EWTN Catholic Q&A
Sick Popes
Question from martin deschner on 04-02-2005:

I was wondering in papal history, has a regent ever been appointed to rule on behalf of an ailing pope?

Answer by David Gregson on 04-03-2005:

Actually the members of the Pope's Curia are his regents in certain areas, e.g., doctrine, worship, but there are some things only the Pope himself can do, e.g., appoint bishops and canonize Saints. That's not a power that can be delegated.