That's IT! IsoflourIne
I was close
There's another gas called Sevoflourine that is safe as well. They do wake up much faster with the gas, and chance of overdose is smaller with the gas as well. You can stop the gas and the effects start going away immediately, injectables are in their bodies and it's way too easy to give too much
I hope that everyone here helped ya. Yes, get them neutered but do it safely. I'm so happy that you're a smart person and you're doing your homework first!