The Facebook post is a heart-wrencher. Pictures of 2-year-old Matthew Ouimet, hours after double transplant surgery, wearing a gauze cap to hold EEG probes in place. Reports from his mother Kristi of a strange episode in which, though sedated, he sits up in bed and opens his eyes, looks confused and doesn't immediately respond to pain stimulus.

It's touching. It's frightening. It begs 1,000 questions. Why is this happening? Is this normal? Is it because he's a child? Are there special challenges to performing transplant surgery on pediatric patients as opposed to adults?

Dr. Peter Stock, surgical director of the pediatric renal transplant program at UCSF's Benioff Children's Hospital and one of the surgeons who operated on Matthew, can answer that last question: Yes.

"Pediatric is more challenging in terms of size, and from a personal point of view," Stock said Thursday. "When you operate on a kid and things aren't perfect, it's so hard. You can explain to an adult that there are these risks and complications, but kids don't see that. Obviously, I want all my patients to have perfect outcomes. With a child, when you don't, when you walk into that room, it takes a toll. You can only imagine what it's like to see these adorable kids ... "

Matthew's situation is rare, as children comprise a small fraction of transplant recipients. According to the Organ Procurement and Transplantation Network, only 7.4 percent of all transplants performed in the U.S. since Jan. 1, 1988 involved patients 18 years old or younger.

It has little to do with the lack of suitably sized organs, Stock said.

"It's more that people don't proceed to end-stage kidney disease until they're older," he said. "(Children) don't have hepatitis, which is the most common reason we do liver transplants."

Sometimes the challenges are legal. On Thursday a judge ruled in favor of a 10-year-old Pennsylvania girl dying from cystic fibrosis whose family sued to get her placed on the adult waiting list for a lung transplant. The Organ Procurement and Transplantation Network, which has a priority policy of first offering adult lungs to adults and adolescents, complied with the ruling and added Sarah Murnaghan to the adult list, increasing her chances of lifesaving surgery.

The ruling could potentially have far-reaching consequences regarding what transplant candidates are eligible for what organs. A second lawsuit, on behalf of a Pennsylvania boy who also has cystic fibrosis, was filed Thursday.

The good news regarding Matthew, an Antioch toddler who is adorable by any objective criteria, is that he is recovering well from his 13-hour kidney and liver transplant that ended Wednesday morning. According to Kristi Ouimet, the bleeding around the transplanted liver which concerned doctors on Wednesday had slowed on Thursday. Doctors monitored his brain activity after the sitting-up episode, one of three he experienced Wednesday night, but found no abnormalities. His recovery seems to be going as well as can be expected.

"He is holding strong and doing great," Kristi Ouimet wrote in a more upbeat Facebook post on Thursday.

Matthew's surgery, like all pediatric transplants, presented technical challenges to Stock, who handled the kidney, and Dr. John Roberts, who handled the liver. For starters, size matters. A new kidney, for example, has to be small enough to fit inside a toddler's torso but big enough to withstand the rigors of transplantation.

"Rejection happens," Stock said, "and we can usually reverse it. If the rejection happens to a small kidney, it won't be able to recover. The kidney has to be big enough to resist the hits that happen after transplantation."

Matthew posed a challenge even beyond that. He was born with the genetic condition primary hyperoxaluria Type 1, a defect in his liver which left it unable to remove oxalates from his blood. Oxalate buildup can cause kidney failure, which Matthew experienced when he was 5 months old. For 23 months he required six four-hour dialysis treatments per week, which sustained him until his transplant. But it didn't completely clear his body of oxalates. That process could take another month.

"He was even more compromised because he needed a kidney and a liver," Stock said. "When we do a kidney transplant, there's a problem with (a recipient's) antibodies directed against the antigen in the (transplanted) kidney. That makes it difficult to match. If you need a kidney and a liver -- ideally from the same donor -- and the kidney needs to be well matched, it decreases the number of donors possible."

It took 15 months to find a matching kidney for Matthew. The accompanying liver had to be pared down.

"When you use a segment of a liver it increases the degree of difficulty," Stock said. "There is a higher rate of problems."

One universal challenge with all transplants is post-surgical complication.

"I, like my colleagues, hate any kind of complication and do not handle them well," Stock said. "I handle them less well when it's a child."

Contact Gary Peterson at 925-952-5053. Follow him on Twitter at twitter.com/garyscribe.