Search strategy and selection criteria
Our methodology followed the reporting guidelines of Meta-analysis Of
Observational Studies in Epidemiology (MOOSE) and Preferred Reporting
Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We
electronically ran a search on CENTRAL, MEDLINE/PubMed, Cochrane
Library, and Scopus. On Pubmed the
word search used was (COVID OR
SARS COV2 OR pandemic) AND (ARDS) OR (acute respiratory distress
syndrome) OR (acute lung injury) OR (respiratory failure) OR
(respiratory insufficiency) OR (ECMO) OR (extracorporeal membrane
oxygenation)).
We contacted authors for some missing data, searched trial registries,
included the grey literature, and used studies accepted and ahead of
print. We did our search from inception up to May 28, 2020, which was
the date of our final search without language restrictions. We used both
subject headings and text word terms to search for articles about ECMO
or mechanical ventilation with ARDS in COVID-19 patients. There were no
language restrictions. Inclusion criteria were (all criteria should be
concomitantly met for study inclusion): a) study reporting on 5 or more
patients with final outcomes; b) with confirmed COVID 19 infection; c)
receiving venovenous ECMO. Exclusion criteria were (one criterion was
sufficient for study exclusion): a) inclusion of <5
patients with COVID-19 infection treated ECMO (thereby, any study
reporting on fewer than 5 patients or case reports treated with ECMO
were excluded); b) duplicate publication (in which case only the
most recent report from the same study group was included in the
systematic review). Use of a sample size cut-off was chosen to limit the
risk of imprecision and publication bias c) Studies in which the
main focus was veno-arterial ECMO for treating COVID-19 or d)studies with insufficient data about outcome endpoints (mortality,
extubation, weaning, and discharge). AH, TA and HY independently
reviewed the titles and abstracts of all citations. Then, they
independently reviewed the full text of both definite and potentially
eligible studies for inclusion. Disagreements were reviewed by a fourth
reviewer HE, who had a deciding vote. The study protocol link is at
www.crd.yorl.ac.uk/PROSPERO
under registration number CRD42020183861