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Cochrane Injuries Group Albumin Reviewers Cochrane Injuries Group,
Department of Epidemiology and Public Health, Institute of Child
Health, London WC1N 1EH
Ian.Roberts{at}ich.ucl.ac.uk
Objective: To quantify effect on mortality of
administering human albumin or plasma protein fraction during
management of critically ill patients.
In patients with acute and chronic illness serum albumin
concentration is inversely related to risk of death. A systematic
review of cohort studies meeting specified criteria estimated that for
each 2.5 g/l decrement in serum albumin concentration the risk of
death increases by between 24% and 56%.1 The association
persists after adjustment for other known risk factors and pre-existing
illness, and some commentators have suggested the possibility of the
albumin molecule having a direct protective effect.1
Partly as a result of the association between serum albumin and
mortality, human albumin solutions are now used in the management of a
diverse range of medical and surgical problems. Licensed indications
for human albumin solution are the emergency treatment of shock and
other conditions in which restoration of blood volume is urgent, the
acute management of burns, and clinical situations associated with
hypoproteinaemia.2
Compared with other colloidal solutions and with crystalloid solutions,
human albumin solutions are expensive.3 Volume for volume,
human albumin solution is twice as expensive as hydroxyethyl starch and
over 30 times more expensive than crystalloid solutions such as sodium
chloride or Ringer's lactate. Because of the high cost and limited
availability of human albumin, it is imperative that its use should be
restricted to the indications for which it has been shown to be
effective. To quantify the effect on mortality of human albumin
solution in the management of critically ill patients with hypovolaemia
from injury or surgery, burns, and hypoproteinaemia, we conducted a
systematic review of randomised controlled trials.
Identification of trials
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Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
Design: Systematic review of randomised controlled
trials comparing administration of albumin or plasma protein fraction
with no administration or with administration of crystalloid solution
in critically ill patients with hypovolaemia, burns, or
hypoalbuminaemia.
Subjects: 30 randomised controlled trials including
1419 randomised patients.
Main outcome measure: Mortality from all causes at
end of follow up for each trial.
Results: For each patient category the risk of death
in the albumin treated group was higher than in the comparison group.
For hypovolaemia the relative risk of death after albumin
administration was 1.46 (95% confidence interval 0.97 to 2.22), for
burns the relative risk was 2.40 (1.11 to 5.19), and for
hypoalbuminaemia it was 1.69 (1.07 to 2.67). Pooled relative risk of
death with albumin administration was 1.68 (1.26 to 2.23). Pooled
difference in the risk of death with albumin was 6% (95% confidence
interval 3% to 9%) with a fixed effects model. These data suggest
that for every 17 critically ill patients treated with albumin there is
one additional death.
Conclusions: There is no evidence that albumin
administration reduces mortality in critically ill patients with
hypovolaemia, burns, or hypoalbuminaemia and a strong suggestion that
it may increase mortality. These data suggest that use of human albumin
in critically ill patients should be urgently reviewed and that it
should not be used outside the context of rigorously conducted,
randomised controlled trials.
Key messages
![]()
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
![]()
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
Our aim was to identify all relevant randomised controlled trials
that were available for review by March 1998. A randomised controlled
trial was defined as a trial in which the subjects followed were
assigned prospectively to one of two (or more) interventions by random
allocation or some quasi-random method of allocation. This definition
was agreed at an international meeting held in Oxford in November 1992 in association with the official opening of the UK Cochrane Centre. We
sought to identify all randomised controlled trials of administration
of human albumin or plasma protein fraction (supplemental albumin or
plasma protein fraction compared with no albumin or plasma protein
fraction or with a crystalloid solution) in critically ill patients
with hypovolaemia from trauma or surgery, with burns, or with
hypoalbuminaemia. Studies that compared different levels of albumin
supplementation were also included.
Outcome measures and data extraction
The outcome measure was mortality from all causes at the end of
the follow up period scheduled for each trial. For all trials we
collected data on the type of participants, details about the
interventions, the quality of concealment of allocation, and mortality
at the end of follow up. We rated quality of allocation concealment
using the method proposed by Schulz et al.5 We sought
mortality data in simple categorical form, and we did not extract data
on time to death. If a report did not include the numbers of deaths in
each group, we sought these data from the authors. Two reviewers
independently extracted the data, and any disagreements were resolved
by discussion.
Data analysis and statistical methods
We used the Mantel-Haenszel method to calculate relative risks,
risk differences, and 95% confidence intervals for death for each
trial on an intention to treat basis using RevMan (Review Manager)
statistical software. When there are no events in one group the
software adds 0.5 to each cell of the 2×2 table. We tested
heterogeneity between trials using
2 tests, with
P
0.05 indicating significant heterogeneity. As long as statistical
heterogeneity did not exist, we used a fixed effects model to calculate
summary relative risks and 95% confidence intervals.
