C4. Assessing acute response to bronchodilators
The response to bronchodilators is determined to:
- assign a level of severity of airflow obstruction (post- bronchodilator); and
- help confirm asthma.
The details for this assessment are outlined in Box 5.
The change in FEV1 after an acute bronchodilator reversibility test indicates the degree of reversibility of airflow limitation. This is often expressed as a percentage of the baseline measurement (e.g., 12% increase). An increase in FEV1 of more than 12% and 200mL is greater than average day-to-day variability and is unlikely to occur by chance (Sourk 1983, Pellegrino 2005). An analysis of cross-sectional data from 3,922 healthy never smokers in the BOLD study (Tan 2012) found that the 95th percentiles (95% CI) for bronchodilator response were 284 ml (263 to 305) absolute change in forced expiratory volume in 1 second from baseline. However,this degree of reversibility is not diagnostic of asthma and is frequently seen in patients with COPD (eg, the FEV1 increases from 0.8 L to 1.0 L when the predicted value is, say, 3.5 L). The diagnosis of asthma relies on an appropriate history and complete, or at least substantial, reversibility of airflow limitation (see also below).
Repeat spirometry 15-30 minutes after bronchodilator is given and calculate reversibility.
FEV1=forced expiratory flow in one second.
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