There has been much debate as to whether subjective criteria or objective criteria should be used to determine the outcome of a trial of bronchodilator treatment. There is relatively little correlation between symptoms and lung function in individual cases of COPD . It is also possible that some patients may have physiological benefits such as reduced residual volume or reduced gas trapping that may not be detected by simple lung function tests . Therefore, it is reasonable to aim at maximal symptom relief rather than maximum lung function as the main objective of bronchodilator therapy in COPD.
Many clinicians find it helpful to monitor FEVi or peak flow improvement during bronchodilator therapy, especially as a large change in FEV1 or PEF may suggest that the diagnosis is asthma rather than COPD. Measurement of exercise capacity such as 6-minute walks, shuttle walks or step tests are helpful in research studies but they are of little value in assessing individual responses to treatment because improvements tend to be small (and variable). The main subjective criteria which are used are the patients' sensation of breathlessness and wheeze and their ability to undertake everyday activities. Patients should be specifically asked about these issues following a trial of bronchodilator therapy.
Sophisticated quality-of-life measures such as the St George's Respiratory Questionnaire are useful in trials involving large numbers of patients but they are insensitive (and inconvenient) for use in the management of individual cases. Additional benefits might include enhanced mucus clearance or reduced exacerbation rates. The presence or absence of side-effects is another important factor in determining whether or not to continue an inhaled treatment.
In summary, it is helpful to make objective measurements of lung function but bronchodilator therapy is given for symptomatic relief so most emphasis should be put on subjective benefit (and side-effects) when deciding whether or not to continue an individual bronchodilator agent.
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