I've never had the issue come up. I guess if they really refused, I'd have them sign an AMA. Or...they could get out and walk.
If they refuse, I'd have someone else do it.. I had that happen occasionally during clinicals. I was fine with it.If they are only refusing a procedure you do not have the right to refuse further care. Patients have the right to decide what they allow you or even the doctor to do. If they refuse a procedure, explain the risks, then treat them to the best of your ability with what they do allow.