fluid management

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					Fluid Management

Some general principles which I think are important to stress:
* Hypervolaemia is not good for you. It does not occur in nature and compensatory mechanisms are
poor. It disrupts the endothelial glycocalyx, encouraging interstitial oedema.
* Elective patients are normovolaemic. They are only dehydrated, which is essentially an intracellular
water deficit unless is is allowed to become very severe.
* Colloids stay in the intravascular space until they are metabolised, when the water redistributes
throughout the extracellular space. Balanced salt solutions also only redistribute to the extracellular
fluid. As such, neither make much sense as treatments for dehydration.
* Evaporative losses during surgery are much less than traditionally taught.
*Treating blood loss with crystalloids results in 3 times more oedema than volume effect.
* There is nothing normal about normal saline. It is acidic and has too much sodium and *way* too
much chloride.
* Intra-operative urine output is a poor gauge of volume status

My approach is to limit my fluid therapy to first address the intracellular deficit. I aim to give about 5
ml/kg of dextrose/saline (Hartmann's/Ringer's for diabetics) over the first half hour or so, and
thereafter limit maintenance fluids to about 2 ml/kg/hr to cover evaporative losses. Hypotension
due to anaesthetic drugs is managed with sympathomimetics if necessary (usually small doses of
metaraminol or ephedrine in my practice) rather than buckets of fluid. Any significant blood loss is
replaced by synthetic colloids and/or blood products.

I will typically finish a major colorectal case with the second litre of crystalloid hung, but not finished.
Post-operatively I aim for maintenance fluids at about 1 ml/kg/hr.

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