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.

Pope Francis, battling double pneumonia, remains in a critical condition and his prognosis is still guarded because of the "complexity" of his clinical condition, the Vatican said on Sunday.

What does Pope Francis having "double pneumonia" mean? What should you look for in the elderly? How can you avoid getting pneumonia?