One method used by surrogate decision makers to make health care choices for others is the standard of substituted judgment. This standard is used when the patient has expressed preferences before becoming incapacitated, and the surrogate knows the patient well enough to determine what he or she would decide. Surrogate decision makers are best assisted in making choices based on the person's own preferences if he or she has completed a document known as a Health Care Directive. Even when the standard of substitute judgment is used, however, the decision maker and physicians must nevertheless keep in mind the best interests of the patient.

Example: Thirty-year-old Michael, the father of two small children, arrives at the emergency room in critical condition after an auto accident. He has a signed Health Care Directive, which he completed after watching his great-grandfather die slowly of cancer, "attached to machines," as he put it. Michael was so adamant that he never be left in the same state that he included an instruction refusing mechanical ventilation and medically assisted nutrition and hydration. His wife is acknowledged as his surrogate decision maker, since he is unconscious. Physicians tell her that while he is in critical condition, they believe that he might not only survive, but will probable be "good as new" within a year. At the moment, however, he needs surgery, and will likely need to be on a ventilator and medically assisted nutrition and hydration for a few weeks. Though his Advanced Directive specifically say not to use such technology, his wife and physicians agree that it would be in his best interest to do so. This ethical decision is made for several reasons: (1) His wife is sure that what Michael meant was that he did not want such technologies on a permanent, or even long-term basis. (2) She is assured that physicians do not believe that is the case, and (3) if it is, the technologies could be removed at a later date. In essence, with a good prognosis for full recovery, it is determined to be in his best interest, and not really contrary to his intention in making his advance directives, to use the technologies for a trial period. In this way, his autonomy is respected, at the same time that he is being treated with beneficence (Also see the Best Interest Standard.)