Probably not a HIPAA violation, but I think you are best never posting anything about work on FB. I had a NM that talked to us, as a unit, and said that not to post about patients, not to post anything negative about the hospital, doctors, etc. She said it would be OK to say "I had a really tough day at work today." I mentioned this to a friend who is a nursing educator. She said, even this is not a great thing to post. She tells her students to not post anything work related on FB--even the "tough day" comment could be taken out of context by a potential employer, and they could look at someone as a whiny employee. In a competitive job market, the hospital could just steer clear of hiring someone like that.
In addition, a potential employer could look at the "tough day" comment and think, "oh, great, someone who is going to put their thoughts on work on social media," and, again, go with someone else. Why take the chance.