BMJ 2003;326:185 ( 25 January )
Papers
Non-invasive positive pressure ventilation to treat respiratory failure
resulting from exacerbations of chronic obstructive pulmonary disease:
Cochrane systematic review and meta-analysis
Josephine V Lightowler, specialist registrar in respiratory medicine a,
Jadwiga A Wedzicha, professor of respiratory medicine b, Mark W Elliott,
consultant respiratory and general physician a, Felix S F Ram, research
fellow in respiratory medicine c.
a Department of Respiratory Medicine, St James's University Hospital, Leeds
LS9 7TF, b Academic Respiratory Medicine, St Bartholomew's School and the
Royal London School of Medicine and Dentistry, London EC1A 7BE, c Department
of Physiological Medicine, St George's Hospital Medical School, University
of London, London SW17 0RE
Correspondence to: Felix S F Ram [log in to unmask] <mailto:[log in to unmask]>
Abstract
Top <http://bmj.com/cgi/content/full/326/7382/#Top>
Abstract
Introduction <http://bmj.com/cgi/content/full/326/7382/#SEC1>
Methods <http://bmj.com/cgi/content/full/326/7382/#SEC2>
Results <http://bmj.com/cgi/content/full/326/7382/#SEC3>
Discussion <http://bmj.com/cgi/content/full/326/7382/#SEC4>
References <http://bmj.com/cgi/content/full/326/7382/#References>
Objectives: To determine the effectiveness of non-invasive positive pressure
ventilation (NPPV) in the management of respiratory failure secondary to
acute exacerbation of chronic obstructive pulmonary disease.
Design: Systematic review of randomised controlled trials that compared NPPV
and usual medical care with usual medical care alone in patients admitted to
hospital with respiratory failure resulting from an exacerbation of chronic
obstructive pulmonary disease and with PaCO2 >6 kPa.
Results: The eight studies included in the review showed that, compared with
usual care alone, NPPV as an adjunct to usual care was associated with a
lower mortality (relative risk 0.41 (95% confidence interval 0.26 to 0.64)),
a lower need for intubation (relative risk 0.42 (0.31 to 0.59)), lower
likelihood of treatment failure (relative risk 0.51 (0.38 to 0.67)), and
greater improvements at 1 hour in pH (weighted mean difference 0.03 (0.02 to
0.04)), PaCO2 (weighted mean difference -0.40 kPa (-0.78 to -0.03)), and
respiratory rate (weighted mean difference -3.08 breaths per minute (-4.26
to -1.89)). NPPV resulted in fewer complications associated with treatment
(relative risk 0.32 (0.18 to 0.56)) and shorter duration of stay in hospital
(weighted mean difference -3.24 days (-4.42 to -2.06)).
Conclusions: NPPV should be the first line intervention in addition to usual
medical care to manage respiratory failure secondary to an acute
exacerbation of chronic obstructive pulmonary disease in all suitable
patients. NPPV should be tried early in the course of respiratory failure
and before severe acidosis, to reduce mortality, avoid endotracheal
intubation, and decrease treatment failure.
What is already known on this topic
Prospective studies, especially the larger studies, have shown that
non-invasive positive pressure ventilation (NPPV) reduces the need for
intubation, improves survival, and reduces complications in patients with
respiratory failure resulting from exacerbation of chronic obstructive
pulmonary disease (COPD)
A previous meta-analysis showed NPPV to be an effective intervention,
including for acute exacerbations of COPD, but some studies in this
meta-analysis contained mixed groups of patients and were not of good
quality
What this study adds
Evidence from good quality, randomised controlled trials shows that NPPV is
an effective treatment for acute exacerbations of COPD
NPPV should be considered early in the course of respiratory failure and
before severe acidosis ensues, to avoid the need for endotracheal intubation
and reduce mortality in patients with COPD
Introduction
Top <http://bmj.com/cgi/content/full/326/7382/#Top>
Abstract <http://bmj.com/cgi/content/full/326/7382/#Abstract>
Introduction
Methods <http://bmj.com/cgi/content/full/326/7382/#SEC2>
Results <http://bmj.com/cgi/content/full/326/7382/#SEC3>
Discussion <http://bmj.com/cgi/content/full/326/7382/#SEC4>
References <http://bmj.com/cgi/content/full/326/7382/#References>
Patients with chronic obstructive pulmonary disease (COPD) are prone to
respiratory failure, often resulting in admission to hospital. Between a
fifth and a third of patients admitted with hypercapnic respiratory failure
secondary to acute exacerbation of COPD will die in hospital, despite
mechanical ventilation. 1-5 <http://bmj.com/cgi/content/full/326/7382/#B1>
Conventional treatment aims to ensure adequate continuous oxygenation and to
treat the cause of the exacerbation---usually achieved through treatment
with bronchodilators, corticosteroids, antibiotics, and controlled oxygen.
