I recently had to put down my 14yo cat, who was down to 9lbs from his peak at 18lbs in only a year or two. Almost lost him a few times before earlier on. He hung on for me I'd like to believe. That cat chose me from the start. So many memories.
Still thinking about all the mistakes I'd made over the last decade and there were many. The dynamics of stubborn dog/stubborn cat/stubborn human could have been handled differently. He was so social. He would try to sleep with the dog and there would be a musical chairs growling session every night until he gave up and slept elsewhere in the house or went down to look out the window. I could have had him on a towel instead. Even with three kinds of food he'd yowl at me while cooking and I should have given him more love then and there. Too late now. So many things could have been done differently. I'm not a cat person by nature but he was the greatest ever made
in my unbiased view. Would walk out to greet neighbors with dogs on the sidewalk. Always at my my right as soon as soon as I sat down on the porch. That kitty who chases off a coyote to save the human kid? That would have been him.
A small cold turned into another round of full blown seizures and he was unable to walk. We had a good evening together watching a movie together and some purring sessions where I managed to get a few needle-less syringes of water into his mouth, but he threw up everything else. The procedure did not go as smoothly as it could have. After not eating or drinking for three days he was completely dehydrated. He got a sleeping shot before the final of pentobarbital/oxybarbiturate but the vet couldn't get a good vein at first.
I asked the vet about nitrogen and was told it was not applicable for some animals and not 'tested' enough or 'certified' by the powers that be. They replied they would look into it as a possibility. I've heard it is used in assisted suicides successfully. In retrospect the gas would probably not be safe to store inside a closed heated facility, and any long-term safety of a pressurized tank is always a concern.
It is used in executions though:
https://oklahomawatch.org/2018/07/17/puzzle-of-nitrogen-execution-could-present-issues-for-state/
Several breaths can render a person unconscious, with death following in four to five minutes, according to Copeland’s report. That’s based on experiences of people who have used nitrogen for suicides.