Cristina finds Derek at the computer, bidding on scalpels from the 1860s for his wife. I'd make a crack but I actually find that perfect and surprisingly endearing, though I will forever be confused by his about-face. He is so caught up in that special eBay euphoria that comes in the last few minutes of an auction that when Cristina runs in and tells him that Meredith has to talk to him, he doesn't pick up on her urgency. She finally has to tell him that Janet called and her tone and her face make it fairly apparent that the news was not good. Derek thinks for just a moment and then bolts.
So it appears that the page Alex got was from Arizona, pertaining to the phone call she received: a baby was born a couple of hours ago with something that has a whole lot of syllables and involves a connection between the trachea and esophagus, which really cannot be in any way good since, as Alex points out, the baby's lungs can fill with secretions and have a hard time both breathing and feeding. The tiny hospital they are at isn't set up to handle such a sick baby so he needs to go pick her up and bring her back so that Arizona can take care of her as soon as she's done putting the face back on her dog bite victim. She orders Alex to basically outfit the ambulance like a NICU and also to find a buddy to go along. She sees Meredith sitting where Cristina left her and tells her she is going; when Mere protests that she has to talk to Derek she sounds far too normal and like she might be talking to him about a grocery list. Arizona isn't swayed at all and just shoots back that a baby's life is hanging in the balance, so she has to make it fast.