Pope Francis is in critical condition and his "prognosis remains guarded" as he experienced a respiratory crisis Saturday morning requiring oxygen and blood transfusions, the Vatican said Saturday night.

The 88-year-old pontiff, who was admitted to the hospital last week, is being closely monitored by doctors as he undergoes treatment.

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