Impact of inaccuracy of peak flowmeters with Wright scale on asthma severity assessment in children

Introduction Measurement of daily variability of peak expiratory flow (PEF) is widely accepted as an objective method to assess asthma severity. Recent investigations have proved nonlinearity of original Wright scale of peak flowmeter. All country members of European Union have been obliged to implement a new scale according to standard EN 13826 since 2005. This study examined whether the correction of PEF values for the inaccuracy of the scale would affect asthma management based on their daily variability. Material and methods We analyzed PEF values (2352) in 34 children, aged 5-16, during 3-5 weeks of monitoring in order to establish the diagnosis of asthma by using peak flowmeters with Write scale. The correction of measured values for inaccuracy was managed with original Dr M. Miller's predictive equation. The daily variability of PEF (amplitude percent mean) up to 20% was considered as 'normal', 20-29.9% as 'raised', and 30% and above as 'high'. The assessment of daily variability was performed before and after correction. Results There was no significant change in the number of days with airway liability as regarding the assessed whole study group (p=0.475). However, 22 (64.7%) of children had at least one false clinical message about daily variability during the monitoring. It was overestimated in 12 (7%) days in younger (6.6±0.8 years) or of shorter stature (122.6±3.6cm) and underestimated in 13 (4%) days in older (11.1±2.7) or taller ones (150.9±12.5 cm) (p<0.001). Conclusion Usage of peak flowmeters with Wright scale may lead to an error in asthma severity assessment based on daily variability of PEF. It may cause overtreatment or undertreatment of asthmatic children.