I am so sorry. Last month we had to do the same for our 18 year-old cat. She also had renal failure. This time we had the vet come to the house rather than make that one, awful last trip to her office. It costs a little more but works out the best for everyone.
I had a vet that would come to my home for Foster Cat.
Foster Cat was supposed to be at my house for a while. Her parents never came back from California to pick her up. She and I finally got used to each other and actually grew to have a strong relationship.
Foster Cat did NOT WANT TO GO TO THE VET. So I had the Traveling Vet come to her. That was until Foster Cat bit Traveling Vet and sent her to the hospital. Vet would never come back.
I loved Foster Cat.
I have Backyard Cat now. Funny feral cat. She wants to come to me, gets close, realizes she is close and hisses. So funny. She has been coming here every day for over a year. Very noisy. Probably part Siamese. Fortunately the Friends of Feral Felines, bless them, have neutered her. I know this because her left ear is clipped.