What I usually do is work through my pile of abstracts (easiest for me to do this on hard copy) and make clear notes on each one about whether or not it fits my search criteria. This is usually not that hard.
For example, say I'm doing a lit review of cost-effectiveness of treatments for multiple sclerosis. Up front, I have a list of reasons for excluding articles altogether:
- Not an economic analysis
- Review/opinion article with no meta-analysis
- Fewer than 30 subjects per study arm
- Trial not conducted in a relevant country (often I'm looking specifically for US studies)
- Study concerns a treatment that is no longer in use in the US