Asthma - how to use your peak flow meter

Written by The National Asthma Campaign, and Dr Martyn R Partridge, consultant physician



Peak flow meters are available on NHS prescription in the UK. Some people may find it useful to have a peak flow meter to help them manage their asthma, so you could ask your doctor to prescribe one for you. You can also purchase one from a pharmacy. There are several different makes of peak flow meter and two different types known as low and standard range.

Standard range peak flow meters are suitable for both adults and children.

Low range peak flow meters are designed for adults and children with severely impaired function of the lungs.

Your doctor should normally state the make and type on your prescription, but the manufacturer of the peak flow meter is not important because they all do the same thing, which is measure your expiratory flow rate. In simple terms this means how hard and quickly you blow air out of your lungs. The meter has a marker that slides up the scale as you blow out. The better controlled your asthma, the harder you will be able to blow out and the higher your peak flow score will be. Peak flow readings are measured in litres per minute.

Why should I measure my peak flow?

You will be able to tell what is going on in your airways rather than just guessing by the way you feel.

You can find out if your treatment is having the effect it should on your asthma.

You will know whether you need to change your treatment.

Your doctor or practice nurse will be able to see how well you have been.

Who can use a peak flow meter?

A peak flow meter can be used by most adults and children over six years of age. Children under six years of age are not usually prescribed peak flow meters because they might confuse the blowing out for a peak flow reading with the sucking in of their inhaler medication. It is more important to concentrate on getting a child to take their medication effectively and gauge asthma control by their symptoms.

If you use a peak flow meter your readings will vary according to your age, height and whether you are male or female. Peak flow readings also vary from person to person, so it is difficult to say exactly what a person's best peak flow should be. For example you can expect:

a 25-year-old man, who is 6'1" (185cm or 1.85m) tall, to have an average peak flow of 627 litres per minute.

a 40-year-old woman, who is 5'2" (157cm or 1.57m) tall, to have an average peak flow of 427 litres per minute.

a child who is between 6 and 15 years of age and 4'7" (140cm or 1.40m) tall, to have an average peak flow of 254 litres per minute.

However, a person's peak flow could be less than this and still be completely normal. Your doctor or practice nurse can advise you about your probable best peak flow reading.

How to use a peak flow meter

A single reading is not very useful in helping decide how well your asthma is under control. Instead it is best to take a series of peak flow readings over a few weeks. You should take three readings every morning and evening, before using your inhaler. This will help to show how your asthma varies from the beginning to the end of the day. It is common for morning readings to be lower than evening readings.

You can use the interactive asthma diary to plot the results on a chart, which you can then print out and take to your next appointment with your doctor or nurse. The differences between each reading will show whether your asthma is being properly controlled.

To take a peak flow reading you should:

check that the pointer is at zero.

preferably stand or sit in a comfortable, upright position.

hold the peak flow meter level (horizontally) and keep your fingers away from the pointer.

take a deep breath and close your lips firmly around the mouthpiece.

then blow as hard as you can - as if you were blowing out candles on a birthday cake - remember it is the speed of your blow that is being measured.

look at the pointer and check your reading.

reset the pointer back to zero.

do this three times and record the highest reading in your daily asthma diary.

What will my readings tell me?

With practice and help from your doctor or nurse you will be able to understand what your peak flow readings mean. When your asthma is well controlled, there should be very little difference between the day-to-day readings or between the morning and evening readings. The main clue to uncontrolled asthma is readings that change a lot from day-to-day or between morning and evening.

You will first need to find out what your normal readings should be. Your highest peak flow reading, taken when your asthma is well controlled, will usually be taken as your normal reading. Once your doctor or nurse has identified what this is and, through looking at your peak flow readings, he or she will be able to decide what treatment to give you. At this point your doctor may decide to work out a self-management plan with you. This will show you what to do when your asthma gets worse or when your peak flow reading falls.

What does a self-management plan look like?

There is no one standard self-management plan. They can vary from being quite complex, with a number of steps to be taken, to quite simple, for example 'if your peak flow drops below 'x' then take two puffs of your reliever inhaler'. All, however, should be written plans because research has shown that they are more effective when written down.

A good model for a self-management plan is one that is divided into zones and each zone should broadly describe your asthma as:

well controlled

poorly controlled

severe

emergency.

The self-management plan should then tell you what action to take according to the zone you are in.

Your doctor or nurse will help you to produce a tailored self-management plan and show you how to use it to control your asthma. Peak flow readings will form an important part of the plan. For example, you may agree with your doctor that if your peak flow readings drop by a certain percentage, you will increase your preventer medication. If the readings fall further, your doctor may suggest that you start taking steroid tablets or seek urgent medical attention. On the other hand, if your asthma symptoms improve significantly, your doctor may decide to reduce your treatment.

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