A teenage girl who was near death after surgeons mistakenly implanted a heart and lungs with the wrong blood type into her chest underwent an emergency second transplant yesterday in a desperate attempt to save her life.

Jesica Santillan, 17, was in critical condition in the pediatric intensive care unit after her second four-hour heart-lung transplant at Duke University Hospital in Durham, N.C., where the original mix-up occurred.

The case again focused attention on the problem of mistakes in medicine. The National Academy of Sciences estimates they cause as many as 100,000 deaths a year in the United States.

"This particular incident is as horrendous an error as one can imagine," said Thomas Murray, president of the Hastings Center in Garrison, N.Y., a medical ethics think tank. "I was quite shocked to know that there were not multiple independent checks of things as critical as blood type before the organs were even accepted for transplant."

The second transplant operation began at about 6 a.m. yesterday after doctors located new organs that were the right blood type and size. To guard against another mistake, the hospital had three doctors check independently to confirm that the organs matched correctly this time, officials said.

The girl's new heart and lungs were working and she was taken off life-support, officials said. Doctors were optimistic about Santillan's prospects, but said it was too soon to know whether she would recover. About half of heart-lung transplant recipients survive five years, and Santillan may have suffered damage to other organs because of the botched transplant.

"She's as critical as a person can be, " said Duane Davis, a surgeon on the transplant team. "She has a number of hurdles to overcome."

Santillan's family was ecstatic that new organs were found so quickly. "Her parents feel some relief right now," said Renee McCormick, spokeswoman for a charity raising money for the teenager's care. "Everyone is incredibly hopeful and we're just so pleased, so thankful."

The United Network for Organ Sharing (UNOS) in Richmond, which coordinates organ distribution nationwide, is investigating the incident. Duke officials said the mistake occurred because doctors incorrectly assumed the blood type of the organ donor matched the recipient and failed to check for themselves. The hospital will now require additional compatibility checks in all transplants to make sure it does not happen again, officials said.

"This has been a difficult and heart-wrenching time for many people. At Duke, it has resulted in a tense reexamination of internal controls in transplantation," said William Fulkerson, the hospital's chief executive officer.

The hospital, UNOS and Carolina Donor Services, which obtained the organs, would not identify the new donor. The only details released were that the organs were not the result of a "directed donation," in which a donor's family specifies who will get the organs. But officials said Santillan received no preferential treatment.

Outside experts speculated that Santillan's rapidly deteriorating condition pushed her to the top of the waiting list to receive any suitable organs that became available.

Santillan was born in Guzman, Mexico, a small town near Guadalajara, with a deformed heart that caused a fatal condition known as restrictive cardiomyopathy. Three years ago, the teenager's parents paid a smuggler to spirit the family into the United States in hopes of getting her a transplant.

They settled in Louisburg, N.C., near Duke, but the girl's condition deteriorated and the family could not afford the $500,000 operation.

After hearing about her plight, a local building contractor, Mack Mahoney, established a foundation to raise the money for her transplant, which was performed Feb. 7.

The surgery went well, but doctors immediately realized their mistake when the teenager's body started rejecting the new organs. The organs were from a donor with type A blood; Santillan has type O blood.

The case illustrates that despite years of warnings, many hospitals have yet to add backup checks to life-and-death decisions, experts said.

"Carpenters have a rule: Measure twice, cut once. If it's good enough for carpenters it ought to be good enough for transplants," said Murray, the ethicist.

Kenneth McCurry, director of heart and lung transplantation at the University of Pittsburgh, said Santillan's prospects for survival were diminished somewhat since she had probably suffered damage to her kidney and liver from being kept on life-support machines after the first transplant.

Vital organs can be damaged while on life support because of a lack of adequate blood flow. She also faces a higher risk of infection from having undergone two operations.

"If these organs function well and she makes it through this period and the other organs recover, then she will have as good a chance of surviving as well as any other patient," McCurry said. "Only time will tell."

McCurry worried that the negative publicity from the case might discourage people from donating organs, exacerbating what is already a severe shortage. "There are literally thousands and thousands of transplants each year in the United States, and these things happen very infrequently," he said. "We need more organs, not fewer."

Santillan's second surgery was made possible when another donor was found at about 11:30 p.m. Wednesday. After the compatibility of the organs was confirmed, Santillan's family was notified early yesterday morning, and the second surgery was scheduled to be performed by James Jaggers, who did the first operation.

Santillan will be monitored "extremely carefully," said Davis, the surgeon. While "many body parts . . . aren't working as well as we'd like them to be working," there is "nothing that we know of that says any of the damage is irreversible," he said.

Since 1988, there have been nearly 800 heart-lung transplants in the United States. In 10 cases, the operation was performed twice on the same person, according to UNOS, but never before for this reason.

Santillan's benefactor, Mahoney, complained that Duke waited too long to admit its mistake. If Duke had taken action a few days earlier, Santillan would not have had to spend so much time on life support, he said.

"If you make a mistake, admit your mistake and take care of that child," Mahoney said.

Heather Adams, 12, a friend of Santillan's, made a brief, tearful appearance at the hospital's briefing on the teen's condition. "It was terrible when I found out, but now I just hope she makes it," she said. When a reporter asked Heather what she would ask others to do, she said: "Pray for her."

Special correspondent Bill Hatfield contributed to this report from Durham.

Jesica Santillan was listed in critical condition.Federico Santillan, an uncle of Jesica Santillan, leads family members in prayer in the visitors' room at Duke University Hospital in North Carolina.