Perhaps you should try some spelling variations:
intraoperative oxygen » intraoperative opioid
oxygen administration » opioid administration
intraoperative public » intraoperative fluid, intraoperative opioid
public administration » opioid administration

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( intraoperative oxygen administration ) or ( intraoperative public administration ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( intraoperative oxygen administration ) OR ( intraoperative public administration )).
• Adding a wildcard symbol may retrieve word variants: (( intraoperative oxygen administration ) or ( intraoperative public administration ))*.