Both Donnelly and Shields are better pitchers against lefties than Christiansen is. MUCH better. I really don't see Christiansen helping all that much (unless he can bat 4th/5th and protect Vlad.)
If you guys don't remember who Christiansen is, he gave up 5 ER's against the A's in 1 inning in that 16-0 blowout against the A's... He faced every lefty in the A's lineup (because the A's batted around) and I think he gave up a hit to each of em. He's the guy who got mad because Dan Johnson hit a 2 run single off him, then tried to hit Nick Swisher, only for Swisher to get up and hit a 2-run HR off him.
A's lefties vs. Christiansen
Chavez: .400 AVG/.800 OPS
Hatteberg: .500 AVG/1.150 OPS
Johnson: 1.000 AVG/2.000 OPS
Kotsay: .143 AVG/.286 OPS