Literature reviews can range from quick and dirty to detailed and thorough. When searching for the evidence or working under the title of 'evidence based' it's best to be as detailed and thorough as possible.
documenting your work - where & how you searched;
searching multiple databases;
using multiple terms for each of your PICO concepts;
using AND/OR (Boolean logic)- correctly of course!
asking a librarian either for assistance or to perform the literature search for you