Here’s a link to an interesting article in the New York Times about advance directives.  Much like birthing plans, it is difficult to know in advance exactly what care you will want to have when the time comes.  Better to designate a person you know and trust to make health care decisions for you if you are unable to make such decisions for yourself.  Make time to discuss at length your thoughts on quality of life with that person on a regular basis so he or she feels comfortable in the decision making.  Be sure your health care providers have the documentation in your medical records with current contact information for your designated agent.