Hi Erin,
If the Ivig is no longer helping, perhaps you need to switch to another therapy. It's too dangerous to not be able to breathe adequately. I know. Been there, done that.
Unfortunately, Ivig did not turn me around when I was in a crisis, but plasmapheresis did.

Some doctors have adopted a concept in stubborn cases of performing a series of plasmapheresis followed by Ivig. That way you can get the benefit of both. The next round of plasmapheresis takes out the Ivig, but then it is immediately replaced.

Hope you get some help soon.