Urea monitoring during dialysis: the wave of the future. A tale of two cities.

The National Cooperative Dialysis Study (NCDS) suggested that the removal of small molecules controls the adequacy of the dialysis prescription, and it would seem appropriate that renal units regularly carry out formal urea kinetic modeling to ensure that the adequacy of dialysis is provided. Current methods of calculating Kt/V (urea) are complex and require the accurate measurement of dialyzer urea clearance and calculation of the volume of distribution of urea. This may be done by the direct measurement of total urea removed or by the use of computer programs that examine plasma urea and weight changes over time. Both methods have inherent problems, and this has stimulated the search for easier "bedside" formulas for the calculation of Kt/V. These newer formulas involve examination of the percentage reduction in blood urea concentration during hemodialysis. Two such formulas were examined and applied to 78 patients undergoing hemodialysis in two centers. One center routinely carried out formal urea kinetic modeling; the other did not. In the first center, it was found that the majority of patients were receiving more dialysis than necessary to achieve Kt/V (urea) = 1 when the latter was judged by those formulas. This suggested the possibility of time savings, with considerable implications for cost efficiency. In the second center, the majority of patients required more dialysis. It was concluded that intermittent formal urea kinetic modeling tends to overshoot the necessary prescription to allow for occasional "imperfect" dialyses and also that it is impossible to base dialysis prescriptions on routine pre-dialysis blood work and a "feel" for patients' needs.(ABSTRACT TRUNCATED AT 250 WORDS)