Thoughts about judging dialysis treatment: mathematics and measurements, mirrors in the mind.

This article considers the contributions of the urea kinetic parameters, , Kt/V and nPCR, to beliefs about judging dialysis treatment. The values calculated from any set of data depend on the model (eg, 1 pool, 2 pool, or so forth) and the mathematics used to derive the values. Yet, the medical community debates the value of Kt/V at which patients should be treated even as they debate the mathematics by which Kt/V should be calculated. The resulting ambiguities about proper targets and methods may actually frustrate large-scale clinical quality enhancement initiatives. The casual use of mathematical models can mislead unwary clinicians and compromise quality enhancement. For example, the observation that a high Kt/V is associated with a high nPCR leads to the widespread belief that improving Kt/V must substantially improve nutritional status. The association, however, results mainly, if not solely, from mathematical coupling rather than biological cause and effect. The misguided belief could contribute to ineffective treatment of malnourished patients. Complicated mathematical models are useful tools for describing and evaluating evolving concepts about the physical properties of dialysis and for estimating the effects of new therapies. However, the changing nature of concepts, and therefore the mathematical models designed to support them, makes clinical care ideas that attempt to shoehorn old concepts into new equations. It is the result of the dialysis treatment, not the mathematical path by which it is achieved, that is associated with improved patient health. Consequently, clinical care should be guided by simple measurements that reflect the outcome of the treatment, not by mathematical parameters.