Mo. Rev. Stat. § 194.005: Death, legal definition.

For all legal purposes, the occurrence of human death shall be determined in accordance with the usual and customary standards of medical practice, provided that death shall not be determined to have occurred unless the following minimal conditions have been met:

(1) When respiration and circulation are not artificially maintained, there is an irreversible cessation of spontaneous respiration and circulation; or

(2) When respiration and circulation are artificially maintained, and there is a total and irreversible cessation of all brain function, including the brain stem and that such determination is made by a licensed physician.