Isotonic dehydration. Help!

[Vani1925]

So I'm having a hard time understanding isotonic dehydration. So as far as I understand isotonic dehydration is when you lose water and electrolytes from the extracellular space (both intravascular and interstitial spaces). The part that confuses me is that there is no shift of fluid from the intracellular space to the extracellular space to try and balance everything out. I went and asked my instructor but to be honest it was like she was speaking a whole different language. I didn't understand anything at all whatsoever. I actually think she didn't understand what I really was asking. I do not understand why there would not be any shift in fluid from the ICF to the ECF. Isn't your body always aiming at homeostasis? Isn't that the whole purpose of osmosis, diffusion, and filtration? Why is it not happening in this case? This is what my book says:

"Dehydration may occur with just water loss or with water and electrolyte loss (isotonic dehydration). Isotonic dehydration is the most common type of fluid loss problem. Fluid is lost only from the extracellular fluid (EFC) space, including both the plasma and interstitial spaces. There is no shift of fluids between spaces, so the intracellular fluid (ICF) volume remains normal. Circulating blood volume is decreased (hypovolemia) and leads to inadequate tissue perfusion.

All along they have been teaching us that if the concentrations between fluid spaces are not in balance fluid will shift to equalize the concentration. So now I'm all confused because in this instance is not happening. I though that if you have a decreased blood volume, which you would have in this case, fluid would move from the inside of your cells, making the shrink, so that your blood volume increases. I'm I wrong? Now I feel like I'm crazy -_- Or is it because since you are losing both water and electrolytes at the same time it is still technically in balance but in smaller amounts, so your body doesn't think that there needs to be a fluid shift?? HELP please!

[203bravo, MSN, APRN]

Or is it because since you are losing both water and electrolytes at the same time it is still technically in balance but in smaller amounts, so your body doesn't think that there needs to be a fluid shift?? HELP please!

Isotonic dehydration actually refers to a condition when someone loses water and sodium at the same time thus their serum sodium levels would remain normal. Since sodium is the main solute that determines the tonicity of the extracellular fluids, if the fluid remains isotonic (equal) there would be no fluid shift.

[Vani1925]

Thank you! That makes sense YAY!

[DougR]

Thanks so much for asking this question. I was reading the same paragraphs and having a hard time understanding also. Thanks Vani1925 for clarifying this. Seems so simple now that it was explained better.

[Vani1925]

Yay! I'm glad that you were able to benefit from this as well.