There is currently no general agreement on the definition of an exacerbation in COPD. Definitions of exacerbations in COPD are based on increasing symptoms and/or increased health care utilisation.²⁶ In some studies exacerbations have been defined in operative terms according to the type and number of symptoms. A commonly used definition is based on an increase in symptoms of dyspnoea, sputum volume and sputum purulence with or without symptoms of upper respiratory infection.²⁷

Bacteria are isolated from between 40-60% of acute exacerbations of COPD. Three bacterial species account for most isolates: Haemophilus influenzae, Streptococcus pneumoniae and Moraxella cattarhalis. Haemophilus parainfluenzae, Pseudomonas aeruginosa, Staphylococcus aureus and Enterobacteriaciae are encountered less frequently. Haemophilus influenzae is present in about 50% of culture positive sputa in most clinical trials. Variation in incidence between trials may be accounted for by patient selection criteria, previous antibiotic exposure and sputum culture techniques. ^{3,28,29,30,31,32,33,34,35,36,37,38,39,40,41}

4.1 Investigation

4.1.1 SPUTUM EXAMINATION

Sputum analysis is controversial and possibly for this reason has not featured prominently in studies of LRTI. In selected cases however, it has a role in the management of patients with exacerbations in COPD.⁴²

A questionnaire survey of GPs submitting sputum samples for analysis found that the most common reason for submitting a sample was failure of antibiotic treatment.⁴³ In 25% of the samples in which a pathogen was identified, this did influence antibiotic prescribing. Paradoxically, interpretation of a positive sputum culture is difficult and potentially less useful once antibiotics have already been prescribed. A significant number of GPs feel that the culture results are not available rapidly enough to influence prescribing. Where same day laboratory access is possible, the preliminary overnight analysis can be used to reduce the number of antibiotic scripts by 60% and lead to a reduced repeat visit rate in patients compared to those given empirical antibiotics.⁴⁴ Evidence level 2+

A British study of COPD exacerbations in primary care has demonstrated that green (purulent) sputum is a good indicator of a high bacterial load and that patients with lack of purulence will improve without antibiotic therapy.⁴⁵ Evidence level 2+

Visualise sputum in patients with an exacerbation of COPD. Where sputum purulence is present and antibiotic treatment is intended, obtain sputum culture if overnight analysis is available. Base antibiotic choice on the result of the sputum culture. If overnight analysis is not available, proceed with empirical therapy, if appropriate.

4.1.2 CHEST X-RAY

Chest x-ray is not normally useful for patients presenting with acute symptoms but should be considered in the convalescent period in those who smoke or if patients do not make satisfactory progress.

Chest x-ray should not be used routinely for patients presenting with acute symptoms of exacerbations of chronic obstructive pulmonary disease (COPD).

Consider chest x-ray in the convalescent period in COPD patients who smoke or if patients do not make satisfactory progress.

4.1.3 PULMONARY FUNCTION TESTS

Two studies ^46,47 have shown a correlation between the forced expiratory volume in one second (FEV₁) and sputum cultures. A severe impairment of FEV₁ may be associated with the presence of organisms which are more likely to be resistant to normal antibiotic therapy, such as Pseudomonas during an exacerbation of COPD. Thus knowledge of baseline FEV₁ may be useful when deciding on empirical antibiotic therapy. In contrast, peak flow measurements do not influence management of LRTI symptoms in patients without asthma. Spirometry (FEV₁ and forced vital capacity) is of importance in confirming airways obstruction and is essential in the diagnosis of COPD. Evidence level 3

Measure FEV1 in smokers who may have early COPD.

4.1.4 PULSE OXIMETRY

Pulse oximetry, where available, may provide useful additional data for patient management. A study has looked at the impact of pulse oximetry on the management of 14,059 patients admitted to an emergency room with a wide range of conditions.⁴⁸ They looked at the management of the patient before and after the physician was made aware of the pulse oximetry reading. A total of 22% of the 1,220 with a saturated oxygen (SaO2) of <95% had investigations or treatment changed compared to 2.2% of patients with an SaO2 of >95%. Management changes were less common in patients with an SaO2 of <89%, perhaps suggesting that physicians can detect severe hypoxia clinically but find it difficult to detect mild degrees of hypoxia. The value of pulse oximeters in general practice in the UK has not been evaluated.

4.2 TREATMENT

There have been a number of randomised placebo controlled trials of antibiotic therapy (usually aminopenicillin or tetracycline) in patients with exacerbation of COPD. A systematic review of these trials has shown a small benefit for those patients receiving antibiotic rather than placebo, although a small number of patients was used in each of the original study groups.⁴⁹ Evidence level 1-

In one study the sub-group of patients showing most benefit from antibiotics were those with two or all of the following symptoms: increasing breathlessness, sputum volume and sputum purulence.²⁷ Patients in this study had significant baseline obstruction with a mean FEV₁ of 33% of predicted. In patients with COPD, sputum purulence is a good guide to the presence and number of bacteria and whether antibiotic treatment is likely to be beneficial.^40,50 Evidence level 1

Patients with significant airway obstruction who have an increase in breathlessness and sputum purulence should be treated with an antibiotic.

The antibiotic of choice should be an aminopenicillin, a macrolide or a tetracycline.

Quinolones have performed equally well in clinical trials, but no clinical superiority over other antibiotics has yet been shown.⁵¹

For further information on choice of antibiotic, see Annex 1 to this guideline on the SIGN website.