The U.S. Department of Justice and the inspector general in the Department of Health and Human Services are investigating Medicare billing practices at Vanderbilt University Medical Center. The probe, which was acknowledged by medical center officials, dates back several months and includes requests for extensive records for services provided to Medicare patients in the four intensive care units at Vanderbilt. Internal Vanderbilt memos reviewed by The Tennessean indicate the inquiry is focused on records showing when physicians were scheduled to staff the medical center's intensive care units.