This chapter reviews approaches to the definitions, severity and impact of exacerbations in COPD. The “clinical diagnosis of exclusion” approach to COPD exacerbation, used in daily practice, contrasts with the symptom-based and healthcare utilisation definitions of exacerbation employed in clinical trials. There are strengths and weaknesses to these different definitions that should be considered when interpreting research. There remains no biomarker of exacerbation, in part because exacerbations are heterogeneous events. What is loosely called “exacerbation severity” is in fact a composite of the severity of the underlying COPD and the severity of the exacerbation insult. There are several scores that may aid the prediction of poor outcomes at exacerbation. Exacerbations affect lung function, health status, the timing of future exacerbations and mortality, and therefore the exacerbation-susceptible “frequent-exacerbator” phenotype experiences a particular burden of disease. Exacerbations also contribute significantly to healthcare expenditure. Prevention and mitigation of exacerbations are therefore key goals of COPD management.

Cite as: Simons SO, Hurst JR. COPD: definition, severity and impact of pulmonary exacerbations. In: Burgel P-R, Contoli M, López-Campos JL, eds. Acute Exacerbations of Pulmonary Diseases (ERS Monograph). Sheffield, European Respiratory Society, 2017; pp. 13–24 [https://doi.org/10.1183/2312508X.10015616].