S.D. Codified Laws § 34-12C-3
In the absence of a durable power of attorney for health care or the appointment of a guardian of the person, or if neither the attorney in fact nor guardian is available to consent, a health care decision for an incapacitated person may be made by the following persons or members of the incapacitated person's family who are available to consent, in the order stated:
However, any person may, before a judicial adjudication of incompetence or incapacity, disqualify any member of the person's family from making a health care decision for the person. The disqualification shall appear in a document signed by the person or may be made by a notation in the person's medical record, if made at the person's direction.
Any member of the incapacitated person's family may delegate the authority to make a health care decision to another family member in the same or succeeding class. The delegation shall be signed and may specify conditions on the authority delegated.
Any person authorized to make a health care decision for an incapacitated person shall be guided by the express wishes of the incapacitated person, if known, and shall otherwise act in good faith, in the incapacitated person's best interest, and may not arbitrarily refuse consent. Whenever making any health care decision for the incapacitated person, the person available to consent shall consider the recommendation of the attending physician, the decision the incapacitated person would have made if the incapacitated person then had decisional capacity, if known, and the decision that would be in the best interest of the incapacitated person.
SDCL 34-12C-3