International nurse ICU specialist starting in the US

I move to the US over a year ago and just got my RN license. I have a BSN degree valid in the US also in Brazil I'm specialized in intensive care (adult, pediatric and neonatal). I did a 2 years residency in a hospital there to get this specialist title. But here in the US it is not valid as a specialist, what should I do now? What kind of classes should I take to become a specialist here?