Heat exhaustion, dehydration and kidney failure

May I recommend looking at this great index assembled by James Macdonald? It might be helpful.

Yes, this is plausbile from a medical standpoint. As a child, your char was at greater risk than a healthy adult, so write carefully (she wasn't out in the desert without water for a week or several days, she didn't walk 50k in the sun, she wasn't at the point of having seizures, renal function impaired but not quite failed...have her at the edge of heat stroke, but not there long without medical care.) You can build up the stages of her distress as she gets to the point of a dire situation.

You'll be fine.

I am actually currently suffering from heat exhaustion, dehydration, sun poisoning, and minor kidney problems. I am an extremely pale red-head who stupidly went canoeing for five hours in 96 degrees without any water. Needless to say, that was monday and I still feel horrible....

Anyway, if you need any specifics on what it feels like just let me know, I can give you details.

I've suffered through heat exhaustion/heat stroke through my life more times than I could think of counting - I'm very very prone to it and have to be careful to prevent it now that I'm living in a tropical country. If you have any questions, I'll do my best to help.

You might study a bit about acute vs chronic renal failure (depending on if you want to discuss her situation vs just mention it). Acute renal failure varies depending on the situation, and the chance of full recovery depends on it as well. As long as nothing has hit the point of no return, the kidney regenerates very nicely (and if a few bits die off, no worries, there's plenty of excess baggage in that organ.)

Somewhere in my piles of notes I have two good sections on the kidney (physiology and disease), but I wouldn't find them anytime soon (buggar)

If all you have is some dehydration, then your character is suffering from acute renal disease and would have a pre-renal azotemia. Since no water is being taken in, the body is trying to conserve water by constricting the blood flow to the kidneys. This effectively "increases" the electrolytes (actually, they're being concentrated, not increased).

Rehydration will have to be performed slowly so as not to cause salt toxicity in which the electrolyte concentrations rapidly draw water into the cells causing cellular swelling. This would occur throughout the body, but is especially important in the brain as it can cause seizures and brain damage. (I'm assuming your doctors know what they are doing, so this shouldn't happen).

As for permanent renal damage...there would be some, but there is so much redundant tissue that a small amount of damage is neglible.

If you need details, chat with an ER physician or critical care nurse at your local hospital. Just tell them you're writing a novel and need some information, use e-mail so they can reply when they have time (they won't take personal calls while on duty).

Good Luck!

Mild kidney failure is definitely a possible side effect of dehydration and heat exhaustion. My dad's going through that right now. For your character, she might have to undergo dialysis a few times but then be fine. (That's what they're saying for my dad, btw, I really didn't just pull it out of the blue.)

If I remember correctly, five days is about the point where the brain damage from dehydration starts to become permanent.