As far as the breathing, my only guess the same kind stuff they put under the tongue of lethargic newborn pups to get them to breath (and people too??)..could be the same drug just as a shot. Also I know with humans at least, when you go under for major surgery, you - don't - breath on your own. So my guess is when the shot is to kick start this process when they are brought out of the anesthesia.
Anyways - this might sound bad or something, maybe I am just not as informed, but I didn't worry much at all when our pets were spayed/neutered. I was actually excited for them because as a kid we had 14 barn/shed cats at one point (maybe more..) because of the consequences of not
having it done. It bothered me and when I finally talked my mom into having the cats done I was very excited about it more than anything. Your mama will do great I'm certain