Randomised Controlled Trials in Airways Disease. 2001/3
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The Cochrane Collaboration
Randomised controlled trials (RCTs) provide the least biased
evidence for a treatment's effectiveness, but there are often
too many trials for individuals to access and use. The Cochrane
Collaboration is an international organisation that was set up
to prepare and disseminate systematic reviews of RCTs in prevention
and treatment in many different areas of health care. Systematic
reviews provide the starting point for much evidenced-based practice
since they provide the best available estimate for the average
efficacy of a treatment. Not all patients behave as if they were
the average, and systematic reviews can also be used to test for
identifiable subgroups of patients who may respond more or less
than average, or identify specific combinations of therapy that
may be more effective. Each review produced within the Collaboration
synthesises all known RCTs on a given topic, and thus provides
an extremely valuable source of evidence on the validity and scope
of interventions in health care.
The Cochrane Airways Group
The Cochrane Airways Group has reviewers in 21 countries world-wide.
The authors of the reviews are professionals from medicine and
allied disciplines. They receive support from the editorial base
and supervision from an international editorial team of experts
in respiratory medicine.
Table 1:Summary of reviews by the
Cochrane Airways Group.
Most (67%) of the completed reviews are in asthma, with 46% of
all reviews in chronic asthma. The asthma reviews tend to include
a slightly larger number of trials than those in COPD although
on average, the COPD RCTs tend to include more patients. On average,
the reviews include data from over 750 patients and they examine
the effects of interventions on variety of outcome measures. In
addition to the 72 reviews already produced, there are 83 in progress.
Cochrane reviews are updated at 1-3 year intervals to take into
account publication of new primary trials. Protocols and reviews
are published on the Cochrane Library which is updated every three
months.
The Cochrane Airways Group web page, with summaries of reviews,
may be viewed at www.cochrane-airways.ac.uk.
The Cochrane Library is available from Update Software, Summertown
Pavilion, Middle Way, Oxford OX2 7LG or from www.update-software.com.
Airways disease reviews
Two examples of the wide range of topics covered in the Airways
Group reviews are illustrated here. The first shows how subgroup
analysis may identify the most effective type of intervention
while the second illustrates the value of reviewing an established
therapy. The charts, known as forest plots, show the size of the
effect for each study under review as well as the combined effect
of all studies (a meta-analysis). The estimate for the individual
study effect is illustrated by a square whose size reflects the
number of subjects in that study, together with a 95% confidence
interval <glossary.htm> (CI). The combined estimates are
shown as diamonds in which the 95% CI reflects variation within
and between the individual studies.
- Self-management education and regular practitioner review
for adults with asthma
Figure 1:Hospital admissions
in adults following self-management programmes
A key component of many asthma management guidelines is the
recommendation for patient education and regular medical review.
Asthma education programmes improve patient knowledge, but their
impact on health outcomes is less well established. This review
of 25 trials was conducted to test whether four types of such
programmes influence health outcomes. The 9 trials that showed
the effect on hospital admissions are presented in Figure 1
with odds ratios for each program type. Though there was a significant
overall reduction in hospital admissions in the intervention
group (mean estimate to the left of the line of unity), this
effect was confined to patients who received 'optimal' care
in whom the odds of admissions were reduced by a third (OR=0.35).
Here, 'Optimum' comprised self-monitoring, regular review and
a written self-management plan. Similar beneficial effects were
seen in emergency room visits, patients with days off work or
school, unscheduled hospital visits and the frequency of nocturnal
asthma. Lung function did not improve. Asthma care that includes
a written self-management plan, self-monitoring and regular
clinician review improves outcomes and reduces health care resource
use.
- Addition of intravenous aminophylline to b2-agonists
in adults with acute asthma
Figure 2:FEV1 in adults treated with
aminophylline compared to placebo
Aminophylline has been used extensively in acute asthma, but
its role is unclear especially with respect to any additional
benefit when added to b2-agonists. Fifteen trials were eligible
for inclusion in this review, although the quality of the studies
was only moderate. When added to b2-agonists, there was no statistically
significant effect of aminophylline on airflow measurements
at any time period, or on hospital admissions. Subgroup analysis
found no difference in mean airflow by use of corticosteroids,
or baseline airflow limitation. Aminophylline treated patients
reported significantly more palpitations, arrhythmias and vomiting.
Aminophylline offers no benefit when added to b2-agonists and
has substantially greater toxicity. It has no place in routine
management of acute asthma. The review cannot exclude the possibility
that some patients may benefit, but these do not form an identifiable
subgroup.
References
Self-management education and
regular practitioner review for adults with asthma, Gibson PG
Coughlan J Wilson AJ Abramson M Bauman A Hensley MJ Walters EH,
Cochrane Library, 1, 2001
Addition of intravenous aminophylline
to b2-agonists in adults with acute asthma, Belda J Parameswaran
K Rowe BH, Cochrane Library, 1, 2001
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