Acute exacerbations of chronic obstructive pulmonary disease: causes and impacts.

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are recognised clinically as episodes of increased breathlessness and productive cough requiring a more intensive treatment. A subset of patients with this disease is especially prone to such exacerbations. These patients are labelled as 'frequent exacerbators'. Though yet poorly characterised in terms of host characteristics, including any genetic basis, these patients are believed to represent a distinct phenotype as they have a different natural history with a more progressive disease and a poorer prognosis than those who get exacerbations infrequently. Most exacerbations appear to be associated with infective triggers, either bacterial or viral, although 'non-infective' agents, such as air pollution and other irritants may also be important. Susceptibility to exacerbations is determined by multiple factors. Several risk factors have been identified, some of which are modifiable. Chronic obstructive pulmonary disease (COPD) exacerbations are major drivers of health status and patient-centered outcomes, and are a major reason for health care utilisation including hospitalisations and intensive care admissions. These are associated with considerable morbidity and mortality, both immediate and long-term. These episodes have a negative impact on the patient and the disease including high economic burden, increased mortality, worsening of health status, limitation of activity, and aggravation of comorbidities including cardiovascular disease, osteoporosis and neuro-psychiatric complications. Exacerbations also increase the rate of progression of disease, increasing the annual decline in lung function and leading to a poorer prognosis. Evaluation of risk of exacerbations is now included as a major component of the initial assessment of a patient with COPD in addition to the traditionally used lung function parameter, forced expiratory volume in one second (FEV1). Decreasing the risk of exacerbations and their prevention is a major therapeutic goal of management in COPD.