What Is a Peak Flow Meter?
A peak flow meter is a handheld device that measures the peak expiratory flow rate (PEFR), or the volume of air that can be forcibly expelled from the airways.
Peak Expiratory Flow Rate (PEFR)
PEFR is the number value given after the patient takes the deepest breath possible and blows into a peak flow meter in a single, forceful blast. PEFR measures one aspect of airway obstruction and is an economical means of monitoring lung function at home. It is also effort-dependent, meaning that a poor effort will yield poor results. Because asthma is a disease that affects airflow, measuring PEFR can be very helpful in detecting changes in airway function.
How to Use Your Peak Flow Meter
Included with every peak flow meter are the following:
Read the instructions that come with your peak flow meter carefully. They will explain how to operate and clean the peak flow meter, record your daily PEFR, use the nomogram, and make sure your peak flow meter is operating correctly.
The technical procedure for using a peak flow meter is standard with all models:
- Move the sliding indicator to the base of the peak flow meter.
- Stand up. Take a deep breath to fully inflate your lungs (be sure to remove any gum or candy from your mouth first!).
- Put the mouthpiece of the peak flow meter into your mouth and close your lips tightly around it.
- Now, (this is very important) with as much force as possible, blow out as quickly as you can.
- The force of your breath moves the indicator along the numbered shaft of the peak flow meter. The number opposite the indicator tells the PEFR.
- Repeat these steps two more times and keep a written record of the highest number you reach (it is recommended that you blow three times whenever you use the peak flow meter).
Your PEFR will improve as symptoms are better controlled. Your target PEFR is the number you should be able to achieve when your asthma is under control. The 1997 Guidelines for the Diagnosis and Management of Asthma by the National Heart, Lung and Blood Institute’s National Asthma Education and Prevention Program (NAEPP) recommend that a decrease of more than 20 percent target PEFR is a sign of a change in lung function that requires a medical response.
However, the Guidelines acknowledge that some people may require an earlier response time. For example, some people need to begin medications after a variation of only 10 or 15 percent from normal. You and your physician will establish your personal target PEFR and a corresponding asthma management plan.
This plan should be reviewed periodically. Children’s PEFRs will change as they mature, and your physician may adjust your target PEFR as you learn to manage your asthma more effectively.
Peak Flow Zones
The NAEPP has tried to simplify the process of computing the percentages or zones using the colors of a traffic light. You and your physician can use this information as a starting point for determining your personal zones according to your true needs.
GREEN (80 to 100 percent of target PEFR) signals all clear: No asthma symptoms are present, and the routine treatment plan for maintaining control can be followed. If you take medications every day and have consistent readings in the green zone, you may want to ask your physician about reducing medications.
YELLOW (50 to 80 percent of target PEFR) signals caution: An episode of asthma may be present that requires a temporary increase (step-up) in medication. Yellow may mean that your overall asthma condition is not under sufficient control, and your physician may increase your daily medications.
RED (below 50 percent of target PEFR) signals a medical alert: A fast-acting bronchodilator should be used immediately and the physician should be notified if PEFR measures do not immediately return to and remain in the yellow or green zone.
First published: Allergy & Asthma Health, 2002
Reviewed: March 2009