The above photo is of Smokie, the cat I've had since the age of 3 months, and would turn 21 years old in May. (She is 17 or 18 in the photo.)
She has suffered from advanced kidney failure for 3+ years; we've addressed it by giving her plenty of water, low-protein canned food, prescription kidney dry food, onion-free and sodium-free chicken stock, and 100 mL daily of IV fluids. Unfortunately, she's been at her minimum possible weight (5 1/4 pounds) for a few months and won't eat very much. At her last checkup (in December), she was well past the "red line" for kidney function I remember she had a score of 60 where anything past 25 or 30 was abnormal - but there's nothing more, short of a transplant, we can do for her. She has also noticeably weakened: she "misses" when trying to jump on the couch about half the time, and on slick floors her rear legs bow outward. Despite all of this, she has no other health problems - she still has good vision and hearing, steady heartbeat, etc.
I could have lived with all of this indefinitely, because until very recently, she still seemed pretty happy - she would come climb on my lap and "snuggle", purr when I pet her, look forward to me coming home from work, etc. She was also decently mobile in my apartment, and showed healthy protests whenever I gave her her IV fluids. At her December checkup, the vet described her as "spunky". But in the past month or so she's REALLY slowed down...she often spends all her time sleeping or lying awake on a rug in the kitchen, and only gets up every once in a while to eat a couple bites or use the litter box. She is starting to have trouble breathing - due to the IV fluids - and it's more difficult, though still possible, to get her to purr. She rarely protests (audibly or with paws) during the IV injection, though she does still try to get away. And she's also started "licking" where the fluid accumulates under her skin, like it's hurting her. And yet, she doesn't yelp when she moves around - she has no arthritis - and only rarely when I pick her up; she also hasn't taken the "nose to the floor" position I was warned about. And she still enjoys some things--I got her to take interest in a piece of string briefly tonight, and she got excited when I got a can of food out for her.
I'm providing all of this description, because I'm trying to figure out whether she's just slowing down due to the kidney disease - which is to be expected - or whether she's actually hurting. I don't mind this change in behavior so long as it's not due to pain. I know I'll have to put her to sleep soon, if nature doesn't take its course...I'm just not sure if it's that time yet. Any thoughts are appreciated.