Entenox is a mixture of O2 and nitrous oxide. It's used for pain relief. It comes in a tank which you have to invert 3 times before use and then the patient sucks on it through a by demand valve. Basically, it's what us non-super leet ALS guys have to use instead of morphine. It actually works great, you just have to make sure that the vents are on in the back of the bus, cause Entenox can make you giddy. One day I forgot to turn it on, and when we got to the hospital, my partner opened up the back door to find me and the patient laughing our heads off.