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. A peak flow meter, when used properly, can reveal narrowing of the airways in advance of asthma symptoms. Peak flow meters can help determine:

  • When to seek emergency medical care

  • The effectiveness of your child's asthma management and treatment plan

  • When to stop or add medication, as directed by your child's health care provider

  • What triggers the asthma attack, such as exercise

Why should a peak flow meter be used?

The PFM removes a lot of guesswork out of managing your child's asthma. It can help you, your child's 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 medication or routine to help prevent your child's asthma symptoms from getting worse. The PFM can also help you know when you need to call your child's provider or go to the hospital emergency department.

How do you use a peak flow meter?

Use the PFM as instructed by your child's provider. For example, 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 his or her mouth. Lips should be sealed tightly around the mouthpiece.

  5. Your child should blow out as hard and as fast as he or she can.

  6. Write down the number where the pointer has stopped on the scale.

  7. Reset the pointer to zero.

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

  9. The highest of the three 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 provider will help determine your child's peak flow zones. The three peak flow zones include:

  • Green: This is the go zone! This zone is from 80 to 100 percent 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 his or her airways and that your child can do the usual activities and go to sleep without trouble. When the peak flow readings are in this zone, your child should:

    • Avoid asthma triggers.

    • Use controller medications every day.

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

  • Yellow: This is the caution or slow down zone! This zone is from 50 to 80 percent of your child's personal best peak flow reading. This is a clue that his or her 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 his or her chest is tightening. These symptoms may keep your child from his or her usual 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 will need to:

    • Continue to use the controller medication as your child's provider has ordered and avoid asthma triggers.

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

    • Make sure your child is using his or her inhaler and spacer correctly.

  • Red: This is the stop zone! This zone is less than 50 percent of your child's personal best peak flow reading. Readings in this zone are a medical emergency and you will 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. Your child may also have problems walking and talking. Have your child take his or her reliever medication and call your child's provider. Or, go to the hospital emergency department or call 911.

Zones with a smaller range, such as 90 to 100 percent, may be recommended by some health care providers.

How is a personal best peak flow measured?

Each child's peak flow zones are based on his or her personal best peak flow. To establish your child's personal best peak flow, have your child take his or her peak flow measurement each day at the same time for two to three weeks, when the asthma is under control. The highest reading over this period of time is your child's peak flow.

Your child's 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 your child's provider about when to check for a new personal best peak flow.

When should a peak flow meter be used?

Peak flow meters 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 medications are working. The National Heart, Lung, and Blood Institute (NHLBI) recommends measuring lung function during the following times:

  • Every morning, before taking asthma medications

  • When having asthma symptoms or an asthma flare-up

  • After taking medication for an asthma flare-up

  • Other times as recommended by your child's provider

How can I get a peak flow meter?

Talk with your child's provider about getting a peak flow meter and step-by-step instructions on how to use it.

If your child is using more than one peak flow meter, be sure they are the same brand.

What is an oximeter?

An oximeter is a small device that measures oxygen saturation (the amount of oxygen) in your child's blood.

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 and the red light does not get hot.

What is a spirometer?

A spirometer is a device used by your child's doctor to assess lung function. Spirometry, the evaluation of lung function with a spirometer, is one of the simplest, most common lung function tests and may be necessary for any of the following reasons:

  • To monitor lung disease

  • To monitor the effectiveness of treatment

  • To determine the severity of lung disease

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

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