The main objective of this study is to determine if the systemic (intravenous) administration of corticosteroids, as compared to placebo, increases the number of ventilator-free days (VFD) and alive at day 28 in COPD patients admitted to an ICU, a step-up unit or a respiratory care unit for an ACRF requiring ventilatory support, either invasive or non-invasive.

Inclusion Criteria:

1. Patients aged ≥ 40 years

2. Strongly suspected or documented COPD, defined by the presence of the following criterias:

   • Persistent respiratory symptoms (dyspnoea, chronic cough or sputum)
   • History of exposure to a risk factor such as tobacco smoke
   • If available, pulmonary function tests showing airflow limitation not fully reversible (post-bronchodilator ratio of FEV1/ FVC ratio < 0.7)

3. ACRF, defined by the presence of the two following criteria:

   • COPD exacerbation defined by a change in the patient baseline respiratory symptoms at least 24 hours and requiring a change in regular respiratory medication
   • Acute respiratory failure <24h (polypnea ≥ 30 breaths.min-1 or use of accessory respiratory muscles) requiring ventilatory support, either invasive (implemented because of respiratory distress) or NIV (implemented because of hypercapnic acidosis with PaCO2 ≥ 45 mmHg and pH ≤ 7.35).

4. Admission to an ICU, a step-up unit or a respiratory care unit

5. Inform consent from the patient or his surrogates. In patients who are not able to consent on admission an emergency inclusion procedure will be allowed, with a mandatory delayed consent.

6. Affiliation to (or benefit from) French health insurance system

Exclusion Criteria:

• Previous diagnostic of asthma, according to "GINA" international guidelines (40)
• Recent use of systemic corticosteroids, defined by systemic corticosteroids use in the past 7 days
• Contra-indication of systemic corticosteroids treatment: allergy to corticosteroids, uncontrolled severe arterial hypertension, uncontrolled diabetes mellitus, gastro-intestinal ulcer bleeding
• Pneumothorax at randomization
• Extracorporeal life support (ECMO or ECCO2R) at inclusion
• Moribund patient life expectancy < 3 months
• Pregnancy
• Patients protected by law
• Exclusion period due to other interventional clinical trial enrolment which can influence primary outcome
• Previous inclusion in the present study