Traditionally, patients who do not respond to conventional treatment are
given invasive ventilation. The procedure of tracheal intubation and
assisted ventilation is associated with high morbidity, and it may be
difficult to wean these patients from ventilation. 6
<http://bmj.com/cgi/content/full/326/7382/#B6> 7
<http://bmj.com/cgi/content/full/326/7382/#B7> Furthermore, although it is
common practice to give intubation and mechanical ventilation, complications
can result from the intubation process (damage to local tissue) and during
the course of ventilation (pneumonia and sinusitis associated with
ventilators), prolonging stay in intensive care. 8-11
<http://bmj.com/cgi/content/full/326/7382/#B8>
Non-invasive positive pressure ventilation (NPPV) is an alternative
treatment for patients admitted to hospital with hypercapnic respiratory
failure secondary to acute exacerbation of COPD. 12
<http://bmj.com/cgi/content/full/326/7382/#B12> In NPPV the patient
receives air or a mixture of air and oxygen from a flow generator through a
full facial or nasal mask, and thus ventilation is enhanced by the unloading
of fatigued ventilatory muscles. Over the last decade NPPV has been
increasingly used as an adjunct treatment in the management of acute
exacerbations of COPD, supported by a number of case series and randomised
controlled trials. 2-4 <http://bmj.com/cgi/content/full/326/7382/#B2> 13-15
<http://bmj.com/cgi/content/full/326/7382/#B13> However, NPPV is not
successful in all cases of acute or chronic respiratory failure in patients
with COPD. 16 <http://bmj.com/cgi/content/full/326/7382/#B16> Failure rates
of between 9% and 50% have been reported. 17
<http://bmj.com/cgi/content/full/326/7382/#B17> 18
<http://bmj.com/cgi/content/full/326/7382/#B18> We conducted a systematic
review of the literature to determine the effectiveness of NPPV in patients
with respiratory failure resulting from an acute exacerbation of COPD.
Methods
Top <http://bmj.com/cgi/content/full/326/7382/#Top>
Abstract <http://bmj.com/cgi/content/full/326/7382/#Abstract>
Introduction <http://bmj.com/cgi/content/full/326/7382/#SEC1>
Methods
Results <http://bmj.com/cgi/content/full/326/7382/#SEC3>
Discussion <http://bmj.com/cgi/content/full/326/7382/#SEC4>
References <http://bmj.com/cgi/content/full/326/7382/#References>
Inclusion and exclusion criteria
Interventions ---Trials were considered for inclusion if the intervention
was NPPV, applied through a nasal or face mask, in addition to usual medical
care. Usual medical care could include supplemental oxygen, antibiotics,
bronchodilators, steroids, respiratory stimulants, and other suitable
interventions (for example, diuretics and methylxanthines) but could not
include treatment with NPPV.
Types of trials and participants ---We considered randomised controlled
clinical trials of any duration. We excluded trials where patients had a
primary diagnosis of pneumonia, weaning trials, trials whose patients had
other underlying pathologies, and trials where continuous positive airway
pressure or endotracheal intubation preceded recruitment. All patients
entered into the trials had to have an acute exacerbation of COPD and a
baseline PaCO2 at admission of >6 kPa.
Identification and selection of trials
We identified trials by searching the Cochrane Airways Group trials
database, as well as other relevant databases (for example, the Science
Citation Index, PubMed, the UK National Research Register), up to and
including June 2002. No language restrictions were applied in the retrieval
of citations.
We assessed the methodological quality of the trials by using the Cochrane
approach to assessment of allocation concealment: all trials were scored as
"adequate concealment" (grade A), "uncertain" (grade B), or "clearly
inadequate concealment" (grade C).
<http://bmj.com/cgi/content/full/326/7382/185/F1>
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Fig 1. Process of inclusion of studies and useable information
Data abstraction and analysis
We used standard forms to abstract all data. Whenever possible we contacted
an author of each trial included in the study to verify the accuracy of the
abstracted data and to obtain further information. Review Manager version
4.1 (Cochrane Collaboration software) was used to combine data from the
trials. Weighted mean differences (and 95% confidence intervals) were used
to pool data in continuous variables. For dichotomous variables, relative
risks (and 95% confidence intervals) were calculated. The number needed to
treat (and 95% confidence interval) was calculated in an internet based
program called Visual Rx ( www.nntonline.net <http://www.nntonline.net> ).
