the observed event rate is lower than expected by the protocol hypothesis.

The primary objective of the study is to evaluate the efficacy of Helium/Oxygen (He/O2) 78%/22% compared to a conventional Air/O2 mixture in reducing endotracheal intubation rate and mortality in patients with severe hypercapnic exacerbations of Chronic Obstructive Pulmonary Disease (COPD) during their index Intensive/Intermediate Care Unit (ICU) stay.

Patients eligible for this study are critically ill patients with COPD admitted in Intensive Care Unit for an exacerbation of their chronic disease with hypercapnic acute respiratory failure. The patients will receive an Helium/Oxygen mixture or an Air/Oxygen mixture for a maximum of 72 hours during Non-Invasive Ventilation (NIV) and NIV-free sessions.

During NIV sessions, gas mixtures will be administered using a ventilator suitable for NIV with either He/O2 or Air/O2 and a NIV facemask.

Patients will be followed until hospital discharge and then contacted by phone up to the 6th month after randomization.

Inclusion Criteria:

• Patient with known or suspected COPD
• Patient presenting current exacerbation of COPD with hypercapnic acute respiratory failure
• Patient eligible for Non-Invasive Ventilation (NIV)
• Patient admitted in an ICU

Exclusion Criteria:

• Patient who had lung transplant
• Patient having a contraindication to NIV
• Patient with tracheostomy
• Patient requiring Oxygen flow rate > 6 L/min or Inspired Oxygen Fraction (FIO2) > 0.50
• Patient admitted in the ICU for more than 24 hours and/or having received NIV in ICU for more than 6 hours (in total) for the current exacerbation of COPD