BackgroundCOVID-19-associated acute respiratory distress syndrome (ARDS) supported by veno-venous extra-corporal membrane oxygenation (vv-ECMO) results in a high in-hospital mortality rate of more than 35%. However, after cannulation, no prognostic factor has been described to guide the management of these patients. The objective was to assess the association between static respiratory compliance over the first 10 days post-vv-ECMO implantation on 180-day mortality.ResultsIn this multicentric retrospective study in three ECMO referral centers, all patients with COVID-19-associated ARDS supported by vv-ECMO were included from 03/01/2020 to 12/31/2021. Patients were ventilated with ultra-protective settings targeting a driving pressure lower than 15 cmH2O. 122 patients were included. Median age was 59 IQR (52–64), 83 (68%) were male, with a median body mass index of 33 (28–37) kg/m2. Delay between first symptoms to vv-ECMO implantation was 16 (10–21) days. Six-month death was 48%. Over the first ten days, compliance increased in 180 day survivors [from 18 (12–25) to 20 (15–27) mL/cmH2O] compared to non-survivors [from 12 (9–20) to 10 (8–14) mL/cmH2O,pinteraction < 0.0001]. A time varying multivariable Cox model found age, history of chronic lung disease, compliance from day one to day ten and sweep gas flow from day one to day ten as independent factors associated with 180-day mortality.ConclusionsIn COVID-19-associated ARDS, static respiratory compliance course over the first ten days post-vv-ECMO implantation is associated with 180-day mortality. This new information may provide crucial information on the patient's prognosis for intensivists.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13613-023-01152-7.