Yep, they still use nitrous at homebirths in the UK.
I'm not sure why they don't use it here in the US. Could be that it's really cheap, and epidurals are such a nice way to gain extra money for the hospital and the anesthesiologists. (sarcasm there)
But, yeah nitrous has Very little side effects - in fact, it wears off quickly from the mother and Very little gets to baby. If the mother is controlling the intake from a handheld mask, if she gets too much and feels loopy, the minute she pulls the mask away from her face (or it falls off), she starts to improVe.
Maybe someone has a reason why nitrous isn't used in the US. I'Ve eVen asked a dr about this, he had no idea.