In addition to keywords, there are many other ways to limit your search. In an advanced search in CINAHL (Before you click search), you'll see a lot of options scrolling down the page. Here are some of the important ones.
This option allows you to restrict to Nursing jounal collections only.
Restricts you to a geographic locale, like the United States. This controls the location where journals are PUBLISHED, so you'll still get overseas topics and authors.
This restricts to all articles based on observable data, frequently quantitative research studies. These tend to be peer-reviewed by default.
Here are some other useful limiters: