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Extracorporeal Membrane Oxygenation in Acute Respiratory Distress Syndrome-More Research Is Needed.

Extracorporeal membrane oxygenation (ECMO) is increasingly being used in patients with noncardiac respiratory failure, with a 70% relative increase in the use of ECMO in patients with acute respiratory distress syndrome (ARDS) between 2008 and 2012 (1). In 2015, it was estimated there were around 300 centers worldwide capable of providing ECMO support (2). This number has continued to increase in the last few years despite a lack of high-quality evidence supporting the role of ECMO in respiratory failure. Until recently, much of the data examining this question has been observational. One retrospective study reported on the outcomes of 68 patients with severe H1N1 influenza-associated ARDS who were treated with ECMO in ICUs across Australia and New Zealand (3). The mortality rate in these patients was 21% (95% CI, 11–30%); much lower than their predicted mortality, suggesting a possible beneficial effect of ECMO in this population (3). Another retrospective observational study from Saudi Arabia reported on patients with refractory hypoxemia caused by Middle East respiratory syndrome coronavirus infection and found lower in-hospital mortality in those receiving ECMO (65% vs 100%; p = 0.02) (4). The Conventional Ventilatory Support Versus ECMO for Severe Adult Respiratory Failure (CESAR) trial examined the role of ECMO in patients with severe ARDS of any etiology using an open-label, concealed allocation, randomized controlled trial (RCT) design (5). CESAR randomized 180 patients with severe ARDS to either conventional management or referral to an ECMO-capable center with consideration for treatment. Only 75% of patients randomized to the intervention actually ended up receiving extracorporeal support. Although there was uncertainty about the effect on mortality (relative risk [RR], 0.75; 95% CI, 0.53–1.06), those in the intervention arm had higher rates of survival to 6 months without disability (RR, 0.69; 95% CI, 0.05–0.97) and higher quality-adjusted life years (0.03) (5). In addition to the fact ECMO was not delivered to a quarter of those randomized to the intervention arm, there was significant variation in ventilation practices in the conventional ventilation arm, some inconsistent with best practices in ARDS (e.g., tidal volumes > 6 mL/kg). CESAR has not had a significant impact on clinical practice perhaps due to the perceived limitations of the trial design. The ECMO to Rescue Lung Injury in Severe ARDS (EOLIA) RCT (6) was designed to overcome some of the limitations that were inherent to CESAR. EOLIA enrolled 249 patients from 64 centers across France, Canada, and the United States with very severe ARDS as defined by the study authors despite optimal conventional mechanical ventilation to receive ECMO or conventional mechanical ventilation. As opposed to CESAR, 97.6% of patients who were randomized to the intervention arm in EOLIA actually received ECMO. Also, patients randomized to the conventional ventilation arm in EOLIA were strongly encouraged to receive all evidence-based ventilation strategies and adjuncts for ARDS; 90% were proned, whereas 100% received neuromuscular blocking agents (6). The sample size calculation for EOLIA (n = 331) assumed a 60% 60-day mortality in the conventional ventilation arm, and the trial was powered for a 20% absolute reduction in mortality with 80% power and an alpha level of 5%. Interim analysis, performed after 240 patients were enrolled, found the results had crossed the prespecified lower boundary of the stopping rule, and this led the Data Safety Monitoring Board to recommend stopping the trial early for futility in the primary outcome. 1Department of Medicine, McMaster University, Hamilton, ON, Canada.