Peak flow reading

Peak expiratory flow rate readings, often abbreviated to peak flow readings, form the cornerstone of the management of many chronic and acute respiratory disorders, especially asthma. It is an inexpensive test to undertake and one which the nurse can teach patients to further their ability to manage their own respiratory disease more effectively (Myatt, 2015).

Nurses may identify the need to undertake peak expiratory flow reading in any patient who presents with breathlessness. It is particularly useful as an objective measure of disease severity and the success of treatment in patients with known respiratory diseases, eg asthma and chronic obstructive pulmonary disease (So et al, 2015).

It may be inappropriate to try to attempt gaining a peak flow reading in a patient who presents extremely breathless. The National Institute for Health and Care Excellence (NICE, 2023) counsel against obtaining objective measures when they will interfere or delay the treatment of an individual who is in obvious respiratory distress.

The peak expiratory flow is a measure of the flow, that is rate not volume, of air that a patient can forcefully exhale after having taken a full and deep breath (Myatt, 2015). Peak expiratory flow is measured in litres per minute and maximum flow occurs

The equipment required in order to undertake a peak expiratory flow reading is a flow gauge device. Mini-Wright peak flow meters are most commonly used, and many people living with asthma own these and should be encouraged to bring them to appointments so that direct comparisons using the same device may be undertaken (Carvalho et al, 2021). Some meters are digital and enable the patient or nurse to take a measure of the forced expiratory volume in one second (FEV1) as well as the peak expiratory flow. This procedure article focuses mainly on the peak expiratory flow, as it is the more common of the two measurements undertaken.

In the clinical setting, the nurse will also need a disposable mouthpiece for the meter unless they are using the patient’s own device, which should be either under 1 year old (Hill, 2019) or recently calibrated to ensure accuracy.

The nurse should

The nurse should ensure they gain consent before undertaking peak expiratory flow readings by explaining to the patient the nature of the procedure as well as why it is being undertaken. Nurses should observe hand hygiene procedures prior to taking a peak expiratory flow reading to aid in the prevention of the spread of infection.

The patient should be rested and comfortable and the nurse should attend to any privacy and dignity issues associated with the procedure. The nurse should observe the patient for any signs that they may be breathless or otherwise unwell. Key visual indicators of breathlessness include:

• laboured breathing and inability to speak
• a blue/grey colouring to the skin and/or around the lips (depending on skin tone)
• noisy breathing
• audible wheezing

The nurse should take note of these additional signs and symptoms which may validate, or call into question, the reading from the peak flow meter.

Hill (2019) identified the following contraindications for undertaking a peak expiratory flow reading:

• patients who are severely breathless
• patients who cannot inspire properly
• patients who are physically unable to undertake the procedure or lack capacity
• patients recovering from recent thoracic, abdominal or cranial surgery

The greatest risk with the peak expiratory flow is the inability of the patient to be able to coordinate undertaking it. Therefore, providing either no reading or a spurious reading, which may not be useful in informing their management.

As with all mechanised physiological measures, nurses should also ensure they use their existing patient assessment skills to validate what the device is telling them. They should familiarise themselves with the use of the type of peak flow meter and any normal values charts that are in use where they work.

Nursing and Midwifery Council: standards of proficiency for registered nurses

Part 2: Procedures for the planning, provision and management of person-centred nursing care

8. Use evidence-based, best practice approaches for meeting needs for respiratory care and support, accurately assessing the person’s capacity for independence and self-care and initiating appropriate interventions

8.1 observe and assess the need for intervention and respond to restlessness, agitation and breathlessness using appropriate interventions

8.3 take and interpret peak flow and oximetry measurements

Carvalho F, Breen E-C, Bullock Z et al. Observations. In: Lister S, Hofland J, Grafton H and Wilson C (eds). The Royal Marsden Manual of Clinical Nursing Procedures. 10^th edn. Chichester: Wiley Blackwell; 2021;719-800

Dobra R, Equi A. How to use peak expiratory flow rate. Arch Dis Child Educ Pract Ed. 2018;103(3):158-162. https://doi.org/10.1136/archdischild-2017-313178 

Dobson C, Simpson T. Clinical measurement In: Delves-Yates C (ed). Essentials of nursing practice. 10th edn. London: Sage; 2022

Hill B. Measuring peak expiratory flow in adults with asthma. B J Nurs.  2019;28(14):924-926

Myatt R. Measuring peak expiratory flow rate: what the nurse needs to know.  Nursing Standard. 2015;31(20):40-44. https://doi.org/10.7748/ns.2017.e9783

National Institute for Health and Care Excellence (NICE).  Asthma.  2023. https://cks.nice.org.uk/topics/asthma/ (accessed 30 January 2024)

So JY, Lastra AC, Zhao H et al. Daily Peak Expiratory Flow Rate and Disease Instability in Chronic Obstructive Pulmonary Disease.  Chronic Obstr Pulm Dis. 2015;3(1):398-405. https://doi.org/10.15326/jcopdf.3.1.2015.0142