Mo. Rev. Stat. § 404.822

In making any health care decision in accordance with sections 404.800 to 404.865, the attorney in fact shall seek and consider information concerning the patient's medical diagnosis, the patient's prognosis and the benefits and burdens of the treatment to the patient. In withdrawing treatment, which withdrawal will allow the preexisting condition to run its natural course, the attorney in fact shall seek evidence of the medical diagnosis and the prognosis and the benefit and burden of the treatment to the patient to the extent possible within prevailing medical standards.