Peak flow diary

What is a Peak Flow Meter?

A peak flow meter is a device, which records the peak or maximal flow during a forced expiratory manoeuvre (PEFR = Peak Expiratory Flow Rate). In other words, a peak flow meter measures how fast air can be expelled from the lungs.

Why use a Peak Flow Meter?

A Peak Flow Meter is used for the following purposes:

  • where diagnosis of asthma is uncertain
  • to assess asthma severity
  • to establish what is the ‘best’ peak flow obtainable during intensive treatment
  • to assess response to changes in asthma therapy
  • to identify triggers
  • to recognise the pattern of asthma over time
  • to allow a Self Management Plan to be developed
  • to diagnose occupational asthma

Not a stand-alone tool

Peak flow monitoring should not be used as a substitute or stand-alone tool for monitoring asthma severity. It should be used in conjunction with symptom assessment, which is the first and simplest means of monitoring. Research suggests that a simple symptom diary may be as useful as serial PEFR in monitoring ‘flare-ups’. It is an objective tool to confirm subjective ‘perceptions’ of an individual’s asthma.

Limits on usefulness

Because PEFR is dependent on the level of client effort and because it may be more sensitive to large airway than small airway narrowing, its usefulness may be limited in some populations, e.g. young children or individuals who are not highly motivated to give their best effort. Always do a ‘best of three’ reading.  Spirometry measuring FEV1 is more sensitive to minor narrowing of the airways.

Who should use a Peak Flow Meter?

Children: In a child 6 years of age and over, a Peak Flow Meter is likely to be reliable. Children should first master the use of their inhaler (inhalation) prior to using a Peak Flow Meter (exhalation).

Adults: Most adults are capable of utilising a Peak Flow Meter, but will it be used? Realistic goals need to be defined so as to improve acceptance of the strategy.

Why use a Peak Flow Meter?

Diagnosing Asthma

  • When diagnosing asthma, a peak flow diary is useful in monitoring variations, particularly in the early morning.
  • Peak flow values will reflect the use of the bronchodilators.  Usually routine readings are taken prior to their use unless performing before and after documentation.
  • To assess occupational asthma – monitor peak flows at least 4 times a day.

Developing a Self Management Plan

  • Self Management Plans are developed in partnership with the health professional writing the plan and the client, based on information from symptom and/or peak flow diaries.
  • Mutually agreed upon symptoms and/or peak flow ranges as well as management action are written into the plan 
  • Inflammation although present all the time to some degree, may be aggravated by a trigger.  Symptoms often get worse before PEFR drops.
  • When early warning symptoms occur, this is the time when clients who do choose to use their Peak Flow Meter, begin routine assessment for self-management (i.e. PEFR being below morning target or into the yellow zone).

Maintenance

The person with asthma should be encouraged to monitor their peak flow when:

  • they have a runny nose or feel a cold coming on
  • they don’t feel as well as usual
  • they know they have been exposed to a trigger
  • their treatment has been changed
Note: Most clients appear to prefer making management decisions based on symptoms rather than on their PEFR.  However there is a significant proportion (15–30%) of people who cannot detect changes in their lung function – these people must measure their PEFR to detect exacerbations.

How to clean a Peak Flow Meter

  • Peak Flow Meters are widely used for hospital and domiciliary purposes, thus cross-contamination is a concern. 
  • Fungal contamination can occur without a routine cleaning procedure.
  • Follow the manufacturer’s instructions. Clean every few weeks when in use. Most Peak Flow Meters can be cleaned without being taken apart.  Washing with soapy water, rinsing, shaking dry (or blow dry with a hairdryer) is the usual procedure.

How to use a Peak Flow Meter

  1. The steps below describe how to instruct a client in the use of a Peak Flow Meter. 
  2. Sit upright or stand up
  3. Slide the marker to the very end of the scale (mouthpiece end)
  4. Hold the meter level, ensuring that fingers do not obstruct the marker
  5. Take as deep a breath as possible (using diaphragmatic breathing)
  6. The meter is placed in the mouth and the lips closed tightly around the mouthpiece ensuring that the tongue is kept away from the mouthpiece.
  7. The client then blows out (huffs) as hard and as fast as they can (ensuring they do not use a cough as the manoeuvre)
  8. The reading is noted
  9. Steps 2–7 are repeated twice and the highest of the three readings is recorded in the peak flow diary.

Calculating predicted peak expiratory flow rate (PEFR)

 

 

A nomogram is utilised (deHamel nomogram preferred by the Asthma and Respiratory Foundation of NZ) to calculate predicted PEFR for adults and children.

Click here to view a full sized nomogram.

 

 

 

 

To calculate an adult's predicted PEFR:

  • Determine correct age, sex and height (in cms) of your client.
  • Find your client’s age on the horizontal axis of the nomogram.
  • Find your client’s height on the diagonal line NB different for men and women
  • Place a cross where these intersect
  • Follow across to vertical axis for predicted PEFR.

Note: The diagonal lines across the nomogram are there to show that as a person grows older, their PEFR will be lower if they remain at the same height. They are not to be used for calculating predicted PEFR.

To calculate  a child’s predicted PEFR:
  • Determine the height only (in cms) of your client
  • Find their height on the horizontal axis of the normogram
  • Using a ruler, follow the height of the client upwards toward the intersecting lines and note where the height of your client intersects on all 3 lines
  • Either draw a horizontal line or use your ruler to move to the left on the vertical axis.  Three lines will be drawn to give you 3 readings
  • The 3 readings give you a ‘range’ to expect your clients PEFR to fall between (minimum, mean, maximum)

Note: Values may vary up to 20% above and below any given value and still be ‘normal’.  The level of symptoms is an important factor to take into account when determining asthma severity.