Even though it can meet the ARDS Berlin definition, the COVID-19 pneumonia is a specific disease with peculiar phenotypes. Its main characteristic is the dissociation between the severity of the hypoxemia and the maintenance of relatively good respiratory mechanics.

Indeed, the median respiratory system compliance is usually around 50 ml/cmH2O. Of note, the patients with respiratory compliance lower or higher than the median value experience hypoxemia of similar severity.

We propose the presence of two types of patients (“non-ARDS,” type 1, and ARDS, type 2) with different pathophysiology.

When presenting at the hospital, type 1 and type 2 patients are clearly distinguishable by CT scan.

If the CT scan is not available, the respiratory system compliance and possibly the response to PEEP are the only imperfect surrogates we may suggest.

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