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To paraphrase Henry Kissinger's infamous quote ascribing the vicious nature of academic politics to their lack of importance, it seems that precisely because exacerbations of COPD are so important, they are so infrequently studied. COPD is one of the most common reasons that people are admitted acutely to hospital. An OECD (Organisation for Economic Co-operation and Development) report indicates that the rate of admissions is 164 for women and 251 for men per 100 000 population.1 The median length of stay is 5 days and 5%–7% of people die during the course of the admission. While many recover to be discharged, 30% are readmitted within the subsequent 90 days.2 Clinically, compared with all patients with COPD, those who experience exacerbations suffer increased morbidity, reduced quality of life and have shortened life expectancy. One important feature of COPD exacerbations about which we have relatively little information is which clinical features, on presentation, indicate that an individual person is at risk of a poor outcome. In this month's Thorax, work from Dr Bourke's group have addressed this important question and report a validation study of a previously described risk assessment score, termed DECAF.3
To put this study into context, it is worthwhile reviewing the nature of an exacerbation of COPD. Most exacerbations are precipitated by infections, both viral and bacterial. As there is a seasonal pattern to these exacerbations, temperature change, variations in environmental pollution levels and poor adherence to preventer inhalers are additional causative factors.4 Locally, the airway responds to these insults with increased production of protective mucus and a resulting increased cough frequency. Infection increases the individual's metabolic demand and the resulting increase in VO2, leads to an increase in respiratory rate. In obstructed airways, the increased rate of ventilation and the impairment of airflow, from …
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