Fellowship during residency instead of research???

I don't know of any centralized database which lists all GS programs which offer a critical care fellowship, but there are several out there. As long as the fellowship year(s) are ACGME accredited, you should be able to sit for the Critical Care boards.

According to the ACS, applicants who complete an accredited fellowship after completion of three years of general surgery residency may apply for certification and take the examination while still in residency. A full and unrestricted medical license would not be required at that time. However, the certificate is not awarded until certification in general surgery is achieved.

The experience would be most valuable if you are entering a specialty (GS) or subspecialty (ie, fellowship after GS) in which critical care is a common occurence. For fellowships without much critical care medicine required (ie, Breast Surgery, MIS) it might not be as highly regarded but shouldn't be considered a detriment. You are however likely to be better served doing research in an area (especially for competitive fellowships) relevant to the fellowship rather than a CC year if it isn't frequently used in your field of choice.