), especially in cases of septic shock, congestive heart failure or acute renal failure. Traditionally, point-of-care ultrasound (POCUS) has been used to assess the inferior vena cava (IVC) for an estimation of fluid status and responsiveness. However, relying exclusively on the IVC diameter and collapsibility has been shown to be insensitive for identifying fluid tolerance in critically ill patients.
Like central venous pressure, estimation of the IVC is not a reliable measure of preload in the left ventricle. The IVC might be dilated in various euvolemic conditions, including pulmonary hypertension and valvulopathies, and it might also be dilated as normal physiologic variance in trained athletes. Another drawback of estimating fluid status only from the IVC is that this ignores the amount of congestion in other vital organs such as the lungs, liver, kidneys and gastrointestinal tract.
THEORETICAL CONSTRUCT
Venous congestion can first be appreciated in the IVC: its size increases proportionally to CVP until it reaches its maximum dilation. Pressure is then transmitted in a retrograde fashion through the veins to the abdominal organs.
The Venous Excess Ultrasonography Score (VExUS) is a 4-step protocol that not only evaluates the presence of congestion in the IVC, but also assesses the severity of congestion in three target organs: the liver, the gut and the kidneys. Emergency physicians can easily utilize this protocol to guide fluid management in their patients. For example, a positive VExUS score might suggest conservative fluid administration or lead to the administration of diuretics and vasopressors.
HOW TO PERFORM A VEXUS EXAM
In preparation, the patient should lie supine with the head of the bed lowered to 0º and legs bent to relax the abdominal wall. The operator should be positioned on the patient’s right side to facilitate simultaneous scanning and manipulation of the controls. A curvilinear probe will result in a higher resolution of the vessels, but a phased array probe may be used as well. You will need an ultrasound system with color Doppler and pulse wave Doppler capabilities to perform a successful exam.
Step 1 – IVC assessment (B-mode)
Where to look: Place the probe on the patient in the subxiphoid location in the sagittal plane. You should see the IVC entering the right atrium. The hepatic vein may be seen entering the IVC.
What to look for: The diameter of the IVC is commonly measured approximately 3-4 cm from the junction of the IVC and the right atrium, or 1-2 cm caudal to the confluence of the hepatic vein and the IVC.
If the diameter is < 2 cm, there is no congestion. If the VExUS score is 0, and you do not need to proceed further.
If the diameter is > 2 cm, congestion is present. Further examination is necessary to determine the severity of congestion and VExUS scores 1-3. This is described in the following steps.
Where to look: Any of the three hepatic veins (right, middle and left) can be evaluated. However, the middle and right hepatic veins are easier to obtain, as they are less likely to be obscured by bowel/stomach gas. First, find the hepatic veins in B-mode. Place your probe in the right upper quadrant, fanning anteriorly and posteriorly. The hepatic veins are thin walled and communicate with the IVC. In the transverse view, the confluence forms the “Playboy Bunny” sign (Fig. 1). Next, assess the vessels with color Doppler. The veins should be blue (flow away from the probe). Finally, place the pulsed wave Doppler gate in the hepatic vein proximal to where it enters the IVC.
What to look for: The normal flow pattern in the hepatic veins closely resembles a CVP tracing with three waves: a small retrograde A wave, followed by anterograde S and D waves.
In a healthy patient, the S wave should be much larger in magnitude than the D wave, with both showing negative deflections as blood flows away from the probe.
In the setting of worsening venous congestion, the magnitude of the S wave will decrease as systolic phase venous flow decreases and eventually becomes positive, corresponding to a reversal of blood flow. At this point, venous congestion is severe enough that flow will be away from the IVC, and forward flow will only occur as the ventricle relaxes and fills during diastole.
Limitations: Hepatic vein Doppler is strongly influenced by tricuspid regurgitation, and in these patients, this step may not be suitable.
Where to look: First, find the hepatic portal veins in the B-mode. Place your probe in the right upper quadrant, mid axillary line, and fan anteriorly and posteriorly. The portal veins are best identified by the presence of thick and hyperechoic walls. Next, assess the vessels with color Doppler. The portal veins should be red (flowing towards the probe). Finally, place the pulsed wave Doppler gate in the hepatic portal vein.
What to look for: Between the GI tract and the liver, the portal system should have constant monophasic flow with minimal variation. As venous congestion increases and pressure from the hepatic veins is transmitted across the hepatocytes into the portal system, the flow becomes pulsatile. The Pulsatility Index quantifies the degree of pulsatility:
Pulsatility index = Flow max — Flowmin Flow max
Flow max is measured as the distance between the baseline and the peak of the wave and Flowmin is measured as the distance between the baseline and the trough of the wave. A pulsatility index of less than 30% is normal; between 30 and 49% denotes mild portal vein abnormality; and greater than 50% indicates severe portal vein abnormality.
Where to look: First, find the renal veins in the B-mode. Place your probe in the right posterior axillary line. The target vessels are the interlobar or arcuate renal veins located in the renal cortex. Next, assess the vessels with color Doppler (Fig. 2). Finally, since the arteries and veins run antiparallel to each other, the arterial and venous flows can be assessed simultaneously with a single pulsed wave Doppler gate placed over the color signal. Arterial flow will show a positive tracing, while venous flow will show a negative tracing.
What to look for: Normal renal veins have uninterrupted monophasic flow. As venous congestion increases, the systolic component of the flow decreases. The waveform becomes biphasic, with discrete diastolic and systolic phases. Eventually, in severe congestion there is only diastolic flow, and systolic flow is absent.
Limitation: The difficulty in visualizing the renal vessels might preclude the successful performance of this step.
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Fig. 1: The confluence of the middle and left hepatic veins enter the IVC to form the “Playboy Bunny” sign. Fig. 2: Color Doppler is used to localize the renal arteries & veins so they can be assessed with the pulsed wave Doppler.
