A 17-year-old girl who underwent two heart and lung transplants at Duke University this month has suffered irreversible brain damage, according to doctors treating her.

Brian damage is a risk whenever doctors place patients on heart-lung machines, and Jesica Santillan had to undergo lengthy periods on the machine after doctors botched her first transplant by giving her organs not matched to her O-positive blood type. She had a second transplant Thursday with organs that matched her blood type.

A brain scan conducted early yesterday showed swelling in her brain along with some bleeding, said Karen Frush, Duke's medical director for children's services. A neurologist assessed Santillan and concluded that "irreversible brain damage" had occurred.

Doctors said that Santillan's family, who brought her from Mexico to the United States for the potentially lifesaving operation, had been informed.

Santillan's new heart and lungs appeared to be working well, despite the teenager's critical condition, Duke doctors said.

Last evening, Duke officials sent a letter to the United Network for Organ Sharing, which is investigating the case, acknowledging that doctors' errors had led to transplanting mismatched organs into Santillan, and laying out a list of procedures that the hospital is implementing to prevent such a mistake from happening again.

While brain damage is a risk whenever patients require a heart-lung machine to purify and pump their blood, the teenager was placed on a machine for longer periods than usual because of the back-to-back surgeries she required.

Santillan's brain damage was caused by one of two scenarios, said Kenneth McCurry, director of lung and heart lung transplantation at the University of Pittsburgh Medical Center.

Before patients can be placed on a blood purifying machine, doctors need to thin patients' blood to reduce the risk of clotting, McCurry said. The same thinning process, however, increases the risk of bleeding and brain damage.

After receiving blood thinner, Santillan could have bled into or around her brain, he said. If significant bleeding occurred, the blood could have put pressure on the brain and, since the skull is a confined space, the pressure would have caused the brain to swell in response to the injury. Eventually, he said, the process can lead to brain death.

An alternate hypothesis is that Santillan may have been deprived of oxygen or blood pressure during the various procedures she underwent. Eventually, that could also have led to brain damage and swelling, and the same prognosis.

"There's not a whole lot you can do under those circumstances," said McCurry. "They were forced to use the machine to keep her alive. Under those conditions you try to use enough blood thinner, but not an excessive amount and you try to control the blood pressure as much as you can. And then you hope there's not a whole lot of injury."

Santillan's case first made headlines after doctors admitted they had transplanted the teenager with organs from a type-A donor from Boston. After the operation on Feb. 7, Santillan suffered a heart attack on Feb. 10, and a seizure on Feb. 16, as her body's immune system -- sensing the presence of foreign proteins -- began to attack the organs.

Doctors and the family appealed for new organs, and at 11:30 p.m. Wednesday, Duke doctors were informed that a match had been found. McCurry said that Duke's doctors had likely determined that Santillan was not suffering from brain damage, since surgeons will not transplant scarce organs into patients unlikely to survive.

While patients who need organs are usually placed on long waiting lists, a computer algorithm moves patients who are at serious risk of death to the front of the line, said Anne Paschke, spokeswoman for the United Network for Organ Sharing in Richmond, which keeps track of organ requests and organ donations and matches them.

"There are a whole lot of factors; for each match there is a different ranked list," she said, adding that Santillan's second set of organs were not made available to her because the case was so publicized. "Location and geography play a role. With Jesica's case, the thoracic organs, heart and lung, have a much shorter preservation time, so we look at geography a little differently."

At 12:30 a.m. Thursday, Santillan's family was briefed and consented to a second transplant. She was wheeled into the operating room a few hours later, and the transplant operation was finished by 10:15 a.m. Thursday.

According to Duke, the warning sign that something was seriously wrong came at 3 a.m. yesterday -- and a neurologist confirmed that Santillan's brain damage was irreversible.

McCurry said that, in general, doctors are sometimes able to retrieve a transplanted heart from a patient who did not survive and use it to save another recipient's life. He said that lungs, which tend to suffer injury during surgery, are less likely to be reused.

The outcome of Santillan's case is likely to intensify the ethical debate over re-transplantation. However, R. Alta Charo, an ethicist at the University of Wisconsin, pointed out that Santillan's case is unusual, in that it was medical error that caused the first transplant to fail.

"This is not a case to generalize from," she said. "This is a sadly unique situation."

Karen Frush of Duke University Hospital tells reporters about Jesica Santillan's irreversible brain damage at a news conference yesterday.