VExUS score in V-V ECMO: the B-wave,Critical Care

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VExUS score in V-V ECMO: the B-wave
Critical Care ( IF 8.8 ) Pub Date : 2024-12-18 , DOI: 10.1186/s13054-024-05206-5
Dion O. Gajadin, Wouter A. van der Heijden, Maarten van den Berg

The venous excess ultrasound (VExUS) score, introduced in 2020, has emerged as a valuable tool for assessing venous congestion in clinical practice [1]. With great interest, we read the brief report by Longino, A.A., et al. on the reliability of VExUS, inter-observer variability and reproducibility [2]. Their work represents an important step toward the broader adoption of this tool across diverse patient populations.

The authors rightly highlight that a variety of comorbidities, such as mechanical ventilation or severe respiratory failure, can influence VExUS grading and its interpretation. We wish to add a key consideration regarding the use of VExUS in specific critical care scenarios. They state that flow can be determined in any of the hepatic veins as per the current VExUS protocol. However, patients on venovenous extracorporeal membrane oxygenation (V-V ECMO) with femoro-jugular vein cannulation, can manifest different flow patterns depending on which hepatic vein is assessed, warranting extra caution when using the VExUS protocol in this subset of patients.

In this correspondence, we present a high-velocity wave observed in a patient undergoing V-V ECMO with femoro-jugular vein cannulation, which we have termed the “B-wave.” We hypothesize that this wave is generated by the continuous flow of blood through the ECMO circuit. Its dependence on ECMO flow rates and patient positioning, coupled with its selective detection in hepatic veins, introduces a novel challenge for accurate VExUS interpretation.

The pulse wave (PW) Doppler signals in the hepatic vein are very similar to the jugular vein pressure wave forms and are illustrated in Fig. 1 [3]. No congestion shows the S wave larger than the D wave. If the venous congestion increases, the compliance of the right atrium decreases and the S waves becomes smaller than the D wave in mild congestion and a positive deflection in severe congestion. Be aware that this same phenomenon, called systolic flow reversal, is seen in severe tricuspid regurgitation. In the portal vein there is normally a continuous flow towards the liver, with almost no pulsatility. As congestion increases, the pulsatility of the flow in the vena porta increases. Because of their size, when assessing the interlobar renal veins, the arterial and venous wave forms are observed simultaneously. The normal flow here will be continuous on the venous side. Progressive congestion will result in separated systolic and diastolic waves (biphasic) in mild congestion and only diastolic waves, with systolic flow reversal in severe congestion.

A 44-year-old female was admitted to the ICU after a severe car accident. She soon developed severe ARDS secondary to chest trauma and was placed on V-V ECMO due to persistent hypoxemia. During derescuscitation, VExUS was performed to evaluate the possibility of hypervolemic hypernatremia (Fig. 2A). The left hepatic vein (LHV) showed a novel, high-velocity wave (Fig. 2B), which was less prominent in the middle hepatic vein (MHV, Fig. 2C) and absent in the right hepatic vein (RHV, Fig. 2D). The different flow patterns in each hepatic vein would confer to a different interpretation of the VExUS score and subsequent clinical interpretation. The portal vein (Fig. 2E) showed no pulsatility and the interlobar renal vein (Fig. 2F) showed biphasic venous flow. Severe tricuspid regurgitation and stenosis was ruled out.

The waveform started in the middle or right at the end of the P wave on ECG and abruptly diminished after the QRS complex, corresponding directly with atrial contraction and ruling out systolic flow reversal. It was also too prominent to be a C wave. The flow velocity of this wave decreased instantaneously as the ECMO flow rate was reduced from 3 L/min to 1 L/min, and vice versa, suggesting a direct link between ECMO flow and this pulsatile pattern (Fig. 3). The peak velocity measured around 185 cm/sec also corresponded well with our calculated estimations using a flow of 3L/min and an infusion cannula of 17Fr (Maximum velocity ≈202 cm/sec).

We propose that the ECMO circuit creates this pulsatile wave in the hepatic vein due to backflow during atrial systole. As the right atrium contracts, pressure here increases and the blood subsequently follows the path of least resistance. This would then be the VCI, where the drainage cannula is positioned.

To test this hypothesis ultrasound contrast (agitated saline) was injected through a central venous catheter port in the vena cava superior, parallel to the jugular cannula, whilst all three hepatic veins were assessed simultaneously using two separate ultrasound machines. This confirmed that the LHV and MHV were receiving pulsatile backflow, while minimal contrast entered the RHV (Fig. 4) and a significant amount entered the drainage cannula.

The wave in the LHV disappeared when the patient’s position was changed (slight lateral tilt position), further illustrating its mechanical properties. Retracting the drainage cannula in the IVC past the hepatic vein (because of recirculation) might have also contributed to this wave reaching the liver.

To the best of our knowledge, this wave has not yet been described in the literature. Because it originates from backflow of the ECMO circuit, it was aptly named the ‘B wave’.

Misinterpreting the B-wave as systolic flow reversal could result in overestimation of the VExUS score. For instance, this patient would be classified VExUS grade II, potentially leading to unnecessary or aggressive fluid removal strategies. Making use of an ECG-tracing and awareness of this ECMO-related phenomenon is critical for practitioners using VExUS to avoid clinical misjudgments.

In conclusion, we introduce the ‘B-wave’, an ECMO flow rate-dependent and position-dependent PW Doppler signal in some but not all hepatic veins that may be observed in some patients on V-V ECMO. When using the VExUS protocol in this subset of patients with femoro-jugular cannulation, scanning of all three hepatic veins and using an ECG tracing is necessary to prevent overestimation of venous congestion.

No datasets were generated or analysed during the current study.

HV:: Hepatic vein
LHV:: Left hepatic vein
MHV:: Middle hepatic vein
PV:: Portal vein
PW:: Pulse Wave
RHV:: Right hepatic vein
VCI:: Vena cava inferior
VExUS:: Venous Excess Ultrasound
V-V ECMO:: Venovenous Extracorporeal Membrane Oxygenation

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Authors and Affiliations

Radboudumc, Nijmegen, The Netherlands
Dion O. Gajadin, Wouter A. van der Heijden & Maarten van den Berg

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Dion O. GajadinView author publications
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Wouter A. van der HeijdenView author publications
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Contributions

D.G., W.H. and M.B. performed the measurements, D.G. processed the experimental data, performed the analysis, drafted the manuscript and designed the figures. W.H. and M.B. aided in interpreting the results and worked on the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Maarten van den Berg.

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The authors declare no competing interests.

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Gajadin, D.O., van der Heijden, W.A. & van den Berg, M. VExUS score in V-V ECMO: the B-wave. Crit Care 28, 418 (2024). https://doi.org/10.1186/s13054-024-05206-5

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