I am a respiratory therapist and I drawn ABG's on patients all the time. The problem with them is that to get to your artery you have to go right by a bundle of nerves hence the pain. I can only say that it is a useful tool for someone having surgery because it can be an indicator of an underlying condition.
An ABG measures blood pH, oxygenation, CO2 and bicarb levels.
I know that doesnt help the pain but I had to put my two cents in since I'm usually the one on the other side of the needle lol.