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:
- Age 18-30
Explaining how to use a peak flow meter
- 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.: