Unless a court orders that her feeding tube be reinserted, Terri Schiavo will probably die in the next three weeks of a fatal heart rhythm brought on by the chemical imbalances that arise from extreme dehydration, according to several experts on end-of-life medical care.
But, they are quick to add, that is just a guess.
Very little is known about the timing and mechanism of death when food and water are withheld from people with severe brain damage who are otherwise in fairly good health. Not many people have that experience. Studying their deaths is an extremely low priority.
"I usually tell families not to expect that it will necessarily be very quick," said Joanne Lynn, a researcher at Rand Corp. and an expert on care of the terminally ill. In her experience, patients who forgo even water can live as long as 21 days, although most die in seven to 10. But there is no large series of cases on which to base predictions because "nobody has actually sat down and studied this."
With advanced dehydration, the functioning of many vital organs -- heart, brain, kidneys, lungs -- worsens. But it is difficult to say which is first to fail, tipping a person irreversibly toward death, said Porter Storey, a leader of the American Academy of Hospice and Palliative Medicine who was the medical director of a hospice in Houston for 18 years.
"Their breathing slows down, and then their next breath doesn't come," he said yesterday. "Does that mean the brain, which sends a signal to the lungs, goes first? Or does it mean the lungs failed? We do not precisely know why people die, and it is not something that can be answered by scientific experiment."
Each day the body produces waste (such as acid, potassium and a nitrogen-containing compound called urea) that must be excreted in urine to prevent it from accumulating to toxic levels. To do that, the kidneys require a minimum volume of water, which they extract from the blood, in which to dissolve those substances.
When dehydration becomes severe, the kidneys essentially run out of water to make urine. As production of urine falls, the concentration of toxins rises.
The effect on organs is varied and profound. Ammonia-like substances have a sedating effect on the brain. High concentrations of potassium alter the heartbeat and eventually stop it -- which is the mechanism of the injection used for execution.
Whatever the mechanism of death, experts are virtually unanimous in saying it does not appear to be painful.