Mo. Rev. Stat. § 459.020: Revocation — mental or physical condition not considered part of medical records — liability for failure to act, when.

1. A declaration may be revoked at any time and in any manner by which the declarant is able to communicate his intent to revoke, without regard to mental or physical condition.

2. The attending physician or health care provider shall make the revocation a part of the declarant's medical record.

3. There shall be no criminal or civil liability on the part of any person for failure to act upon a revocation made pursuant to this section unless the revocation is in the patient's medical record or unless that person has actual knowledge of the revocation.