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Peak flow measurement

The peak expiratory flow rate or peak flow is a measurement of the maximum speed of expiration, starting from full lung inflation. It is a useful aid for assessing the degree of large airway obstruction.

Peak flow meter


  • Wash hands; Introduce self; ask Patient’s name, DOB and what they like to be called; Explain
  • Explain peak flow measures the maximum speed of expiration 
  • Give patient specific details of what they should do:
    • Stand or sit upright
    • Set the meter dial to zero
    • Hold the meter horizontally and ensure they are not touching the dial
    • Take a deep breath in to full capacity
    • Place lips tightly around the cardboard tube to form a tight seal
    • Blow out as hard and as fast possible (it measures the first puff, so they do not need to expire fully)
  • Demonstrate for them with a different cardboard tube  
  • Observe them doing it and comment on any mistakes
  • Ask patient to perform test three times at one minute intervals

To complete

  • Thank patient and ask if they have any questions
  • Bin the cardboard tube
  • Document in the notes the best of the three readings (in litres/minute)

Test your knowledge

What is the ‘expected’ peak flow based on?

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How is the severity of an asthma exacerbation classified, based on peak flow results?

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