ROME, Italy — 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.

Earlier on Friday, Francis had spent the morning alternating high flows of supplemental oxygen with a mask and praying in the chapel. He had breakfast, read the day’s newspapers and was receiving respiratory physiotherapy, the Vatican said.

The Vatican also published a document signed by Francis on Feb. 26 “From the Gemelli Polyclinic,” a new official tagline that showed Francis was still working from the hospital.

Late on Friday, Francis’ closest friend in the Vatican bureaucracy, Argentine Cardinal Victor Manuel Fernández, led the nightly prayer in St. Peter’s Square to pray for Francis’ health.

With other cardinals bundled against the night chill, Fernández urged the crowd to pray not just for Francis but for others as the pope himself would.

“Certainly it is close to the Holy Father’s heart that our prayer is not only for him, but also for all those who in this particular dramatic and suffering moment of the world, bear the hard burden of war, of sickness, of poverty,” said Fernández, the Vatican’s doctrine chief.

In Mexico City, a few dozen people gathered Thursday night at the cathedral to pray for Francis’ recovery.

“He is like part of the family,” said Araceli Gutiérrez, who treasures the time she saw the pope during his trip to the country of nearly 100 million Catholics in 2016. “That’s why we feel so concerned for him.”

María Teresa Sánchez, who was visiting from Colombia with her sister, said that she has always felt close to Francis — the first Latin American pope.

“That’s like having a relative within the higher-ups, with God,” she said. “He has done so much for religion; he’s such a humble person.”

Given his continued hospitalization, Francis’ near-term upcoming calendar of events was being changed: The Vatican canceled a Holy Year audience scheduled for Saturday, and it remained to be seen if Francis would skip his Sunday noon blessing for the third week in a row. With Ash Wednesday now delegated to a cardinal, the next major events come during Holy Week and Easter, which this year falls on April 20.

In past years, when Francis has battled bronchitis and influenza in winter, he curbed his participation in Ash Wednesday and Holy Week events, which call for the pope to be outdoors in the cold leading services, participating in processions and presiding over prayers in the solemn period in which the faithful commemorate Christ’s crucifixion and resurrection.

Beyond that, Francis has a few major events coming up that he presumably would hope to keep if well enough. On April 27, he is due to canonize Carlo Acutis, considered to be the first millennial and digital-era saint. The Vatican considers the Italian teenager, who died of leukemia in 2006 at the age of 15, an inspiration for young Catholics.

Another important appointment is the May 24 commemoration of the 1,700th anniversary of the Council of Nicea, Christianity’s first ecumenical council. The spiritual leader of the world’s Orthodox Christians, Patriarch Bartholomew I, has invited Francis to join him in Iznik, Turkey, to commemorate the anniversary, which he has called an important sign of reconciliation between the Catholic and Orthodox churches. Before he got sick, Francis said he hoped to go, though the Vatican hasn’t confirmed the trip.

Maria Hernandez contributed from Mexico City.

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