Efficacy of Helium/Oxygen Compared to Air/Oxygen in Severe Exacerbation of Chronic Obstructive Pulmonary Disease (COPD)

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