Data analysis
A meta-analysis was conducted to examine the mortality incidence in venovenous ECMO treatment for COVID 19. Data were summarized using the risk ratio (95% confidence interval (CI)). The data were pooled using DerSimonian-Laird random effects model (16). P value of 0.05 or less was statistically significant. Cochran Q and I2 were used to assess heterogeneity between studies. The degree of heterogeneity was categorized as either low (I2 < 25%), moderate (I2 = 25%–75%), or high (I2 > 75%) (17). A P value of ≤ 0.05 indicated significant heterogeneity. A subgroup meta-analysis according to the study’s country of origin was conducted to investigate the high heterogeneity detected. Exploratory meta-regression analysis was performed to identify significant moderators using the inverse-variance weighted-least-squares linear regression analysis. Studies that included a control group with patients treated with mechanical ventilation were independently studied and mortality estimates were pooled using odds ratio and 95% CI. Secondary outcome measures included age, ventilation days before ECMO, and duration time on ECMO. Publication bias was examined by visual inspection of the funnel plot and tested by Egger’s test and Begg and Mazumdar test. A P value of ≤ 0.05 indicated the existence of publication bias. All analyses were performed using Open Meta Analyst software Windows 10 version.
The data used in the meta-analysis in each study were the number of mortality events and the number of closed cases (either cured or dead). Patients who were still on treatment were not included in the final analysis of cases of the study. The corresponding authors of the studies were contacted by email to provide additional information regarding the patients who were still receiving treatment. The numbers used in Jacobs et al (2020) and Beyls et al (2020) were not those reported by the study but rather provided by the author (unpublished data).
Trial was registered with PROSPERO at www.crd.yorl.ac.uk/PROSPERO under registration number CRD42020183861