A CAT (critically appraised topic) is a way of seeking answers to your clinical questions.
Here is an example from a dental student in the US about whether to use composite or amalgam in posterior teeth.
The search strategy doesn't need to be complex. The two studies identified in this one are two I have previously discovered using a much more complex strategy, but which found no additional ones.
What is missing in this CAT is a formal assessment of the validity of the trial reports. Both these studies have shortcomings (not least that confidence intervals aren't reported in one, from what I recall) and it is worth considering these before making decisions about how to act on your new knowledge. The CASP series of critical appraisal tools are useful for this.
If anyone would like to practice doing a CAT, let me know.