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Learn More About Peak Flow Meters

If you have a question about peak flow meters that is not covered here, please e-mail us at and we will do our best to answer it.

What is a peak flow meter?

A peak flow meter is a small, easy-to-use instrument that measures your peak expiratory flow - a number that tells you how fast you or your child can blow out air after a maximum inhalation. It reveals how well your or your child's lungs are working. This number is very useful for you and your doctors.

Sometimes peak flow numbers will decrease hours, or even a day or two, before other asthma symptoms become evident. When you monitor peak flow numbers on a daily (or regular) basis, you can identify this drop and take steps to prevent an asthma episode. The peak flow numbers, along with watching for asthma symptoms can be used to make decisions about asthma treatment.

You and your doctor may find it easier to develop an asthma management plan for you/your child if you check peak flows on a routine basis. Also, it is important to talk with your doctor about the steps you should take when your peak flow number drops.

What is the difference between a standard range and a low range peak flow meter?

Low range peak flow meters are designed to be used by children, whose peak flow numbers are less than those of adults. Standard range peak flow meters are calibrated for most adults.

Who needs a peak flow meter?

Adults and children (over 5 years of age) who require medication for asthma on a daily or near-daily basis.

What is my Personal Best?

How do I establish my Personal Best? The highest number regularly blown is your personal best. This is done by recording the peak flow values for two weeks first thing in the morning before taking any medications and late afternoon when your asthma is under control.

Once you know you or your child's personal best, it may be helpful for you and your doctor to use peak flows numbers for your treatment "zones". Zones will help you decide what to do when you have changes with your asthma The zone system can be compared to the colors of a traffic light.

Click here to see an example of how these zones work. The table can be printed to serve as a reminder. Your doctor can help you create a similar table for your own asthma.

How do I use a peak flow meter?

  1. Stand up or sit up straight.
  2. Slide indicator to base of meter.
  3. Take in deep breath.
  4. Place mouthpiece in mouth and seal lips around it.
  5. Blow out as hard and fast as you can (one quick blow).
  6. Repeat process 2 more times.
  7. Select highest number of the 3 efforts.
  8. Record this number on your peak flow diary or on a graph.
This is how a peak flow meter is used correctly

How often should I check my peak flow?

The peak flow should be checked once a day (morning or evening) if the numbers do not change much from time to time. When you are doing well you can use the peak flow meter two times during the week and once on the weekend.

We suggest you check your peak flow number more often when you or your child:

  • Begin to wake at night with asthma symptoms
  • Are having more daytime asthma symptoms
  • Have a respiratory infection (a cold)
  • When you are sick or have asthma symptoms - check your peak flow at least twice a day (once in the morning and once in the evening).
  • When you need to use "rescue medicine". This is medicine prescribed by your doctor to be used for quick relief of asthma symptoms. If you can, check your peak flow before taking the rescue medicine. Then check it again 20-30 minutes later.

When should I report Peak Flow numbers to my doctor?

Take your peak flow meter and Asthma Health Diary with you each time you visit with your doctor or nurse. If you have an Asthma Action Plan from your doctor, follow the Plan for each peak flow zone.

Compare your peak flow numbers to your Personal Best:

If your peak flow is less than 80% of your Personal Best, take your rescue medication. Wait 20 to 30 minutes and check your peak flow again. If your peak flow is not back above 80%, report this to your doctor. If your peak flow is back above 80%, recheck your peak flow about every 4 hours for a day or so. Call your doctor if you continue to need rescue medicine.

If your peak flow is less than 60% consider this an emergency: Take your rescue medicine, and call your doctor or go to the Emergency Room right away! Your peak flow meter is only an aide to you. Do not rely on your peak flow numbers alone when deciding whether to take your rescue medicine or call your doctor. Your symptoms also need to be considered.

How do I keep track of my peak flow numbers?

Write your peak flow numbers on your peak flow sheet or Asthma Health Diary. (You can make your own if you do not have one.) Be sure to write down any peak flows that are different from your usual daily readings.

Record the date, time, and peak flow numbers. Also note any changes in how you feel or changes in your medicines. List anything you think may be making your/or your child's asthma worse.

What are some signs that my asthma is getting worse?

In addition to measuring your or your child's peak flow on a daily basis, you need to look out for early warning signs of an asthma attack. Early warning signs of an asthma attack are:
  • Runny, stuffy nose
  • Fatigue
  • Chin or throat itches
  • Headache
  • Moodiness
  • Cough with activity or laughing
  • Wheezing with activity
  • Waking up at night or early morning with a cough or wheeze
  • Faster breathing rate
  • Irritability
Babies may be fussy or may not want to eat. They may begin to cough when they cry. Babies may also have noisy, wheezy breathing when they are resting. They may have a faster breathing rate or difficulty feeding and may prefer sitting to lying down.

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