Erowid's link to that study no longer works. Perhaps it was removed because it was proven inaccurate. Furthermore, that Erowid answer states explcitly:
Another possibility,
which we have been unable to find support for, is that the nitrous oxide is actually replacing the oxygen which would normally bind to hemoglobin. One reference (
http://www.unco.edu/chemist/aichun/pub/NO2.pdf) indicates that nitrous oxide does bind to hemoglobin (along with other proteins) and mentions structural changes that could affect oxygen's ability to bind, but does not directly mention oxygen displacement.
Sounds link that was a lab result based on playing with pure chemicals nothing even close to a medical "study" which examined use in humans.
Here, this study IS specifically medical/human in nature and mentions NOTHING about oxygen binding, so that's just more scare-mongering... this seems VERY thorough and I have little doubt they would have looked for it:
Recent advances in understanding the actions and toxicity of nitrous oxide
M. Maze, M. Fujinaga; Anaesthesia, Volume 55, Issue 4, pages 311–314, April 2000
http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2044.2000.01463.x/full
I honestly don't think it would be used as a surgical and dental anesthetic if it was binding to hemoglobin enough to make your lips turn blue.... and as I said neither I nor no one I asked ever saw anyone turn blue from nitrous. HAVE YOU???
I stand by that it is scare-mongering and object to its being trotted out... I doubt the OP has ever personally seen people turn blue from it either.
Sorry to earn a "sheesh" but such presumptions and scare-mongering at BL really piss me off.