Broadening the Berlin definition of ARDS to patients receiving high-flow nasal oxygen: an observational study in patients with acute hypoxemic respiratory failure due to COVID-19 par Fleur-Stefanie L. I. M. van der Ven, Christel M. A. Valk, Siebe Blok, Michelle G. Brouwer, Dai Ming Go, Amanda Lokhorst, Pien Swart, David M. P. van Meenen, Frederique Paulus, Marcus J. Schultz, for the PRoAcT–COVID study investigators