Peak Expiratory Flow
The peak flow meter is a home-use device for people with asthma and is not
adequate for routine asthma management by doctors.16
<LE IV>
It is used to detect and measure any variation from a person’s predetermined
best peak flow and so indicate the presence and degree of airflow obstruction as
an aid to self-management.17
What is Peak Expiratory Flow (PEF)?
This is a measure of maximum expiratory flow occurring just after the start
of a forced expiration from the point of maximum inspiration (total lung
capacity). PEF is used to provide a measure of airway calibre or airflow.
However, it is dependent not only on airway calibre, but on lung elastic recoil,
patient effort and patient cooperation.
What are the limitations of PEF?
PEF has a significantly larger degree of variability than the gold standard
for the measurement of airway calibre – FEV1.18
<LE IV> There is also a fairly wide normal range
and PEF measurements do not necessarily parallel those of FEV1. It is
important to consider PEF data in conjunction with the patient’s asthma
symptoms. The readings are effort dependent and it is important that the user
appreciates the need for maximal effort.
You should be aware that there can be a great degree of variability from
meter to meter, even within the same brand. If peak flow is performed routinely,
the same meter should be used.
When is PEF useful?
Many patients will not comply with a request to continuously monitor their
PEF, but it can be useful in the management of some patients.
Short-term monitoring is useful following a recent diagnosis of asthma, a
change in asthma treatment, or discharge from hospital. PEF readings may be
recorded for 2-3 weeks when the patient is asymptomatic to:
- determine their personal best reading (for reference during acute
exacerbations);
- examine their peak flow variability – a pre-bronchodilator day-to-day
PEF variability greater than 15% suggests that the maintenance treatment is
suboptimal and that medical review is advisable;
- assist with asthma management in patients who are poor perceivers of
their asthma severity; and
- allow parents to assess the severity of their child’s asthma.
PEF can be very useful in diagnosing occupational asthma, as you may not be
able to demonstrate variability of airflow in the surgery.
PEF may be useful in some adults and children with acute asthma. If
the personal best PEF is considered to be 100% lung function for that patient,
the PEF during acute asthma may provide a useful measure in addition to the
patient’s clinical symptoms. This is particularly useful in patients who are
poor perceivers of their asthma symptoms (see below).
A written Asthma Action Plan for your patients may be symptom based
and/or PEF based. However, peak flow measurements are not reliable for
children under 6-7 years. During acute attacks older children may not
produce reliable measurements. In young people more attention should be given to
asthma symptoms. Older patients may also have difficulty producing reliable
measurements and often deliver very low peak flow.
Long-term regular PEF monitoring should be considered in persistent poor
perceivers.19
<LE II>
