Can the hospital release my son to someone who is not a parent or guardian?

I got divorced in December and found out my son had to have surgery on his mouth due to neglect of his hygiene. During the surgery, I informed the hospital that I am my son's mother and would like to be in recovery when he came out. They informed me that I will have to switch off with my son's grandmother because she had the security bracelet. I told them that was wrong because she has no authority over me to my son. My divorce decree says nothing about my son's grandmother. When he was out of surgery, I was NOT informed and the hospital released my son to his grandmother which is an employee of the hospital. My question is, what are my rights as my son's mother versus his grandmother as well as the hospital itself?