ROME — Pope Francis remained in critical condition Sunday and blood tests show early kidney failure but he remains alert and “well-oriented,” and attended Mass, the Vatican said, as the 88-year-old pontiff battles pneumonia and a complex lung infection.

The announcement on Saturday evening indicated that Francis’ medical condition had become more complicated since an update from his doctors on Friday.

The death of a sitting pope initiates a profound period of mourning and transition within the Roman Catholic Church, marked by a meticulously structured process to elect a new pontiff