I have an 18 year old cat who developed really bad bloody diarrhoea, and I think is on the way out 
Just over a week ago, dh took her to the vet and said we just wanted him treated to keep him comfortable and if we couldn't do that we wanted him put down. She gave him antibiotics and suggested a gentle diet, which we've been following for the last ten days (and we took him to see her again on Monday). But he is no better, and has lost a lot of weight (though is still eating). It's got to the stage we can't have him in the house with us because he's leaving bloody diarrhoea all over the place - he won't use the litter tray, he just shits wherever he is - so we've had to shut him in the porch or the utility room.
The cat hates the cage, the car and the vet, so dh rang her to ask what the next step is. I want to have him put down. The vet wants to take blood tests and treat him actively. dh is stuck in the middle.
He's almost 19, ffs. He's an outdoor cat, he doesn't want to be kept in all the time. I also don't want to refuse to have him in the sitting room. I don't want him treated actively, taken in overnight, put on a drip, I don't want to drag it all out for weeks. Nor do I want to go to another vet, as that means more time in the car.
He's had a great life, I think the vet should allow me to decide enough is enough.