A peak flow meter is a device used to measure how well your asthma is under control.
The device measures air flow out of the lungs (peak expiratory flow rate or PEFR), as you blow into it. When used correctly, a peak flow meter can show narrowing of the airways before you have symptoms. Peak flow readings can help you know:
When to seek emergency medical care
How well your asthma treatment plan is working
When to stop or add medicine, as directed by your healthcare provider
What triggers asthma symptoms
Peak flow zones may be part of your asthma action plan. If you don't have an asthma action plan, or if yours isn't up-to-date, make sure you talk with your healthcare provider. The 3 zones tell you when your asthma is controlled, when it is getting worse, and when it is severe. They are based on the traffic light concept. Green means safe. Yellow means caution. Red means danger. Based on your personal best peak flow measurement (your best lung function), your 3 peak zones include:
Green. 80% to 100% of your personal best peak flow measurement. This means your asthma is under control.
Yellow. 50% to 79% of your personal best peak flow measurement. This is a sign that your asthma is getting worse. You may need to use quick-relief medicines or other medicine, as directed by your healthcare provider.
Red. Below 50% of your personal best peak flow measurement. This is a medical emergency. You should take quick-relief medicine and seek medical help right away.
Using peak flow zones helps you see when your asthma may start to become uncontrolled. The goal is to stay in the green zone. Zones with a smaller range, such as 90% to 100%, may be recommended by some healthcare providers.
The National Heart, Lung, and Blood Institute (NHLBI) recommends that the numbers for each of your peak flow levels be marked on your meter. If you need help with this, ask your provider or nurse. Your provider will also include your usual symptoms and what you should do for each zone as part of your asthma action plan. The steps could be such things as what medicine to take, when to call the healthcare provider, or when to go to the emergency room.
Your peak flow zones are based on your personal best peak flow. To find your personal best peak flow, take your peak flow measurement each day at the same time (middle of the day) for 2 to 3 weeks, when your asthma is under control. Write down all of the readings. Your personal best is the highest number during this time. This number is important if your asthma provider has given you an asthma action plan that uses your peak flow.
Your personal best peak flow measurement may change over time. Talk with your healthcare provider about when you should recheck your personal best.
Use your peak flow meter regularly to check how well your asthma is being controlled. NHLBI recommends measuring peak flow at the following times:
Each morning, before taking asthma medicines
When you have symptoms or an asthma flare-up
After taking medicine for an asthma flare-up
Other times as advised by your healthcare provider
Make sure you discuss when and how often you should be checking your peak flow readings, and share your peak flow readings with your healthcare provider.
Peak flow meters are available at most drugstores or pharmacies. Some providers may also have them in their offices. Make sure you read all instructions that come with the meter. If you have any questions, ask your provider or nurse. The best way to know if you are using the meter correctly is to use it in front of your provider or nurse.