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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Results
  • Discussion
  • Disclosures
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

This protocol outlines the use of point-of-care ultrasound (POCUS) to monitor patients on peripheral veno-arterial extracorporeal membrane oxygenation (V-A ECMO) without left ventricular venting. It evaluates left ventricular distension, intracardiac or aortic root thrombus, and identifies useful cardiac POCUS parameters for weaning from V-A ECMO.

Abstract

Over the past several decades, veno-arterial extracorporeal membrane oxygenation (V-A ECMO) has become a critical tool in the management of patients with severe cardiogenic shock and cardiopulmonary failure. Due to the inherent instability of these patients, their transport away from intensive care units is fraught with risk. As a result, bedside diagnostic tools are essential for their daily care. One such tool is point-of-care ultrasound (POCUS) of the heart, which can non-invasively assess several parameters: left ventricular (LV) performance (size, systolic function, stroke volume, aortic valve opening), right ventricular (RV) performance (size, systolic function), and the presence of intracardiac thrombus. Additionally, POCUS can assist in evaluating readiness for V-A ECMO weaning and eventual decannulation. Despite its potential, the use of POCUS in the context of V-A ECMO remains inconsistent due to variability in provider training. This study aims to address this gap by detailing POCUS image acquisition in V-A ECMO, particularly in the absence of LV venting. It covers key aspects such as patient positioning, transducer selection, probe placement, acquisition sequence, and image optimization.

Introduction

Extracorporeal membrane oxygenation (ECMO) is a potentially life-saving temporizing strategy for patients, which has seen an ever-increasing utilization rate1,2. ECMO has two different configurations: veno-venous (V-V) and veno-arterial (V-A). Over the past several decades, V-A ECMO has emerged as a fundamental tool in the care of patients with severe cardiogenic shock and cardiopulmonary failure3,4,5,6. The two cannulation strategies for V-A ECMO are central and peripheral7. Central V-A ECMO usually requires sternotomy for direct cannulation of the right atrium for venous drainage and proximal aorta for antegrade arterial return. On the other hand, peripheral V-A ECMO has arterial return via the femoral artery via a retrograde mechanism. This retrograde flow can cause the following issues: differential oxygenation of the upper and lower body, worsening biventricular function, and LV distension, particularly if there is no strategy in place to unload the LV8. These complications of peripheral V-A ECMO, in addition to the inherent risks with ECMO, necessitate frequent, vigilant monitoring9,10,11. Due to the inherent instability of these patients, it is not practical to frequently transfer them out of the intensive care unit (ICU) for diagnostic testing and evaluation of their mechanical circulatory support and evolving cardiopulmonary status3,6. Therefore, bedside diagnostic tools are essential in their daily care. One such tool is point-of-care ultrasound (POCUS)12,13,14,15 of the heart, which can be used to assess all of the following non-invasively: left ventricular (LV) performance (size, systolic function, stroke volume, aortic valve opening)3,13,14,16,17,18,19, right ventricular (RV) performance (size, systolic function)20,21, and presence versus absence of intra-cardiac thrombus10,11. Furthermore, POCUS can be used to assess readiness for V-A ECMO weaning and eventual decannulation22,23,24,25,26,27,28.

Diagnostic ultrasound generally falls into two categories: point-of-care and consultative29,30 Consultative ultrasound is an exam requested by a patient's primary treating provider but performed by a separate specialist team29,30, whereas point-of-care ultrasound is performed and interpreted by a patient's primary treating provider29,30,31. Although ultrasound assessment of the heart on V-A ECMO has traditionally been performed through consultative services, such services are not always immediately available around the clock to meet an ECMO unit's high-volume and unpredictable sonographic needs. Thus, it behooves ECMO intensivists to be able to perform serial cardiac point-of-care ultrasound (POCUS) exams on their own patients for more efficient and timely patient care.

The utilization of POCUS in the V-A ECMO setting, however, remains heterogeneous due to the variability in training among providers. This study aims to address this gap in training by describing the POCUS image acquisition in peripheral V-A ECMO, particularly in the absence of LV venting, including details on patient positioning, transducer selection, probe placement, acquisition sequence, and image optimization. Other ECMO scenarios, such as LV venting in place, will be covered separately in other manuscripts in this special collection on diagnostic POCUS image acquisition.

Protocol

All procedures performed in studies involving human participants were in accordance with the ethical standards of the Vanderbilt University Medical Center institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The protocol was derived after a review of the published literature by an expert panel of intensivists16,21,22,23,25,28,32,33 representing five health systems across the United States. Imaging was performed on the authors themselves for the normal images and as part of routine educational ultrasound scans done for teaching purposes for the positive images. The inclusion criterion was any patient on V-A ECMO, and the exclusion criterion was a refusal to undergo an ultrasound exam. The equipment used in the study is listed in the Table of Materials.

1. Safety procedures

  1. Utilize nitrile or latex-free gloves. Follow infection control processes for the individual institution as applicable.
    NOTE: If the patient has surgical wounds in stages of active healing, use sterile, individually processed ultrasound jelly packets.

2. Probe selection

  1. Utilize a sector arc or sector array probe (colloquially called a β€œphased-array probe-)34,35,36,37.

3. Machine preset

  1. Set the machine to the cardiology (CARDIAC) preset function, which will then have the indicator on the right-hand side of the ultrasound screen.

4. Patient positioning

  1. Place the patient in a supine position.
    NOTE: If supine is not possible, maintain the patient in the most favorable position so that ECMO cannulas are not displaced.
  2. Place blankets or ramps to slightly position the patient in a left-side down trajectory while maintaining safety with ECMO cannula placement if image quality is substandard.

