Peak Expiratory Flow Rate Underestimates Severity of Airflow Obstruction in Acute Asthma

BACKGROUND Several investigators have demonstrated a considerable disagreement between FEV1 and PEFR to assess the severity of airflow obstruction. The purpose of this study was to examine whether the discrepancy between the two measurements affects the assessment in the severity of acute asthma. METHODS Thirty-five consecutive asthma patients measured both FEV1 and PEFR at 0, 1hr, 1, 3, 5, 7 days of an emergency room admission using a spirometer and a Ferraris PEFR meter. The degree of discrepancy between FEV1 and PEFR expressed as % predicted values was determined. RESULTS When predictive equations that recommended by the instrument manufacturers were used. PEFR measured with the PEFR meter (f-PEFR) was significantly higher than FEV1 at all time points, with 16.1% mean difference and unacceptable wide limits of agreement (-20.0-52.3%). The classification in severity was significantly different between FEV1 and f-PEFR (p < 0.001). The discrepancy was inter-instrumental in large part because f-PEFR was 10.1% higher than spirometric PEFR. Different predictive equations altered the degree of the differences but could not completely correct it. CONCLUSION These results indicate that f-PEFR values underestimate the severity of airflow obstruction in acute asthma despite using recommended predictive equations. Therefore, these confounding factors should be considered when the severity of airflow obstruction is assessed with PEFR.