PS: When I realized the effects of that preshot and why they give it (King Tut had fallen completely limp and out like a light off right after the shot! I was shocked at how fast it knocked him out) I asked right then to not give it to my cats anymore.
My vet back then said he could just give the gas but he has to place a gas mask on them to get him to sleep and it takes a few minutes or so and they had to be ready right away for the surgery. I said OK let’s just do that. This is not an invasive way so don’t let a vet say it is. I watched my boys many times in the surgery room going under with the mask and it didn’t scare them; my vet then knew me very well so allowed me in often for teeth cleaning procedures and is how I learned what goes on in there . Before that they used to use a glass tank to sedate cats that were too wild to handle that would pump gas in and relax them to sleep; My King Ramses always needed gas before they took blood so this is how I know of it. They switched to just using the mask later and got rid of the tank because it was easier on the cat. I knew to gas the cat was a better way and they woke up really fast and ready to go home; easier on all their organs too and less a chance to kill the cat. The smarter vets do this for all older cats naturally.
I always waited for my cats in the waiting room when they went on for teeth cleaning. It was a joy to see how fast they woke up and ready to go home all wide eyed and purring I don’t expect all you to be able to have this done by your vet because many of them are too busy to accommodate you or just don’t want to. My wish is that you can find ones that will for the sake of your fur friends.