I've been in nursing for over 20 years, and haven't found anything about "regulations", as this is pretty institution-dependent. Our PICU really has a battle with this, as they are connected to the Burn unit (which takes all burns regardless of age, pedi burns do not go to PI), which is connected to the SICU. Traumas get admitted to SICU, teens go either to PICU or SICU depending on surgeon preference and bed availability. If PICU is not full and admissions needs an adult bed, guess where they go? At another Level I center in the city, PICU does NOT EVER take adults--period. (Which is how I think it should be). Last winter, RSV and other illnesses were very rampant in this area, and we had peds. cases spread all over the hospital
That was quite an experience for everyone involved--hope this winter is not quite so crazy.
We had a brief interlude a few years ago when a new nursing manager set her foot down and told administration PICU would not take adult patients. At that time, the unit was in a different area of the hospital than it is now; when the new unit was built as an extension of SICU and Burn, the gig was up. Also, that manager has not been with the institution for quite some time; the subsequent managers since then were not as successful in keeping the same demand.
I'm sorry I don't have any good suggestions, but thought you'd like to know you weren't alone.