How should we define and classify exacerbations in chronic obstructive pulmonary disease?

Chronic obstructive pulmonary disease (COPD) is a chronic disorder whose clinical course may be punctuated by exacerbations characterized by a sudden symptom worsening beyond the expected daily variations. Exacerbations bear clinical and prognostic relevance, and may result in marked functional and clinical deterioration. The varying presentations of COPD mean that exacerbations, although more frequent in patients with severe or very severe disease, may occur regardless of the degree of functional impairment. The new Spanish COPD Guideline (GesEPOC) has provided new insights into the management of the disease. The GesEPOC defines various disease phenotypes with different clinical, prognostic and therapeutic implications. One of these phenotypes is the so-called 'exacerbator', characterized by the incidence of an increased number of exacerbations (two or more moderate-severe exacerbations in the last year). An exacerbation must be defined by: an increase in symptom intensity occurring after a certain period of time since the last exacerbation (so that treatment failure can be excluded as the cause of the event); and the contribution of social criteria or reasons concerning the choice of therapy. The availability of certain tools to detect exacerbations would enable establishment of a homogeneous definition of exacerbation, and improved diagnosis, a suitable treatment choice and a more appropriate patient selection for clinical studies. Validated clinical questionnaires and biomarkers are the most helpful instruments to reach the above objectives. Following the clinical diagnosis of a COPD exacerbation, associated comorbidities must be evaluated and an etiologic diagnosis must be made, all of which will partially drive the choice of treatment. Once a diagnosis has been made, the severity of the exacerbation should be established in order to define where and how the patient should be treated. Based on the patient's clinical history, clinical examination and diagnostic tests, the severity will be classified in one of these four degrees: very severe, severe, moderate and mild.