I interview a lot of nurses in my current job. It is not PICU but I suspect some of the same ideas apply. DRESS NICELY. No jeans, no sweats, remove all tongue and nose studs. You can wear scrubs
if you don't have a nice suit or dress but I think the more professionally you can dress... the better.
Don't "diss" your previous employer, supervisor or co-workers. Nothing scares an potential employer quicker than immediately complaining about the job you are leaving. (The best predictor of the future is the past, if you hate them, you'll hate us).
Spend time selling yourself. Tell them how quickly you learn, how organized you are, how responsible, how excited you are about being a team member. Now is NOT the time to tell them you have to leave at 2:45 on Tuesdays to pick up your daughter at her dance lessson. Nor is it time to be modest. If you have been a leader or an organizer for anything, mention it as an example of skills that you have that benefit you on this job. If you rarely took sick leave, provided a lot of back up coverage at your last job whatever... mention that. If you were in the top 5% of your class and mentored other students... that's more "bragging rights" for you.
I think it is also helpful to send the interviewer a thank you note. They interview a lot of people and it is hard to keep the applicants straight and in your mind after awhile. Your thank you note will remind them (positively) of you and help keep you at the top of the list.
Hope this helps and good luck!!