Where is the imperceptible difference?

With great interest, we read the recent article by Whebell and colleagues [1] and were appealed by the beneficial effect of extracorporeal membrane oxygenation (ECMO) on survival in patients affected by acute respiratory distress syndrome (ARDS) due to coronavirus disease 2019 (COVID-19). The gratifyingly low mortality rate in this ECMO cohort (25.8%) stands in remarkable contrast to other reports in COVID-19 patients [2]. Such excellent results are attributable to (1) very strict selection criteria to reduce candidate eligibility to those with the absolute best chances, resulting in cohort of young patients [46 (39–52) years] with isolated respiratory failure [Sequential Organ Failure Assessment (SOFA) 5 (4–7)] and little to no comorbidities [frailty scale 2 (1-2)]; (2) excellent clinical expertise provided by specialized ARDS/ECMO centers. However, analogous to the Cesar-trial [3] discussion 12 years ago, insights of the present study are similarly hampered by the unpredictable bias introduced through the comparison of highly experienced ARDS centers with peripheral, less experienced hospitals [4] making an assessment of the pure ECMO effect difficult to estimate.