High-flow nasal cannula is an oxygenation technique increasingly used for patients admitted for acute respiratory failure. Literature essentially concerns "de novo" acute hypoxemic failure and the interest of high-flow during take care of chronic obstructive pulmonary disease patients is few studied. Physiological studies reported potential benefits of high-flow nasal cannula oxygenation in chronic obstructive pulmonary disease patients including dead space clearance and decrease of respiratory, which lead to decrease work of breathing. As inhaled bronchodilators are part of treatment of chronic obstructive pulmonary disease exacerbation, nebulization could be also provided through high-flow nasal cannula oxygen therapy. The aim of our study is to determine whether a beta-2 agonist nebulization administered through High-flow nasal cannula is efficient to improve spirometry of patients for admitted hronic obstructive pulmonary disease exacerbation.

Inclusion Criteria:

• Arterial pH over 7.25,
• Respiratory rate under 35 breaths/mn
• Glasgow Coma Scale equal to 15,
• indication of beta-2 agonist nebulization less than 8 per day (time between two nebulization more than 3 hours),
• NIV sessions spaced more than 6 hours.

Exclusion Criteria:

• Urgent endotracheal intubation;
• Contraindication to beta 2 adrenergic agonist;
• Another organ failure (hemodynamic and neurological instability);
• Cardioselective beta-blocker during treatment of copd exacerbation;