After a breathing crisis on February 28 that involved Francis nearly choking on his vomit, "there was a real risk he might not make it," said Sergio Alfieri, a physician at Rome's Gemelli hospital.
"We had to choose if we would stop there and let him go, or to go forward and push it with all the drugs and therapies possible, running the highest risk of damaging his other organs," Alfieri told Italy's Corriere della Sera in an interview published on Tuesday.
"In the end, we took this path," he said.
Francis, 88, returned to the Vatican on Sunday after the most serious health crisis of his 12-year papacy.
He was admitted to Gemelli hospital on February 14 for a bout of bronchitis that developed into double pneumonia, an especially serious condition for him, as he had pleurisy as a young adult and had part of one lung removed.
Alfieri had previously said that two of the crises were critical, putting Francis "in danger of his life". In the new interview, the doctor said it was the pope's personal nurse who, after the vomiting episode, instructed the medical team to keep going with treatment.
"Try everything; don't give up," came the message from Massimiliano Strappetti, the pope's nurse, as recounted by Alfieri.
"For days, we were risking damage to his kidneys and bone marrow, but we went ahead, and his body responded to the drugs and his lung infection lessened," said Alfieri.
Francis has been prescribed a further two month period of rest since leaving hospital to fully heal. It has not been made clear how much he will be seen in public in coming weeks.
Recounting the pope's first public appearance since entering hospital, when Francis appeared on a hospital balcony to greet well-wishers on Sunday, Alfieri said that was the moment of the pope's treatment that struck him the most.
"I saw him leave the room on the 10th floor of the Gemelli dressed in white," said the doctor. "It was the emotion of seeing the man become again the pope."
