The Berlin definition of acute respiratory distress syndrome: should patients receiving high-flow nasal oxygen be included?

The 2012 Berlin definition of acute respiratory distress syndrome (ARDS) provided validated support for three levels of initial arterial hypoxaemia that correlated with mortality in patients receiving ventilatory support. Since 2015, high-flow nasal oxygen (HFNO) has become widely used as an effective therapeutic support for acute respiratory failure, most recently in patients with severe COVID-19. We propose that the Berlin definition of ARDS be broadened to include patients treated with HFNO of at least 30 L/min who fulfil the other criteria for the Berlin definition of ARDS. An expanded definition would make the diagnosis of ARDS more widely applicable, allowing patients at an earlier stage of the syndrome to be recognised, independent of the need for endotracheal intubation or positive-pressure ventilation, with benefits for the testing of early interventions and the study of factors associated with the course of ARDS. We identify key questions that could be addressed in refining an expanded definition of ARDS, the implementation of which could lead to improvements in clinical practice and clinical outcomes for patients.