Methods: Chronic respiratory failure patients with an acute decompensation and requiring MV for more than 48 hours will be randomized to 2 groups at the initiation of weaning schedule: the studied group (20 patients): chair-sitting group will be transferred from bed to arm chair for at least 1 hour and once a day; the control group will stay in bed until extubation. Ventilator free days, extubation failure, nosocomial infections, ICU mortality, ICU length of stay are assessed and compared between groups. Expected results: Early chair sitting would decrease MV duration, number of extubation failure, nosocomial infections and ICU mortality. Feasibility and safety of this intervention will also be evaluated and also the related work load.