The most appropriate person to act as substitute decision-maker is someone appointed by the patient while he or she is still capable, or by a proxy advance directive or by a court. Other substitute decision-makers, in their usual order of ranking, include the patient's spouse or partner, child, parent, sibling or other relative. In some jurisdictions a public official will serve as substitute decision-maker for a patient who has no such person available. The criteria on which the decision should be based are the specific wishes previously expressed by the patient, the patient's known values and beliefs, and the patient's best interests. The patient's wishes are those preferences expressed by the patient while he or she was competent that seem to apply to the decision that needs to be made.
Some patients record their wishes in an advance directive.
Values and beliefs are less specific than wishes but allow the substitute decision-maker to infer, in light of other choices the patient has made and his or her approach to life in general, what he or she would decide in the present situation. The calculation of a patient's best interests is based on objective estimates of the benefits and burdens of treatment to the patient. The role of the health care professional is to facilitate the process of substitute decision-making by providing information that will enable the substitute to make an informed choice on the patient's behalf. When it is apparent that the substitute is making a choice that is significantly different from what the patient might have chosen, health care providers find themselves in a difficult situation and should seek advice from colleagues, ethics committees and legal counsel. The cases Mr. N is incapable because of his AIDS-related dementia.