Remember to use the drug name for pharmaceuticals with the brand name. Brand names are not always used in research articles.
EtCO2 may mean end-tidal carbon dioxide to you, but it could be something else in a different field. Instead of searching only the abbreviation type out the terms and place them inbetween quotation marks, then include the abbreviation using an OR and surround the terms with parentheses.
To search for time it is more useful to use controlled vocabulary such as:
Searching phrases like "9 months" or "3 years" in a database is not helpful.