Your Child's Asthma: Peak Flow Meters, Oximeters, and Spirometers

What is a peak flow meter?

A peak flow meter (PFM) is a device used to measure how well your child's asthma is under control. The device measures air flowing out of the lungs, called peak expiratory flow rate (PEFR), as a child forcefully blows into the device. When used correctly, a peak flow meter can reveal narrowing of the airways before asthma symptoms appear. PFM can help determine:

  • When to get emergency medical care

  • How well your child's asthma management and treatment plan is working

  • When to stop or add medicine, as directed by your child's healthcare provider

  • What triggers the asthma attack, such as exercise

Why should a peak flow meter be used?

The PFM takes a lot of guesswork out of managing your child's asthma. It can help you, your child's healthcare provider, or even your child's teachers know if your child's airways may be narrowing.

Using a PFM every day will let you know when your child's peak flows are starting to drop. This allows you to make early changes in your child's medicine or routine. This can help prevent your child's symptoms from getting worse. The PFM can also help you know when you need to call your child's healthcare provider. Or when you should go to the hospital emergency room.

How do you use a peak flow meter?

Use the PFM as directed by your child's provider. For instance, some people use a PFM every day at about the same time.

  1. Hold the PFM by the handle.

  2. Before each use, make sure the pointer is reset to zero.

  3. Have your child stand up straight.

  4. Have your child take a deep breath and put the mouthpiece in their mouth. Lips should be sealed tightly around the mouthpiece. Your child's tongue shouldn't block the mouthpiece.

  5. Your child should blow out as hard and as fast as they can.

  6. Remove the PFM from your child's mouth. Write down the number where the pointer has stopped on the scale.

  7. Reset the pointer to 0.

  8. Repeat these steps 3 times. You will know your child has used the PFM correctly when the numbers from all 3 tries are close together.

  9. The highest of the 3 readings is your child's peak flow.

What are peak flow zones?

Peak flow zones are used to show how well your child's asthma is controlled. These zones are different for each person. Your child's healthcare provider will help determine your child's peak flow zones. Examples of peak flow zones are included below. Zones with a smaller range, such as 90% to 100%, may be advised by some healthcare providers.


This is the  go zone. This zone is from 80% to 100% of your child's personal best peak flow reading. This is the zone your child should be in every day. This is a signal that air moves well through their airways. And it means that your child can do their normal activities and go to sleep without trouble. When the peak flow readings are in this zone, your child should:

  • Stay away from asthma triggers.

  • Use controller medicines every day, as directed by your child's healthcare provider.

  • Use the reliever medicines 15 to 20 minutes before exercise if your child's asthma is triggered by exercise, as directed by your child's provider.


This is the caution or slow-down zone. This zone is from 50% to 80% of your child's personal best peak flow reading. This is a clue that their airways are starting to narrow. Your child may begin to have mild symptoms. Your child may be coughing, feeling tired, feeling short of breath, or feeling like their chest is tightening. These symptoms may keep your child from their normal activities or from sleeping well. To keep your child's peak flow numbers from getting worse and get your child's asthma back under control, you'll need to:

  • Keep using the controller medicine as your child's healthcare provider has ordered.

  • Stay away from asthma triggers.

  • Use the reliever medicine as ordered by your child's provider.

  • Make sure your child is using their inhaler and spacer correctly.


This is the  stop zone. This zone is less than 50% of your child's personal best peak flow reading. Readings in this zone are a medical emergency. You'll need to get help right away. This means there is severe narrowing of the airways. Your child may be coughing, very short of breath, and wheezing. They may also have problems walking and talking. Have your child take their reliever medicine. And call your child's provider. Or go to the hospital emergency room or call 911.

How is a personal best peak flow measured?

Each child's peak flow zones are based on their personal best peak flow. To establish your child's personal best peak flow, have your child take their peak flow measurement each day at the same time for 2 to 3 weeks. Do this when their asthma is under control. The highest reading during this time is your child's personal best peak flow.

Your child's healthcare provider will use peak flow and spirometer results, discussed below, to help set up your child's asthma management plan.

Your child's personal best peak flow may change over time. Talk with their provider about when to check for a new personal best peak flow.

When should a peak flow meter be used?

PFMs are used regularly to check how well asthma is being controlled. In addition, the peak flow meter may be used during an asthma flare-up. It can help determine how well short-term, quick-relief asthma medicines are working. Ask your child's healthcare provider how often to use the PFM. The National Heart, Lung and Blood Institute (NHLBI) advises measuring lung function during these times:

  • Every morning, before taking asthma medicine

  • When having asthma symptoms or an asthma flare-up

  • After taking medicine for an asthma flare-up

  • Other times, as advised by your child's provider

How can I get a peak flow meter?

Talk with your child's healthcare provider about getting a PFM. Ask for step-by-step directions on how to use it.

If your child is using more than 1 peak flow meter, make sure they're the same brand.

What is an oximeter?

An oximeter is a small device that measures the amount of oxygen (oxygen saturation) in your child's blood. It's sometimes called a pulse oximeter (or pulse ox). That's because it can show your child's heart rate and blood oxygen levels.

To get this measurement, a small sensor is placed onto your child's finger or toe. When the oximeter is on, a small red light can be seen in the sensor. The sensor is painless. The red light doesn't get hot.

Talk to your child's provider about if and when to use an oximeter. Also ask about your child's ideal oxygen saturation range.

What is a spirometer?

A spirometer is a device used by your child's healthcare provider to assess lung function. This test is called spirometry. It's one of the simplest, most common lung function tests. It may be needed for any of these reasons:

  • To diagnose lung diseases, such as asthma

  • To monitor lung disease

  • To monitor how well treatment is working

  • To determine how serious the lung disease is

  • To determine if the lung disease is restrictive (decreased airflow) or obstructive (disruption of airflow)

After taking a deep breath, your child breathes into the spirometer as completely and forcefully as possible. The device measures the amount of air expelled. And it measures how quickly the air was expelled. The measurements are recorded by the spirometer.

Online Medical Reviewer: Amy Finke RN BSN
Online Medical Reviewer: Deborah Pedersen MD
Online Medical Reviewer: Jessica Gotwals BSN MPH
Date Last Reviewed: 4/1/2022
© 2000-2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.