(5-9)
Another option for severe refractory ARDS patients is venovenous extracorporeal membrane oxygenation (ECMO) which is considered as a rescue therapy. ECMO appeared to be beneficial during the influenza A (H1N1) pandemic back in 2009, with a mortality rate of 21% (10). In another observational study on patients with H1N1 related ARDS, the mortality rate was 23.7% for ECMO patients in versus 52.5% for non ECMO patients (11). In 2018, a retrospective study was conducted on middle east respiratory syndrome (MERS) patients with refractory ARDS and showed that ECMO should be used as a rescue therapy because it is associated with lower mortality when compared to conventional mechanical ventilation group (65 vs. 100%, P = 0.02) (12). No ECMO report was published on SARS (coronavirus emerging in 2002) related ARDS.
The role of ECMO in the management of COVID- 19 ARDS remains unclear. The initial reports of using venovenous ECMO with COVID- 19 patients suffering from intractable hypoxemia observed a high mortality rate and recommended using ECMO with caution in the current pandemic (13). According to the interim guidance made by the World Health Organization (WHO), venovenous ECMO could be considered as a salvage therapy for COVID-19 with refractory hypoxemia in expert centers with enough cases to ensure clinical expertise (14) .
In view of the current growing pandemic and the fact that only a little experience with using ECMO to support COVID-19 patients is available, we aimed to estimate the effect of venovenous ECMO on mortality from COVID-19 patients with respiratory failure via all available studies by performing a systematic review and meta-analysis.