Unlike other life-sustaining measures, like feeding and breathing tubes, which afford families and physicians a bigger window of time to make decisions, CPR is an emergency procedure. That is one reason hospitals want a DNR order in place if a patient suffers a cardiac arrest.

Patients can choose not to be resuscitated, and their informed consent to a DNR order is generally inviolate. But friction arises when a patient is near death and has not been interviewed about resuscitation, and the doctors need to obtain that consent from the patient's representative, usually a family member. Doctors initiate these painful conversations when they believe a resuscitation effort would be "medically futile," a term whose definition is debated widely in medical and bioethics journals.

Doctors can fumble this most delicate of conversations. "With gravely ill patients, doctors sometimes foster these DNR disputes by saying that a patient is getting better," said Dr. Joseph J. Fins, author of "A Palliative Ethic of Care: Clinical Wisdom at Life's End." "We focus on the minutiae of one organ system at a time, fostering hope when there is nothing but the grim reality that the patient will die. Then all of a sudden we tell the family it's futile and we're surprised that they're surprised."

Jane Greenlaw, an ethicist at the University of Rochester Medical Center, said that in New York, if neither a patient nor a representative has consented to a DNR order, medical personnel have to try to resuscitate patients "because you don't have permission not to."

But, she said, "it's the medical person's decision about when it's time to stop. That person can say after 15 minutes, 'This is over, we've tried.' And to some families, that means everything."

Families often believe that consenting to a DNR order implies they are giving up on their loved one, signing a death warrant, turning their backs on hope. They can be haunted by guilt and a fear that they have betrayed their religious faith.

One woman, who did not want to be identified out of concern for family privacy, felt trapped between her medical knowledge and her family's wishes. Last year, she was the health care agent for her father, who was treated for end-stage cancer of the larynx in the intensive care unit at New York-Presbyterian Hospital/Columbia. He developed acute respiratory disease. The cancer had metastasized: tumors were punching bulges in his forehead. He was too sick to endure more chemotherapy or radiation. After he languished for nearly two months in the intensive-care unit, the doctors approached the woman with a DNR consent form.

The woman, a nurse in the hospital's coronary care unit, understood the implications fully. But she also had to face her grieving mother.