Extracorporeal membrane oxygenation (ECMO) is an accepted salvage therapy for severe acute respiratory distress syndrome (ARDS) after conventional mechanical ventilation with low tidal volumes, neuromuscular blockade and prone positioning have failed. ECMO has been proposed as the ultimate lung protection strategy for ARDS, because it bypasses the lungs entirely. So why shouldn't it be first-line therapy for ARDS? A recent trial conducted in France asked that question.

Investigators randomized 240 patients to receive veno-venous ECMO or usual ARDS care within 7 days of intubation. At enrollment, all patients received low tidal volume ventilation, almost all had received neuromuscular blockers, and most had been proned. 60-day mortality was the primary endpoint.

Target enrollment was 330 patients, but an interim safety analysis indicated futility and the trial was terminated.

60-day mortality was not significantly reduced by ECMO compared to usual care (35% vs 46%, P=0.09).

The results were confusing, however, because 35 patients (28%) crossed over from usual care to receive salvage ECMO. "Only" 20 (57%) of those who crossed over died. Did ECMO save some of them and inflate the control group's survival, concealing ECMO's benefit in the final results? Reaanalyzing the data with this in mind resulted in a survival benefit for ECMO, but this wasn't the trial design. Fewer ECMO patients required renal replacement therapy, but more had significant bleeding. These results offer something for everyone. They do not suggest that ECMO as a first-line therapy for severe ARDS is harmful, and so continued use and study is ethical. Centers with strong ECMO experience can confidently continue to push the envelope by treating severe ARDS with ECMO on a case-by-case basis, until current and planned trials provide additional guidance.

Source: NEJM