Nitrogen is way better than CO. They just fucked up the delivery system, as government usually finds a way to fuck up somehow.

The problem with injections is they have to use a mishmash of different drugs because no drug company wants to have their products associated with executions and everybody reacts differently to drugs so you can't predict how long or how violently it might result in.

Everyone reacts the same to nitrogen gas though, it's predictable and peaceful and cheap as long as you do it right. One theory I heard was that they used a mask which was a closed system so he was able to breath his own breath for a long time since you don't use all the oxygen in every breath. They should have had a system where each breath is expelled out from the mask and in from the nitrogen source, like a back flow stop valve or something.