I passed my CEN by using the CEN Review Manual from the ENA and by taking lots of test questions and then looking up and reviewing wrong answers in my Sheehy's Manual of Emergency Nursing and Sheehy's Emergency Nursing Principles and Practices. I didn't have specific Patho review book. However I just re-certified my CEN by IBT (tough test actually!) and I did consult Prentice Hall Nursing Reviews & Rationales: Pathophysiology and, same series, Reviews and Rationales: Pharmacology. I like those books a lot because they give you review and rationale and then practice tests. And again I used my Sheehy's quite a bit.