During residency, Sarah Faubel, and I wrote this programmed text on electrolytes. The process galvanized my interest in nephrology. The Acid Base and Electrolyte Companion is a highly styled book with a picture on every page along with simple questions at the bottom of each page to make sure you understand concepts before mindlessly flipping the page. It is highy regarded with 5 stars at Amazon. You can download the entire book (591 pages!) as a single PDF (28 mb). More info and a link to the free download here.
Now updated with the introduction, colophon, credits, dedication and table of contents.