Sounds like a bad idea to me to try and do this out in field, take them to the station or local hospital and do it in a more controlled setting
I reall liked this quote
"Starr hopes the new system will cut down on the number of drunken driving trials. Officers can't hold down a suspect and force them to breath into a tube, she noted, but they can forcefully take blood — a practice that's been upheld by Idaho's Supreme Court and the U.S. Supreme Court"
What happens if a neddle gets broken off in a suspect that is struggling?