[Effects of nonlinear error correction of measurements obtained by peak flowmeter using the Wright Scale to assess...

Monitoring of peak expiratory flow (PEF) is recommended in numerous guidelines for management of asthma. Improvements in calibration methods have demonstrated the inaccuracy of original Wright scale of peak flowmeter. A new standard, EN 13826 that was applied to peak flowmeter was adopted on 1st September 2004 by some European countries. Correction of PEF readings obtained with old type devices for measurement is possible by Dr M. Miller's original predictive equation.

Assessment of PEF correction effect on the interpretation of measurement results and management decisions.

In children with intermittent (35) or stable persistent asthma (75) aged 6-16 years, there were performed 8393 measurements of PEF by Vitalograph normal-range peak flowmeter with traditional Wright scale. Readings were expressed as percentage of individual best values (PB) before and after correction. The effect of correction was analysed based on The British Thoracic Society guidelines for asthma attack treatment.

In general, correction reduced the values of PEF (p < 0.01). The highest mean percentage error (20.70%) in the measured values was found in the subgroup in which PB ranged between 250 and 350 l/min. Nevertheless, the interpretation of PEF after the correction in this subgroup changed in only 2.41% of measurements. The lowest mean percentage error (15.72%), and, at the same time, the highest effect of correction on measurement results interpretation (in 22.65% readings) were in children with PB above 450 l/min. In 73 (66.37%) subjects, the correction changed the clinical interpretation of some values of PEF after correction. In 13 (11.8%) patients, some corrected values indicated the absence or a milder degree of airflow obstruction. In 27 (24.54%) children, more than 10%, and in 12 (10.93%), more than 20% of the corrected readings indicated a severe degree of asthma exacerbation that needed more aggressive treatment.

Correction of PEF values obtained by peak flowmeters with traditional Wright scale shows a possibility of overtreatment in younger or short stature children and undertreatment in older or taller ones if we use old type of metres. The correction of peak flowmeter for non-linear error is a prerequisite in the application of asthma guidelines in PEF measurements.