Peak flow recording

What is peak flow recording?

Peak flow, or peak expiratory flow, is a measure of the maximum air flow rate during a forceful expiration, following full inspiration. Peak flow readings are affected by the degree of bronchial obstruction.

Peak flow monitoring can be used recommended for the ongoing management of asthma and during exacerbations. It is less used these days for the initial diagnosis of asthma, clinicians being encouraged to use more accurate measurements of lung function such as spirometry and the fractional exhaled nitrous oxide (FeNO) test. However, it still has a part to play if diagnostic uncertainty remains after these tests have been completed, and is useful if other objective tests are not available.¹

There has been much debate in recent years as to whether routine self-monitoring of peak flow for patients with asthma improves management. Evidence suggests that individualised written action plans based on peak flow readings are equivalent to action plans based on symptoms, for self-management of asthma.² It may however be useful in people who have poor perception of airflow limitation (for whom symptom-based plans are less effective), and people with severe asthma.³

Home monitors which provide FEV1 readings are available and give a more accurate assessment of lung function. However, they are expensive. For patients with stable asthma whose symptoms correlate well with peak flow, a peak flow monitor is adequate. Educating the patient in recognition of symptoms which indicate deterioration is nearly as effective.

Peak expiratory flow (PEF) measurement cannot usually be reliably used as the only diagnostic test for chronic obstructive pulmonary disease (COPD) because of its weak specificity.

However, one study suggested it could be used to rule out severe to very severe COPD, which may be useful if access to spirometry is limited.⁴

Indications for peak flow recording^{1 5}

PEF measurement may be used for:

Diagnosis

Peak flow variability should be monitored for 2-4 weeks in adults (aged 17 and over) in whom diagnostic uncertainty remains after initial assessment and a FeNO test, and they have either:

• Normal spirometry; or

• Obstructive spirometry, reversible airways obstruction but a FeNO level of 39 ppb or less.

A value of more than 20% variability should be regarded as a positive test.

Consider monitoring peak flow variability for 2-4 weeks in adults (aged 17 and over) in whom diagnostic uncertainty remains after initial assessment and a FeNO test and they have either:

• Normal spirometry; or

• Obstructive spirometry, irreversible airways obstruction and a FeNO level of 35 ppb or more.

A value of more than 20% variability should be regarded as a positive test.

Peak flow diaries are also useful in identifying situational triggers for asthma, included as part of the workup for occupational asthma.³

NB: further tests such as estimation of bronchial hyperreactivity using direct bronchial challenge with histamine or methacholine may be required if diagnostic uncertainty remains.

Monitoring

• Peak flow monitoring may be used:³

  • For short-term monitoring:

    • To monitor recovery after an exacerbation.

    • To objectively measure treatment response, following a change in treatment.

    • To obtain an objective measurement of lung function impairment, if symptom severity seems discordant.

    • To help identify occupational or domestic triggers for poor asthma control.

  • For long-term monitoring:

    • For earlier detection of exacerbations, but mostly in patients with poor perception of airflow limitation.

    • For patients with a history of sudden severe exacerbations.

    • For patients with difficult-to-control or severe asthma.

• The use of peak flow recording in monitoring asthma should be part of an individual management plan that also includes education and symptom recognition.

• Quality-of-life indicators may be as good as peak flow for predicting exacerbations:
  

  • Have you had any asthma symptoms during the day?

  • Have you had any difficulty with sleeping because of symptoms?

  • Has the asthma interfered with usual activities - eg, work, school?

• The patient must have a clear understanding of how to interpret symptoms and peak flow results, and how to use these to adjust treatment and seek medical advice when necessary.

Adults should have their peak flow reassessed every five years, to monitor the decrease in lung function with age.

PEAK FLOW CHARTS

Method

Many paediatric and adult patients do not use peak flow meters correctly. It is important to observe how patients use peak flow meters - to detect errors and help ensure correct use and accurate PEF measurements.⁶

• The patient can be standing or sitting down.

• Ensure that the marker on the scale is set to zero.

• After a full breath in, the patient should then breathe out with a rapid forced maximal expiratory puff through the mouth and into the meter.

• Repeat to give a total of three readings. Take the best reading as the result.

Self-management plans¹

• Written personalised action plans as part of self-management education have been shown to improve health outcomes for people with asthma.

• They are very important for all patients with asthma, but especially those with moderate-to-severe disease.

• Self-management plans improve outcomes such as self-efficacy, knowledge and confidence.

• The National Asthma Campaign provides resource materials useful for providing patients with a self-management plan.⁷ These resource materials can be downloaded.
  

Peak expiratory flow prediction

You can calculate PEFR here. Other calculators also input race or ethnicity, which is likely to incorporate inaccurate assumptions.⁸ It can be used in those patients with asthma from ages 5 to 80.