The hard-throwing right-hander joined Triple-A Syracuse on July 21 and did not allow a run in 12.0 innings pitched. He was touched for just six hits and racked up 14 strikeouts while walking only one.
Treinen worked multiple innings in each of his International League appearances.
In 32 games out of the Nationals' bullpen this season (41.0 IP), Treinen is 2-2 with a 4.39 ERA. He struck out 44 of the 180 batters he faced (9.7 K/9.0 IP).
Barrett, 27, is 3-3 with a 4.60 ERA in 40 appearances (29.1 IP) this season. The right-hander has struck out 10.74 batters per nine innings, ranking him 21st among National League relievers in that category.