Chronic Obstructive Pulmonary Disease (COPD) patients are more likely to develop acute hypercapnic respiratory failure. In the acute phase, non invasive ventilation has been shown to improve mortality and reduce intubation rate. Few studies are available about long term benefits of home non invasive ventilation in COPD patients with chronic hypercapnic respiratory failure who survived after an acute episode. The purpose of this study is to determine whether home non invasive ventilation can reduce recurrent acute hypercapnic respiratory failure in COPD patients who survived an acute hypercapnic respiratory failure episode treated by non invasive ventilation.