Results
From 1647 initial citations, 34 full text articles were analysed and 12 studies were selected, including 194 patients with confirmed COVID 19 infection requiring ICU admission and venovenous ECMO treatment. Median New Castle Ottawa scale was 6 indicating acceptable study validity. 136 patients reached an endpoint of weaning from ECMO or death while the rest were still on ECMO. The median Berlin score for ARDS prior to starting ECMO was III. Patients received mechanical ventilation before ECMO implementation for a median of four days and ECMO was maintained for a median of 13 days. In hospital and short-term mortality were highly variable among the included studies ranging between 0% and 100%. Random-effect pooled estimates suggested an overall in-hospital mortality risk ratio of 0.49 (95% confidence interval 0.259 to 0.721; I2 = 94%). Subgroup analysis according to country of origin showed persistent heterogeneity only in the 7 Chinese studies with pooled estimate mortality risk ratio of 0.66 (I2 = 87%) (95% CI = 0.39-0.93), while the later larger studies coming from the USA showed pooled estimate mortality risk ratio of 0.41 (95% CI 0.28-0.53) with homogeneity (p=0.67) similar to France with a pooled mortality risk ratio of 0.26 (95% CI 0.08-0.43) with homogeneity (p=0.86). Meta-regression showed only younger age as a predictor of mortality (p=0.02). Publication bias was excluded by visualizing the funnel plot of standard error, Egger’s test with p=0.566 and Begg&Mazumdar test with p=0.373