ER Nurse transitioning to ICU

Good Morning guys,

I am currently an emergency room travel nurse and planning to transition to an ICU nurse for continuing education purposes. I am planning to take the CCRN to make myself more marketable for ICU. Granted, I have three years of ER experience, all of which have been in Level I and III trauma and teaching facilities but I do know that some ICU's still require you to have experience in ICU. What is the best study material for the CCRN? My purpose for attaining ICU experience is to apply for a CRNA program. Do all programs require you to have ICU experience? Is organic chemistry a pre requisite for all or most programs?