Subject is in coma how to take informed consent?

Ask for living will or DNR order.Otherwise next of kin. If none available, must petition court, having court appointed, disinterested advocate for patient. Patient may have Healthcare or Durable Power of Attorney with a non-related friend or partner. In an emergency, doctor may administer treatment as s/he sees fit if none of these options are available and timely treatment is necessary to save a patient's life.