In an attempt to conform clinical outcomes to theoretical constructs, we have analyzed the spectrum of HD prescriptions according to interdialytic intervals. The following figure shows the shortest and longest dialysis-free intervals for various prescriptions.

Cumulative weekly dialysis time versus dialysis-free interval for various prescriptions

It is evident that there was no correlation between clinical outcomes (such as those of Tassin and Lecce) with total weekly dialysis time.  While Tassin provides twice as many dialysis hours as conventional thrice weekly HD, it only reduces the longest interdialytic interval by 6% (from 68 to 48 hours).  The long interdialytic interval can only be significantly reduced by increasing frequency beyond thrice weekly.  There is little difference between the longest intervals for the various “increased frequency schedules” (range 40-45.5 hrs) despite a total dialysis time range from 14 to 48 hours.  Increasing the frequency beyond 3.5 times per week has little additional effect on the long interdialytic interval.  The long and short interdialytic intervals of HD_3.5 are identical.  This combination is associated with the best clinical outcomes adjusted for total length of dialysis.