STANDARDIZATION OF AMBULATORY PEAK FLOW MONITORING - THE IMPORTANCE OF RECENT BETA(2)-AGONIST INHALATION

Standardization of conditions for peak expiratory flow (PEF) monitorin g is much more difficult in practice than for laboratory spirometry. P atients are usually asked to record PEF before medication. The aim of this study was to determine the effect of prior bronchodilator use on PEF outcome measures in a clinical trial. Electronic PEF records from 43 subjects with poorly controlled asthma were examined to determine t he frequency with which beta(2)-agonist was inhaled <4 h before PEF me asurement, as such PEF are potentially ''postbronchodilator'', The eff ect of inclusion of such PEF values on improvement in PEF outcome meas ures after 8 weeks of inhaled budesonide was calculated, Subjects were asked to record PEF before medication. During run-in, the median freq uency of postbronchodilator PEF was 29%,falling to 0% after 8 weeks of budesonide, Inclusion of postbronchodilator PEF led to an overestimat ion of average morning, evening and daily PEF during run-in (p<0.001), Improvement in these indices with treatment was, therefore, underesti mated. Minimum morning PEF expressed as percent personal best was unaf fected, Subjects may not be able to withhold beta(2)-agonist for 4 h b efore every peak flow reading, This may change as the level of asthma control changes, leading to a systematic bias in clinical trial end-po ints or inaccuracy in individual treatment decisions. Simple changes t o peak expiratory flow instructions and analysis are proposed.