The Nationals recalled Poulin from Triple-A Rochester on Saturday.
Poulin will return to Washington's bullpen after giving up three earned runs in five innings since his demotion to Triple-A in late May. The 29-year-old southpaw owns a 3.28 ERA and 1.46 WHIP through 24.2 frames with the Nationals this season and will presumably work in middle relief as long as he's with the big club.