Hospital readmission rates for COPD patients are high, with two-week readmission rates of 22% being recorded in one study of patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). In a separate study, patients admitted with PaCO2> 50 mm Hg had a readmission rate of 40% at six months. There are no agreed clinical evidence factors that determine readmission. A few studies have reported that readmission is associated with an individual’s inability to cope with the disease, and that anxiety and socioeconomic status are important variables. Others argue that readmission relates to severity of lung function abnormality, changes in atmospheric pollution, and impaired quality of life (QoL).