There is evidence that noninvasive mechanical ventilation (NIV) is effective in the treatment of severe exacerbations of COPD presenting respiratory acidosis.

The aim of the study is to evaluate the benefit of adding NIV to conventional treatment in patients with COPD exacerbation and hypercapnic respiratory failure without acidosis requiring hospital admission. It is known that NIV improves respiratory mechanics, so the primary outcome will be respiratory muscle function.

All patients admitted to the hospital for COPD exacerbation and hypercapnic respiratory failure without acidosis will be included for a period of 12 months. The patients will be randomized into two groups (conventional treatment or conventional treatment plus NIV). Clinical data, blood gases, muscle strength parameters will be collected at the inclusion time and 24h after starting NIV. Quality of life and hospital stay will be measured at discharge. All patients will be followed for a year.

Inclusion Criteria:

• Diagnosis of COPD according to international guidelines ( GOLD)
• COPD exacerbation requiring hospitalization
• Initial blood gases: PaCO2> 50 mm Hg and pH> 7.35.
• If the patient does not have COPD diagnosis at the time of inclusion, it could be included if the diagnosis is confirmed within three months after the exacerbation.

Exclusion Criteria:

• Patients with a pH below 7.35
• Patients with intubation criteria
• Other chronic respiratory diseases (fibrothorax, cystic fibrosis, significant ribcage alterations)
• Neuromuscular Diseases
• Significant associated chronic systemic diseases (severe liver disease, chronic renal failure requiring dialysis, severe heart disease and active neoplasia)
• COPD exacerbation secondary to pulmonary embolism, pneumonia or pneumothorax
• Patients in active treatment with CPAP or home ventilation