Daily dialysis: the long and the short of it.

There is considerable enthusiasm for daily hemodialysis despite the increased time commitment required of patients because of reported improvements in patient well-being, appetite and blood pressure control. To date, this therapy has been largely empirical and has been defined primarily by treatment time (t) and categorized as short daily hemodialysis (SDHD) with t about 2 h and long nocturnal hemodialysis (LNHD) with t 8-9 h. It is the authors' view that studies comparing clinical outcome with SDHD and LNHD to conventional hemodialysis (CHD) must have dialysis dosage well defined if they are to provide generalizable results. There is a broad range and overlap in the magnitude of solute removal in reported studies of SDHD, LNHD and CHD, which is illustrated here through kinetic consideration of four solutes: (1) urea; (2) inorganic phosphorus (iP); (3) beta(2)-microglobulin (beta(2)M) and (4) Na/water. The following observations can be made: (1) Patient subjective reports of increased appetite and protein intake may correlate poorly with kinetic calculation of protein catabolic rate. (2) A model of iP mass balance was developed and indicates that iP removal with CHD is inadequate; current SDHD is also inadequate to highly excessive depending on the dose of dialysis. (3) beta(2)M removal with SDHD is virtually the same as reported for LNHD, reflecting major differences in dialyzer membranes used. (4) The decrease in predialysis overhydration is a predictable function of the number of dialyses per week and may be one of the most important benefits of more frequent dialysis. (5) The standard K(t)/V (stdK(t)/V) provides a uniform method of dose calculation but the therapy prescription should also include consideration of the other solutes evaluated above.