Using a Peak Flow Meter
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Theory – PEFR – (peak expiratory flow rate) is a measure of the maximum speed of expiration. It is measured in litres/minute. It is used to asses if bronchoconstriction is reversible – i.e. the test is diagnostic for asthma. Not only is it used to diagnose asthma, but it can also be used to monitor the effectiveness of drugs.
Normal values are related to age, gender and height. You don’t need to learn this, this can be found on tables and charts. The value is increased if you are:

  • Male
  • Tall
  • Age 18-30

Explaining how to use a peak flow meter

Introduce yourself, check you have the right patient, explain what you are going to do and why!
  • Establish if the patient is using the peak flow meter to make a diagnosis of asthma, or to measure how well the disease is being controlled
  • Gain consent

Position – the patient should be sitting upright or standing
Meter – should be set to 0

  • Make sure the patient’s finger is not covering the meter, as this can block the slider moving up the scale.
  • Also, make the sure patient’s finger does not cover any of the slide scale at all – as sometimes this can create a spring effect; and the slider can zoom off and give a higher reading than the true value.

Tell the patient to take a deep breath in, and then make a tight seal around the mouth piece, then blow out as hard and as fast as they can.

  • The patient does not need to do a full expiration

You should do a minimum of three readings. If the reading differ wildly, then you should continue until you have three roughly consistent readings. If the results vary like this it is likely the patient is not following the right procedure.

  • You should record the highest reading

DEMONSTRATE THE TECHNIQUE, AND THEN ASK THE PATIENT TO SHOW YOU – so you know they are doing it correctly.
Keeping a diary – sometimes the patient may wish to/ be asked to keep a peak flow diary. This mainly assesses diurnal variation. This is usually kept for a period of two weeks. The results may be drawn on a graph to show the variation, e.g.:

The days with the least variation show when the disease is being best controlled. Thus in the example on the right, we can see that the disease gradually becomes better controlled over time


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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