In the swan song of ERcast Lite, we speak with Scott Weingart about the truths, misunderstandings, and physiology of ECMO.
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Pearls:
- VV ECMO takes over lung function and is used for those with severe lung disease (ie. ARDS, pneumonia, severe asthma).
- VA ECMO takes over the heart and lung. Ideal candidates are patients with massive PE or cardiogenic shock.
- Intubated patients who you can’t oxygenate despite rapidly escalating PEEP and a high FiO2 should be considered for VV ECMO.
There are 2 primary types of extracorporeal membrane oxygenation (ECMO): veno-venous (VV) and veno-arterial (VA).
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- VV ECMO takes over lung function.
- It drains blood from the IVC or SVC, sends it through a pump which delivers it to an oxygenator (a membrane which allows the influx of oxygen and removes CO2), and then pumps the oxygenated blood back into the right heart system (returning it to the IVC or SVC).
- Useful for those with severe lung disease but decent heart function.
Examples: pneumonia, ARDS, severe asthma with CO2 retention, immunologic lung diseases, cystic fibrosis awaiting lung transplant
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- Limited by its complications, cost, and logistical catastrophes.
- VA ECMO takes over lung AND heart function.
- It drains blood from the IVC/SVC, pumps it out and sends it to an oxygenator, and then returns the blood retrograde up the aorta so it can perfuse the abdominal viscera, brain, and possibly even the heart.
For patients with cardiogenic shock or massive PE.
- Does not yield as much benefit for patients with septic shock or other vasodilatory states (unless they had a sepsis-induced cardiomyopathy).
- Shares the same limitations as VV ECMO, with the addition that the physiology induced by the VA ECMO itself can be deleterious.
Which patients might benefit from transfer to an ECMO center?
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- The threshold for transfer depends in part on the capabilities at your institution for advanced ventilatory modalities (ie. airway pressure release ventilation, proning patients, nitric oxide).
- A large percentage of patients transferred for ECMO never end up receiving or needing it. However, they still greatly benefit from moving to a facility that has the ability to provide other nuanced critical care options.
- In general, transfer young patients who are on very high vent settings and not getting better.
- At a community hospital with few vent resources, these patients should be transferred within hours.
- At bigger institutions, transfer within 48 hours. Often people wait too long (5-7 days) to initiate the transfer.
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Use the ARDSnet Mechanical Ventilation Protocol and Murray Score to help decide if a patient would be a good VV ECMO candidate.
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- The ARDSnet protocol is evidence-based and communicates where the patient is on their vent settings. It gives receiving centers a clean way to evaluate patients for potential transfer.
- Patients should be <65 years old (though physiologic age is taken into consideration)
- The patient should have a reversible cause of respiratory failure and no severe comorbidities (no past history of cirrhosis, end-stage CHF/cancer/COPD).
- Not improving despite maximal adjunctive ventilatory support
- Varies based on the capability of your center
- Some patients at small community hospitals could benefit from transfer to a bigger medical ICU, not necessarily to an ECMO center.
- PaO2 should be <150 on high FiO2 of >0.6.
- A Murray Score ≥2.5 is a standard cutoff for ECMO candidates.
- Murray Score considers:
- How much consolidation there is on CXR
- PaO2/FiO2 ratio
- Amount of PEEP
- Lung compliance [TV/(PIP-PEEP)]
When should we begin thinking about VV ECMO or advanced ventilatory measures for an intubated ED patient?
- Think ECMO if you can’t oxygenate a patient despite rapidly escalating the PEEP and a high FiO2.
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- Example: a patient whose PEEP = 20 and FiO2 = 100%, yet oxygen saturation hovers in the 80s and CXR shows white out.
What is the tipping point for VA ECMO in patients with massive PE?
- Consider ECMO for patients who:
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- have contraindications to thrombolysis,
- are not improving/getting worse despite thrombolysis, or
- require high vasopressor doses.
- VA ECMO “solves the problem” for massive PE.
VA ECMO referrals for cardiomyopathy are typically for post-viral CM or post-myocardial infarction CM (since these patients tend to be younger with few comorbidities).
- When considering transfer for a patient in cardiogenic shock, if you have an interventional cath lab capable of placing a mechanical circulatory support device (ie. an Impella or left ventricular assist device), contact them first.
- ECMO criteria for patients in cardiogenic shock includes lack of improvement with an Impella.
Who tends to recover well from ECMO?
- Patients with an acute indication for ECMO and minimal comorbid disease have the best outcomes.
What is the minimal infrastructure and training level needed to start an ECMO program?
- Starting a program is complicated. And VV ECMO is more complex than VA ECMO (due to using bigger cannulae, positioning requirements, etc).
- It’s possible for small facilities to initiate VA ECMO for cardiac arrest or PE patients in the ED/ICU while awaiting an ECMO retrieval team from a major center. This requires that all the details be worked out between the facilities ahead of time.
- What’s more realistic is for the receiving ECMO center to retrieve those patients and decide whether they want to initiate ECMO with their own equipment and then take the patient back to their facility.
