There are two types of Advance Directives. The one most people have heard about is a "Living Will." This is a document in which you specify exactly the sorts of treatment you want or do not want only if you become terminally ill and are no longer able to direct your own care. They typically offer choices of such medical procedures as cardiac resuscitation, being placed on a ventilator, being fed and kept hydrated artificially, and having antibiotics administered.
The second type is called a "Health Care Proxy," or Health Care Power of Attorney. This document names the person or persons you have the most confidence in to direct you health care if you cannot. It can be exercised only when you are unable to speak for yourself, for instance if you are anesthetized or in a coma. This document is considerable more flexible than a Living Will, which is a great advantage in a serious, but not necessarily fatal situation.
Both of these documents are revocable at any time, and can be canceled or changed by your vocal orders.
