If review contains a lot of files it's quite probable it won't be completely reviewed at once, but a reviewer start on it, then switch to another task, then continue.
For that purpose it's important to remember which files were already reviewed and which were not.
Code Collaborator (code review tool by Smart Bear) has such functionality, reviewer can mark the file as "Overall accepted", which will not have an influence on a review in general, but will mark a file as reviewed for the reviewer, so lately he can skip the file.
Below are the screenshots describing what am I talking about. The latter screenshot is from the Code Collaborator