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Measuring peak expiratory flow rate: Clinical skills notes




Measuring Peak Expiratory Flow Rate


Peak expiratory flow rate, or PEFR for short, is the fastest and the hardest someone can exhale after a full inspiration. This can be used to measure the client’s ability to push air out of their lungs and, thus, measure the amount of obstruction in the airways of clients with certain respiratory conditions, like asthma. This is essential to determine how open their lungs are, if their treatment is working properly, and if they need a dose adjustment or even a new medication.

Figure 1: Peak expiratory flow rate measures amount of obstruction in airways.

Device and components

Measurement of PEFR is performed with a special portable handheld device called a peak flow meter. This is made up of a mouthpiece attached to a numbered scale with a small arrow that moves as the client blows air out, indicating the speed of airflow measured in liters per minute.

Figure 2: Peak flow meter.

Common care tips

  • Clients who are experiencing pain, motor function impairments, and people with dementia or other cognitive impairments might be unable to measure PEFR independently. 
  • Those who can, should perform PEFR measurements at home or in a healthcare facility.
  • Measurements are done regularly at certain times, such as first thing in the morning and last thing at night, before or after using asthma medications, or when experiencing symptoms of an asthma exacerbation, like shortness of breath, cough, or wheezing.


  1. Make sure the client is standing erect if they’re able. 
  2. Make sure the arrow is set to the zero mark.
  3. Attach a clean, disposable mouthpiece to the device.
  4. Instruct the client to inhale deeply through the mouth and place their lips tightly around the mouthpiece, keeping their tongue away from the opening.
  5. Then, the client should exhale as fast and forcibly as possible.
  6. Repeat this process twice more. Each time, make sure their head remains in the same position and that arrow is reset to zero.
  7. Dispose of the mouthpiece and practice hand hygiene before and after the procedure.

Figure 3: Measuring peak expiratory flow rate. A. Make sure the peak flow meter is at zero mark. B. Before starting, instruct client to inhale deeply. C. Client should exhale as fast and forcibly as possible through the peak flow meter. This process should be repeated twice more. D. Dispose mouthpiece and practice hand hygiene. 


When assisting a client with measuring their PEFR, there are a few things you should report to the healthcare provider. These include:
  • the client being unable to perform the exercise 
  • if the client has signs or symptoms of respiratory distress
  • any values that differ significantly from previous measurements 

Document the date and time of the procedure.

For the measurements, record the highest value reached by the client and match it to the green, yellow, or red zones. These are unique for each client and depend on their age, sex, and size.
  • Green zone: 80–100% of their personal best; means the condition is under control
  • Yellow zone: 50–80% of their personal best; report this number to the healthcare provider and assess the client
  • Red zone: < 50% of their personal best; report this number to the healthcare provider too

If the client is instructed to measure PEFR at home, make sure they know how to read the machine, and classify the results based on the green-yellow-red zone guidelines. Keep a record of these results to share with their healthcare provider.

Figure 4: Green, yellow and red zones of the peak flow meter unique to a client.