The term you're looking for is "pre-renal azotemia". I didn't pay close attention to your first post. Are you giving him water sub-Q? I don't understand that. I wouldn't think pets would be that much different than humans in renal treatment. You wouldn't give water sub-q to a person. You would give IV solution. It's been years since nursing school and I don't practice, but this just doesn't sound right to me. I'm not saying your vet is wrong, I just dont get it. Maybe because he is so little, sub q works. ??
I hope he is doing better. Let us know!
Here's a web site about his condition. Push those fluids!
http://www.peteducation.com/article.cfm?articleid=351