As Ariel Sharon nears death from kidney failure, medical experts in the United States say it is "remarkable" that the former prime minister of Israel has stayed alive for eight years in a vegetative state.
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Sharon, who is 85 and can breathe on his own, has been in a coma and on a feeding tube since suffering a stroke at the height of his power in 2006.
"It's pretty amazing they have kept him alive for as long as they have," said Dr. James L. Bernat, a professor of neurology at Dartmouth-Hitchcock Medical Center in New Hampshire. "It's unusual for someone to survive that long. But the plan was to treat him aggressively, and that is not always the case in this country. Often the decision is made to let nature take its course."
Any number of illnesses can cause death for someone in this state, despite aggressive care, said Bernat.
"He obviously has some kind of disorder that affects the kidneys," he said. "That sort of thing can happen when you're vulnerable because you are bed-bound and the blood isn't circulating."
Bernat said medical literature has reported a patient living as long as 37 years in a vegetative state. In one high-profile case, American socialite Sunny von Bulow was stayed in such a state for 28 years until her death in 2008.
The person believed to have lived the longest in a vegetative state, and who is still alive, is Iain Wilson, a former British Royal Marine who suffered severe brain injuries after he was knocked over by a car in 1989.
Dr. Zeev Rotstein, director of Tel Hashomer hospital outside Tel Aviv, where Sharon is being treated, said a number of his organs were in "critical malfunction," according to The Associated Press.
"He is in critical condition, and his life is definitely in danger," Rotstein told reporters. "The feeling of the doctors treating him and also that of the family with him is that there is a turn for the worse."
In 2010, when Sharon had been comatose for four years, his son reported that his father could respond to some requests. At the time, he had been moved from a hospital outside Tel Aviv to the family ranch in southern Israel.
"When he is awake, he looks at me and moves fingers when I ask him to," Gilad Sharon told The New York Times. "I am sure he hears me."
In a biography of his father, "Sharon: The Life of a Leader," his son described his father's condition this way: "He lies in bed, looking like the lord of the manor, sleeping tranquilly. Large, strong, self-assured. His cheeks are a healthy shade of red. When he's awake, he looks out with a penetrating stare. He hasn't lost a single pound; on the contrary, he's gained some."
The book said the medical team at Hadassah University Hospital in Jerusalem, where Sharon was initially treated, wanted to withdraw life support, saying that based on brain scans, "the game was over."
But his sons, who have been responsible for their father's care since the death of his two wives, insisted on aggressive treatment, including surgery.
Last year, scientists said they had found activity in Sharon's brain, suggesting he might be able to hear and understand, the Times reported.
A patient in a vegetative state is considered alive because the brain stem is still functioning and allowing the person to breathe and respond to some stimuli, according to Dartmouth's Bernat. In brain death, "there is zero activity in any part of the brain."
A vegetative state is a syndrome that can be caused by a variety of conditions, usually a traumatic brain injury but also by lack of blood flow caused by cardiac arrest or stroke.
"A person's brain stem is spared, so they have eye movement – their pupils react to light and they open and close," Bernat said. "People breathe on their own and spontaneously have a sleep cycle, closing their eyes when they sleep."
Damage is usually diffuse in the cerebral cortex, thalamus or in the white matter that connects the thalamus to the cortex.
"In the typical vegetative state, we believe they are unconscious and lack the ability to perceive their environment or themselves," said Bernat. "But it's difficult for doctors to be conclusive about that when they can't get into their head and experience what [the patient] experiences."
Sometimes a true vegetative state is misdiagnosed and a patient wakes up, but that is rare, he said. Typically, a family member sees evidence of consciousness, which can be verified in a functional MRI.
"Only a very few medical centers have these [MRI machines] and very rarely in a case of traumatic brain injury you can see something that can't be detected on examination," said Bernat.
In one of the most famous cases, the family of Terry Schiavo, a Florida woman who was kept alive for 15 years, insisted she was fully conscious.
Schiavo, who suffered a profound brain injury, was at the center of a seven-year legal tug-of-war that involved Congress, the U.S. Supreme Court and even President George W. Bush before a judge granted her husband the right to allow her to die in 2005. She was 41.
An autopsy later revealed she had been in a vegetative state.
Patients can live in a vegetative state for decades, "with adequate nursing care and feeding and hydrating them and treating complications like infections."
Young patients can be kept alive "for decades," but older patients, such as Sharon, usually don't live as long, even with the best of care, said Bernat.
"There are cases of people coming out of it, but that usually happens a short time after the brain injury," said Bernat. "It's rare to regain awareness after six months. And recovery isn't to normal but a severely disabled state.
"Maybe they gain awareness, but not independence," he said. "One might argue it's worse to be aware."