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Education and debate
Does animal experimentation inform human healthcare? Observations from a
systematic review of international animal experiments on fluid resuscitation
Ian Roberts
a Cochrane Injuries Group, Public Health Intervention Research
Unit, London School of Hygiene and Tropical Medicine, London WC1B 3DP, b Accident
and Emergency Department, Leicester Royal Infirmary, University Hospitals of
Leicester NHS Trust, Leicester LE1 5WW
Correspondence to: I Roberts Ian.Roberts@lshtm.ac.uk
The Italian pathologist Pietro Croce criticised vivisection on scientific
grounds. He argued that results from animal experiments cannot be
applied to humans because of the biological differences between
animals and humans and because the results of animal experiments are
too dependent on the type of animal model used.1 Croce's
arguments were based on insights into zoology and pathophysiology. In
this paper, we make some methodological observations on animal experiments.
Our observations were made in the context of a systematic review of
all available randomised controlled trials of fluid resuscitation in
animal models of uncontrolled bleeding. We conducted this review
because we wanted to assess the scientific basis for fluid resuscitation.
A previous systematic review of randomised trials of fluid
resuscitation in bleeding trauma patients had provided no evidence
that fluid resuscitation improved outcome.2
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Summary points
New drugs and procedures are
usually tested in animals before conducting clinical trials Validity of animal experiments is
essential for human health care and fundamental to animal welfare A systematic review of animal
experiments on fluid resuscitation found that most studies were underpowered
and provided little information on possible bias Systematic reviews of animal
experiments allow a more objective appraisal of the evidence and reduce the
chance of false negatives results Systematic reviews across species
would help determine whether the results could be generalised to humans |
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Systematic
review of fluid resuscitation in uncontrolled haemorrhage |
We did a systematic review of randomised controlled trials of the timing or
volume of fluid administration in animal models of uncontrolled
haemorrhage. Details of the review methods, search strategy, and included
trials are available on bmj.com. The combined electronic search
strategies identified 3193 potentially eligible reports. Two
reviewers examined each of these records and 104 reports were
retrieved in full. From these, we identified 44 randomised controlled
trials meeting the inclusion criteria. The 44 trials included a
total of 2039 experimental animals (1772 rats, 251 pigs,
and 16 sheep). Mortality data were reported in 42 trials, of
which 31 were in rats, 10 in pigs, and one in sheep. In most of
the rat experiments uncontrolled bleeding was induced by resecting the
tail. Three trials in large animals (pigs and sheep) could not be
included in the meta-analysis because they did not include a no
fluid resuscitation group: one compared early and late resuscitation and
two compared different blood pressure resuscitation targets. Three
trials in rats could not be included in the meta-analysis: one
compared early and late fluid resuscitation, one compared different
blood pressure resuscitation targets, and one presented time to
death data only.
The pooled odds ratio (fixed effect) for death in large animals (pigs and
sheep) with fluid resuscitation was 0.63 (95% confidence interval
0.15 to 2.61) but there was statistical heterogeneity (
2 =16.84, df=7,
P=0.018). The pooled odds ratio (fixed effect) for death in small
animals with fluid resuscitation was 1.14 (0.65 to 2.02).
Again, there was substantial heterogeneity (2 =93.40, df=27,
P<0.0001). When the meta-analysis was stratified according to how
uncontrolled bleeding was induced, a large amount of the
heterogeneity was accounted for. Figure 1 shows the results
of meta-analysis of the 16 randomised controlled trials of fluid
resuscitation in rats in which bleeding was induced by resecting the
tail. The meta-analysis is stratified according to where the tail
was cut. Fluid resuscitation seems to be harmful (odds ratio=2.88, 95%
confidence interval 1.72 to 4.80) with less than 50% tail resection
(2 =5.57, df=7,
P=0.59) but beneficial (odds ratio=0.25, 0.15 to 0.42) with
greater than 50% tail resection (2 =6.14, df=7,
P=0.52).
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Are
the individual experiments valid? |
In clinical trials, systematic error can arise from problems with the study
design, especially if allocation of treatment is inadequately
concealed.18
Bias is avoided by ensuring strict randomisation with well concealed
treatment allocation. The extent to which inadequate concealment of
allocation might introduce bias in animal experiments is uncertain. However,
it is easy to imagine how bias could arise. For example, weaker
animals may be easier to catch than healthy animals, and this could
result in systematic differences between the intervention and
control groups on baseline prognostic factors. Of the 44 randomised controlled
trials meeting the inclusion criteria, only two described how the
animals were divided into treatment groups; both of these trials
used alternation.
