After days of a cautious optimism, the 88-year-old pontiff suffered a setback on Friday, experiencing an "isolated breathing crisis" that required non-invasive, mechanical ventilation, the Vatican said.
The pope, it said, also had "an episode of vomiting with inhalation and a sudden worsening of the respiratory condition." He needed aspiration to help remove the vomit from his airways, the Vatican added.
His doctors are expected to take 24-48 hours to evaluate how the episode will impact the state of his clinical condition.
"The night passed peacefully, the pope is resting," the Vatican said on Saturday, giving no further details. The next medical bulletin is expected at around 7 p.m. (1800 GMT).
Francis was admitted to Rome's Gemelli hospital on February 14 with a severe respiratory infection that degenerated into double pneumonia - a serious infection of both lungs that can inflame and scar them, making it difficult to breathe.
Francis has suffered several bouts of ill health over the past two years and is especially prone to lung infections because he developed pleurisy as a young adult and had part of one lung removed.
