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Timing of peak flow readings

While isolated PEF measurement can indicate a restriction in air flow, in general sequential measurements are of more use, displaying trends essential to understanding the severity and progression of the disease (Quanjer et al. 1997). However, there may be significant diurnal variations, with the lowest measurements occurring during the night and first thing in the morning (Quanjer et al. 1997). Therefore, it is recommended that measurements should be taken on waking, in the afternoon and prior to going to bed and the results documented (Frew and Holgate 2009). If it is suspected that the patient may have restricted air flow due to occupational causes, the patient should take measurements for a minimum of 2 weeks while at work and 2 weeks while not at work to enable a comparison (Frew and Holgate 2009).

Preprocedural considerations

Equipment

The Wright and miniWright peak flow meter

The Wright peak flow meter was developed in 1959 and was a portable, simple device for monitoring PEF in the home. It has since been redesigned as the miniWright peak flow meter which is commonly in use today (Ruffin 2004). Peak flow is measured by the patient exhaling as quickly and forcefully as possible following maximal inspiration; the maximum expiratory flow is measured and usually occurs early in expiration (Bongers and O’Driscoll 2006). In September 2004 the scales of measurement used on peak flow meters were changed to a new EU scale (Bongers and O’Driscoll 2006). This increased the accuracy of the assessment and enhanced the ability to compare measurements with conventional spirometry (MHRA 2004). Although all new prescriptions of peak flow meters after this time were for the new model, some patients may still have the older one which will read up to 30% higher in the midrange readings so it is important to check which device they are using; the new model is labelled as ‘EN 13826’ or ‘EU scale’ (MHRA 2004). If the patient is unable to use their own meter then multiple patient use meters are available in clinics and hospital; these are valved and have disposable single patient use mouthpieces to prevent infection (Booker 2009).

Spirometers

Spirometers can produce a reading for PEF alongside other lung function measurements such as FVC. However, these results may not be comparable to those obtained using a miniWright meter due to both the equipment and technique used. Therefore, the patient should use the same equipment and technique each time to enable comparisons with past results (Bongers and O’Driscoll 2006).

Assessment and recording tools

Recording peak flow measurements on individualized action plans/booklets gives patients a greater degree of control and awareness about when they need to access medical care. The use of these recording tools is strongly advocated (British Thoracic Society/Scottish Intercollegiate Guidelines Network 2009, Gibson et al. 2002).

Specific patient preparations

The procedure should be performed when the patient is at rest (unless otherwise specified) and may be performed with them sitting upright or standing as long as their neck is not flexed (Quanjer et al. 1997). To increase reliability and enable comparisons to be drawn, it is advisable that they use the same posture each time (Booker 2009).

Education

The practitioner must ensure that the patient is fully informed about how to perform the procedure and performs it accurately, as even small alterations in technique may produce inaccurate results. If the patient has never performed the procedure, then education should be given and they should have the opportunity to have it demonstrated for them and have their own practice attempts (Quanjer et al. 1997).

Procedure guideline 12.5 Peak flow reading using a manual peak flow meter

Essential equipment

Peak flow meter (calibrated and working correctly)

Disposable mouthpiece

Peak flow chart to document results on and a pen

Optional equipment

Other lung function tests including pulse oximetry