As for the dehydration, you will probably be hooked up to an IV while you are there. If you aren't, you might request one just to be sure that you are well hydrated from NPO the night before. Or at least talk to the dr about it. Get their opinion.
Best of Luck to you.
Diagnosed with CD in 1979, many resections and meds
Perm Ileostomy July 1984 at Cleveland Clinic
Disease free since surgery