Surgeons at Johns Hopkins Hospital tethered a 25-year-old woman to a pig's liver in August to save her from certain death, then transplanted a human organ into her the next day when one suddenly became available.
It is thought to have been the first successful use of an animal liver as a bridge to a human transplant.
The announcement at Hopkins Hospital came yesterday, a day after a woman who had received a transplanted pig liver at Cedars-Sinai Medical Center in Los Angeles died of complications from acute liver failure, though the animal's liver had been functioning, doctors said.
In the Hopkins Hospital procedure, the pig's liver was kept in a plastic bag at the woman's bedside, bathed in fluids secreted as part of the organ's natural processes.
The organ, which filtered toxins from her bloodstream, was connected to her body by two plastic tubes.
"It was the shortage of human organs that really makes this necessary," said Dr. Andrew Klein, director of the Hopkins Hospital liver transplantation program.
Susan Okon of Hyattsville said yesterday she was surprised but not at all bothered to learn after the transplant that a pig's liver had been used to buy her extra time.
Dr. Jeffrey Fair, a member of the surgical team, said the decision was made to use the liver as an external filter -- rather than transplanting it -- because it was a minimally invasive procedure involving the connection of tubes to two veins in her groin.
Ms. Okon suffered from hepatitis B but did not suffer serious liver problems until last summer, when she became jaundiced and plunged into acute liver failure. Within a week, she was in a deep coma at Washington Adventist Hospital in Takoma Park.
She wasn't there 12 hours before doctors realized she would die without a liver transplant, and had her transported to Johns Hopkins Hospital.
Her brain had become extremely swollen because of the toxins circulating in her bloodstream.
When it became apparent that no livers were available, doctors decided that an animal graft was the only option that offered any hope of keeping her alive while the search continued for a human organ.
"As far as we knew, she had no other illness that should be robbing her of a full life," said Dr. Anna Mae Diehl, a liver specialist who cared for Ms. Okon.
"This was a new procedure, and we had to make sure all of us were in agreement that this was the thing to do."
She said doctors had no ethical problems with sacrificing a pig to keep the patient alive. The ethical question was whether the procedure itself was right for her medically.
A proposal to try the procedure on Ms. Okon was presented to an in-house ethics committee that reviews uses of animals, and it approved.
"This is a decision you have to make in your heart of hearts," Dr. Klein said. "Seeing a young girl dying, I thought it was appropriate to do exactly what we did."
Dr. Klein said he feels more comfortable about sacrificing a pig to support human life rather than using endangered species like the chimpanzee or baboon. Recent attempts at using primate organs have failed.
The technique of filtering blood externally through an organ is called xenoperfusion.
In the United States and Britain, attempts at xenoperfusion were made in the 1960s and 1970s but they failed because doctors did not have the long-term solution of transplanting a human organ.
Dr. Fair said the pig's liver offers a one- to two-day window before a human liver must be transplanted. Any longer than that, and the body will reject the animal organ to the point where it would no longer be viable.
One tube carried blood from a vein in Ms. Okon's groin to a pump, which sent the blood along to the liver. After circulating through the organ, the blood returned to her body via a tube connected to another vein in her groin.
As the pig's liver did its work, Ms. Okon gradually emerged from her coma. She became so alert that doctors decided to sedate her out of fear she would start tearing at her tubes.
"I remember one point when I opened my eyes," she said yesterday. "I was lying down. I looked at the right, and saw an IV pole. I looked to the left, and a nurse was coming my way. I thought, 'What am I doing in the hospital? This has to be a nightmare.' "Then I closed my eyes. I think I was asleep for a while."
Ms. Okon said her next memory was waking up hours after the transplant.
The pig's liver functioned so well that doctors disconnected it after four hours, feeling that the patient's condition was stable enough for her to remain off the liver for several hours.
Also, they had heard that an organ had been found and was hours away from arriving at the hospital.
The pig liver was disconnected at 11:10 p.m. on August 3. By noon the next day, the new human liver was functioning inside Ms. Okon's body.