What is a COPD exacerbation? Current definitions, pitfalls, challenges and opportunities for improvement.

Chronic obstructive pulmonary disease (COPD) is a chronic illness that can be periodically punctuated by exacerbations, characterised by acute worsening of symptoms, including increased dyspnoea, cough, sputum production and sputum purulence. COPD exacerbations are common and have important clinical and economic consequences, including lost work productivity, increased utilisation of healthcare resources, temporary or permanent reductions in lung function and exercise capacity, hospitalisation, and sometimes death. Over the past two decades, clinicians and researchers have broadened their treatment goals for COPD to extend beyond improving lung function and symptoms, and have begun to address the importance of preventing and reducing exacerbations. However, despite the best efforts of clinicians and guideline committees, current definitions of COPD exacerbations are imperfect and fraught with problems. The cardinal symptoms of a COPD exacerbation are nonspecific and can result from acute cardiorespiratory illnesses other than COPD. A proposed definition, which may be more specific than current definitions, suggests that COPD exacerbation be defined as an acute or subacute worsening of dyspnoea (≥5 on a visual analogue scale that ranges from 0 to 10) sometimes but not necessarily accompanied by increased cough, sputum volume and/or sputum purulence. Necessary laboratory criteria for an exacerbation include oxygen desaturation ≤4% below that of stable state, elevated levels of circulating blood neutrophils or eosinophils (≥9000 neutrophils·mm-3 or ≥2% blood eosinophils) and elevated C-reactive protein (≥3 mg·L-1 ), without evidence of pneumonia or pulmonary oedema on chest radiography and with negative laboratory test results for other aetiologies. Herein, we discuss the current state of the art with respect to how we define COPD exacerbations, associated pitfalls and challenges, and opportunities for improvement.