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Peak Flow Meter: How to Monitor Asthma

What is a peak flow meter?

A peak flow meter is a small hand-held device that measures the fastest speed you can blow air out of your lungs, which is one way to tell how well you are breathing. Peak flow readings will tell you if your asthma is in good control, if you need to take medicine, or if you need to get help right away. The peak flow meter has a sliding marker that moves as you blow air forcefully into the device. The marker stops at a place on a numbered scale that measures the amount of air you breathed out with one big breath. The numbered scale usually ranges from 0 to 750. There are several different types of peak flow meters, so for accurate readings, it is very important to follow the instructions carefully.

When should I use a peak flow meter?

The first thing you will need to do is 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. The personal best reading will help you and your health care provider have a measure to judge all of your future peak flow measurements by. You should update your personal best reading every year or when you get a new meter.

Your health care provider may recommend that you keep a daily record of the peak flow readings or suggest that you take readings 2 or 3 times a week. Use a chart to record your peak flow readings along 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).

  • Daily use: If you need to record your peak flow every day, the first reading should be a morning reading (before taking 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, another reading should be done 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 there is more than a 20% variation between mornings and evening readings, talk to your health care provider about how to manage your asthma better.

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

What do the peak flow numbers mean?

Because everyone has a different lung capacity, everyone has a different "personal best" peak flow reading. Your health care 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, then you need to take your quick-relief medicine right away and get additional help from your health care provider. If your peak flow is low, but you feel fine, then you need to recheck the peak flow test, making sure you are blowing hard into the meter.

These numbers depend on you giving your best effort each time you do a peak flow. Your numbers can be in error if you don't give a 100% each time you check the peak flow.

How is the peak flow meter used?

Each brand of peak flow meter works a little differently. Ask your 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 (unless it is one solid unit).
  2. Place 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 peak flow meter 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.

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