Your PICO should help you choose keywords and key phrases for your search. If you combine these with the AND operator your results should include ALL the terms. Many databases allow you to search for keywords one at a time, and then combine the search sets later, using your Search History. It is best to search this way if you are using a thesaurus such as CINAHL Headings or MeSH.
For each concept that you identify, consider using synonyms (alternative terms) including alternative spelling. You can combine these using the OR operator.
Consider searching in a selected field(s), such as title or subject. Searching using CINAHL Headings or MeSH (Medical Subject Headings) is the most advanced way to do this.
Consider limiters that will restrict your search, such as language, date of publication, type of study, age group etc. These can usually be applied either as part of your search, or after your search has been run. The specialised health & medicine databases usually have specialised limiters.
CSU Library has a general guide to Database Help.
You can also get help from the Help sections within the databases. For example: