For a comprehensive search you will need to combine keyword and subject searches.
A combined search means that you search for your keywords, and also for your subject headings for each concept of your search strategy. Then combine the keyword and subject heading searches with OR. Finally, combine the resulting search results for each concept with AND.
Note that a combined search will retrieve more records than a subject or keyword search alone.
The screenshot below shows a combined search in the Search History of Ovid Medline.
In disciplines that commonly use subject heading hierarchies for indexing content, (such as biomedical and health sciences), a search strategy that combines keyword and subject heading searching is likely to be the best and easiest way to get a comprehensive review of the literature.