Notwithstanding the provisions of sections 334.400 to 334.430, or the rules of the Missouri state board of registration for the healing arts, the governing body of every hospital shall have full authority to limit the functions and activities that an anesthesiologist assistant performs in such hospital. Nothing in this section shall be construed to require any hospital to hire an anesthesiologist who is not already employed as a physician prior to August 28, 2003.