An advance care directive is a document that specifies the care a person wishes to receive in case that they are unable to communicate their wishes, such as being in a coma. To be enforceable, the person making the directive must be of sound mind, meaning that they are still able to think rationally and communicate their wishes in a clear manner. The document must be signed and notarized according to the laws in your state. Laws governing advance care directives vary by state, so local laws should be consulted for specific requirements in your area.
A durable power of attorney for health care is a power of attorney where the principal appoints an agent to make health care decisions for the principal and is remains effective even after the incompetence of the principal. It is often used as a form of advance health care directive.