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Gill Schierhout Department of
Epidemiology and Public Health, Institute of Child Health, University
College London Medical School, London WC1N 1EH
Correspondence to: Dr Schierhout
Objective: To determine the effect on mortality of
resuscitation with colloid solutions compared with resuscitation with
crystalloids.
Fluid resuscitation for hypovolaemia is integral to the acute
medical management of critically ill patients. Although recent studies
have suggested that the timing of volume replacement deserves careful
consideration,1 when it comes to selecting the
resuscitation fluid doctors are faced with a range of options. At the
most basic level the choice is between a colloid or crystalloid
solution. Colloids are widely used, having been recommended in a number of resuscitation guidelines and intensive care management
algorithms.
2 3
The American hospital consortium
guidelines recommend that colloids are used in haemorrhagic shock until
blood products become available and in non-haemorrhagic shock after an
initial infusion with crystalloid. A 1995 survey of American academic
health centres, however, found that the use of colloids far exceeded
these recommendations.4 Surveys of burn care in the United
States5 and Australia6 found that the use of
colloids for resuscitation varied without a set pattern. The choice of
fluid has considerable cost implications: volume replacement with
colloids is considerably more expensive than with
crystalloids.
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Abstract
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Abstract
References
Design: Systematic review of randomised controlled
trials of resuscitation with colloids compared with crystalloids for
volume replacement of critically ill patients; analysis stratified according to patient type and quality of allocation concealment.
Subjects: 37 randomised controlled trials were
eligible, of which 26 unconfounded trials compared colloids with
crystalloids (n=1622). (The 10 trials that compared colloid in
hypertonic crystalloid with isotonic crystalloid (n=1422) and one trial
that compared colloid in isotonic crystalloid with hypertonic
crystalloid (n=38) are described in the longer version on our website
www.bmj.com).
Main outcome measures: Mortality from all
causes at end of follow up for each trial.
Results: Resuscitation with colloids was
associated with an increased absolute risk of mortality of 4% (95%
confidence interval 0% to 8%), or four extra deaths for every 100 patients resuscitated. The summary effect measure shifted towards
increased mortality with colloids when only trials with adequate
concealment of allocation were included. There was no evidence for
differences in effect among patients with different types of injury
that required fluid resuscitation.
Conclusions: This systematic review does not
support the continued use of colloids for volume replacement in
critically ill patients.
Key messages
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Introduction

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A longer version of this article is available on our website
Clinical studies have shown that colloids and crystalloids have different effects on a range of important physiological parameters. Because of these differences, mortality from all causes is arguably the most clinically relevant outcome measure in randomised trials comparing the two fluid types. Although there have been meta-analyses of mortality in randomised trials comparing colloids and crystalloids, 7 8 neither of these satisfies the criteria that have been proposed for systematic reviews9 and they predate most of the trials that have been conducted with synthetic colloids and hypertonic crystalloid solutions. The purpose of this review was to identify and synthesise all available unconfounded evidence of the effect on mortality in critically ill patients of colloids compared with crystalloids for volume replacement.
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Methods |
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Identification of trials
Our aim was to identify all relevant randomised controlled trials
available for review by June 1997. Relevant trials were those in which
critically ill patients (excluding neonates) who required fluid
resuscitation were assigned to colloid or crystalloid resuscitation
protocols on the basis of random or quasi-random allocation. If the
allocation procedure could not be fully ascertained from the published
report, the author was contacted for clarification.
Outcome measures and data extraction
The principal outcome measure was mortality from all causes
assessed at the end of the follow up period scheduled for each trial.
In trials among surgical patients we sought prospectively gathered
information on hospital stay and renal and pulmonary complications as
the death rate in these trials was likely to be low (for details, see
longer version on our website). For all trials, we extracted
information on the type of participants, type of colloid and
crystalloid used, duration of follow up, mortality at the end of follow
up, and quality of concealment of allocation. We rated quality of
concealment of allocation according the criteria proposed by
Schulz.10 We sought data in simple categorical form, and
we did not extract data on time to death. When a report did not include
mortality data at all, or when data were incomplete for all patients
initially randomised, we sought these data from the trialists.
Data analysis and statistical methods
Before analysing the results, we identified a number of hypotheses
concerning underlying differences in the studies that might require
separate analyses or explain heterogeneity in an overall analysis. As
efficacy of crystalloids and colloids for resuscitation is thought to
differ between different patient types, we stratified the analysis by
patients' injury
trauma, burns, surgery, and other conditions,
including septicaemia and vascular leak syndrome. Finally, as it has
been shown that studies with poor concealment of allocation tend to
overestimate the effectiveness of interventions,10 we
regarded the level of concealment of allocation as a possible source of
heterogeneity in study findings. We conducted an additional analysis
using only trials with allocation concealment that was known to be
adequate.
2 tests, with P
0.05 indicating significant
heterogeneity. When there was no significant heterogeneity we used a
fixed effects model to calculate summary relative risks and 95%
confidence intervals for dichotomous data. In the event of significant
heterogeneity that could obviously be related to type of injury or
allocation concealment, we stratified the analyses on that dimension.
As statistical tests of heterogeneity are known to lack power, we also
present graphical displays for the summary effect measures of
individual trials.
