Hi Blue Grass,
As you know the general rule is that the parents of a child have the authority to consent to or refuse medical treatment and procedures as long as it is in the best interests of the child, unless the child is of an age such that they are considered to have the capacity necessary to make the decision themselves (i.e. what the court may consider a "mature minor")
Both parents have the authority to authorise treatment of a child so usually consent of either parent will be sufficient. Unless there is a family court order removing one parent's responsibility or authority, even parents who are legally separated each retain responsibility to make decisions in the best interests of the child. However if both parents cannot agree about whether to authorise a medical procedure on behalf of the child, the decision may need to be made by a court.