Canadian Health&Care; Mall

If peak flows are to be used as a basis of action, the criterion of a 30% decrease in PEF to define an acute exacerbation needs review. Changes in peak flow are less sensitive than deterioration in symptoms during an acute exacerbation and are less sensitive than changes in forced expiratory volume in 1 s . In the study of Chan-Yeung et al , only 27% of subjects had a decrease in PEF of more than 30% from baseline during an acute exacerbation. Similarly, Charlton et al concluded that patients with a symptom-based action plan implemented higher doses of inhaled corticosteroids earlier in the attack and were, thus, more likely to respond than patients who waited until their peak flow fell to 70% of normal. In a study of back titration of inhaled corticosteroids in patients with moderate or severe asthma, it was found that when peak flow had fallen by 20% or more, patients had a moderately severe attack requiring more than one week of oral corticosteroids (unpublished data). Gibson et al have recommended using individualized PEF action thresholds because they were more sensitive in identifying exacerbations and had fewer false positives than previous recommendations.