He has fluid around his lungs, preventing them from fully expanding, so he is being kept in an oxygen-rich atmosphere. Ellen won't be able to hold him to nurse for at day or two more, but is pumping breast milk for the bottles for him, so she'll be ready when he is.
I don't know what kind of Neanderthal hospital they're in that doesn't realize babies who are separated from their mothers experience stress levels equivalent to babies in serious pain! Or whether Ellen has a good lactation consultant to let her know she should be pumping every 2-3 hours.
Let's all pray that Aiden will be breathing normally ASAP so they can all be together as they should be.