Predicting treatment dose for novel therapies using urea standard Kt/V

Calculation of urea standard Kt/V (stdKt/V) as a dose measure for guiding novel hemodialysis or hemofiltration therapy prescription is complex since this parameter depends on the magnitude of posttreatment urea rebound. We propose here a two-step procedure for calculating urea stdKt/V from single-pool urea Kt/V values (spKt/V) determined from serum urea concentrations in pretreatment and posttreatment blood samples. First, the dependence of urea stdKt/V on equilibrated Kt/V (eKt/V) was derived from a fixed-volume single-pool model. Second, an empirical equation for predicting urea eKt/V from urea spKt/V values was determined using multiple linear regression and available data during 4-hour hemodialysis, 2-hour hemodialysis, and 2-hour hemofiltration treatments. This empirical (rate/dose) equation is likely more robust for novel therapies than other equations derived from only data during conventional (4-hour) hemodialysis treatments. The combination of these formulas allowed construction of nomograms for calculating urea stdKt/V from spKt/V during novel therapies. These principles were further illustrated by calculating the predicted treatment dose for daily (six times per week) hemofiltration therapy required to achieve a given urea stdKt/V.