Comment by carbocation | Hacker News Reader

Comment by carbocation | Hacker News Reader

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ECMO is high risk for the patient, especially venoarterial (VA) ECMO which is probably not what is being described in this article. Venovenous (VV) ECMO doesn't dump blood into the arterial tree, so your risk of stroke or other arterial thrombotic complications is much lower. You still risk infection and venous clotting (and therefore the risks of iatrogenic anticoagulation), but I think most of us would accept those risks.

From a systems standpoint, the use of mechanical support usually makes sense in the context of being a bridge to somewhere that is not in-hospital, even in the event of non-recovery. At least where I practice, we want to be able to offer a durable device, or transplantation, if you don't recover. If you live in a place where the health system would not offer transplantation (e.g., because of some risk factor like advanced age), then offering ECMO makes less sense because it is not a bridge to anywhere, particularly for VA ECMO.

For VV ECMO, I think there has long been a recognition that people can do OK for an extended period of time (in contrast to VA ECMO, where the risks are higher and there are also destination therapies like ventricular assist devices). And if you're waiting for a lung transplant vs recovery, you may be waiting for quite awhile. To this end, there are special catheters for VV ECMO that facilitate mobility so you can retain some degree of strength and mobility while on ECMO (e.g., https://www.getinge.com/int/product-catalog/avalon-elite-bi-... ).

I'm closer to VA ECMO than to VV ECMO (but do neither); still, your comments ring more true for me about VV ECMO (which again I think is the subject of this article), whereas I think that patient risk + superior bridging/destination strategies really do dominate the VA ECMO discussion.

One important distinction is to understand that VA ECMO is more often used as mechanical circulatory support in cases of severe heart failure leading to cardiogenic shock. Used alone or in conjunction with other mechanical devices (balloon pumps or impella pumps) it can augment cardiac output to provide sufficient perfusion and oxygenation of your organs and distal extremities.

VV ECMO, on the other hand, is used purely for gas exchange (O2 and CO2) due to respiratory failure. Much of the debate in the critical care community is centered around which circumstances and patients derive the most benefit from initiation of VV ECMO. The best studied use case, is in the setting of acute respiratory distress syndrome, which is defined by very specific criteria (bilateral noncardiogenic pulmonary edema with ratio of arterial oxygenation partial pressure to fraction of inspired oxygen less than 300 mmHg). The EOLIA trial published in NEJM in 2018 looked at early initiation of VV ECMO in patients with severe ARDS [1]. It demonstrated no mortality benefit of ECMO, however many say that the study was not appropriately powered as the assumptions used to design the study were from 2008 when mortality from ARDS was much higher. Re-analysis of the data from the EOLIA trial using bayesian methods suggests that there might actually some benefit to early initiation of ECMO [2]

1. https://www.wikijournalclub.org/wiki/EOLIA

2. https://jamanetwork.com/journals/jama/fullarticle/2709620

Thank you for this reply. Highly informative.

> whereas I think that patient risk + superior bridging/destination strategies really do dominate the VA ECMO discussion.

Is the idea here that when doctors are considering VA ECMO for a patient there is usually some non-trivial chance that the patient survives without it? In that case the choice, I guess, is between higher survival with more complications (VV ECMO) and lower survival with fewer complications (no ECMO)?

Sort of a facile response but we'll at least consider VA ECMO if we think the benefits outweigh the risks. E.g., a person in worsening cardiogenic shock because of a usually reversible insult (e.g., severe stress cardiomyopathy, or a refractory ventricular arrhythmia) has a very good chance of surviving the acute hospitalization but if I'm worried they will die tonight (even if they'd be fine 2 days from now after some recovery time) then will discuss VA ECMO with the people who actually do it for a living. VA ECMO's complications are a consideration in that calculus. That's the kind of decision where I think an observer could argue (especially if things go well) that there was a non-trivial chance that the patient would have survived without ECMO.

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