I just read about nitrous oxide during labor and it doesn't sound good, check out this website.
it says it's not very good for relieving pain during labor and your child is 5 and a half times more likely to become addicted to amphetamines later in life.
I struggled with an amphetamione addiction a little while ago and it is a tough habit to kick.
I don't know how reliable any of this is, but a lot of sites say the same thing. I'm not trying to interfere or be a bummer, I was honestly just curious, but I thought you should know. If I were you i'd talk to my doctor about an epidural babe.