A DNR, also known as a Do Not Resuscitate order, is a legal document stating that the patient for whom it is for desires not to have CPR, or any type of resuscitation, performed if they go into respiratory arrest or cardiac arrest.
For some people, this form may sound like a grand idea. "If I go, I want to go, not risk being turned into a lifeless, but alive, being by attempts to bring me back." Or, "I've had enough of all of this pain, I just want to go in peace."
From an emergency services standpoint, this is one of the most incredibly difficult situations to walk into. You have a patient who has signed a DNR. Suddenly they begin having chest pain, or difficulty breathing. They get scared. Their family gets scared. They call 911. We come out there, do our thing, transport them to the hospital, and then they go home.
One day, they start having this difficulty breathing again. Their family is gathered around. The family calls 911. While we are responding out to the patient, the patient stops breathing. The family freaks out, and continues to freak out as we arrive on scene. Their dad/mom/sister/brother/child is not breathing. The family knows the patient has a DNR. They tell us the person has a DNR. They can't find the DNR.
We begin resuscitation.
Please, please, please remember that if you desire to have a DNR, talk it over with your family. Tell them your wishes, and hear their wishes as well. Make sure your family is comfortable with your wishes (just like being an organ donor). Make sure they know what to do when you pass away. Then, if you do desire a DNR order, make sure the original copy is clearly posted. We can not legally accept someone's word. We can not accept a copy. We have to have the original DNR order. If we don't, we have to begin CPR, making an already horrible situation even worse than it is.
For more information about DNRs see your local laws. I also found some pages giving a good overview of the process: