It added that the pope needed supplemental oxygen and blood transfusions.
The Vatican said in a statement that the 88-year-old pontiff, who is suffering from double pneumonia, experienced a prolonged "asthma-like respiratory crisis" on Saturday morning, "which required the administration of high-flow oxygen."
"Today's blood tests also revealed thrombocytopenia, associated with anemia, which required the administration of blood transfusions," the statement said.
Pope Francis. Photo: PAP/EPA/VATICAN MEDIA HANDOUT
"The Holy Father's condition continues to be critical," the Vatican announced. "The Pope is not out of danger."
The statement added that Francis "remains alert and spent the day in an armchair, although he is more uncomfortable than yesterday."
"At the moment, the prognosis remains guarded," the Vatican said.
Francis, who became pope in 2013, was admitted to Rome's Gemelli hospital on February 14 after experiencing difficulty breathing for several days, the Reuters news agency reported.
Francis, pictured on February 12, two days before he was admitted to Rome's Gemelli hospital. Photo: PAP/Abaca
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Source: IAR, PAP, Reuters, vaticannews.va