A peak flow meter for asthma is like a thermometer for a fever. Both are tools to help monitor what is going on in your body. For instance, there may be times when you feel feverish, but when you take your temperature with a thermometer it is normal. With asthma, sometimes you may feel your breathing is fine, but when you measure it with a peak flow meter your lung function is slightly decreased.
The readings on a peak flow meter tell you how open your airways are, so you can better manage your asthma.
What Does a Peak Flow Meter Do?
A peak flow meter is a portable device that measures air flow, or peak expiratory flow rate (PEFR). It can be used to:
• Determine the severity of your asthma attack
• Check your response to treatment during an acute asthma episode
• Monitor progress in treatment of chronic asthma and provide information for any changes in your therapy
• Detect worsening lung function and avoid a possible serious asthma flare-up
A peak flow meter can help you and your allergist / immunologist, often referred to as an allergist, evaluate how severe your asthma is at any point in time. With a peak flow meter, you can often see a drop in your readings even before your symptoms (like coughing or wheezing) get worse. Decreases in peak flow may show that you need to increase your medication.
How to Use a Peak Flow Meter
Follow these steps:
• Make sure the device reads zero or is at base level.
• Stand up (unless you have a physical disability).
• Take as deep of a breath as possible.
• Place the meter in your mouth and close your lips around the mouthpiece.
• Blow out as hard and as fast as possible into the peak flow meter (one to two seconds).
• Do not cough, spit or let your tongue block the mouthpiece.
• Write down the number.
• Repeat two times, and record the highest of the three numbers in your chart.
All three measurements should be about the same to show that a good effort was made each time. This is especially important if you are evaluating your child's asthma. Keep a chart of peak flow readings to track your asthma symptoms. Peak flow meters need some care, so make sure to follow the cleaning instructions.
Your allergist may ask you to record your peak flow before and after using your rescue inhaler. If your medicine is working, you should see an improvement in your reading.
Finding Your Personal Best Reading
Although your predicted "normal" peak flow is determined by your height, age and gender, you should measure your asthma control by comparing your daily peak flow recordings with your "personal best" reading. Your personal best is the highest peak flow number you can get over a two to three week period when your asthma is under good control.
To determine your personal best:
• Always use the same peak flow meter.
• Record your peak flow twice a day for two weeks when you are well.
Traffic Light System
Once you and your allergist have found your personal best peak flow, you should make every effort to maintain values within 80% of this number so you feel your best. The following traffic light system can serve as an easy guide:
Green zone: PEFR 80 to 100% of personal best. All systems "go." You are relatively free of symptoms and can maintain your current asthma management program.
Yellow zone: PEFR 50 to 80% of personal best. "Caution," as your asthma is worsening. Contact your allergist to fine-tune your therapy if you do not see improvement.
Red zone: PEFR below 50% of personal best. "Danger," your asthma management and treatment program isn't controlling your symptoms. Use your inhaled bronchodilator per your action plan – this may be as many as three times in one hour. If peak flow readings do not return to at least the yellow zone, contact your allergist. If you worsen at any time when in the red zone seek emergency care immediately.
Successful control of your asthma depends upon a partnership between you and your allergist. If you monitor your peak flow, your allergist can use this data to design and adjust your medication to keep your asthma under control.
• Stand up, take a very deep breath and blow hard into the meter to get the best reading possible. Repeat this three times and make sure the device is at base level before you start again. Record the best of the three trials.
• Keep a chart of peak flow readings to track your asthma symptoms. Share the results with your allergist to design a treatment plan that is right for you.
• After finding your personal best reading, use the traffic light zones (red, yellow and green) as guidelines to manage your asthma. Remember that if peak flow readings do not return to at least the yellow zone, contact your allergist. If you worsen at any time when in the red zone, seek emergency care immediately.
The AAAAI's Find an Allergist / Immunologist service is a trusted resource to help you find a specialist close to home.
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This article has been reviewed by Andrew Moore, MD, FAAAAI