ROME >> Pope Francis suffered an isolated coughing fit on Friday that resulted in him inhaling vomit and requiring non-invasive mechanical ventilation, the Vatican said in relaying an alarming setback in his two-week long battle against double pneumonia.

The 88-year-old pope remained conscious and alert at all times and cooperated with the maneuvers to help him recover. He responded well, with a good level of oxygen exchange and was continuing to wear a mask to receive supplemental oxygen, the Vatican said.

The episode, which occurred in the early afternoon, resulted in a “sudden worsening of the respiratory picture.” Doctors decided to keep Francis’ prognosis as guarded and indicated they needed 24 to 48 hours to evaluate how and if the episode impacted his overall clinical condition.

The development marked a setback in what had been two successive days of increasingly upbeat reports from doctors treating Francis at Rome’s Gemelli hospital since Feb. 14. The pope, who had part of one lung removed as a young man, has lung disease and was admitted after a bout of bronchitis worsened and turned into pneumonia in both lungs.

Dr. John Coleman, a pulmonary critical care doctor at Northwestern Medicine in Chicago, said the episode as relayed by the Vatican was alarming and underscored Francis’ fragility and that his condition “can turn very quickly.”

“I think this is extremely concerning, given the fact that the pope has been in the hospital now for over two weeks, and now he’s continuing to have these respiratory events and now had this aspiration event that is requiring even higher levels of support,” he told The Associated Press.

“So given his age and his fragile state and his previous lung resection, this is very concerning,” added Coleman, who is not involved in Francis’ care.

Dr. William Feldman, a pulmonary specialist at Brigham and Women’s Hospital in Boston, said it was a good sign that the pope remained alert and oriented, but concurred that the episode marked “a worrying turn.”

“Often we will use noninvasive ventilation as a way of trying to stave off an intubation, or the use of invasive mechanical ventilation,” Feldman said.

Types of noninvasive ventilation include a BiPAP machine, which helps people breathe by pushing air into their lungs. Doctors will often try such a machine for a while to see if the patient’s blood gas levels improve so they can eventually go back to using oxygen alone.

The episode, which doctors described as an “isolated crisis of bronchial spasm” began as a coughing fit in which Francis inhaled vomit. The longer respiratory crisis Francis suffered on Feb. 22 was a longer crisis in actually breathing, the Vatican said.

Doctors did not resume referring to Francis being in “critical condition,” which has been absent from their statements for three days now. But they say he isn’t out of danger, given the complexity of his case.