We used the DerSimonian and Laird method to test for heterogeneity among
pooled estimates; results were considered significant at the P<0.05 level.
Where heterogeneity was present, the fixed effects model was used to report
results; otherwise the random effects model was used. If there were
sufficient numbers of studies for a particular outcome, and it was
heterogeneous, we investigated it on the basis of study quality, duration of
NPPV, type of NPPV, and type of mask used to administer NPPV. We also
planned funnel plots to detect publication bias.
An intention to treat analysis was used in all studies except one, which we
excluded from sensitivity analyses. 16
<http://bmj.com/cgi/content/full/326/7382/#B16> We considered it important
that studies use an intention to treat analysis, as there is anecdotal
evidence that some patients drop out or withdraw after randomisation and at
the initiation of treatment, because of the discomfort of NPPV.
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Fig 2. Risk of treatment failure (mortality, need for intubation, and
intolerance) in seven studies of non-invasive positive pressure ventilation
(NPPV) as an adjunct to usual medical care
Results
Top <http://bmj.com/cgi/content/full/326/7382/#Top>
Abstract <http://bmj.com/cgi/content/full/326/7382/#Abstract>
Introduction <http://bmj.com/cgi/content/full/326/7382/#SEC1>
Methods <http://bmj.com/cgi/content/full/326/7382/#SEC2>
Results
Discussion <http://bmj.com/cgi/content/full/326/7382/#SEC4>
References <http://bmj.com/cgi/content/full/326/7382/#References>
Figure 1 <http://bmj.com/cgi/content/full/326/7382/#F1> summarises the
search for trials and reasons for exclusion, as well as the numbers of the
eight trials included in the review with usable information on particular
outcomes. 2 <http://bmj.com/cgi/content/full/326/7382/#B2> 3
<http://bmj.com/cgi/content/full/326/7382/#B3> 14-17
<http://bmj.com/cgi/content/full/326/7382/#B14> 19
<http://bmj.com/cgi/content/full/326/7382/#B19> 20
<http://bmj.com/cgi/content/full/326/7382/#B20>
Methodological quality of included studies
According to the Cochrane system for grading concealment of allocation,
seven studies were grade A 2 <http://bmj.com/cgi/content/full/326/7382/#B2>
3 <http://bmj.com/cgi/content/full/326/7382/#B3> 14
<http://bmj.com/cgi/content/full/326/7382/#B14> 15
<http://bmj.com/cgi/content/full/326/7382/#B15> 17
<http://bmj.com/cgi/content/full/326/7382/#B17> 19
<http://bmj.com/cgi/content/full/326/7382/#B19> 20
<http://bmj.com/cgi/content/full/326/7382/#B20> and one was grade B. 16
<http://bmj.com/cgi/content/full/326/7382/#B16> The seven grade A studies
all used the same method for concealing treatment allocation: a randomly
generated sequence of treatment allocation, contained in sealed envelopes.
As all studies were of good methodological quality, it is unlikely that the
quality of the studies would influence heterogeneity tests or the overall
results.
Efficacy variables
We defined treatment failure as the combination of mortality, need for
intubation, and intolerance to the allocated treatment. Data from seven of
the studies showed that NPPV resulted in a significantly lower risk of
treatment failure (relative risk 0.51), compared with usual medical care,
with a number needed to treat for NPPV to have a benefit of five (figure 2
<http://bmj.com/cgi/content/full/326/7382/#F2> , table 1
<http://bmj.com/cgi/content/full/326/7382/#T1> ). 2
<http://bmj.com/cgi/content/full/326/7382/#B2> 3
<http://bmj.com/cgi/content/full/326/7382/#B3> 14-16
<http://bmj.com/cgi/content/full/326/7382/#B14> 19
<http://bmj.com/cgi/content/full/326/7382/#B19> 20
<http://bmj.com/cgi/content/full/326/7382/#B20> NPPV significantly reduced
the risk of mortality (relative risk 0.41), with a number needed to treat of
eight (figure 3 <http://bmj.com/cgi/content/full/326/7382/#F3> , table 1
<http://bmj.com/cgi/content/full/326/7382/#T1> ). The risk of endotracheal
intubation was more than halved with NPPV, and for every five patients
treated with NPPV one patient would avoid intubation (figure 4
<http://bmj.com/cgi/content/full/326/7382/#F4> , table 1
<http://bmj.com/cgi/content/full/326/7382/#T1> ). NPPV also reduced
complications of treatment and length of stay in hospital (tables 1
<http://bmj.com/cgi/content/full/326/7382/#T1> and 2
<http://bmj.com/cgi/content/full/326/7382/#T2> ). NPPV significantly
improved pH, PaCO2, and respiratory rate within one hour of initiation
(figure 5 <http://bmj.com/cgi/content/full/326/7382/#F5> , table 2
<http://bmj.com/cgi/content/full/326/7382/#T2> ).
