Centra is building a regional emergency medical center in Gretna and the public has the unique opportunity to leave a lasting mark on the state-of-the-art facility. Residents are invited to sign their names to the final beam, which will be hoisted into place marking the end of steel construction next month. The beam is on display until January 10 at the Hampton Inn on Route 40. The Centra Gretna Medical Center is on pace to open next winter.