In order to test whether the results of the meta-analyses might have
been biased because of selective publication of randomised trials with
positive findings (publication bias), we used the regression approach
to assessing funnel plot asymmetry proposed by Egger et
al.11 Using simple unweighted linear regression, the
inverse of the variance of each study is regressed against the standard
normal deviate. The larger the deviation of the intercept of the
regression line from zero, the greater the asymmetry and the more
likely it is that the a meta-analysis will yield biased estimates of
effect. As suggested by Egger et al, we considered that P<0.1
indicated significant asymmetry.
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Results |
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We identified a total of 48 apparently randomised trials of fluid resuscitation in critically ill patients, of which 37 met the inclusion criteria. Reasons for exclusion of trials were the use of a crossover design (two trials); testing a resuscitation algorithm (three trials); and the intervention being used for maintaining serum albumin concentrations (three trials), for haemodilution (one trial), for fluid loading (one trial), and for reducing intracranial pressure (one trial).
The table gives key details of the 26 unconfounded trials that compared colloids with crystalloids (see longer version of article on our website for details of the 10 trials that compared colloid in hypertonic crystalloid with isotonic crystalloid and the one that compared colloid in isotonic crystalloid with hypertonic crystalloid). Nineteen of the 26 eligible trials reported mortality. For the other seven trials, we contacted the trialists to ask for any mortality data available for the 307 participants, but no additional information was forthcoming. Our analysis was therefore based on mortality data for 1315 participants from 19 trials. The figure shows that the summary relative risks were similar for all types of injury except surgery, for which the summary measure was imprecise because of small numbers of patients and a low overall mortality (4.7%).
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In four of the trials concealment of allocation was adequate. There was
no overall heterogeneity between trials (
2=11.67, df=16,
P=0.75). The pooled relative risk of death for all patient groups was
1.19 (95% confidence interval 0.98 to 1.45). The risk of death in the
patients given colloids was 24% and the risk of death in the patients
given crystalloids was 20%, giving an increase in absolute risk of
mortality for resuscitation with colloids of 4% (0% to 8%). The
pooled relative risk based only on trials with adequate allocation
concealment was 1.29 (0.94 to 1.77), with an increase in absolute risk
of mortality for resuscitation with colloids of 7% (
1% to 15%).
The regression approach to funnel plot asymmetry yielded an
intercept of 0.006 and P=0.308, indicating no statistical evidence for
publication bias.
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Discussion |
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This systematic review synthesised the evidence from randomised controlled trials comparing colloid and crystalloid fluid resuscitation across a wide variety of clinical conditions. There was no statistical evidence of heterogeneity in trial results. The pooled relative risks showed no advantage for resuscitation with colloids, and when we excluded trials with inadequate allocation concealment the pooled relative risk shifted to increased mortality for colloids compared with crystalloids (relative risk 1.29 (95% confidence interval 0.94 to 1.77)).
There was no statistical evidence that the effect measure for colloids compared with crystalloids was overestimated because of publication bias. Although the regression test of asymmetry has been shown to have predictive validity,12 the few trials in our meta-analysis (19 trials) may mean that detection of such biases would be difficult. Assuming that colloids were the "intervention," publication bias would have resulted in a pooled estimate that understated the extent to which colloids were associated with increased mortality.
Limitations of study
In common with all meta-analyses, our systematic review may have
included studies in which interventions and patient characteristics were sufficiently incomparable that the calculation of a summary effect
measure may be questioned. The resuscitation regimen differed between
trials, with some trials randomising participants to an initial
quantity of colloid or crystalloid and then proceeding with some form
of standard resuscitation for all participants, and other trials
resuscitating with the randomised fluid to predetermined end
points, either resuscitation end points or, in the case of trauma,
until corrective surgery. In addition, the type of colloid or
crystalloid, the concentration, and the protocol to determine the
quantity of fluid varied.
Other studies
Our results differ from those of Velanovich's meta-analysis of
mortality, which concluded that resuscitation with colloids had a
beneficial effect on mortality among non-trauma patients compared with
crystalloids.7 This conclusion was based on three studies
of a total of 96 non-trauma patients. Our meta-analysis, based on more
than twice the number of patients undergoing surgery (191), failed to
support this conclusion. For patients with burns, we also found no
evidence for a beneficial effect of colloids. The effect measure for
surgery was extremely imprecise, owing to the small number of patients
and a low event rate.
Conclusions
Resuscitation with colloid solutions was associated with an
absolute increase in the risk of mortality of 4% (95% confidence interval 0% to 8%), or four extra deaths for every 100 patients resuscitated. As colloids are not associated with improved survival and
are considerably more expensive than crystalloids, it is hard to see
how their continued use outside randomised controlled trials in
subsets of patients of particular concern can be
justified.
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Acknowledgments |
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We thank the Intensive Care National Audit and Research Network in London, for help with identifying trials for this review through their extensive hand searching activities.
Contributors: GS designed the protocol, undertook the literature searches, discussed core ideas about the study design and interpretation of results, and jointly wrote the paper. IR initiated the project, participated in all aspects of the research, and jointly wrote the paper. IR is guarantor for the paper.
Funding: This study was funded by the NHS R&D Programme: Mother and Child Health.
Conflict of interest: None.
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References |
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(Accepted 3 December 1997)
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