This article, the second in a six-part series on respiratory procedures, discusses the measurement of peak expirato…
VOL: 103, ISSUE: 33, PAGE NO: 26
Phil Jevon, PGCE, BSc, RN, is resuscitation officer/clinical skills lead, Manor Hospital, Walsall and honorary clinical lecturer, University of Birmingham Medical School
This article, the second in a six-part series on respiratory procedures, discusses the measurement of peak expiratory flow (PEF), which can be defined as the maximum flow achieved on forced expiration from a position of full inspiration (Miller et al, 2005).
It is a simple method of measuring the degree of airway obstruction, and helps to detect and monitor moderate and severe respiratory disease. It is mainly used in diagnosing and monitoring asthma, particularly when assessing the severity of an asthma attack and monitoring response to therapy (Booker, 2007).
Why measure PEF?
PEF reflects a range of physiological characteristics of the lungs, airways, and neuromusculature (Ruffin, 2004). These include lung elastic recoil, large airway caliber, lung volume, effort, and neuromuscular integrity. The reflection of airway calibre makes the PEF meter suitable for measuring variation in PEF over time to provide support for:
- Confirming a diagnosis of asthma;
- Diagnosing occupational asthma;
- Monitoring variation in PEF over time;
- Identifying asthma control.
- Self-management of asthma by patients (Ruffin, 2004).
Indications for recording PEF
PEF readings are usually undertaken four times a day, both before and after the administration of bronchodilators (out of hospital this is usually twice a day). The results aid in diagnosing asthma and are crucial to deciding treatment (Miller et al, 2005). They also indicate how well the patient is responding to treatment and help to measure the recovery from an asthma attack (Miller et al, 2005).
The Wright PEF flow meter was introduced in 1959 and has been superseded by a range of relatively cheap and reasonably reliable PEF meters.
The old Wright PEF scale has been shown to be inaccurate in the low and high-reading ranges (Booker, 2007). EU standard EN 13826 PEF meters introduced in 2004 are more accurate (see www.peakflow.com) and should be used. The scale on the EN-13826 compliant Wright PEF meters depicts blue numbers on a yellow background.
The normal range for PEF readings are influenced by age, sex and height. They are usually higher in men than women and peak in the 30-40 years age group (Partridge, 1997). PEF varies throughout the day; it is often higher in the evenings than in the mornings (Jevon and Ewens, 2007).
Nunn and Gregg’s (1989) reference values for normal PEF flow readings are widely accepted, and have been adapted for use with the new EU standard meters (Fig 1).
When assessing asthma attack severity:
- PEF reading <50% of the reference value indicates severe asthma;
- PEF reading <33% of the reference value indicates life-threatening asthma.
If the patient’s own best values are known these should be used instead of predicted values.
- Wash and dry hands.
- Assemble the necessary equipment: PEF meter and a clean mouthpiece (Fig 2), and the patient’s observation chart/PEF diary.
- Explain the procedure to the patient and obtain informed consent.
- Set the pointer on the peak flow meter scale to zero (Fig 3).
- Ask the patient to adopt a comfortable position, either sitting or standing. Ensure that the same position is used for each recording to allow accurate comparison.
- Ask the patient to take a deep breath in through the mouth to full inspiration.
- Holding the PEF meter horizontally, ask the patient to place their lips and teeth around the mouthpiece, ensuring a good seal.
- Ask the patient to breathe out as hard and as fast as possible into the PEF meter (Fig 4).
- Note the reading on the PEF meter (Fig 5) and then return the pointer to zero.
- Ask the patient to repeat the procedure twice; after each time note the reading on the meter scale and return the pointer to zero.
- Document the highest of the three readings following local protocols (Fig 6).
- Inform the nurse in charge if the PEF reading is abnormal.
- Dispose of the mouthpiece (Jevon and Ewens, 2007).
Unreliable PEF readings
Potential errors resulting in unreliable PEF readings include (Booker, 2007):
- Failing to take a deep breath in;
- Incorrect exhaling technique, for example ‘coughing’ or ‘spitting’ technique;
- Blocking the mouthpiece with the tongue or teeth;
- Lack of an effective seal between the mouthpiece and the patient’s mouth.
Patients who have never done PEF readings will improve their values over the next few days as their technique improves. This is in part why three recordings are taken. It can be difficult to obtain accurate PEF readings in children and older people.
This procedure should be undertaken only after approved training, supervised practice and competency assessment, and carried out in accordance with local policies and protocols.
This article has been double-blind peer-reviewed