The appropriate number of search results is not straightforward, especially when doing a systematic review. If the topic has been studied extensively, the set of search results will naturally be large. If, on the other hand, there has been very little research on the topic, you may need to broaden your search to find all the articles that at least touch on the topic.
Your main focus should be on justifying your search results in your report based on your carefully formulated search plan.
Once you have completed your search, it is worthwhile to look at the results and reflect further:
You can evaluate your search with the PRESS checklist, a condensed version has been produced by the Karolinska Institutet. If you wish, you can consult the original checklist (see Table 1 in the linked publication).
In our example topic, "Nursing students' hand hygiene skills", one could consider if it is necessary to include terms related to skills in the search, or whether it is sufficient to search using only the terms "nursing students" and "hand hygiene". If you search using search terms already related to nursing education or student nurses, do all search results already automatically relate to skills or competencies acquired during studies, without including terms related to skills or competencies?
It is advisable to test and review your search string before running your final search.