You have to learn to distinguish between "your concern" (imagination) and reality.
Your concern is legitimate. Definitely.
The reality is, no dog is going to piss-out 1000 ml of fluids faster than you can get it into him with a bolus dose of IV Fluids.
And hell, if the dog does piss out a big amount of fluids, CELEBRATE!, because it means his kidneys are now working
And then, guess what? You can run another bag of fluids in him and not give anymore dex/solu ... and keep him hydrated
Again, these drugs at that dose are for the VERY short term. ONCE ... maybe TWICE ... but no more
If they make him have to get up and piss, great! That is progress and a big relief!
You can discontinue (or drastically lower) the cortic-steroid dose, and keep on giving IV fluids.
When he's eating, and drinking, you stop giving those drugs altogether at that point, and continue with fluids and antibiotics.
You're welcome
Honestly, I haven't used it. The symptoms show an irregular heart beat and I am not sure that is something I would want to do in a life-n-death thing.
But I have no experience, and know of no one who has either, so I can't be of much help here, sorry.
Jack