I recently went through something similar. Our cat stopped eating and drinking, and the vets couldn't figure out why. We tried to feed him through a syringe and, like you, we injected saline, but his gastrointestinal system was shutting down (which, we were informed, usually indicates a terminal illness like cancer). In the end, we had to euthanize him.
I very sincerely hope that your kitty can cope and will live to a natural end. Good luck to you.
