LONDON (AP) — Pope Francis was admitted to a Rome hospital for abdominal surgery on Wednesday afternoon after developing a painful hernia linked to a 2021 operation to remove a significant portion of his large intestine, the Vatican said.

Here's a look at what we know about the operation and what potential complications doctors will be watching for in the 86-year-old pontiff.

WHAT KIND OF SURGERY IS THE POPE HAVING?

Pope Francis is undergoing a laparotomy, a surgery that involves opening up the abdomen to expose internal organs, and doctors planned to insert a prosthesis while he was under general anesthesia.

Doctors not linked to the pope's care said hernias were a known complication after previous operations and typically only become problematic when patients develop a bulge in their abdomen and experience significant pain. The Vatican said Francis had been in increasing pain.

Dr. Walter Longo, chief of colon and rectal surgery at Yale University School of Medicine, said the pope's physicians were likely concerned that the hernia might mean that Francis' intestines were “trapped," which could lead to severe bowel problems.

“When you're older and not in great shape, you can get a hernia through the (surgical) incision,” he said. That could result in twisted intestines that cut off the blood supply to the bowel, ultimately leading to gangrene, if left untreated.

“They have to fix it, there's no other option,” Longo said.

Dr. Manish Chand, a British colorectal surgeon, said the addition of a mesh prosthesis should significantly reduce the chances that the Pope would need further intestinal surgeries.

“The mesh is there to reinforce that area so this problem doesn't happen again in the future," Chand explained.

WHAT OTHER COMPLICATIONS ARE POSSIBLE?

Francis had 33 centimeters (13 inches) of his large intestine removed two years ago. He was hospitalized earlier this year for bronchitis, and lost part of one lung decades ago.

Doctors noted that patients older than 80 are often more susceptible to complications after general anesthesia and said the team treating the pope at Rome's Gemelli hospital would be monitoring him for problems such as stroke, heart issues, kidney failure and pneumonia.

“When you operate on older people and they’re frail and fragile, they’re not as peppy as they once were,” Longo said. “But if he gets through the operation and does fine, he should be OK.”

Dr. Robin Phillips, an emeritus professor of colorectal surgery at Imperial College London, pointed out that abdominal surgery can also compromise lung function.

“I suspect they are doing it now because they are worried it might become more complicated and result in an emergency operation which would carry an even bigger risk than leaving it alone or operating now,” Phillips said.

HOW LONG WILL IT TAKE THE POPE TO RECOVER?

In a best-case scenario, probably at least six weeks. Chand described the procedure as “straightforward” and said most patients are discharged from the hospital within about a week.

How long it takes the pope to resume his normal duties will depend on his doctors' ability to manage his pain. The chances of a recurrence are also highest within the first six weeks, Chand said.

Doctors said the recovery time would also depend on what they find during his surgery, noting it might be necessary to remove more of his large intestine.

Dr. P. Ravi Kiran, chief of colorectal surgery at Columbia University, said it was possible the pope's intestines might have been damaged if the blood supply was constricted. That might require removing another section of his colon.

“That then has implications for healing, where the bowel has been joined back together,” Kiran said. He said it would take several days for Francis' bowels to start working again and to recover from the effects of anesthesia.

Kiran recommended the pope stick to a healthy diet with lots of fiber but said he did not anticipate any major changes to the pontiff's lifestyle following Wednesday's surgery. Others said they expected Francis to be able to resume his travel schedule within weeks.

“Any weakness in his abdominal wall ... (,) provided it's fixed securely, shouldn't be a problem,” Kiran said. “I'm really wishing the pope a speedy recovery.”