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Results |
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We identified a total of 32 randomised controlled trials that met the study's inclusion criteria.7-38 The table shows details of these trials. Mortality data were available either from the published report or on contact with the authors in 30 of these trials. The two trials for which mortality data could not be obtained included a total of 42 randomised patients, comprising 3% of the total number of randomised patients in all trials meeting our inclusion criteria. 22 31 One of the trials was an unpublished trial registered in the Medical Editors' Trial Amnesty, and we obtained further details, including data on mortality, directly from the trialist. In six trials there were no deaths in either the intervention or comparison groups. 8 12 23 25 26 35
The trial by Lucas et al was reported in five publications. 21 39-42 An early report gave the mortality data for 52 randomised patients, 27 allocated to receive albumin and 25 allocated to receive no albumin.21 Subsequent publications indicated that recruitment to the trial continued until 94 patients were randomised. Mortality data for all the 94 patients were not published, nor were they available on contact with the author. Consequently, we present the outcome data for the 52 patients.
Of the 24 trials in which one or more deaths occurred in either the intervention or control groups, 13 included a method of allocation concealment that would be expected to reduce the risk of foreknowledge of treatment allocation (pharmacy controlled randomisation or serially numbered sealed opaque envelopes). In seven trials this was unclear, and in four trials concealment was inadequate (table).
In each of the patient categories the risk of death in the albumin
treated group was higher than in the comparison group (fig 1). For
hypovolaemia the relative risk of death after albumin administration
was 1.46 (95% confidence interval 0.97 to 2.22), for burns the
relative risk was 2.40 (1.11 to 5.19), and for hypoalbuminaemia the it
was 1.69 (1.07 to 2.67). There was no significant heterogeneity either
between or within the groups of trials, or overall
(
2=15.32, df=23, P>0.2). The pooled relative risk of
death with albumin administration was 1.68 (1.26 to
2.23).
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There was no significant heterogeneity in the risk difference for
mortality (
2=36.69, df=29, P>0.1). The pooled
difference in the risk of death with albumin was 6% (95% confidence
interval 3% to 9%).
Figure 2 shows a funnel plot for the 24 trials in which deaths
occurred. There was no clear evidence of asymmetry, and the regression
approach to funnel plot asymmetry yielded an intercept of
0.39 and
P=0.33, indicating no statistical evidence of selection
bias.
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We repeated the analyses for the 13 trials with deaths in which
allocation concealment was
adequate.
13 15 16 19 20 24 27-29 32 34 37 38
For hypovolaemia the relative risk of death with albumin administration
was 1.39 (0.80 to 2.40), for burns the relative risk was 2.47 (0.69 to
8.79), and for hypoalbuminaemia it was 1.71 (0.92 to 3.18). There was
no substantial heterogeneity between the trials in the various
categories (
2=4.42, df=12, P>0.2), and the pooled
relative risk of death with albumin administration was 1.61 (1.09 to
2.38). Thus, restricting the analyses to the adequately concealed
trials had almost no effect on the relative risks in each group or
overall.
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Discussion |
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We found no evidence that albumin reduced mortality and a strong suggestion that it might increase the risk of death in patients with hypovolaemia, burns, or hypoproteinaemia. Overall, the risk of death in patients treated with albumin was 6% (95% confidence interval 3% to 9%) higher than in patients not given albumin.
Limitations of study
Mortality was selected as the outcome measure in this systematic
review for several reasons. In the context of critical illness, death
or survival is a clinically relevant outcome that is of immediate
importance to patients, and data on death are reported in nearly all
studies. Furthermore, one might expect that mortality data would be
less prone to measurement error or biased reporting than would data on
pathophysiological outcomes. The use of a pathophysiological end point
as a surrogate for an adverse outcome assumes a direct relationship
between the two, an assumption that may sometimes be inappropriate.
Finally, when trials collect data on a number of physiological end
points, there is the potential for bias due to the selective
publication of end points showing striking treatment effects. Because
we obtained mortality data for all but two of the included trials, the
likelihood of bias due to selective publication of trial outcomes is
minimal. We examined mortality from all causes because the attribution
of cause of death in critically ill patients, many of whom may have
multiorgan failure, can be problematic and may be prone to bias. Length
of follow up was not specified in many of the trials, but when these
data were available, follow up was for the first week or until hospital
discharge.
Implications of results
To what extent are the results of this review of 30 relatively
small randomised trials of albumin administration generalisable to
clinical practice? We believe that this is a matter for judgment by the
responsible clinician faced with an individual patient.43
However, the advantage of an overview such as ours is that, since it
includes many studies, the results are based on a wide range of
patients. Because the results were consistent across the studies, they
might reasonably be taken to apply to this wide variety of
patients.43 Moreover, the evidence that we have brought
together is, as far as we can ensure, the totality of the available
randomised evidence for the use of albumin in hypovolaemia, burns, and
hypoalbuminaemia, the indications for which albumin is currently
licensed.
