COPD which means chronic obstructive pulmonary disease, is a group of progressive lung diseases with an indeterminate course and variable prognosis. Its prognosis depends on several factors including genetic predisposition, environmental exposures, and comorbidities and, to a lesser degree, acute exacerbations. Although short-term survival for patients with COPD and respiratory failure depends on the overall severity of acute illness, long-term survival is primarily influenced by the severity of COPD and the presence of comorbid conditions. For people with mild COPD (stage I) the prognosis is very good and they may have a relatively normal life expectancy but this decreases as the severity of staging increases.