Random error in clinical trials is minimised by increasing the number of
randomised participants.19
However, animal researchers are encouraged to reduce the number of
experimental animals to a minimum. Indeed, the need to use the
minimum number of animals to obtain valid results is embodied in the
Animals (Scientific Procedures) Act 1986 and European
legislation.20
As a result, some animal experiments are underpowered and provide
little reliable information. All of the animal experiments in our
systematic review were small (fig 2). The average number
of animals per trial was 46 (2039/44), and the largest trial
included only 207 animals (rats). None of the trials would have
been large enough to detect reliably a 10% absolute difference
(halving) in the risk of death between the intervention and
comparison groups. Moreover, many of the trials included several
different fluid resuscitation groups, which we combined for our
analyses. The average number of experimental animals per treatment
group was only 13 (160 groups). If, as was the case in
most trials, the aim was to compare the effects of different fluid
resuscitation regimens, the studies had little power.
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Has
all the evidence been assessed? |
Although each individual animal experiment provides little reliable
information on the effectiveness of fluid resuscitation, each contributes
to the total body of evidence. Any inferences should be based on all
the evidence.21
A 1996 narrative review of fluid resuscitation in animal experiments
included only nine of the 24 trials (38%) that were available at
that time.22
Systematic reviews and meta-analyses of animal experiments are uncommon.
About 1 in 1000 Medline records pertaining to human research
is tagged as a meta-analysis compared with 1 in 10 000 records
pertaining to animal research. In his book The Principles of
Humane Experimental Technique, William Russell proposed the principle
of reduction
that is, the use of methods to "reduce
the number of animals needed to obtain information of a given amount
and precision."23
Meta-analyses of the results of previous animal experiments would
increase the precision of estimates of treatment effects and
therefore reduce the number of animals needed in future experiments.
Publication bias may be as potent a threat to validity in systematic reviews
of animal experiments as it is in systematic reviews of clinical
trials. We contacted the authors of included trials to ask about
unpublished studies but none were identified. However, it would be
surprising if there were no unpublished trials meeting our inclusion
criteria. Prospective registration of animal experiments at
inception may help to avoid the problem of publication bias.24 In
the United Kingdom, the Animals (Scientific Procedures) Act 1986 regulates
"any experimental or other scientific procedure applied to a
protected animal which may have the effect of causing that animal
pain, suffering, distress, or lasting harm." Researchers must
have a project licence from the Home Office before conducting any
animal research, and the licence application describes the experimental
protocol. These data could be used for prospective registration of
all animal experiments.
Systematic reviews of animal models could, like ours, include a range of animal
species and models. If the results were consistent across species
and models this would indicate that they might also apply in humans.
Since the primary aim of animal experimentation is to inform human
experimentation, this would be valuable information.
We found substantial statistical heterogeneity in our meta-analysis, making
it impossible to interpret the odds ratios. Investigation of
heterogeneity is essential and can increase the scientific and
clinical relevance of their results. In our meta-analysis, stratification
according to how uncontrolled bleeding was induced accounted for a
large amount of the heterogeneity, but these results need to be
interpreted with caution. Meta-analytic subgroup analyses are akin
to subgroup analyses within trials and are prone to bias. Although
we specified in our protocol that the analyses would be stratified
according to the animal model used, we did not specify that we would
stratify according to where the tail was cut. Nevertheless, the
meta-analysis provides an insight into model dependency that could
be taken into account in future animal experiments and when considering
whether the results can be generalised to humans.
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Implications
for human health |
Animal experiments can inform human health care only if their results are
valid and can be generalised. However, little information is
available on the methodological determinants of bias in animal experiments,
and in our example the sample sizes were too small to obtain precise
estimates of the effects of the interventions. Systematic reviews of
animal experiments would help to ensure that animal experiments do
not set out to answer questions that have already been answered,
reduce bias and increase precision, and provide reassurance about
whether the results can be generalised. Prospective registration of
animal experiments would help to avoid publication bias. In a recent
editorial, Smith promoted the three Rs of animal research first
suggested by William Russell: replacement, reduction, and
refinement.25
On methodological grounds, animal experimentation would better
contribute to human health care if we promoted registration,
randomisation, and systematic reviews.
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Acknowledgments |
We thank Sir Iain Chalmers for his comments on
the manuscript and the authors of the included trials who responded to our
requests for further information.
Contributors: IR and PE proposed the study. IR drafted the protocol that was
revised following comments from all authors. IR and SH examined the electronic
search results for reports of possibly relevant randomised controlled trials.
IR, PE, and SH applied the selection criteria independently to the trial
reports. IR and IK extracted information from the included trials. IK contacted
authors for further information and IK and IR conducted the analyses. IR
drafted the paper that was revised on the basis of comments from IK, PE, SH. IR
will act as guarantor.
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Footnotes |
Funding: None.
Competing interests: None declared.
The methods of the
systematic review and details of included trials appear on bmj.com
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References |
|
1. |
Croce P. Vivisection or science? An investigation into
testing drugs and safeguarding health. London: Zed Books, 1999. |
|
2. |
Roberts I, Evans A, Bunn F, Kwan I, Crowhurst E.
