Background
Patients with respiratory failure due to Chronic Obstructive Pulmonary Disease (COPD) have decreased diaphragmatic mobility [1]. Non Invasive Mechanical Ventilation (NIMV) is a cornerstone in COPD exacerbation therapy. The availability of early predictors of NIMV failure may be helpful to guide decision-making. Only pH, respiratory rate and PaO2/FiO2 have been considered predictors of response to NIMV [2]. Ultrasonographic (US) assessment of diaphragmatic kinetic is a fast, reliable and reproducible method [3], but its predictive value on NIMV success is not known.