“This is the first time I had a patient ready to be wheeled into the operating room when I received a call like this,’’ said Dr. Elizabeth Pomfret, chairwoman of the of the department of transplantation at Lahey. “It certainly added to the stress.’’

But a member of the medical team who flew to St. Louis to inspect the organ found it had suffered too much trauma.

On Jan. 3, Theerman checked in at the Lahey Clinic in Burlington. His son was taken to Children’s Hospital Boston. Just as doctors inserted intravenous lines and prepared to wheel the father into the operating room, they received a call telling them to stop. A liver from a dead infant had possibly become available.

Since such procedures began in Chicago in 1989, only 1,036 livers have been transplanted from a living parent to a child, according to the Organ Procurement and Transplantation Network, a Virginia-based organization that oversees organ transplants nationally for the federal government.

There are roughly 600 pediatric liver transplants every year nationwide, but only about 10 percent come from a living donor, which is almost always a relative, officials at the Lahey Clinic Medical Center in Burlington said.

“Because he was not getting offers, we didn’t want to wait until he was extremely sick before he got a transplant,’’ Jeremy Theerman said yesterday. “The options were pretty stark. If you don’t do it, your kid has a pretty good chance of not pulling through. So you just do it. I had no hesitation.’’

By January, the desperate family decided to take the ultimate risk: Jeremy Theerman, the boy’s father, volunteered to have a portion of his liver removed to try to save his son’s life. The rare operation carried the small possibility the father might die.

Three months after the boy’s name went on the list, and even though he had received priority status, no donor for Tristan could be found.

The odds were long, given that more than 16,000 people in the country were seeking a liver transplant and only about 6,000 donations are made each year. The odds were more difficult for Tristan, because babies usually require transplants from other infants or a living relative, or part of an adult cadaver’s liver. And infants have the highest mortality rate of those on the waiting list, his doctors said.

“I was a wreck,’’ said Caroline Theerman, the boy’s mother. “He seemed fine other than being jaundiced.’’

A few weeks and some medical tests later, the Worcester parents discovered their son had an extremely rare disease. Without a liver transplant within a few months, they were told, he would die.

Soon after his birth in June, it became clear something was deeply wrong with Tristan Theerman. The baby boy’s eyes and skin looked sallow. He failed to gain weight and refused to eat. His belly grew distended, filled with fluid.

Three days later, Theerman came back to Lahey for the five-hour operation. Doctors opened his abdomen and removed about 15 percent of the left lobe of his liver, which they soaked in a special solution and put in an ice-packed cooler.

A Children’s Hospital doctor then ferried the portion of liver to Boston, where the boy was being prepped for his own procedure, one designed to cure his biliary atresia, a congenital disease that destroys the liver’s bile ducts and affects 0.005 percent of children.

The boy had been surviving to that point on a feeding tube through his nose. He faced a 20 percent chance of dying as a result of the operation.

“It’s definitely a day I never want to have to relive,’’ the boy’s mother said. “I experienced tons of emotions. I felt bad that I couldn’t be there for Jeremy, and I couldn’t really do much for Tristan. I was just so lucky that it was finally happening.’’

The results seemed almost instantaneous.

When the father awoke and reached his wife on the phone, they shared good news. His operation went well, and their son was in recovery, with his skin already looking normal, his belly drained of fluid, and with enough strength that he was pulling out his intravenous lines.

“It was just such a relief,’’ Caroline Theerman said. “He was hooked up to a lot of monitors, but he just looked awesome.’’

Her husband spent the next four days in the hospital. But he has since made almost a full recovery, and his liver is expected to regenerate fully within a year.

When Jeremy Theerman finally saw Tristan, who spent several weeks at Children’s, he knew the pain was worth it.

“It was very emotional to see him, and to see how well he was doing,’’ he said. “He looked like a totally new person — much, much healthier. It was just great, very uplifting. Before, I was absorbed with what was going on with me, and that brought me back to the big picture.’’

Tristan now has to take about eight medications a day to ensure his body does not reject the liver and to strengthen his immune system. His doctors say his outlook looks good, but because such procedures are relatively new, they cannot say for certain whether he will be able to live a full life or require a new transplant.

“The prognosis is excellent, but he needs lifelong immunosuppressant drugs,’’ said Dr. Scott Elisofon, associate director of the Center for Childhood Liver Disease at Children’s Hospital Boston and the boy’s primary liver doctor. “I think he can expect to live a long life.’’

In the meantime, his parents are ecstatic.

They watch with joy as he eats and gains weight. They encourage him as he starts to roll around. He has even started babbling what sounds like words.

“Dada,’’ he says now. “Dada.’’

His mom insisted she takes no offense. “I’ll let it slide,’’ she said. “After all, he has his liver.’’

His dad says he now looks at the world differently and appreciates what he has even more.

“All I can say is that we are very, very fortunate,’’ Jeremy Theerman said. “It’s a lot to go through, but when your kid’s life is at stake, you do what you have to do.’’

David Abel can be reached at dabel@globe.com.

© Copyright 2011 Globe Newspaper Company.