There are a couple of different things to think about. Are you wanting someone to tell doctors what you want if you are not able to speak for yourself? If so you might want to look into a living will or power of attorney. Are you wanting someone to be contacted in the case that you are incapacitated? Do you have any friends who you would want to be contacted? If not a friend a religious/spiritual leader? You should figure out what you want for this person to be able to do for you. Checking with a lawyer about what the legal options you have would be a good idea to find out what would fit your situation and needs best.