What exactly is the difference between crystalloids and colloids?

[scilearner]

Hello guys,

I'm bit confused here, hope you guys can help me out.

1. Crystalloid- Ok they contain water soluble molecules. So eg is Saline (NaCl). Now book says if I infuse crystalloids then only 1/3 of of my infusion would remain in the intravascular compartment. Now my question is why is this? If I add lot of salt to intravascular compartment eg by giving saline, shouldn't I suck more water from extracellular compartment, why am I losing 2/3 instead.

What I think: Is it because Saline contains like 0.9% Saline. So this is actually more like you are adding more water to the intravascular compartment rather than salts, so some water may leak out. Does this mean if I give 5% Saline solution more water would stay in the intravascular compartment than 0/9%.

2. Colloid- Ok why are they called plasma expanders

What I think: Ok they are big molecules, increasing colloid osmotic pressure and sucking water from extracellular environment into blood vessels. But crystalloids should also then be considered plasma expanders because add the end, they also increase the fluid even if it is not as great as colloids.

Thanks a lot in advance.

 

[John Cuthber]

Not my field but...

How much "space" is there in the cells?

How much in the extracellular compartment?

 

"But crystalloids should also then be considered plasma expanders because add the end, they also increase the fluid even if it is not as great as colloids."

Yes, but what happens next?