[Dialysis adequacy: the clinical illogicality of Kt/V urea]

In the 1980s Gotch and Sargent proposed a mathematical model based on the dialytic removal of urea, introducing the concept of Kt/V urea. The main issue which justifies the fact that Kt/V urea be considered the key of the adequacy of dialysis is that it is related to mortality. However, many studies have highlighted the limits of Kt/V urea: mainly, scaling for the volume of distribution is a confounding factor since gender and body mass index directly affect morbidity and mortality in dialysis patients. On the other hand, several observational studies and preliminary randomized controlled trials have suggested that longer and/or more frequent treatments may lead to better outcomes. In conclusion, an assessment of the amount of dialysis delivered is vital. Kt/V urea, although not perfect, is a useful marker of adequacy. However, the most logical approach in order to diminish the mortality on dialysis must be the individualized prescription of the duration and/or frequency of dialysis treatment, developed through a global assessment of the proven predictors of morbidity and mortality. These parameters include nutrition, albuminemia, mineral metabolism, inflammatory markers, volume control, blood pressure, maintenance of residual renal function, and hemodynamic stability. Each of these variables seems to be associated with the duration and/or frequency of dialysis treatments. Even though several observational studies and preliminary randomized controlled trials seem to confirm these associations, time has come for interventional studies to confirm these complex relationships.