Why you have to infuse 3 times the fluid loss with crystalloids?

[scilearner]

Hello everyone

I still don't understand crystalloids

1) Lets say someone lost 100 ml of blood due to accident. If you are giving crystalloid therapy, why do you have to infuse 3 times the amount.

What I think is when you give crystalloids IV, they go into extravascular and intravascular compartments also, not just stay in plasma . But my question is let's say I give 100 ml of crystalloid to this person, then wouldn't the patients body try to retain this 100 ml in plasma because now the hydrostatic pressures have changed due to the blood loss, shouldn't the body compensate and try to keep this in plasma. In that case why should you infuse 3 times the amount. In normal circumstances I can understand this fluid getting distributed in all the compartments.

2) Why exactly do crytalloid not stay in plasma when you infuse them.

*Do they move out due to normal hydrostatic presurre
*Or do they move out due to tonicity. More salt so water is sucked out from intracellular into plasma. Shouldn't this expand plasma volume.
* When they move out do they distribute in ICF and ECF like in normal water composition in the body, meaning 2/3 ICF and 1/3 ECF.

Thanks a lot

[Chris90]

Im not sure about this but crystalloid do not contain high Mr proteins that stays in the intravascular compartment like colloids and blood plasma do , so giving crystalloid will dilute the blood lowering its osmotic pressure which will cause fluid to move into the extravascular space . this may be the reason why crystalloids are usually given 3 time the volume of blood loss . only intravascular volume directly contribute to blood pressure which must be maintained to prevent hemodynamic shock to happen .