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Peak Flow Meter: Teen Version


What is a peak flow meter?

A peak flow meter is a small hand-held device that measures how well air moves out of your lungs. It does this by measuring how fast you can blow air out of your lungs. It is a way to tell how well you are breathing. Peak flow readings can tell you if your asthma is in good control, if you need to take medicine, or if you need to get help right away.

One type of peak flow meter has a sliding marker that moves as you blow air forcefully into the device. At the end of a forceful breath, the marker stops at a place on a numbered scale that measures the amount of air you breathed out. The numbered scale usually ranges from 0 to 750.

Digital peak flow meters record each reading in the device. This should not replace using a chart to record your peak flow readings. Some units also display "traffic light" colored peak flow zones based on your personal best peak flow reading. An added benefit is that some digital peak flow meters also measure FEV1 (the amount of air blown out in the first second). Some devices have the ability to electronically transmit results to your healthcare provider. This can make it easier to track and compare readings.

There are several different types of peak flow meters, so for accurate readings, it is very important to understand how your healthcare provider wants you use your peak flow meter and to follow his or her instructions carefully. It is also important to use the same peak flow meter for your readings.

When should I use a peak flow meter?

First you need to figure out your personal best peak flow reading. This is done by taking peak flow measurements twice a day for a couple of weeks when you are feeling well and your asthma is under good control. At the end of the 2 or 3 weeks, look over the numbers and pick out the highest readings. These readings determine your personal best peak flow meter reading. Record all of your readings on a chart and take the chart to your healthcare provider. The personal best reading will give you and your provider something to judge all of your future peak flow readings against.

After you have figured out what your personal best is, your provider may recommend that you measure your peak flow every day, or your provider may suggest that you take readings 2 or 3 times a week.

  • Daily use: If you need to record your peak flow every day, the first reading should be a morning reading before you take any medicine. If the reading is less than 80% of your personal best, take your quick-relief medicine, then wait 15 minutes and measure your peak flow again. If your peak flow readings in the morning are low, check your peak flow again in the early afternoon. If you take medicine in the evening, your provider may recommend that you take another reading in the evening before taking your medicine.
  • Weekly use: If you need to take peak flow readings just 2 or 3 times a week, take a reading in the morning and again in the evening each day that you take a measurement. If you are using an inhaler, make sure you take consistent readings. That is, both the morning and evening readings should be done before using the inhaler, or both readings should be done after using the inhaler. If the morning and evening readings are different by more than 20%, talk to your healthcare provider about how to manage your asthma better.

Use a chart to record your peak flow readings with the date and time of day you measured your peak flow. Also record if you used a quick-relief (rescue) inhaler (a bronchodilator, such as albuterol).

You should also take a peak flow reading when you have an asthma attack. Measure your peak flow both before and after using your quick-relief inhaler to check how well the medicine is working.

You should recheck your personal best reading every year or whenever you get a new meter.

What do the peak flow numbers mean?

Because lung capacity is not the same for everyone, personal best peak flow readings are different. Your healthcare provider will give you guidelines to follow based on your personal best reading. In general, if you have a peak flow that is 80% (or better) of your personal best, it means that your asthma is under control. A number between 50% and 80% of your personal best means that you need to take a quick-relief medicine. Lower than 50% means that you are not breathing as well as you should be. If you are having symptoms of shortness of breath, wheezing, and coughing spells, you need to take your quick-relief medicine right away and get more help from your healthcare provider.

If your peak flow is low, but you feel fine, take the peak flow test again, making sure you are blowing hard into the meter.

To have accurate peak flow readings, you need to give your best effort each time you do a peak flow.

How is the peak flow meter used?

Different brands of peak flow meters work a little differently. Ask your healthcare provider for instructions and carefully read and follow the instructions included with your peak flow meter.

General instructions are:

  1. Place the mouthpiece on the peak flow meter. (Some meters have different sizes of mouthpieces for younger and older children and some do not have mouthpieces at all.)
  2. Put the marker at the bottom of the numbered scale (zero or the lowest number on the scale).
  3. Hold the peak flow meter upright, being careful that your fingers do not block the opening.
  4. Stand up straight and take the biggest, deepest breath you can with your mouth open. Hold the meter in one hand and keep your fingers away from the numbers. Place the mouthpiece into your mouth beyond your teeth and make a tight seal around the mouthpiece with your lips. Make sure that your tongue does not block the opening of the mouthpiece.
  5. Blow out as hard and fast as you can. If you cough or make a mistake, do not record the number. Do it over again.
  6. Remove the mouthpiece from your mouth. The marker will have moved up the numbered scale. Do not touch the marker. Find the number where the marker stopped. Write down the number on a chart. If you coughed or made a mistake, do not record the number. Do it over again.

Repeat this procedure 2 more times. Write down each number and circle the highest reading from the 3 tries. Record the date and time of day with this number.

When and how should my peak flow meter be cleaned?

The mouthpiece of the meter should be cleaned weekly with warm, soapy water. Rinse and dry it well.


Written by the Asthma Management Team at The Children's Hospital, Denver.
Published by RelayHealth.
Last modified: 2011-02-11
Last reviewed: 2010-12-13

This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a health care professional.

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