I just passed the CEN, first try. I've been an ER nurse for about 1.75 years now. I don't feel like I ever got great training, so I had to teach myself a lot.
-Mark Boswell Youtube lectures are awesome and free. I listened to all of them, and took notes in a google doc about everything he said. In some ways it's kind of nice that you don't have the powerpoints in front of you because you have to write everything down. I reviewed my notes a day before the test and that helped tremendously. The lectures don't cover everything but they give you a pretty good start. The Toxocology lecture was definitely helpful.
A little lacking on ortho maybe and that's a weak point of mine too. I need to catch up on that.
-The ENA CEN review book is really good and kind of necessary. 5 book tests and 2 online tests. I did all of those tests and then carefully reviewed the answers and rationales. It definitely showed me stuff I was missing.
-I also paid for the Jeff Solheim videos which are online. There's like 7 of them. The topics are pretty sparse, but the electrolyte stuff was really worth knowing well and I'm glad I did them. Apparently he has a taped lecture series but I could never find it.
-I also got a used, somewhat outdated copy of the Lippincot Q&A Certification review in Emergency Nursing. I got the 2005 edition on Amazon used very cheap. There are definitely a few outdated things in it but generally it was totally useable. The questions are HARD and that helped. I never finished the whole book but it was worth buying.
I looked up a lot of stuff on youtube. There's a lot of good ER videos. Larry Melnick is some ER doctor who puts up a lot of live videos in the ER, some of them were helpful. Looking up things like placement for a needle decompression and other things that I've read about but never seen.
-Be prepared to really hunt out an answer. For me the questions on the test were simpler as far as the knowledge required relative to the review book but took a little more figuring out, the answer wasn't obvious, you had to use your knowledge of the situation to piece together the answer. So I'd just be prepared for that. There were no major curve balls though.
-The test is long, long, long. Just get ready for that.
Anyway, good luck! It was totally worth doing. At this point I'm more clear about what I don't know than what I learned but it was helpful for illuminating that.
And a special thanks to Mark Boswell. I appreciate your generosity very much.