The teams announced the deal Sunday.
Perreault has played in 159 games with the Capitals, scoring 70 points with a plus-17 rating. He has won 51.2 percent of his faceoffs.
Perreault began his career in Washington playing for Ducks coach Bruce Boudreau, who also coached Perreault in the AHL.
Mitchell is a left wing who spent last season with the Ducks' AHL affiliate in Norfolk.
The Ducks made more moves on Monday, sending right wing Brad Staubitz, center Richard Rakell, left wing John Kurtz and defenseman Nolan Yonkman to their AHL affiliate in Norfolk. Goalie Igor Bobkov went to an ECHL affiliate in Utah.
Etem was hurt in a preseason collision last Saturday, while Silfverberg has been sidelined with an undisclosed injury since last week. Sbisa's sprained ankle is expected to heal by next week, but Souray is out indefinitely after surgery for a torn ligament in his wrist.
Information from The Associated Press was used in this report.