In the ER, we do have protocols stating that certain things can be done before the pt is seen, i.e. EKGs, monitor for CP, extremity Xrays for injuries, very basic stuff.
However, most nurses, including myself, do go a little further. For example, pts with chest pain, I'll go ahead and put them on the monitor and 2L O2, get a line in, draw blood and order CBC, SMA 7, and Troponin, order a CXR, and do an EKG. You KNOW these things will be ordered- so go ahead and get it going. Things that I'm not SURE will be ordered, I'll hold back on it. I don't give any meds without an order.
In our ER, it seems as if its almost expected sometimes. The doc will see the pt and ask if any labs are back yet (before they've been ordered) I was taught by my preceptor to go ahead and do these things, I never really questioned the legality of it, so its interesting to read these replies.