DNR means Do Not Resuscitate. It's a legal document that patients or (more often) their loved ones sign in the presence of witnesses. It says that if the patient gets into certain kinds of trouble, we're not supposed to use "extraordinary means" to help them out. Typically it means if their heart stops we can't code them and if they have trouble breathing we can't put in the endotracheal tube to keep them breathing on a machine. Implicit, it seems, in a DNR order is the idea that the patient's "quality of life" is so low that it's not worth the pain, discomfort and indignity of coding and ventilation. (Even the most pragmatic fans of DNR feel queasy about adding "and the expense" here.) Also implicit is that the emergency — usually a heart or lung problem — we're not treating because of the DNR order will quickly prove fatal.