Do any U.S.A Labour and Delivery wards have Entanox available for Pain relief?

Hi just about to start my first job in Labour and delivery in the USA, am a Midwife from the U.K. One of the first things I have noticed when shown around hospitals in the USA is that there is no entanox for pain relief. It is a staple pain relief in all hospitals in the uk . It is 50% oxygen and 50% nitrous oxide and is inhaled via a mouthpiece or face mask. No side effects helps the women breathe slow deep breathes and helps pain contraction by contraction also good for oxgenation of baby too. It is a great help to use it if an epidural is not 100% effective or if painkillers are wearing off. It is great for difficult Vag exams or for having an epidural sited. I have helped women to use it in the hundreds of births I have attended.
I personally used it as my only form of painrelief while in labour for both my kids. i had short sharp labours, of course I would have had more painrelief if i had had longer labours but entanox helped me focus and took away the out of control feelings of severe pain. I look back on labour experience as a wonderful thing I dont remember the pain at all .
Are there any hospitals at all that use Entanox? I looked that up on the internet and some people say that Entanox is not used in the USA because anaesthatists would not earn as much if they gave fewer epidurals. What do people think, is entanox being withheld here?
I just don't know, I haven't worked here yet but this subject intrigues me!!