"Call me Ishmael."
Actually, don't. My name is Richard, and I'm an EMT from New York City (born, raised, and employed), not the sole survivor of an ill fated New Bedford Whaler, lost at sea, known as the "Peaquad" (spelling?), under the control of an insane captain named Ahab, and his First Mate, Mr. Coffee, er, Mr. Starbuck.
Step 1: Curse, defecate in pants.
Step 2: Call medical control, who will almost definitely tell you to honor the DNR.
Step 3: Worry. Hope that nothing comes of it even though you did nothing wrong.
Not to play semantic games here, but I would also verify exactly what that DNR said. Was it no advanced interventions, no CPR, no defib, no intubation, no pressors?
I would start CPR and immediately call medical control. Let them decide if you discontinue CPR and honor the DNR.
That is a touchy situation, but as JP said, a DNR is a DNR. Giving adenosine per protocol, patient goes into arrest. What about if the patient went into arrest when you attempted vagal? What about if they went into arrest spontaniously? Your treatment may have caused it or it may not have. This could fall into the same situation when any DNR patient. If you come on scene for lets say.. chest pain, during treatment, the patient codes. If you are presented with a DNR (before arrest), you stop. If you are showed the DNR after the arrest and already doing CPR.. call command.
When in doubt, call medical command.
As well as working as an emt i also volunteer at the local childrens hospital. On this particular day i was in the room of an 11 year old boy with cancer. He knew he was about to get a shot and thus was giving the nurses, volunteers and his mother a very hard time by kicking and screaming. We tried very hard to calm him down to get the medication into him but he was moving to much.. then all of a sudden he stopped moving, stopped crying stopped screaming ect. everyone in the room went into first gear getting oxygen and checking vitals. After a thorough check we found nothing wrong with him and figured he was faking. I figured the nurses would use smelling salts and he would "wake up" but no, the nurse motioned for us to folllow her out of the room. She told us, go along with this and he will wake up. we walk back in the room and the nurse fooled around with the ekg moniter. The screen showed flat line. She then takes the bed sheet and covers the boy up and looks at the mon with a face that looked very serious and she says "ma'm i am so sorry but I think we have lost your son. The boy all of a sudden jumps up and screams, no mommy no I am alive mommy. After a stern talking to he promised he would never do it again and we were able to give the medication. I think he learned his lesson.