None

None

1. moribund status 2. pregnancy or breastfeeding 3. long term corticotherapy at a dose of 0.5mg/kg/j or higher 4. active and untreated bacterial, fungal or parasitic infection 5. not written informed consent from the patient or a legal representative if appropriate 6. hypersensitivity to dexamethasone or to any of the excipients 7. not affiliation to the french social security in the subset of non-mechanically ventilated patients, additional non-inclusion criteria are: 8. anatomical factors precluding the use of nasal cannula 9. hypercapnia indicating niv (paco2 ≥ 50 mmhg)

1. moribund status 2. pregnancy or breastfeeding 3. long term corticotherapy at a dose of 0.5mg/kg/j or higher 4. active and untreated bacterial, fungal or parasitic infection 5. not written informed consent from the patient or a legal representative if appropriate 6. hypersensitivity to dexamethasone or to any of the excipients 7. not affiliation to the french social security in the subset of non-mechanically ventilated patients, additional non-inclusion criteria are: 8. anatomical factors precluding the use of nasal cannula 9. hypercapnia indicating niv (paco2 ≥ 50 mmhg)