Normalising the blood pressure in bleeding trauma patients may be harmful. Lancet
2001; 357: 385-387 |
|
3. |
Bilynskyj MC, Errington ML, Velasco IT, Silva R. Effect of
hypertonic sodium chloride (7.5%) on uncontrolled hemorrhage in rats and its
interaction with different anesthetic procedures. Circulatory Shock
1992; 36: 68-73 |
|
4. |
Gross D, Landau EH, Klin B, Krausz MM. Quantitative
measurement of bleeding following hypertonic saline therapy in `uncontrolled'
hemorrhagic shock. J Trauma 1989; 29: 79-83 |
|
5. |
Krausz MM, Kablan M, Rabinovici R, Klin B, Sherman Y,
Gross D. Effect of injured vessel size on bleeding following hypertonic
saline infusion in uncontrolled hemorrhagic shock in anesthetised rats. Circulatory
Shock 1991; 35: 9-13 |
|
6. |
Krausz MM, Horn Y, Gross D. The combined effect of small
volume hypertonic saline and normal saline solutions in uncontrolled
hemorrhagic shock. Surg Gynecol Obstet 1992; 174: 363-368 |
|
7. |
Krausz MM, Landau EH, Klin B, Gross D. Hypertonic saline
treatment of uncontrolled hemorrhagic shock at different periods from
bleeding. Arch Surg 1992; 127: 93-96 |
|
8. |
Krausz MM, Bar-Ziv M, Rabinovici R, Gross D. "Scoop
and run" or stabilize hemorrhagic shock with normal saline or
small-volume hypertonic saline? J Trauma 1992; 33: 6-10 |
|
9. |
Rabinovici R, Gross D, Krausz MM. Infusion of small volume
of 7.5 per cent sodium chloride in 6.0 per cent dextran 70 for
the treatment of uncontrolled hemorrhagic shock. Surg Gynecol Obstet
1989; 169: 137-142 |
|
10. |
Talmor D, Merkind V, Artru AA, Shapiro O, Geva D, Roytblat
L, et al. Treatment to support blood pressure increases bleeding and/or
decreases survival in a rat model of closed head trauma combined with
uncontrolled hemorrhage. Anesth Analg 1999; 89: 950-956 |
|
11. |
Capone AC, Safar P, Stezoski W, Tisherman S, Peitzman AB.
Improved outcome with fluid restriction in treatment of uncontrolled
hemorrhagic shock. J Am Coll Surg 1995; 180: 49-56 |
|
12. |
Capone AC, Safar P, Stezoski SW, Peitzman A, Tisherman S.
Uncontrolled hemorrhagic shock outcome model in rats. Resuscitation
1995; 29: 143-152 |
|
13. |
Greene SP, Soucy DM, Song WC, Barber AE, Hagedorn FN,
Illner HP, et al. Early isotonic saline resuscitation from uncontrolled
hemorrhage in rats. Surgery 1998; 124: 568-574 |
|
14. |
Kim S, Stezoski SW, Safar P, Capone A, Tisherman S.
Hypothermia and minimal fluid resuscitation increases survival after
uncontrolled hemorrhagic shock in rats. J Trauma 1997; 42: 213-222 |
|
15. |
Sindlinger JF, Soucy DM, Greene SP, Barber AE, Illner H,
Shires GT. The effects of isotonic saline volume resuscitation in
uncontrolled hemorrhage. Surg Gynecol Obstet 1993; 177: 545-550 |
|
16. |
Soucy DM, Rudé, Hsia WC, Hagedorn FN, Illner H, Shires GT.
The effects of varying fluid volume and rate of resuscitation during
uncontrolled hemorrhage. J Trauma 1999; 46: 209-214 |
|
17. |
Soucy DM, Sindlinger JF, Greene SP, Barber AE, Illner HP,
Shires GT. Isotonic saline resuscitation in uncontrolled hemorrhage under various
anesthetic conditions. Ann Surg 1995; 222: 89-93 |
|
18. |
Schulz KF, Chalmers I, Hayes RJ, Altman DG. Empirical
evidence of bias. Dimensions of methodological quality associated with
estimates of treatment effects in controlled trials. JAMA 1995; 273:
408-412 |
|
19. |
Peto R, Collins R, Gray R. Large-scale randomised
evidence: large simple trials and overviews of trials. J Clin Epidemiol
1995; 48: 23-40 |
|
20. |
Guidance on the operation of the Animals (Scientific
Procedures) Act 1986. www.homeoffice.gov.uk/animact/aspag1.htm
(accessed August 2001). |
|
21. |
Chalmers I. Using systematic reviews and registers of
on-going trials for scientific and ethical trial design, monitoring, and
reporting. In: Egger M, Davey Smith G, Altman DG, eds. Systematic reviews
in healthcare: meta-analyses in context. London: BMJ Books, 2001:429-443.
|
|
22. |
Dries DJ. Hypotensive resuscitation. Shock 1996; 6:
311-316 |
|
23. |
Russell WMS, Burch RL. The principles of humane
experimental technique. London: Methuen, 1959. |
|
24. |
Horton R, Smith R. Time to register randomised trials. Lancet
1999; 354: 1138-1139 |
|
25. |
Smith R. Animal research: the need for a middle ground. BMJ
2001; 322: 248-249 |
(Accepted 14 August 2001)
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