The LITFL ECMO literature summaries page is an excellent resource for the time-poor candidate who is in looking for a quick update. A quick update is all that would be required: ECMO is largely neglected by the college examiners, and the only question ever to involve any discussion of the evidence was Question 11 from the second paper of 2010. Later, Question 23 from the first paper of 2014 asked about the indications for ECMO and the relative merits of VV and VA ECMO.
ECMO in neonates
This has been going on since before 1986. Bartlett et al reported that after the experience, 63% of his patients were "normal or near normal". A more recent (2006) review of VA ECMO used as rescue therapy in 27 paediatric and neonatal patients also reported good mortality results, in spite of the fact that many of these littel patients had profoundly (congenitally) abnormal myocardia.
VV ECMO in adults
The 2009 CESAR trial from the UK is quoted in the college answer to Question 11 from the second paper of 2010. This trial randomised 180 patients to ECMO or conventional treatment. The study found a 63% survival at 6 months in the ECMO group, as compared to 47% in the conventional group. Critics of the study pointed out the fact that the groups were treated differently, and received significantly different levels of care (i.e. more lung-protective ventilation and sterids in the ECMO group). Furthermore, almost 25% of the patients who were being considered for ECMO didn't actually receive any - which might have, you know, killed them. These significant confounders make it difficult to make recommendations on the basis of CESAR alone.
The 2009 Australasian H1N1 experience with ECMO found a 21% mortality rate at the end of the 3-month observation period, with many patients still in ICU at the end of the study. Mortality in the non-ECMO group was only 13%, which only goes to show that ECMo was being used as a last-ditch effort to rescue the sickest patients. Furthermore, the ECMO mortality in this ANZ cohort was lower than the worldwide reported mortality (which was around 30%) for ECMO-treated ARDS of a comparable severity.
VA or VV ECMO for heart failure and cardiogenic shock
For these people, ECMO does not appear to be a bridge to anything. In one 2004 study, only 37 out of 219 patients survived to 5 year follow-up. In general, in these older studies nobody over the age of 75 survived to discharge.
VA ECMO as CPR
ECMO as CPR has initially failed to yield satisfying results. In one study from 2003, the survival rate for patients in whom VA ECMO was started during CPR was 31%. Multi-organ system failure was the culprit there. However, a more recent observational study has produced some encouraging data.These days, it is beginning to look more and more promising. The obvious disadvantage is that you need an ED which has a circuit cycling 24/7, as well as dedicated night-time intensivist cover (unless one trusts their senior trainees to insert the cannulae).
Recently, exactly this scenario was played at a local centre of excellence, with encouraging results. As a part of a larger package (involving early reperfusion and therapeutc hypothermia) the CHEER trial demonstrated feasibility of urgent ECMO in the out-of-hospital arrest population. It may even improve outcomes: a 2016 review by Patel et al was able to find several propensity-matched cohort studies to support this assertion. Survival with good neurological outcome appeared to improve substantially; effect size was 28.8% vs 12.3% in one study (in-hospital) and 23.5% vs 5.9% in another (2-year).
Venovenous vs venoarterial ECMO
Each has advantages and disadvantages.
- VA ECMO has the advantage of providing complete cardiorespiratory support, and is therefore applicable in patients with very poor cardiac function (LVEF less than 25%)
- VA ECMO has the disadvantage of large-bore arterial puncture, which is a major problem. VV ECMO is said to have fewer vascular access issues, but is only indicated for patients with good myocardial function.
- However, these general guidelines are open to challenge.
- In neonatal respiratory failure, back in 1996, Knight et al found that the frequency of intravascular thrombosis was significantly lower in patients receiving venovenous ECMO, and that otherwise things which were felt to be contraindications (eg. severe cardiac failure) weren't real barriers to successful VV ECMO.
- A 2000 review agreed with this in principle, but failed to discern any difference in the rate of complications in the neonatal/paediatric population.
- A more recent 2015 conference abstract also failed to find any difference in complications among adults.
- A 2007 opinion piece regarding ECMO in sepsis with or without respiratory failure has cautionsly recommended a broader application.