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2.5.1 TREATMENT TRIALS AND REvERSIBILITy TESTING
Treatment trials with bronchodilators or inhaled corticosteroids in patients with diagnostic
uncertainty should use one or more objective methods of assessment. Using spirometric values
or PEF as the prime outcome of interest is of limited value in patients with normal or nearnormal
pre-treatment lung function since there is little room for measurable improvement. One
study has shown that the sensitivity of a positive response to inhaled corticosteroid, defined as
a >15% improvement in PEF, is 24%. 79 A variety of tools to assess asthma control is available
to assess the response to a trial of treatment (see Table 8).
Using FEv or PEF as the primary method to assess reversibility or the response to treatment
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trials may be more helpful in patients with established airflow obstruction.
In adults, most clinicians would try a 6-8 week treatment trial of 200 mcg inhaled beclometasone
(or equivalent) twice daily. In patients with significant airflow obstruction there may be a degree
of inhaled corticosteroid resistance 87 and a treatment trial with oral prednisolone 30 mg daily
for two weeks is preferred.
A >400 ml improvement in FEv to either β agonists or corticosteroid treatment trials strongly
1 2
suggests underlying asthma. Smaller improvements in FEv are less discriminatory 1 71 and a
decision on continuation of treatment should be based on objective assessment of symptoms
using validated tools (see Table 8). Trials of treatment withdrawal may be helpful where there
is doubt.
C Assess fev (or Pef) and/or symptoms:
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before and after 400 mcg inhaled salbutamol in patients with diagnostic uncertainty
and airflow obstruction present at the time of assessment
in other patients, or if there is an incomplete response to inhaled salbutamol, after
either inhaled corticosteroids (200 mcg twice daily beclometasone equivalent for
6-8 weeks) or oral prednisolone (30 mg once daily for 14 days).
2.5.2 PEAK ExPIRATORy FLOW MONITORING
PEF should be recorded as the best of three forced expiratory blows from total lung capacity with
a maximum pause of two seconds before blowing. 88 The patient can be standing or sitting. Further
blows should be done if the largest two PEF are not within 40 l/min. 88
PEF is best used to provide an estimate of variability of airflow from multiple measurements
made over at least two weeks. Increased variability may be evident from twice daily readings.
More frequent readings will result in a better estimate 89 but the improved precision is likely to
be achieved at the expense of reduced patient compliance. 90
PEF variability is best calculated as the difference between the highest and lowest PEF expressed
as a percentage of either the mean or highest PEF. 91-93
The upper limit of the normal range for the amplitude % highest is around 20% using four or more
PEF readings per day 91,93,94 but may be lower using twice daily readings. 95 Epidemiological studies
have shown sensitivities of between 19 and 33% for identifying physician-diagnosed asthma. 92,96
PEF variability can be increased in patients with conditions commonly confused with asthma
71,73 so the specificity of abnormal PEF variability is likely to be less in clinical practice than it is
in population studies.
PEF records from frequent readings taken at work and away from work are useful when
considering a diagnosis of occupational asthma (see section 7.8). A computer generated analysis
of occupational records which provides an index of the work effect is available. 97
; Peak flow records should be interpreted with caution and with regard to the clinical
context. They are more useful in the monitoring of patients with established asthma than
in making the initial diagnosis.
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