Mo. Rev. Stat. § 431.063
In addition to any other instances in which a lack of consent is excused or in which a consent is implied at law, a consent to surgical or medical treatment or procedures shall be implied where an emergency exists if there has been no protest or refusal of consent by a person authorized and empowered to consent, or, if so, there has been a subsequent change in the condition of the person affected that is material and morbid, and there is no one immediately available who is authorized, empowered, willing and capacitated to consent. For the purposes hereof, an "emergency" is defined as a situation wherein, in competent medical judgment, the proposed surgical or medical treatment or procedures are immediately or imminently necessary and any delay occasioned by an attempt to obtain a consent would reasonably jeopardize the life, health or limb of the person affected, or would reasonably result in disfigurement or impairment of faculties.
§ 431.063, RSMo