The investigators design a pilot randomised, single-centred, controlled trial to compare different withdrawal methods of Non-invasive ventilation. Our study aims at comparing stepwise withdrawal of Non-invasive ventilation versus immediate withdrawal of Non-invasive ventilation. The primary endpoint is to compare the rate of success between two withdrawal methods. The investigators define success as no recurrence of acute hypercapnic respiratory failure or restitution of Non-invasive ventilation within 48 hours after NIV is stopped. The secondary endpoints include time to recurrence of acute hypercapnic respiratory failure measured from the time of randomisation, the total days of Non-invasive ventilation use and the days of hospitalisation. Results from this trial will inform design of future randomised trial in this area.