If you're asking this question, it means your local incidence of these patients is low and therefore unlikely to be a good population to study in your ED. A quick query of your EMR for "agitation" or "cocaine toxicity" would help give you an idea of how many patients your ED sees. Given an incidence and a power calculation, you can determine how many patients your study needs and how long you'll have to enroll. But from your post, it doesn't seem like you have a defined objective, let alone a hypothesis.
So without a solid plan or a relevant patient population, a hard job (i.e., successfully conducting a research project as a busy resident) has been made much more difficult. If you're at the beginning stages, I'd rethink the whole thing. I generally advise residents to only consider projects that fall into one of two groups - retrospective studies (cheap, fast, and the data has already been collected) and studies of normal adults because you can enroll your resident colleagues.