3. Peak Flow Recording

Peak Flow Recording

This PatientPlus article is written for healthcare professionals so the language may be more technical than the condition leaflets. You may find the abbreviations list helpful.

Peak flow monitoring is recommended in the diagnosis of asthma and exacerbations. Over the last decade there has been much debate as to whether routine self-monitoring of peak flow for patients with asthma improves management. There is only low to moderate evidence that peak flow readings are related to symptoms.[1] Educating the patient in recognition of symptoms is nearly as effective as symptom recognition with peak flow monitoring in asthma management.

Peak expiratory flow (PEF) measurement is recommended for:

  • Diagnosis:
    • Diurnal variability of peak expiratory flow rate (PEFR) greater than 20% for at least three days in a week for two weeks is typical of asthma.
    • Or improvement in PEF:
      • 10 minutes after high-dose bronchodilator through a spacer.
      • After a six-week course of inhaled steroids.
      • After 14 days of 30 mg prednisolone.
    • Assessment of the response to treatment.
  • Monitoring:
    • The use of peak flow recording in monitoring asthma must 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

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  • 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 (maximum pause of two seconds in between) and take the best reading as the result.
  • 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.[3] These resource materials can be downloaded.

The European Commission (EC) adopted a standard (EN 13826) for peak flow meters in 2004. This replaced the older Wright scale - which had been previously noted to over-represent changes in airflow in the mid-range, and under-represent changes in the low and high ranges.[4]

Input
Height (in centimetres)
Age (in years)
Results
PEF Female (in L/min)
PEF Male (in L/min)
Formula
PEF Female = e((0.376*ln(Age))-(0.012*Age)-(58.8/Height)+5.63)
PEF Male = e((0.544*ln(Age))-(0.0151*Age)-(74.7/Height)+5.48)
Conversion of Wright McKerrow(W) scale to European standard scale:
EU = 50.356 + (0.4 x W) + (0.0008814 x W2) - (0.0000001116 x W3)

This predicted peak flow calculation is based on the revised Nunn and Gregg equation.[5] This applies for ages 15 to 85 years.

A paediatric calculation for ages below 15 years is taken from Lung Function by J E Coates (Fourth Edition) and is PEF = 455 x (height/100) - 332.

NB: in 2004 the Department of Health initiated a change to PEF meters to align to those that met a new EC standard.The new scale resulted in a conversion being required for PEF recorded using the conventional Wright McKerrow scale to the new European standard.

A conversion equation was developed by Clement Clarke™ that allows conversions of readings from the Wright McKerrow scale to the EN 13826 scale.[6]

EU = 50.356 + (0.4 x W) + (0.0008814 x W2) - (0.0000001116 x W3)

It is therefore necessary when using the above equation for paediatric predicted peak flow, that the value obtained should be converted to the EU scale.

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Further reading & references

  1. Kotses H, Harver A, Humphries CT; Home monitoring in asthma self-management. J Asthma. 2006 Nov;43(9):649-55.
  2. British Guideline on the Management of Asthma; British Thoracic Society (BTS) and Scottish Intercollegiate Guidelines Network - SIGN, 2008 (latest revision May 2011)
  3. Resources for people with asthma; National Asthma Campaign, Asthma UK
  4. Miller MR, Dickinson SA, Hitchings DJ; The accuracy of portable peak flow meters. Thorax. 1992 Nov;47(11):904-9.
  5. Nunn AJ, Gregg I; New regression equations for predicting peak expiratory flow in adults. BMJ. 1989 Apr 22;298(6680):1068-70.
  6. Conversion from Wright peak flow to EU values
Original Author: Dr Hayley Willacy Current Version: Peer Reviewer: Dr Colin Tidy
Last Checked: 31/01/2013 Document ID: 2586  Version: 22 © EMIS

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.