An exacerbation of chronic obstructive pulmonary disease (COPD) is a sustained worsening of respiratory symptoms that is acute in onset and usually requires a patient to seek medical help or alter treatment. The deterioration must be more severe than the usual daily variation experienced. Exacerbations are characterised by increased breathlessness, cough, sputum volume or purulence, wheeze, and chest tightness. Other common features are malaise, reduced exercise tolerance, peripheral oedema, accessory muscle use, confusion, and cyanosis. Other (often coexisting) cardiorespiratory disorders can also cause these symptoms, which may lead to diagnostic uncertainty.

Exacerbations of COPD account for up to 10% of all medical admissions to UK hospitals, equating to more than 100 000 admissions a year, with a mean length of stay of over a week. Exacerbations therefore have considerable costs for secondary care and are partly responsible for high occupancy rates of hospital beds. Patients with frequent exacerbations have an accelerated decline in lung function, impaired quality of life, and restricted daily living activities, and, as a consequence, are likely to become housebound. As the disease becomes more severe, the frequency of exacerbations also increases.