COPD exacerbations: definitions and classifications

The most recent update of the international NHLBI/WHO Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines defines chronic obstructive pulmonary disease (COPD) with respect to its pulmonary and extrapulmonary (systemic) components, but does not mention exacerbations in the main definition, even though they are the main cause of medical intervention and admission to hospital in these patients. In the same guidelines, an exacerbation of COPD is separately defined as ‘an event in the natural course of the disease characterised by a change in the patient’s baseline dyspnoea, cough and/or sputum that is beyond normal day-to-day variations, is acute in onset, and may warrant a change in regular medication in a patient with underlying COPD’. The latest GOLD guidelines also provide a classification of the severity of the exacerbations of COPD based on clinical parameters to drive the necessity and the type of antibiotic therapy. Similarly, the latest update of the Canadian Thoracic Society (CTS) recommendations for the management of COPD defines an exacerbation of COPD as ‘a sustained worsening of dyspnoea, cough or sputum production leading to an increase in the use of maintenance medications and/ or supplementation with additional medications’. The term ‘sustained’ implies a change from baseline lasting 48 h or more. In addition, COPD exacerbations are defined as either purulent or non-purulent on the assumption that this is helpful in predicting the need for antibiotic therapy. Again, in a strict analogy to the latest GOLD guidelines, the CTS update also provides a classification of the severity of purulent exacerbations of COPD, recognising both simple and complicated purulent COPD exacerbations, based on the presence of clinical risk factors that either increase the likelihood of treatment failure or are more likely to be associated with more virulent or resistant bacterial pathogens. Although both the GOLD and CTS definitions and classifications of the severity of COPD exacerbations may provide a useful practical tool for clinical studies, they have not been formally validated in clinical trials and are rather cumbersome and difficult to use in clinical practice. Other definitions derived from the literature are also used and are discussed below.