Can peak expiratory flow predict airflow obstruction in children with asthma?

Study Objectives. A recent trend in the treatment of asthma has been the wi despread, independent use of peak expiratory flow (PEF). We examined whethe r PEF monitoring creates inaccuracies in assessment of children with modera te to severe asthma. Methods. We compared the negative predictive value of PEF in relation to th e forced expiratory volume in 1 second (FEV1), and to the forced expiratory flow between 25% and 75% of the vital capacity (FEF25-75%) at different le vels of air trapping as determined by the residual volume over total lung c apacity ratio (RV/TLC). Results. The study included 244 patients, ages 4 to 18 years with all class es of asthma severity, with FEV1 ranging from 28% to 134% of predicted valu e. We analyzed 367 sets of pulmonary function tests performed throughout a 3-year period. Thirty percent of patients with a normal PEF value had an ab normal FEV1 or FEF25-75%. As air trapping increased, the ability of a norma l PEF to predict normal FEV1 and FEF25-75% readings fell from 83% to 53%. T he negative predictive value was significantly lower for patients with RV/T LC ratio >30 compared with patients with RV/TLC <30. Conclusions. The results of this study suggest that it might be possible to identify children for whom the PEF is likely to give false-negative result s. As air trapping increases, it causes the PEF to give misleading reassura nce of normal pulmonary function. Furthermore, poor predictiveness of PEF i s obtained when values 80% of predicted for age are considered normal.