Could you knock yourself out by...?

I was watching the movie "Shooter" with Mark Wahlberg recently, and right after he went to his old spotter's widows house, he had her operate on him, and he inhaled the air from an air canister, I was wondering if that's really possible or if it was just something in the movies, and if it is possible, how long would you be knocked out for? and could you be woken up by being operated on or from loud noises?