You do not have to sign an AD if you don't like what it says. You can always prepare your own AD instead. I learned that in Oregon, even though doctors were given legal immunity, they say they do not have to follow AD's. In addition, they say that they are not obligated to follow the health care agent's decisions. Select a good health care agent.
Some states prevent certain people from becoming agents.
For example the state of Washington excludes your treating provider, and the operators of certain care facilities. These provisions help prevent conflicts of interest. Make the AD accessible. Ensure that a person's updated AD is at the right place at the right time in a manner that recognizes the principal's need for confidentiality. In urban areas, where someone could be taken to any number of emergency facilities, this is a big barrier.