View this table:
[in this window] <http://bmj.com/cgi/content/full/326/7382/185/T1>
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Table 1. Effects of non-invasive positive pressure ventilation as an
adjunct to usual medical care, compared with usual care alone: overall
results of the review for dichotomous outcome measures
View this table:
[in this window] <http://bmj.com/cgi/content/full/326/7382/185/T2>
[in a new window] <http://bmj.com/cgi/content-nw/full/326/7382/185/T2>
Table 2. Effects of non-invasive positive pressure ventilation as an
adjunct to usual medical care, compared with usual care alone: overall
results of the review for continuous outcome measures
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Fig 3. Mortality in seven studies of non-invasive positive pressure
ventilation (NPPV) as an adjunct to usual medical care
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Fig 4. Risk of endotracheal intubation in eight trials of non-invasive
positive pressure ventilation (NPPV) as an adjunct to usual medical care
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Fig 5. Respiratory rate (breaths per minute) in five trials of
non-invasive positive pressure ventilation (NPPV) as an adjunct to usual
medical care
Discussion
Top <http://bmj.com/cgi/content/full/326/7382/#Top>
Abstract <http://bmj.com/cgi/content/full/326/7382/#Abstract>
Introduction <http://bmj.com/cgi/content/full/326/7382/#SEC1>
Methods <http://bmj.com/cgi/content/full/326/7382/#SEC2>
Results <http://bmj.com/cgi/content/full/326/7382/#SEC3>
Discussion
References <http://bmj.com/cgi/content/full/326/7382/#References>
This systematic review shows a clear benefit of NPPV as an adjunct treatment
to usual medical care in the management of patients admitted to hospital
with respiratory failure secondary to an acute exacerbation of COPD. NPPV
with usual medical care significantly reduces mortality, endotracheal
intubation, treatment failure, complications, length of hospital stay, and
blood gas tensions.
Although NPPV reduces the need for intubation, in some patients NPPV will
fail, and it is essential that a decision be made with the patient on what
should be done in this eventuality. Patients for whom NPPV eventually fails,
despite initial tolerance and effectiveness of the treatment, need to be
distinguished from patients who cannot tolerate it at all. An uncontrolled
study of these "late failures" suggests a poor outcome regardless of whether
the patient is intubated or continues to receive NPPV. 21
<http://bmj.com/cgi/content/full/326/7382/#B21>
NPPV reduced the length of stay in hospital by more than three days, and
length of stay in hospital did not differ between intensive care units and
medical wards. This finding has important resource implications, given the
costs of and pressure on intensive care in the United Kingdom. However, if
NPPV is to be used outside the intensive care unit (for example, specialist
respiratory wards), it is important that staff are fully trained in the
treatment and that monitoring facilities are in place. It is also important
that there is 24 hour cover by appropriately qualified members of the
medical team.
The number of complications associated with treatment was significantly
lower with NPPV, with an overall risk reduction of 68%. Almost all of the
excess complications occurred because of intubation, suggesting that
avoidance of intubation is the major benefit of NPPV.
Acidosis is an important prognostic factor for survival after respiratory
failure in COPD, and thus early correction of acidosis is an essential goal
of treatment. 5 <http://bmj.com/cgi/content/full/326/7382/#B5> This review
has shown that NPPV significantly improves pH, PaCO2, and respiratory rate
within the first hour. The improvement in pH associated with the fall in
PaCO2 indicates an improvement in respiratory failure. A previous study of
patients with respiratory failure secondary to exacerbations of COPD showed
reductions in respiratory rate and transdiaphragmatic activity, with
increases in tidal volume and minute ventilation during NPPV. 22
<http://bmj.com/cgi/content/full/326/7382/#B22> Thus, NPPV not only
improves gas exchange but also facilitates respiratory muscle rest, reducing
the work of respiratory muscles in respiratory failure, and hence allowing
the respiratory muscles to recover and conventional treatments to work.
