It’s a topic not many people like to think about, but one that should be broached among family members: If you were placed on life support, who would you want to be your legal representative? And when is the right time to pull the plug?

These issues usually come into play unexpectedly, as actress Natasha Richardson’s family found out this week when a skiing accident reportedly left the Tony award-winner brain dead. She died Wednesday night after being taken off life support.

“I’m sure Natasha Richardson wasn’t thinking before she went skiing, ‘If I don’t make it down this hill, this is who I want to be my representative,’” Judge Andrew P. Napolitano, senior judicial analyst for FOX News, said Wednesday afternoon.

Brain death is very different from being in a vegetative state, said Dr. Michael DiGeorgia, professor of neurology and director of the Center for Neurocritical Care of University Hospitals Case Medical Center, which is associated with Case Western Reserve University in Cleveland.

According to the American Academy of Neurology, brain death occurs when the patient has no evidence of cortical brain activity or brain stem activity. This means the patient would be unable to cough or swallow or breathe on her own, whereas a patient in a vegetative state may be able to do one or all of those three things, DiGeorgia said.

Once a patient is declared brain dead, the family usually opts to remove uncomfortable tubes and machines quickly, said DiGeorgia, who has not treated Richardson. "Pulling the plug" would render the patient unable to breathe, and the heart would stop beating within minutes, he said.

But if a patient is not brain dead and instead has suffered a catastrophic neurological brain injury, DiGeorgia said, he or she could breathe spontaneously for one or two days before dying.

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Family spokesman Alan Nierob confirmed Richardson's death Wednesday night in a written statement, saying Liam Neeson and sons were "shocked and devastated by the tragic death of their beloved Natasha."

“The law in New York says if two physicians decide the patient is in a ‘hopelessly vegetative state,’ and no natural or unnatural means are likely to return the patient to a cognitive state, and the patient’s representative agrees, then the medical center may terminate life support,” said Napolitano, former vice president and general counsel of Hackensack University Medical Center in New Jersey – where he once was the person charged with making life-and-death decisions for patients on life support.

Lenox Hill would not comment on Richardson’s condition and referred comments to Richardson’s publicist, Rogers and Cowan, which said Wednesday afternoon they had “no new information at this point.”

Dr. Eric Braverman, clinical assistant professor of integrative medicine at Cornell Weill Medical School in New York City, said physicians use the results of electroencephalogram (EEG) tests, which measure the patient’s electrical activity in their brain, MRIs or positron emission tomography (PET) scans in determining when to turn off life support.

“You pull the plug when the person has no brain waves, and no hope of quality of life,” Braverman said.

But a problem can arise if the parties caring for the patient disagree on the decision to terminate life support.

A well-known example was Terri Schiavo, the Florida woman who had been in a permanent vegetative state for eight years when her husband Michael argued in 1998 that he wanted her feeding tube removed. A seven-year battle ensued as Schiavo’s parents fought against Michael Schiavo’s wishes, saying their daughter’s life still had quality. On March 18, 2005, Terri Schiavo’s feeding tube was removed; she died 13 days later of dehydration.

“A judge comes in when there is a difference of opinion, and then you have a hearing,” said Napolitano, adding that sometimes there are instances where the family wants to turn off life support and the doctor does not.

Napolitano said that when he presided over cases similar to Shiavo’s, he went to the patient’s hospital room after hearing testimony to see the patient for himself.

“A neurologist told me to pinch the back of the foot between the ankle and heel to see if there was any response,” Napolitano said. “I don’t have the ability to read MRIs, so I wanted to make sure, I wanted to see the human being.”

Napolitano said everyone should sign a living will that gives specific instructions on health care, which can be given to hospital administrators in the event of such a tragedy.