I'm not sure of the actual title, but a good book I had in school and used for clinicals was by Swearingen and Keene (sp?).
A good handbook is Fast Facts for Adult Critical Care...you can order it and preview it online at
www.kathywhite.com
Also, if you go to
www.aacn.org and click on the bookstore icon, you can get access to a ton of references. They have a book called Core Curiculum for Critical Care which is good.
When you extern this summer will you be doing actual nursing "stuff," taking patients, and learning critical care skills? That will help you learn a lot, and will help you gain confidence.
Good luck