Choosing to Forego Food & Water in Advance Directives

My colleague in UST's Catholic Studies Department, Paul Wojda, had the following question about the recent CDF Responses to the USCCB on withdrawing food & hydration from persons in a persistant vegetative state.

I have yet to see any official consideration of whether an individual may legitimately decide (through an advance directive) whether to withdraw or forego tube feeding in these circumstances. As I read the CDF clarification it really doesn’t say anything new. The commentary is at pains to point out the continuity between Pius XII and JPII on this issue, but that too never addresses the issue from the “agent’s” perspective.

May a Catholic, in good conscience, and through an advance directive, elect that tube-feeding be withdrawn upon diagnosis of PVS?

The CDF statement simply doesn’t address this question, as far as I can tell.

My own answer would be that, yes, a Catholic may do so, based on longstanding principles informing end-of-life decision-making, i.e., determination of excessive burden and hope of success. I believe that Pius XII’s famous statement reinforces this position quite clearly.

I think it's a particularly interesting question to consider in light of the recent press coverage of Pope John Paul II's medical treatment during his last days.  Of course JP2 was not in a PVS, but it raises the possibility that he might have been exercising his own judgement about tube feeding toward the end of his life, and prompts me, too, to wonder whether he might legitimately have made such a decision for himself in an advance directive.