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Medical Devices

How to Use a Peak Flow Meter

A peak flow meter is a device that measures how fast air comes out your lungs when you exhale forcefully. This measure is called a peak expiratory flow, or "PEF" and is measured in liters per minute (lpm). A person's PEF might drop hours or even days before asthma symptoms occur. Readings from the meter can help you or your child recognize early changes that might be signs of worsening asthma. By taking medicine early (before symptoms), you might be able to stop the episode quickly and avoid a severe asthma episode. The peak flow meter can also be used to help you:

What is a peak flow meter?

  • Learn what triggers asthma
  • Decide when to add or stop medicines
  • Know when to seek emergency care

How do I use the peak flow meter?

A peak flow meter is simple to use. Even children ages 4 and up should be able to perform a PEF with good results. To perform a peak expiratory flow:

  1. Stand up straight.
  2. Make sure the indicator is at the bottom of the meter.
  3. Take a deep breath filling your lungs completely.
  4. Place the mouthpiece in your mouth; lightly bite with your teeth, and close your lips on it.
  5. Blast the air out as hard and as fast as possible in a single blow.
  6. Record the number that appears on the meter.
  7. Repeat these steps three times.
  8. Record the highest of the three readings in an asthma diary. This reading is your or your child's peak expiratory flow.

Finding "personal best" peak expiratory flow

The "personal best" peak expiratory flow is the highest peak flow number you or your child can achieve over a two- to three-week period when asthma is under good control

Good control means you feel good and do not have any symptoms. The personal best PEF is the number to which all other peak flow readings you or your child obtains will be compared.

Predicted PEFs based on age, height, and gender are available. These resources might be helpful, but the most important number is your or your child's own personal best peak expiratory flow. A written treatment plan, called the Asthma Action Plan, will include the personal best PEF as part of your self-management plan. To find the personal best peak flow number, take peak flow readings:

  • Twice a day for two to three weeks
  • At the same time in the morning and in the evening
  • Before taking a short-acting beta 2 agonist for quick relief (if you or your child takes this medicine)
  • As instructed by your doctor or nurse

Once you have determined you or your child's personal best PEF, continue to take readings. Daily readings will help you:

  • Recognize early drops in airflow
  • Know when your child's personal best improves naturally as he or she grows

If you or your child's morning PEF drops below 80 percent of the personal best, follow the Asthma Action Plan and check your PEF more frequently that day (as directed by your health care provider).

Finding your asthma zones

Keeping a daily record of your PEFs and understanding how PEFs relate to changes in asthma will help you to better manage asthma episodes. To help patients understand this relationship, health care providers use a system of asthma zones.

There are three asthma zones: the Green zone, the Yellow zone and the Red zone.

  • Green zone: Asthma is well-controlled. PEF is 80 percent to 100 percent of your personal best.
  • Yellow zone: Asthma is flaring up or is poorly controlled. PEF is 50 percent to 80 percent of your personal best.
  • Red zone: Asthma is severe; requires emergency care. PEF is less than 50 percent of your personal best.

To find the ranges for your asthma zones, multiply your personal best PEF by 1 (100 percent), .8 (80 percent), and .5 (50 percent). Record these ranges in an asthma diary so that you can refer to them easily. Here's an example:

Using a PEF number of 400, the zones would be:

  • Green zone: 320 (400 * .8) to 400 (400 * 1)
  • Yellow zone: 200 (400 * .5) to 320 (400 * .8)
  • Red zone: Less than 200 (400 x .5)

Record these ranges in an asthma diary so that you can refer to them easily. These will also be included in your Asthma Action Plan.

If you are in the Yellow or Red zone, you will need to adjust your medicine according to your doctor's instructions. Make sure you understand and can follow the plan. Ask your doctor any questions you might have.

The daily asthma diary

You can record daily PEF and symptom scores in a daily asthma diary (example below). This diary will help you and your doctor evaluate how well your Asthma Action Plan is working. The diary will also help you identify when changes are occurring in your asthma. When you complete the diary, remember to:

  • Fill in the date each day.
  • Take PEF readings each morning before you take your asthma medicine.
  • Compare the PEF reading to your personal best.
    • If your PEF reading is less than 80 percent of personal best, you must follow the instructions you were given in your Asthma Action Plan. Also remember to check your PEF more frequently that day, including an evening peak flow.
    • When performing the evening peak flow, also record any symptoms you or your child might have had during the day and the amount of reliever medication used.(total number of puffs of inhaler or number of nebulizer treatments).
Date PEF Readings
a.m. p.m.
# Puffs of Rescue Inhaler
Cough Wheeze Short Breath Tight Chest

American Academy of Allergy Asthma & Immunology. Patients & Consumers: Tips to Remember: Peak Flow Meter,

American Lung Association. Measuring Your Peak Flow Rate.

Asthma and Allergy Foundation of America. Peak Flow Meters.

© 1995-2010 The Cleveland Clinic Foundation. All rights reserved.

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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 3/8/2007...#4298