5. Patient monitoring

  1. Parasternal long-axis view
    1. Obtain the parasternal long-axis view38 of the heart (Figure 1) and click on Acquire.
    2. Assess the aortic valve3,13,14,18,38.
      1. Assess for the valve opening: well vs. not at all (Figure 2; Video 1). Assess for aortic root thrombus: present vs. absent vs. indeterminate (Figure 2).
    3. Left ventricular internal dimension (LVIDD)38
      1. Activate the caliper tool. Measure LVIDD during the R wave of the QRS tracing on EKG (Figure 2) and click on Acquire.
  2. Apical 4-chamber view
    1. Obtain apical 4-chamber view38 (Figure 3) and click on Acquire. Assess LV cavity for presence of thrombus: present vs. absent vs. indeterminate10,11 (Figure 2; Video 2).

6. Assessing tolerance of V-A ECMO weaning

NOTE: For details on the procedure, refer to previously published reports32,33.

  1. Evaluate cardiac recovery and feasibility of V-A ECMO weaning by asking the following questions to the patients:
    1. Assess whether there has been recovery from the underlying disease process that prompted the initiation of V-A ECMO.
    2. Determine if the patient has regained hemodynamic stability, defined by institution-specific standards16,32,33.
    3. Confirm whether oxygenation and ventilation problems are no longer severe (e.g., check if paO2/FiO2 > 100 and paCO2 < 60)32.
      NOTE: There is no agreed-upon protocol to determine when a patient has recovered from their underlying etiology, which caused them to be cannulated for V-A ECMO. It is recommended that a multidisciplinary team and approach be used to make this clinical decision.
  2. Perform V-A ECMO weaning trial if patient answers to checklist questions are yes32.
    NOTE: Weaning protocols differ between centers, and there is no agreed-upon standardized protocol.
    1. Decrease ECMO flow rates in increments of 0.5 L/min under constant echocardiographic surveillance.
      NOTE: At each incremental drop in ECMO flow, if the MAP falls more than 10-15 mmHg or below 65 mmHg, consider resuming full flow, as this suggests the patient is not yet ready to wean.
    2. Perform echocardiographic evaluation of each ECMO wean.
      1. Parasternal long-axis view
        1. Obtain the parasternal long-axis view38 and click on Acquire. Repeat Step 5.1.3. Qualitatively assess LV systolic function (akinetic vs. some degree of function)39 (Video 3).
      2. Apical 4-chamber view
        1. Obtain the apical 4-chamber view38 and click on Acquire. Qualitatively assess the RV/LV size ratio40 (Figure 4). Activate M-mode to measure Tricuspid Valve Annular Plane Systolic Excursion (TAPSE)40 (Figure 5).
        2. Perform Active tissue Doppler imaging. Measure RV S'40 (Figure 6). Measure the lateral mitral annular S'38Β (Figure 7).
    3. Apical 5-chamber view
      1. Obtain the apical 5-chamber view38,41 and click on Acquire (Figure 8).
      2. To perform left ventricular outflow tract (LVOT) velocity time integral (VTI), activate pulse-wave Doppler (PWD). Place the PWD box in LVOT. Measure LVOT VTI41 (Figure 9).
  3. Decrease the flows to 1-1.5 L/min ECMO flow if previous ECMO weans are tolerated.
  4. Perform echocardiographic evaluation under minimal ECMO settings following steps 6.2.2.2.

7. Follow-up procedures

  1. After the patient passes a bedside tolerance for V-A ECMO weaning based on successful echocardiographic screening, stable hemodynamics, and end-organ function, perform an assessment for decannulation based on institutional protocols with multidisciplinary input.
  2. Continuously monitor for signs of ECMO-related complications such as bleeding, infection, thromboembolism, or organ dysfunction. Adjust treatment as necessary.

Results

This article describes the interpretation of point-of-care cardiac ultrasound in patients supported on peripheral V-A ECMO in two clinical scenarios: (1) As a monitoring tool during ECMO support to assess for the presence of left ventricular (LV) distension and the presence of intracardiac or aortic root thrombus, and (2) as a screening tool to evaluate readiness from liberation of mechanical support.

There is no single accepted...

Discussion

Significance with respect to existing methods
The utilization of V-A ECMO as a rescue therapy for acute decompensated cardiac failure has been on the rise1. Peripheral V-A ECMO is utilized as a temporary intervention to allow time for the acutely failing heart to recover while optimizing end-organ function2,3. Although there is a lack of established guidelines regarding the application of echocardiography in the cont...

Disclosures

The Authors declare no relevant disclosures.

Acknowledgements

This work was supported in part by the Center for Experiential Learning and Assessment (CELA) at Vanderbilt University Medical Center (VUMC), Nashville, TN, USA.Β  The authors would also like to thank the staff, faculty, and personal at CELA for their guidance, assistance, and support throughout this project.Β  Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of CELA or VUMC.

Materials

NameCompanyCatalog NumberComments
AffinitiΒ PhilipsAffinitiΒ 70
Edge 1 ultrasound machineSonoSiteEdge II
Vivid iqGE

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Point of Care UltrasoundPOCUSVeno arterial Extracorporeal Membrane OxygenationV A ECMOCardiogenic ShockCardiopulmonary FailureLeft Ventricular PerformanceRight Ventricular PerformanceIntracardiac ThrombusV A ECMO WeaningImage AcquisitionProvider TrainingPatient PositioningTransducer Selection

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