How to Use a Peak Flow Meter

A peak flow meter is a portable, inexpensive, hand-held device used to measure how well air is moving through your lungs. In other words, the meter measures your ability to push air out of your lungs.

Many doctors believe that people who have asthma can benefit from the use of a peak flow meter. If you need to adjust your daily asthma medicine, a peak flow meter can be an important part of your asthma management plan.

Why Should I Measure My Peak Flow Rate?

Your peak flow rates can show you if your asthma is getting worse, even before you feel symptoms. In addition, measurements with a peak flow meter can help your doctor make decisions about your treatment and adjust your medicines as necessary.

A peak flow meter can be used as a signal to determine if your asthma is getting worse. Asthma sometimes changes gradually. Your peak flow meter may show changes before you feel them. Peak flow readings can show you when to start following the steps on your Asthma Action Plan that you developed with your doctor.

A peak flow meter can also help you and your doctor identify causes of your asthma at work, home or play.

Here are some general steps for how to use a peak flow meter. Always be sure to read the instructions that come with your peak flow meter. Ask your doctor, pharmacist or other health care professional (such as a nurse practitioner, physician assistant, nurse, respiratory therapist or asthma educator) to show you how to use your peak flow meter. Review your technique at each follow-up visit.

  1. Always stand up. Remove any food or gum from your mouth before you begin.
  2. Make sure the marker on the peak flow meter is at the bottom of the scale.
  3. Breathe in slowly and deeply. Hold that breath.
  4. Place mouthpiece on your tongue and close lips around it to form a tight seal (do not put tongue in the hole).
  5. Blow out as hard and fast as possible.
  6. Write down the number next to the marker. If you cough or make a mistake, do not write down that number. Do it over again.
  7. Repeat steps 3 through 6 two more times.
  8. Record the highest of these three numbers in a notebook, calendar or asthma diary.

Compare the highest number with the peak flow numbers on your written Asthma Action Plan. Check to see which zone the number falls under and follow the plan’s instructions for that zone.

GREEN ZONE: 80%–100% of Personal Best
Take daily long-term controller medicines, if prescribed.

YELLOW ZONE: 50%–79% of Personal Best
Add quick-relief medicines as directed and continue daily long-term controller medicines, if prescribed. Continue to monitor.

RED ZONE: Less than 50% of Personal Best
Add quick-relief medicines as directed. Get medical help now.

How Do I Chart My Peak Flow Rates?

Chart the highest of the three readings. This is called “your personal best”. The chart could include the date at the top of the page with AM and PM listed. The left margin could list a scale, starting with zero (0) liters per minute (L/min), at the bottom of the page and ending with 600 L/min at the top.

Don’t forget that your peak flow meter needs care and cleaning. Dirt collected in the meter may make your peak flow measurements inaccurate. If you have a cold or other respiratory infection, germs or mucus may also collect in the meter. Proper cleaning with mild detergent in hot water will keep your peak flow meter working accurately and may keep you healthier.

When Should I Use My Peak Flow Meter?

Use of the peak flow meter depends on a number of things so the best time for you to use it should be discussed with your doctor. If your asthma is well controlled and you know the “normal” rate for you, you may decide to measure your peak flow rate only when you sense that your asthma is getting worse. More severe asthma may require several measurements daily.

What is a “Normal” Peak Flow Rate?

A “normal” peak flow rate is based on a person’s age, height, sex and race. A standardized “normal” may be obtained from a chart, comparing your rate with a population without breathing problems.

A patient can figure out what is normal for them, based on their own peak flow rate. Therefore, it is important for you and your doctor to discuss what is considered “normal” for you.

Once you have learned your “normal” peak flow rate, you will be able to better recognize changes or trends in your asthma.

How Can I Determine a “Normal” Peak Flow Rate For Me?

Three zones of measurement are commonly used to interpret peak flow rates. It is easy to relate the three zones to the traffic light colors: green, yellow and red. In general, a normal peak flow rate can vary as much as 20 percent.

Be aware of the following general guidelines. Keep in mind that recognizing changes from “normal” is important. Your doctor may suggest other zones to follow.

Green Zone:
80 to 100 percent of your usual or “normal” peak flow rate signals all clear. A reading in this zone means that your asthma is under reasonably good control. You should continue your prescribed asthma management program.

Yellow Zone:
50 to 80 percent of your usual or “normal” peak flow rate signals caution. It is a time for decisions. Your airways are narrowing and may require extra treatment. Your symptoms can get better or worse depending on what you do or how and when you use your prescribed medicine. You and your doctor should have a plan for yellow zone readings.

Red Zone:
Less than 50 percent of your usual or “normal” peak flow rate signals a medical alert. Immediate decisions and actions need to be taken. Severe airway narrowing may be occurring. Take your rescue medications right away. Contact your doctor now and follow the plan he has given you for red zone readings.

Some doctors may suggest zones with a smaller range, such as 90 to 100 percent. Always follow your doctor’s suggestions about your peak flow rate.