Peak Expiratory Flow Rate Measurement Technique

Updated: Feb 15, 2022
  • Author: Daniel R Neuspiel, MD, MPH, FAAP; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Measurement of Peak Expiratory Flow Rate

Peak expiratory flow rate (PEFR) measurement (see the video below) depends significantly on patient effort and technique. Therefore, clear instructions, accurate demonstrations, and frequent review of technique are essential.

Peak expiratory flow rate (PEFR) measurement. Video courtesy of Therese Canares, MD, and Jonathan Valente, MD, Rhode Island Hospital, Brown University.

Because of diurnal variation, it is important to measure PEFR at the same time every day. PEFR declines linearly throughout gestation in pregnancy, especially when it is measured in the supine position. [29]

The indicator on the peak flow meter (PFM) is moved to the lowest end of the numbered scale. (See the image below.) For some devices, this requires vigorous shaking. If the device has a separate mouthpiece, it must now be attached.

Peak expiratory flow rate (PEFR) measurement. Star Peak expiratory flow rate (PEFR) measurement. Start with meter indicator at lowest level.

While standing, the patient takes a deep inhalation (see the image below).

Peak expiratory flow rate (PEFR) measurement. Take Peak expiratory flow rate (PEFR) measurement. Take in deep inspiration while standing.

The mouthpiece of the PFM is placed in the patient’s mouth with lips closed around it. The tongue should not be placed in the front hole. The patient blows out forcefully and rapidly in a single exhalation (see the image below).

Peak expiratory flow rate (PEFR) measurement. Exha Peak expiratory flow rate (PEFR) measurement. Exhale forcefully and rapidly with lips sealed around mouthpiece.

These steps are repeated two more times. If the patient coughs or does not perform the technique correctly, the turn is ignored and repeated. The highest number from the three attempts is recorded by the patient. Information about medications, symptoms, and any unusual activities should also be recorded.

Formulae for predicted PEFR vary across the literature. The patient’s personal best PEFR (see below) may be used as a reference; population-based equations may also be used. [30]


Identification of Personal Best Peak Expiratory Flow Rate

The patient’s individual personal best PEFR must be reevaluated to account for both growth and disease progression. PEFR measurement should be periodically correlated with office spirometry. [3]

The patient is instructed to identify his or her personal best PEFR by recording the highest number achieved within 2 weeks when he or she feels relatively well without respiratory symptoms. Details of measurement are as follows:

  • PEFR is measured at least twice a day for 2-3 weeks
  • PEFR should be measured upon awakening and in the late afternoon or early evening
  • PEFR should be measured 15-20 minutes after use of an inhaled short-acting beta2 agonist

After the personal best PEFR is obtained, the patient’s healthcare provider may include this information in an asthma action plan to direct the patient’s self-management.

In general, a PEFR that is less than 80% of the patient’s personal best should trigger the administration of an inhaled short-acting beta2 agonist. A PEFR that is less than 50% of the patient’s personal best should trigger both administration of an inhaled short-acting beta2 agonist and immediate medical attention.

Personal best PEFR measurements reach a plateau of 95% predicted levels 3 weeks after the initiation of inhaled corticosteroid therapy. [18] The predicted PEFR values for African American and Hispanic patients are 10% lower than those reflected in most tables. [31]  The accuracy of PFMs may decrease over time.