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Peak Flows and Asthma

Asthma Basics


Updated May 05, 2008

Peak flows are a good way to monitor how well your child's asthma is doing.

Using a peak flow meter, a small, portable device that your child blows in as hard as he can, you can measure his lung function.

Monitoring peak flows can be a good idea for parents of children:

  • who have moderate or severe asthma
  • who have a history of severe asthma attacks
  • who have trouble telling when they are wheezing or have worsening asthma symptoms
  • who are looking for a way to detect early changes that may indicate that their child's asthma is getting worse

Peak Flows

To measure a child's peak flow, he should stand up, take a deep breath and then blow into his peak flow meter as fast as he can. This measured peak flow can then be compared to a predicted peak flow for your child, which can range from about 150 to 470 L/min and depends on your child's height.

Although peak flows can be helpful, they do depend on your child's ability to blow into the peak flow meter -- something which not all children can do. Younger children, especially those under 3 to 5 years old, may not even be able to use a peak flow meter. Another downside is that peak flows don't always correlate with worsening asthma and they take some time to do.

That leads some pediatricians and parents to skip peak flows all together and make treatment decisions just based on what asthma symptoms a child is having.

Using a peak flow meter is a good tool for those parents who choose to use it. For example, if your child is coughing and you aren't sure if he is having problems with his asthma or simply has a cold, you could take a peak flow measurement. If his peak flow is normal, then it makes it less likely that he is having asthma problems. On the other hand, if he is coughing and has a low peak flow, then he likely is having asthma symptoms and needs to begin his quick relief asthma medication.

Peak Flow Zones

As your child begins to regularly take peak flow readings, you can also compare your child's peak flow against his personal best peak flow, which you may get on a day when he is without any asthma symptoms and is doing well.

Now that you are measuring your child's peak flow, you may be wondering what you are supposed to be doing with this information.

One of the most helpful things that you can do with your child's peak flow is apply it to your child's asthma action plan:

  • Green Zone - peak flows are within 80 to 100% of your child's personal best peak flow.
  • Yellow Zone - peak flows are within 50 to 80% of your child's personal best peak flow.
  • Red Zone - peak flows are within 0 to 50% of your child's personal best peak flow.

In addition to helping you figure out what to do during an asthma attack, measuring peak flows can also help you both monitor and sometimes predict when your child is going to have an asthma attack. For example, if you are measuring peak flows every day, you may notice that they start to drop even before your child begins to have asthma symptoms. This is a likely sign that your child's asthma is getting worse and an asthma attack is about to start. Apply his Yellow Zone asthma action plan.

Peak Flow Meters

Peak flow meters come in a variety of sizes and shapes. There are even digital peak flow meters, such as the Microlife Digital Peak Flow Meter shop online, that can store and print your child's peak flow readings over time.

Examples of more simple, inexpensive peak flow meters include the:

Although you don't need a prescription for a peak flow meter, you should see your pediatrician to understand what your child's peak flow and asthma action plan should be.

Also, except for teenagers who may have a higher predicted and personal best peak flow, you should likely get a "low-range" model peak flow meter for your child. Unlike a "full-range" peak flow meter that gives readings over 850 L/min, a "low-range" peak flow meter usually only goes up to about 390 L/min.


Mason: Murray & Nadel's Textbook of Respiratory Medicine, 4th ed.

National Heart, Lung, and Blood Institute of the National Institutes of Health. Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma. 2007.

Pediatric asthma. Stewart LJ - Prim Care - 01-MAR-2008; 35(1): 25-40, vi.

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