Who can be a patient care advocate in the hospital?

A patient care advocate is a person who speaks on behalf of the patient and insures the best possible care.
It is very difficult to see a loved one in the hospital especially in an Intensive Care setting. It is extremely difficult for a child (no matter the age) to see a parent so vulnerable and helpless.
I have been told that a patient gets better care if a loved one oversees the care of their family member. I have seen this first hand.
What happens in a situation when there is no family nearby, can friends act as the patient advocate? I believe that family has a special bond. While friends can support the caregiver, I think it is imperative for family to interact with the patient. It makes a world of difference.