I would call the SICU and talk to the manager that interview you and explain to her exactly what you explained to us. Tell her your goals, your school choices, and that you were offered a position in the MICU that you didn't want to turn down unless you are able to come to the SICU. She/He will understand. If they wanted to offer you the position they will be thrilled. Trust me. Communication is always key, plus it looks professional on your character. Make sure you also explain your goals to the MICU manager as well that way when you decline her offer she understands why and will respect you for following your dreams and being honest.