High Flow Nasal Cannula and Hypercapnia

In the present investigation, in 50 COPD with persistent hypercapnia after an acute exacerbation, the investigators want to assess the acceptability of HFNC and its effectiveness in further reducing the level of PaCO2, and to eventually verify the hypothesis, based on previous physiological studies, that the response to HFNC is dependent on the level of baseline hypercapnia and eventually on the presence of overlap syndrome. This latter parameters to eventually calculate the sample size and the target population to perform future definitive randomized long term trials vs NIV.