I worked in a small community hospital for several years. Here's what we did: For anyone who came to the ER and needed a specialist (i.e. ortho, surgeon, cardio, etc) and didn't have one for us to call (from their HMO or whatever), the ER had a list of local docs on call each day. For codes, the ER doc responded no matter what, day or night. During the day, though, if the patient's own doc happened to be in the hospital or some other doc responded and got to the patient before the ER doc, then the ER doc would generally get there and just come right back.