Tenet Healthcare is buying Vanguard Health Systems for about $1.8 billion, helping to expand its service offerings and broaden its geographic reach. The companies said Monday that the transaction also includes $2.5 billion in debt and value the entire deal at $4.3 billion. Tenet will pay $21 per share, a 70 percent premium to Vanguard Health's Friday closing price of $12.37. Nashville, Tenn.-based Vanguard Health says its founder, Chairman and CEO Charlie Martin, will join Tenet's board.