Monday - Wednesday | 8AM-5PM. Thursday | 7AM-3PM. Friday - Closed. John M. Guenst, M.D. Dr. Guenst has been with St. Thomas Medical Group since 1995. His undergraduate degree in Biology was earned at Clarkson College in New York in 1989 and his medical degree was received at Vanderbilt University. His residency in Anesthesia was performed ....