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Does animal experimentation inform human healthcare? Observations from a systematic review of international animal experiments on fluid resuscitation

BMJ 2002; 324 doi: (Published 23 February 2002) Cite this as: BMJ 2002;324:474

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Fluid Resuscitation in Animals

The debate concerning whether or not we can 'learn from animals' is
far more subtle than the responses to this article [and others] suggest.
It depends on the problem and on which species, moreover the lessons of
comparative medicine are most useful when the 'model' has sufficient
similarities to suggest its relevance and enough differences to make it
informative. Blanket assertions that we can not learn from animals are
naive but equally, many generalisations about humans fall when we start to
look at ethnic differences and, increasingly,genetic predisposition.

In the speciific instance of this review of fluid resuscitation after
haemorrhage there are some exceedingly odd features. First, it confounds
therapy aimed to increase circulating volume [eg isotonic sodium-based
solutions] with hypertonic sodium solutions whose benefit in shock
probably rests on pharmacological properties other than their minuscule
and transient impact on circulating volume. Second it contains no species
routinely treated for haemorrhage by veterinary surgeons, probably because
it cites no veterinary journals; treatment of haemorrhage in sheep is
scarcely routine and in pigs it is exceedingly unusual. There is a
substantial literature on the use of hypertonic saline and, of course
various other fluids, to treat haemorrhage in other animals, notably cats,
dogs and horses. Finally it makes the usual assumption that research in
animals is synonymous with studies in laboratory animals, mainly rats. The
transected tail model in rats is a particularly misleading one since the
clean transection of the major artery is likely to predispose to re-
bleeding problems once arterial pressure starts to rise. This may be
relevant to some forms of clinical haemorrhage but I doubt if it is a good
model for most. I would also doubt that studies with controls denied any
fluid resuscitation after haemorrhage were any longer scientifically or
ethically justifiable: the use of positive controls is appropriate.

The greatest value of relevant research in appropriate species of
animals is that comparative medicine is essential to remind us that humans
are not unique; they are animals of a particularly interesting type. Only
then can we start to think sensibly about questions such as how much salt
mammals need and how much is detrimental, why some animals are more
suceptible to extremely high blood pressure yet resistant to its damaging
effects, and to capitalise on the fact that spontaneous tumours in
animals, equivalent to those in humans, may be a most useful intermediate
step in evaluating new treatments, between tumours induced in experimental
rodents and those experienced by human patients. Awareness of such
opportunities is all too low in the medical community but it will form the
subject of an all day symposium at the Royal Society of Medicine
[Comparative Medicine Section] later this year.

Competing interests: No competing interests

06 March 2002
Alastair R. Michell
Professor of Comparative Medicine
Univ of London, St Bartholomew's Hospital Med. School., Dept Pharmacology, Charterhouse Sq, EC1M6BQ