My dog suffered heatstroke, took him to the vet..they pump fluid in him..said his kidneys were not working

like they wanted them too....started talking about putting him down..he is only 3yrs. old..he never peed much anyway...We brought him home..he is having trouble water and food down....he is peeing more not and some of the fluid is leaving his body...is there something besides pepto and that kind of thing that can help....