A peak flow meter is a small plastic device with a measuring gauge along the side, which measures how fast you can blow air out of your lungs.
People with asthma can use the meter to get baseline measurements of their normal peak flow, which can then be used to:
- help monitor your condition
- assess how well your asthma medicine is working
- help in self-management (knowing what to do when your asthma flares up).
What does a peak flow measurement tell you?
The speed and force that you can blow air out of your lungs depends on how open your airways are.
- If you are well, the airways are open and your peak flow reading is high.
- If the airways are tight, such as when your asthma is playing up, your peak flow reading will fall.
A peak flow meter will tell you how well your lungs are functioning. However, it is not a standalone tool and it should be used in conjunction with the following symptom assessment:
- Are you sleeping through the night and not waking with asthma symptoms?
- Are you using your reliever inhaler more than 3 times a week?
- Is asthma stopping you from doing your usual activities?
When should I use a peak flow meter?
Initially, you should take your peak flow readings before using your inhalers every morning and again in the evening, for 2 weeks. Your doctor can then see if your values are as high as they should be.
You may choose to either make a graph or keep a diary of these readings and how you feel.
- If your peak flow values are high, your doctor may tell you to reduce your medicine.
- If your peak flow values are low, your doctor may change your medicine or increase the number of puffs you are taking.
- If your treatment is changed, keep using your peak flow meter to monitor any changes in your peak flow.
When you are well and your peak flow reading is at its best and steady, you don't have to use your meter every day.
Peak flow meters should be used when:
- you have a runny nose or feel a cold coming on
- you just don't feel as well as usual
- you know you've been exposed to one of your asthma triggers (eg, something that makes asthma worse)
- your treatment has been changed
- you have had a recent acute asthma attack (keep recording until readings are normal and your symptoms settle down)
- before you visit your doctor.
What is a normal peak flow reading?
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 gender.
Peak flow charts and tools
- Peak flow and symptom diary Asthma & Respiratory Foundation, NZ
- Peak flow chart National Asthma Foundation, Australia
- Peak flow calculator MDCalc, US
What are the benefits of using a peak flow meter?
- It helps you to identify asthma symptoms and triggers.
- You can find out if your asthma treatment is having the effect that it should.
- Your peak flow diary is a record you can show the doctor on the next visit, especially if you are not as well as usual.
- When used with your self management plan, it means that you are in control of your asthma.
How do I use a peak flow meter?
- Sit upright or stand up.
- Slide the marker on the peak flow meter to the zero by the mouthpiece end (as far as it will go).
- Hold the meter level and keep your fingers from obstructing the marker.
- Take a deep breath in.
- Put the meter in your mouth and close your lips tight around the mouthpiece, making a good seal.
- Keep your tongue away from the mouthpiece.
- Blow the air out of your lungs as hard and fast as you can, with a strong huff.
- Note your reading from the marker level.
- Repeat these steps 2 more times.
- Record the highest of the 3 readings.
- If you find that your first blow is always the best, then you only need to blow once.
- Ask your doctor, nurse or asthma educator to check you are using the meter correctly.
What should I do if my readings are down?
Ask your doctor to write you a self-management plan, which tells you what to do if your readings drop and your asthma symptoms increase. If you follow your plan and your readings still keep dropping, see your doctor again.