Short of a broken nose in combination with a broken eye socket and cheek bone i wouldnt class much as GBH.
Also the patient is lieing saying they cant breath. If someone has you in a bear hug from behind. You can still take a breath in.
If the patient was kicking off, what other choice would the nurse have? Its his/her safety too!
You know, ive got to say it. I know people who would pay for that sort of thing.