Limitations of the review
Publication bias is possible, in that by missing unpublished or negative
trials we may have overestimated the beneficial effect of NPPV. However, our
comprehensive, systematic search strategy of the literature would minimise
any biases. We are confident that most research in this field was
identified. We further minimised bias by using two independent reviewers,
with clearly defined written inclusion and exclusion criteria for the
selection of studies. The small number of studies meant that a funnel plot
analysis for the detection of publication bias was meaningless. Also, the
usefulness of funnel plots for this purpose is limited by their moderately
low sensitivity.
In none of the studies included in this review was treatment blinded,
because of the practical difficulties of "sham" ventilation. However, in
three of the studies investigators making clinical management decisions were
unaware of which treatment arm a patient was in until after ventilation
began. 2 <http://bmj.com/cgi/content/full/326/7382/#B2> 3
<http://bmj.com/cgi/content/full/326/7382/#B3> 19
<http://bmj.com/cgi/content/full/326/7382/#B19> In two studies the decision
to intubate was not made by the study investigators. 14
<http://bmj.com/cgi/content/full/326/7382/#B14> 17
<http://bmj.com/cgi/content/full/326/7382/#B17> In another study predefined
criteria were used to determine when to intubate patients in cases of
failure of NPPV. 15 <http://bmj.com/cgi/content/full/326/7382/#B15> In one
study there was no indication as to the protocol for intubation and
treatment failure. 16 <http://bmj.com/cgi/content/full/326/7382/#B16>
Therefore, we cannot be certain that bias in patient management did not
influence the study outcomes.
The data at one hour would not necessarily include all patients who were
started on treatment, as treatment may have failed (for example, intubation
was necessary or the patient died) before the one hour time point.
Therefore, we may have underestimated the difference between the two groups
in changes in pH, arterial blood gas tensions, and respiratory rate.
Conclusions
Despite the limitations, this review has shown convincing evidence from good
quality, randomised controlled trials that NPPV is an effective adjunct to
usual medical care in the management of respiratory failure secondary to
acute exacerbations of COPD. Trialling NPPV should be considered early in
the course of respiratory failure and before severe acidosis ensues, to
avoid endotracheal intubation and treatment failure and to reduce mortality.
Further studies are needed to evaluate the appropriate selection of patients
and to find the best level and schedule of ventilation.
Acknowledgments
We thank the members of the Cochrane Airways Group based at St George's
Hospital Medical School, London. We also thank authors of studies who
responded to requests for further data. 2
<http://bmj.com/cgi/content/full/326/7382/#B2> 15
<http://bmj.com/cgi/content/full/326/7382/#B15> 17
<http://bmj.com/cgi/content/full/326/7382/#B17> 19
<http://bmj.com/cgi/content/full/326/7382/#B19> 20
<http://bmj.com/cgi/content/full/326/7382/#B20>
Contributors: FSFR and JAW revised the original review protocol that was
published in 1996 in the Cochrane Library. FSFR and JVL searched for trials
and abstracted and analysed the data from the included trials. FSFR prepared
the manuscript, with input from JVL, JAW, and MWE. FSFR revised the
manuscript for resubmission and is the guarantor for the paper.
Footnotes
Funding: FSFR is funded by the Netherlands Asthma Foundation. JVL was funded
by a British Lung Foundation project grant.
Competing interests: JAW has received educational grant support from
Respironics, one of the manufacturers of nasal ventilators. MWE has received
an honorarium for lecturing from Respironics, has been lent ventilators for
studies from ResMed and Breas, and has had a contribution from ResMed
towards the salary of a research nurse.
A table showing details of the eight trials included in the systematic
review is shown on bmj.com
References
Top <http://bmj.com/cgi/content/full/326/7382/#Top>
Abstract <http://bmj.com/cgi/content/full/326/7382/#Abstract>
Introduction <http://bmj.com/cgi/content/full/326/7382/#SEC1>
Methods <http://bmj.com/cgi/content/full/326/7382/#SEC2>
Results <http://bmj.com/cgi/content/full/326/7382/#SEC3>
Discussion <http://bmj.com/cgi/content/full/326/7382/#SEC4>
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(Accepted 16 October 2002)
Edward E. Rylander, M.D.
Diplomat American Board of Family Practice
Diplomat American Board of Palliative Medicine
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