#42 ECMO
On this week’s episode of Critical Care Time, we sit down with two brilliant early-career ECMOlogists for an “intro-plus” to VV and VA ECMO. Not only do we cover the basics, but we couldn’t help ourselves and went on some deep dives along the way that you guys will hopefully find interesting! With the help of our good friends Nick Villalobos and Kha Dinh, we review indications for ECMO, approaches to configuration and management, touch on some of the complications and… even spend some time demystifying the European unit for girth! We hope you guys will have as much fun listening to this as we did producing it. If so, leave us a review and let us know what you think!
Definitions
Extra-corporeal membrane oxygenation (ECMO) is a form of extracorporeal life support (ECLS) used in critically ill patients with severe respiratory failure, cardiac failure, or both. ECMO does not treat the underlying issue per se, rather it provides life support to the patient allowing time for the underling organ failure to resolve (or as a bridge to another intervention).
The ECMO circuit consist of the drainage cannula, the pump, oxygenator (membrane lung), and the return cannula.
ECMO is preload dependent and afterload senstiive. Flow is generally rate-limited by the cannula size, though cannula positioning and volume status can significantly effect flows.
Venovenous ECMO (VV-ECMO) replaces the function of the lungs in providing gas exchange.
It is typically used in respiratory failure (ARDS, severe asthma, pneumonia, etc)
VV-ECMO is in parallel with the native circulation
Venoarterial ECMO (VA-ECMO) replaces the function of the heart and the lungs, providing both gas exchange and circulatory support.
It is typically used as a form of temporary mechanical circulatory support (MCS).
VA-ECMO is in series with the native circulation
ICU OnePager guide to ECMO Fundamentals
Types of ECMO: VV vs. VA
Veno-Venous (VV) ECMO: Respiratory Support
Primary indication: Severe hypoxemic respiratory failure (e.g., ARDS, COVID-19, trauma, severe pneumonia).
Oxygenates blood and removes CO₂ but does not provide cardiac support.
Cannulation configurations:
Femoral-femoral (common in EOLIA trial)
Femoral-internal jugular (fem-IJ) – reduces recirculation
Dual-lumen cannula (Avalon or Crescent) – single-vessel option in the IJ
Key considerations for VV ECMO:
Oxygenation depends on flow and FiO₂ of sweep gas (FdO₂).
CO₂ clearance is driven by sweep gas flow.
Challenges: Recirculation, inadequate drainage, ventilator weaning strategies.
VV-ECMO Recirculation Calculator
This calculator determines the percentage of recirculation during VV-ECMO using oxygen saturation values.
VV-ECMO recirculation calculator. The source code is available open source here.
Veno-Arterial (VA) ECMO: Cardiac & Respiratory Support
Primary indication: Cardiogenic shock, cardiac arrest, or biventricular failure.
Functions as a temporary mechanical circulatory support (MCS).
Cannulation configurations:
Peripheral VA (Femoral-Femoral) – Most common
Central VA (Sternotomy, aortic cannulation – post-cardiotomy patients)
Key considerations for VA ECMO:
Provides cardiac output and oxygenation but may cause LV distention due to retrograde aortic flow.
Differential hypoxia (‘North-South’ syndrome): Retrograde oxygenated blood from ECMO competes with native cardiac output, causing cerebral hypoxia.
Management of LV overload:
LV venting via Impella, atrial septostomy, or direct LV vent.
Inodilators (Milrinone, Dobutamine) or afterload reduction (Vasodilators).
ECMO in Cardiac Arrest (ECPR)
Extracorporeal cardiopulmonary resuscitation (ECPR) is an emerging application of VA ECMO in refractory cardiac arrest.
Patient selection:
Witnessed arrest, presumed reversible cause.
Younger patients (<65) with shockable rhythm have better survival outcomes.
Data supporting ECPR:
ARREST trial (Lancet, 2020): Early ECMO in OHCA due to ventricular fibrillation showed survival benefit (7% vs 43%)
INCEPTION trial (NEJM 2023): No clear mortality benefit but highlighted importance of structured ECMO teams.
Challenges: Limited availability, need for rapid cannulation (<60 min from collapse).
ECMO Initiation: Patient Selection & Timing
When should ECMO be considered?
Several scoring systems help identify candidates:
Murray Score (for ARDS severity).
RESP Score (VV ECMO mortality prediction).
SAVE Score (VA ECMO survival in cardiogenic shock).
Cardiogenic shock classifications (SCAI stages).
RESP Score Calculator
The RESP score is used to calculate expected in-hospital mortality in patients undergoing ECMO for respiratory failure (e.g. VV-ECMO). Patients with non-respiratory indications (e.g. cardiogenic shock) were excluded from the cohort used to develop this score.
RESP Score Calculator for predicting mortality in patients undergoing ECMO. See here for the source code (available open source).
Technical Considerations: Cannulation, Flow, and Monitoring
Cannulation Strategies
Drainage cannula (large, multistage – 25-31 Fr).
Return cannula (smaller, typically single-hole).
Placement: Bedside (US-guided), Cath lab (fluoroscopy), or OR.
Circuit Management
Flow (L/min): Determines systemic oxygen delivery.
Sweep gas: Adjusts CO₂ clearance.
Oxygenation index: ECMO flow + FiO₂ of sweep gas.
Monitoring & Complications
SpO₂ trends on ECMO differ from non-ECMO patients (SaO₂ may be misleading).
Hemolysis risk (high delta-P) – check plasma-free hemoglobin.
Bleeding vs. thrombosis balance – anticoagulation strategies (bivalirudin, heparin).
Infection risk: ECMO cannula-related bloodstream infections (CRBSI).
ECMO Cannula Flow Calculator
Dual Lumen IJ Cannula
ECMO Flow prediction based on cannula used. This is a prototype app in development. Please send feedback and suggestions. This is available open source here.
-
ECMO-CS (Circulation, 2022)
ECLS-SHOCK (NEJM 2023)
DanGer SHOCK(NEJM 2024)
ARREST trial (Lancet, 2020)
INCEPTION trial(NEJM 2023)
CESAR Trial (2009, Lancet)
EOLIA Trial (2018, NEJM)
-