Pope Francis has had surgery to remove part of his left colon in what the Vatican has described as a planned procedure. Doctors say the bowel problems that the 84-year-old pope was experiencing are very common in older people, although only about 10% to 20% of people with similar problems require surgery. Here's a look at what we know about the operation and what the pope's doctors will be watching out for:

WHAT KIND OF SURGERY DID THE POPE HAVE?

According to the Vatican, Pope Francis had the left part of his bowel removed in a three-hour operation Sunday at a Rome hospital. Officials said it was required because the pope’s bowel had narrowed.

Dr. Manish Chand, an associate professor of surgery at University College London who specializes in colorectal surgery, said the pope had likely been experiencing painful symptoms long before the bowel procedure. He was not involved in the pope's care.

Although minor symptoms can be treated with antibiotics, Chand said in some older people, the pain becomes so severe that removing part of the colon is the only way to fix it.

“That leads to scarring of the colon, which results in a narrowing part of the colon,” Chand said, explaining that prevents normal bowel movements. “There aren’t any drugs we can use to remedy the situation, so the only way to rid patients of the pain is by removing that narrowed portion of the bowel and join the two healthy ends of the bowel together.”

WHAT ARE THE RISKS OF COMPLICATIONS?

Although the pope's surgery was planned, it was not minor.

“This is a major operation, so as with any big operation, you want to make sure a patient’s heart and lungs are recovering and progressing the way they should after something like this,” said Dr. Walter Longo, chief of colon and rectal surgery at Yale University School of Medicine. Longo said the primary concern is ensuring that the two parts of the bowel that surgeons have stitched together remain attached.

“The biggest risk is that this fails, and the patient experiences more pain, a fever, and there’s evidence of infection,” Longo said. “If that happens, then another operation would be needed to hook (the colon) back together.” He said that is extremely rare and that only two to three out of 100 surgeries would result in a repeat surgery.

Chand said if there are no complications, he would expect the pope to experience an almost immediate improvement in his quality of life and be back to eating regularly within days.

WHAT ARE DOCTORS WATCHING OUT FOR NOW?

The Vatican said Francis is expected to spend a week in Rome’s Gemilli Polyclinic recuperating. Given the pope’s previous respiratory issues — he is missing part of his right lung after having it removed following a severe bout of pneumonia in his youth — Chand said doctors would need to monitor his breathing carefully.

“In the case of having previous problems with the lung, there is always a concern after the major abdominal surgery of the risk of getting a chest infection," Chand said. He said the pain might make it difficult for the pope to breathe deeply, preventing the lungs from expanding fully and getting rid of any fluid that could cause problems.

On Monday, Vatican officials said the pope was breathing on his own.

HOW LONG WILL IT TAKE FOR THE POPE TO RECOVER?

Chand said even if the pope began to feel better soon, it would take weeks for someone to recover from losing half their colon and that he would likely feel very fatigued. Longo said it would likely take the pope about four to six weeks of recovery before he might be able to resume his normal duties.

“This is a big operation for a man in his 80s, even though I understand he was in fine condition before,” Longo said. “There’s no question he will require a lot of physical therapy and recovery time.”

Longo recommended that the pope increase his fiber intake in the future and predicted he would be back to normal within several months.

Shortly before his surgery, the pope announced Sunday that he would visit Slovakia and Hungary for a few days in mid-September.