Don't beat yourself up. You did everything
you could for this sweet little kitten....it was his time to go. It's always very sad when it happens and so suddenly, but I doubt anything could have saved him. Animals seem to know when it's their time. Recently, a friend had a 5 y.o. cat that was fine, and then suddenly she went off her food....all sorts of blood, urine tests, etc. were done, and medication given to her that vet thought might help, but she refused to eat and wouldn't swallow anything even when she was force fed. My friend is able to communicate with animals and said her cat told her it was her time to go. Cat continued to drink water and this went on for about 10 days until she had used up all her fat and was getting weak. My friend took her to the vet who examined her and kept her for observation for a day. The vet agreed with my friend there was nothing more to be done and she purred for the vet and a vet tech and my friend as she was euthanized. Often that's just the way it is. It was your kitty's time to go. That doesn't make it any easier, I know, it's always very sad. My condolences to you.