What is a peak flow meter?
A peak flow meter is a small plastic tube with a measuring gauge along the side, which measures how fast you can blow air out of your lungs.
The speed and force you can blow air out of your lungs depends on how open your breathing tubes are. If you are well the breathing tubes are open and your peak flow is high. If the tubes are tight (when your asthma is playing up) your peak flow will fall.
What is a normal peak flow reading?
You need to know what your best peak flow reading is when you are well. The speed at which you can blow air out of your lungs depends on:
- size - the taller you are the faster you blow
- age - the reading gets higher as a child grows up, reaching a maximum at about 20 years of age and falling steadily after that
- sex - males have higher readings than females
Your doctor, practice nurse or asthma educator (health professional) can work out what your peak flow reading should be based on your height, age and sex.
Who should have a peak flow meter?
Everybody with asthma who uses an inhaler at least once a day. Some 5 year old children can use a peak flow meter but reliable readings might not be obtained until they are 6 or 7 years of age. Also, please note that children must be able to inhale their puffer medication correctly before attempting to exhale into a peak flow meter.
You can obtain a peak flow meter FREE of charge from your local medical centre.
Benefits of using a peak flow meter
- You can tell what’s going on in your breathing tubes rather than just guessing how you feel.
- You can find out if your treatment is effective.
- You will know whether you need to change your treatment.
- It’s a written record you can show your health professional.
These benefits can help you feel more in control, have fewer emergency visits, and spend less money on uncontrolled asthma.
When should you use a peak flow meter?
You should take your peak flow readings every morning and night before taking your usual asthma medication. The morning peak flow is usually the lowest and it is best to take this as soon as you get up. Sometimes you may be asked to record your peak flow 10 to 15 minutes after taking your reliever medication. Initially you should keep a record for two weeks.
From this record your health professional can see if your peak flow is as high as it should be. If peak flows are high, your doctor may tell you to cut down your inhaler dose. If your peak flow is low your doctor may change your medication or increase the number of puffs you are taking.
If your treatment is altered it is important to keep using your peak flow meter to monitor any changes as this is a time when asthma can become unstable. When you are well and your peak flow is steady, you won’t have to use your meter every day. Peak flow meters should be used when:
- you have a runny nose and feel a cold coming on.
- you just don’t feel as good as usual.
- you know you’ve been exposed to one of your asthma triggers.
- your treatment has been changed.
- you have had a recent acute asthma attack (keep recording until readings are normal and symptoms stabilise).
What to do if your readings are down
A Self Management Plan will guide you on the action you should take if your readings drop. If you do not have a Self Management Plan ask your health professional to write one for you (see Asthma and Respiratory Foundation booklet Controlling your Asthma).
A Self Management Plan helps you to identify changes in your asthma and to increase treatment if your symptoms and/or peak flows worsen.
How do you use your peak flow meter?
- Sit upright or stand up
- Push the pointer on the peak flow meter to the lowest point on the sliding scale (as far as it will go down)
- Hold meter level
- Keep fingers clear of the pointer and gauge
- Take as big a breath as you can
- Seal your lips around the mouthpiece
- Blow out hard and fast - a false low reading may be given if maximum effort is not used. Children can be told to imagine they are blowing out candles on a cake - HARD!
- Read where the pointer reaches and write it down
- Repeat these steps 2 - 8 twice more
- Record the highest of the three readings in your peak flow diary.
Ask your health professional to check you are using your meter correctly. Always take your own peak flow meter with you when you visit your health professional as there are significant differences between peak flow meters.
Looking after your peak flow meter
Follow the manufacturer’s instructions. Clean every few weeks when in use. Most peak flow meters can be cleaned without having to be taken apart. Wash the whole meter in warm soapy water. Rinse, shake and leave to dry (or blow dry with a hair dryer).
Peak flow meters should last 2 to 3 years. However, if you drop it or treat it roughly this can reduce its life expectancy.
Taking action
Remember the important thing is not just taking the readings and writing them down, but really using the results to take the appropriate action to keep your asthma under control. Peak flow monitoring is not a standalone tool and it should be used in conjunction with symptom assessment. The basic three questions to assess asthma control are:
- Do I wake at night because of asthma?
- Do I use reliever medication most days of the week?
- Are my activities restricted by my asthma?
How do you record the results?
There are two main ways of recording, either on a graph or just writing down the figures in columns. You can use a simple piece of paper/notebook or a specific peak flow diary. Some diaries combine both symptom and peak flow records. Here are some examples of what to look for in your peak flow diary and the action which may be written in your Self Management Plan.
Your peak flow meter is there to help you help yourself!
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