If you have asthma, it’s important to keep track of how well you are breathing so you can take appropriate medications before your symptoms get out of control. During an asthma attack, the airways become inflamed and can produce excess mucus. At the same time, the muscles around the airways constrict which makes the opening inside the airways smaller. These factors combine to make it harder for air to move in and out of the lungs.
A peak flow meter is a simple way for you to measure how much air your lungs can move at a particular time. This is known as air flow or the peak expiratory flow rate (PEFR). Knowing your PEFR allows you to track your asthma to make sure you are taking the right amount of medication. It can also help you determine if your asthma is worse at a particular time of day such as in the evening, or if certain places or activities can be triggers to make your asthma worse.
The first step in using a peak flow meter is to find out what your “personal best” peak flow number is. The meter measures how much air you can quickly blow out of your lungs (not how long you can blow). To find your “personal best” follow these steps:
• Reset the meter to zero.
• Stand up if you can.
• Take as deep a breath as you can.
• Place the meter in your mouth with your lips closed around the mouthpiece.
• Blow as hard and as fast as you can. Don’t cough or let your tongue block the mouthpiece.
• Look at the meter and write down the reading.
• Reset the meter and repeat the process two more times so you have 3 readings.
• Write the highest of the three numbers in your asthma chart.
If your allergist asks you to do this both before and after using your rescue inhaler, take the first 3 readings and record the highest number. Then use your medication and wait an appropriate time before repeating the three readings and recording the highest again.
Repeat this procedure twice a day for two weeks and keep a record of the best score each time. Do not include scores that are very different from all the others. At the end of two weeks, the highest score recorded is your personal best.
Knowing your personal best number gives you a reference for future readings. If you feel that your breathing is not right, you can use the meter to get your score and compare it to your best score to help you decide if you need to use your inhaler or even if you need emergency help. Many allergists use a simple traffic light system to help you determine if your breathing is okay or not.
• Green zone – Your personal best score counts as 100 percent of your lungs’ ability to push air. Your green zone is from 80 to 100 percent of that score. If your peak flow meter reading is in this range it means your asthma is well controlled with your current medications.
• Yellow zone – From 50 to 80 percent of your personal best is your yellow zone. This range means you are in a warning zone because your asthma symptoms are getting worse. Follow your allergist’s instructions about using your rescue inhaler when you are in this range.
• Red zone – If your peak flow meter reading is below 50 percent of your best score, you are in the danger zone and your asthma is not under control. Use your rescue inhaler right away then take another reading. If your score does not improve into at least the yellow zone, get medical help right away. Once you are out of immediate danger, get in touch with your allergist to talk about whether you need to change your asthma medications.
Once you know your personal best, be sure to calculate and write down the numbers for your three zones. Doing this will let you know immediately what zone your score falls into. You and your allergist should create an asthma plan together that will include specific instructions for what you should do in each of the three zones to best manage your asthma symptoms.
Keep a log of all peak flow meter readings including the day and time you took the reading. Take the log to your allergist appointments so you can discuss how well your medications are working.
Reviewed July 12, 2011
by Michele Blacksberg R.N.
Edited by Alison Stanton