Thanks for the link. You are right that is is not an easy subject. I will read more about it.
Euthanasia and Extraordinary Care
Ordinary and Extraordinary Means of the Preservation of Life: The Teaching of Moral Tradition
NCBC's A Catholic Guide to End-of-Life Decisions (scroll down to Obligatory and Optional Medical Means)
Bioethical Magisterium on Normal Treatment and Ordinary Care: Medically Assisted Feeding and Hydration
Ordinary vs. Extraordinary Care: A Moral Dilemma