The "Rule of 6s" describes an easy way to evaluate the maturity of a recently-placed arteriovenous fistula for dialysis access--and is even mentioned by name in the most recent KDOQI Guidelines for Dialysis Access. The Rule of 6s is as follows:
6 weeks after the AV fistula has been placed, the fistula should:
(a) be able to support a blood flow of 600 ml/min.
(b) be at a maximum of 6mm from the surface.
(c) have a diameter greater than 6mm.
Failure to achieve these goals warrants a further investigation, usually in collaboration with the access surgeon who placed the fistula, into why the fistula did not mature. Ideally, the existing fistula can still be encouraged or modified to eventually achieve maturity; if not, a new access site can be attempted.