This is a prospective, randomized, open labelled study. The primary outcome is nocturnal transcutaneous CO2 (PtCO2) after 3 months of non-invasive ventilation. Three hundred COPD patients on LTOT will be screened and assessed by pulmonary function tests, blood gases and nocturnal PtCO2 at their home. This will allow the determination of the prevalence of nocturnal hypoventilation in COPD patients on LTOT (a secondary outcome) and to select patients who meet the inclusion criteria for the RCT and randomization to NIV + LTOT or to continue LTOT alone (n=38). Patients will undergo the same assessments at the end of the three-month intervention period.
