Consistent with the nature of each right in § 5182 of this title, the entitlement may devolve to the patient representative. Authority to act on behalf of patients who are minors may be exercised by the minor's parent, guardian, or custodian. Authority to act on behalf of an adult patient may be exercised by a guardian acting within the scope of appointment or through an agent acting pursuant to a valid power of attorney, health-care directive, or similar instrument. In the absence of such authorized representative, if the patient's physician determines that the patient is incapable of exercising rights under this subchapter due to mental or physical incapacity, authority to exercise such rights shall devolve to the patient's next of kin.