I think it’s very uncommon for health care proxies to be people who aren’t close to you. What you’re asking about is pretty much what happens if you don’t designate a health care proxy: professionals responsible for your care use their best judgment to do right by you, but don’t really know your wishes and preferences. A well-crafted advance directive can guide those professionals regarding your preferences, but it’s hard to do better than a thoughtful, caring loved one or friend who has agreed to take on the job if it becomes necessary.
A good estate attorney can help you prepare an advance directive that complies with your state’s laws and conforms to your wishes. These documents are typically prepared at the same time wills are prepared or updated.