Conclusions
Because this review was based on relatively small trials in which
there were only a small number of deaths the results must be
interpreted with caution. Nevertheless, we believe that a reasonable
conclusion from these results is that the use of human albumin in the
management of critically ill patients should be reviewed. A strong
argument could be made that human albumin should not be used outside
the context of a properly concealed and otherwise rigorously conducted
randomised controlled trial with mortality as the end point. Until such
data become available, there is also a case for a review of the
licensed indications for albumin use.
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Acknowledgments |
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This review will also be published in the Cochrane Library, where it will be regularly updated to take account of new data and comments on this version.
Contributors (listed alphabetically): Phil Alderson (UK Cochrane Centre) searched The Cochrane Controlled Trials Register for relevant trials, extracted the data from the trials, and commented on the paper. Frances Bunn (Institute of Child Health) searched the Cochrane Injuries Group Specialised Register for relevant trials, obtained copies of relevant papers, wrote to authors for further information on allocation concealment, and commented on the paper. Carol Lefebvre (UK Cochrane Centre) designed the search strategies for The Cochrane Controlled Trials Register and Embase, and searched these two databases for relevant trials. Leah Li (Institute of Child Health) did the funnel plot and the regression test of funnel plot asymmetry. Alain Li Wan Po (Centre for Evidence-Based Pharmacotherapy, University of Nottingham) helped to write the paper. Ian Roberts (Institute of Child Health) designed the protocol, extracted data from the trials, contacted authors for unpublished data, and wrote the paper. Gillian Schierhout proposed the study hypothesis and conducted preliminary searches of Medline, Embase, and BIDS Index to Scientific and Technical Proceedings.
We thank the Intensive Care National Audit and Research Centre in London for help with identifying trials for this review and for their extensive hand searching. We thank A J Woittiez for providing unpublished trial data from the trial that was registered in the Medical Editors' Trial Amnesty. We thank Elizabeth Bryant, information officer at Centeon, and Martin O'Fobve, at Bio Products, for searching their databases for albumin trials. We thank Anne Greenough for re-examining individual patient records in order to provide data on mortality. We thank Iain Chalmers, Jos Kleijnen, Richard Peto, Dave Signorini, and David Yates for their comments on the manuscript.
Funding: The infrastructure of the Cochrane Injuries Group is supported by the NHS Research and Development Programme.
Conflict of interest: None.
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References |
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(Accepted 1 July 1998)
Starling's principle is often represented as the leakage
of fluids from the arterial end of capillaries, where the hydrostatic
pressure is greater than the oncotic pressure (derived from the plasma
proteins), and the reabsorption of fluid into the venous end, where the
oncotic pressure exceeds the hydrostatic pressure. A small excess of
fluid in the interstitial space
when filtration from the capillaries
is greater than reabsorption
is dealt with by lymphatic drainage from
the interstitial space. The rationale for giving albumin solutions
rather than crystalloid solutions in cases of hypovolaemic shock is
that fluid reabsorption from the interstitial space is enhanced, and
fluid therefore remains in the vascular system for
longer.

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But in recent years the assumed reabsorption of fluid at the venous end
of capillaries has been challenged. There is now good evidence to show
that, except in the gut and the renal circulation, there is no
sustained reabsorption of fluid at the venous end of capillaries.
Instead, there is a small constant level of filtration from the
capillaries, restrained by the osmotic pressure of the plasma proteins.
In some rare circumstances
for example, in hypovolaemic shock
there
is a transient reabsorption of fluid, but this lasts for only a few
minutes and it amounts to an "internal transfusion" of about
500 ml of fluid over 15 minutes.
The production of life threatening pulmonary oedema begins when the loss of protein and fluid from the blood vessels exceeds the volume of fluid that can be drained from the interstitial space by the lymphatics. In some disease states or when tissue is damaged, as in severe burns, the capillary walls become very much more permeable under the influence of direct cellular damage and from inflammatory mediators. The filtration of fluids, together with proteins, out into the interstitial space is greatly increased and cannot be matched by lymphatic drainage. The filtration rate may be further increased by a fall in the hydrostatic pressure in the interstitial space as a result of tissue damage, so that even more fluid is sucked out of the capillaries.
Conventionally, colloids such as albumin are administered to these patients in an attempt to maintain their intravascular volume, but because of the increased permeability of the vessels, the albumin solution becomes much less effective in maintaining plasma volume than in healthy individuals who have normal vessel permeability. Thus the rationale for administering albumin solutions becomes much less clear. In disease states such as the nephrotic syndrome, for example, there is new evidence to show that protein is lost not only from the renal circulation owing to greater permeability of the renal vessels, but also from the rest of the systemic circulation. This being the case, it is difficult to see how the administration of albumin could ever replace the deficit without causing further problems.
Abi Berger
Science editor, BMJ
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