Alamo Asthma & Allergy Associates
Drs. Michael and Adrianne Vaughn

115 Gallery Circle
Suite 200
San Antonio, TX 78258
(Stone Oak MRI/Urgent Care Bldg.)
Tel: 210.499.0033
Fax: 210.404.0926

What is a Peak Flow Meter?

A peak flow meter for asthma is like a thermometer for a fever. It's a tool that helps you monitor what's going on inside your body. In some cases, when you are not feeling well, you may feel "hot" or "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 decreased. A peak flow meter can help you determine airway changes and better manage your asthma.

Using a peak flow meter
A peak flow meter is a simple, portable, inexpensive device that measures air flow, or peak expiratory flow rate (PEFR). Asthma sufferers blow into the device quickly and forcefully, and the resulting peak flow reading indicates how open the airways are, or how difficult it is to breathe. If used appropriately, a peak flow meter can be a valuable tool for your asthma management. It can be used to:

  • Determine the severity of asthma and detect day to day variations.
  • Follow your response to treatment during an acute asthma episode.
  • Monitor progress in treatment of chronic asthma and provide objective information to help determine the need for any adjustments in therapy.
  • Detect worsening in lung function before serious symptoms develop and thereby providing an opportunity for early intervention.

One of the most important functions of the peak flow meter is to help you and your physician evaluate asthma severity. Often you can see a drop in peak flow readings even before the symptoms of asthma (like coughing or wheezing) get worse. A decrease in peak flow may indicate that you need to increase your medication. The earlier a warning sign is detected, the sooner the problem can be addressed.

Knowing your normal peak flow values is very important especially if you have to call your physician after hours because of increasing symptoms. How your peak flow has changed from your "best" effort values can give the physician a better idea of how you are doing and how you are responding to treatment at home. Twice per day (am and pm) monitoring is necessary initially to record your "normal" values since these numbers may be different during different times of the day.

Another measure of asthma control is called peak flow variability. A person without asthma or with well-controlled asthma will consistently blow peak flows that vary less than 15%-20%. Most patients who have asthma have asthma symptoms that are usually worse at night. A peak flow meter is useful in monitoring the severity of asthma at night. A decrease of 20% or greater from the previous night's measurement may indicate poorly controlled nocturnal asthma. Similarly, peak flow measurement performed before and after exercise may help identify exercise as a trigger for asthma.

Establishing your personal best reading
Although your expected "normal" peak flow can be predicted by height, age and gender, it is preferable to gauge asthma control by comparing each peak flow recording with your "personal best effort" reading. The "personal best" peak flow is the highest peak flow number a patient can achieve over a 2-3 week period when his or her asthma is under good control.

Personal best values will change as children grow taller and as disease control improves. Peak flow meters need some care, so make sure to follow the cleaning instructions enclosed with each unit. This will help to ensure its accuracy.

How to use a peak flow meter
There are several steps to properly using a peak flow meter. You should blow as hard as you can into the meter to get the best reading possible. Repeat this attempt three times and record the best of the three trials. All three measurements should be about the same to show that a good effort was made each time. This is especially important when parents are evaluating their child's asthma.

Follow these general steps when using a peak flow meter:

  • Make sure the device reads zero or is at base level
  • Stand up (unless you have a physical disability)
  • Take as deep of breath as possible
  • Place the meter in your mouth and close your lips around the mouthpiece tightly
  • Blow out as hard and as fast as possible (within one second)
  • Do not cough, spit or let your tongue block the mouthpiece
  • Write down the value obtained. Repeat the process two additional times, and record the highest of the three numbers in your chart

Your physician may ask you to also record your peak flow before and after using your rescue inhaler. If your medicine is working you should see an improvement in your peak flow reading. Initially keep a chart of peak flow readings daily in the am and pm for at least two weeks to show how your asthma symptoms are doing. Graphs for plotting peak flow readings often come with the devices and can be photocopied for regular use.

Traffic light system/Your Asthma "Action Plan"
Once you and your allergist/immunologist have established your personal best peak flow, your physician should make every effort to maintain values within 80% of this number. The following traffic light system can serve as an easy guide:

Green zone-Peak expiratory flow rate (PEFR) 80-100% of personal best. Asthma is under good control. You should be relatively symptom-free and can maintain your current asthma management program. If you are on continuous medication and your peak flow is constantly in the green zone with minimal variation, your physician may also consider gradually decreasing your daily medication. Never make medication changes without consulting your physician.

Yellow zone-PEFR 50-80% of personal best. Suggests "Caution," as asthma is worsening. A temporary increase in asthma medication maybe indicated. If you are on chronic medications, maintenance therapy may need to be increased or changed. Contact your physician to fine-tune your therapy.

Red zone-PEFR below 50% of personal best. Suggests "Danger," your asthma management and treatment program is failing to control your symptoms. Use your inhaled "rescue" bronchodilator. If peak flow readings do not return to at least the yellow zone, contact your primary care physician or allergist/immunologist, who will help you employ aggressive therapy. Maintenance therapy may have to be increased. You also will likely need to be seen by a physician to be accurately diagnosed as to why the asthma has worsened. The practice of "phone call" medicine places you at risk for misdiagnosis and suboptimal treatment. If you are unable to be seen immediately by your "primary care physician" or specialist when you are in the "red zone," evaluation in an emergency room is recommended. * A severe "asthma attack" should always be seen in an emergency room.

These traffic light zones are broad guidelines designed to simplify asthma management. Successful control of asthma depends upon a partnership between the patient and the physician. This open communication and exchange of information can be improved with peak flow monitoring and reporting. Your physician can use this data to design and adjust your medication to achieve the best asthma control possible for you.

Alamo Asthma & Allergy recommends the "PIKO meter" as the best choice among peak flow meters. It has a small mouth piece which is good for children and is typically very accurate. PIKO's sold at our office for $25.00 as a courtesy to our patients (at our cost). They are available from Walgreen's (210) 403-0002 for about $35.00. Instructions for the use of the PIKO meter can be viewed by clicking here.




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Asthma & Allergy Associates
115 Gallery Circle
Suite 200
San Antonio, TX 78258
(Stone Oak MRI/Urgent Care Bldg.)
Tel: 210.499.0033
Fax: 210.404.0926
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