To address this problem, attempts have been made to develop a consensus definition for COPD exacerbations [15] . Recently, the American Thoracic Society (ATS) and European Respiratory Society (ERS) adopted the following definition: 'an event in the natural course of the disease that is characterised by a change in the patient's baseline dyspnea, cough and sputum beyond day-to-day variability sufficient to warrant a change in management' [1] .