George TO, Priester-Coary A, Dunea G, Schneditz D, Daugirdas JT
Cardiac index affects urea rebound to the extent predicted by the regional blood flow model
Am Soc Nephrol
J Am Soc Nephrol (abstract) (Nov) 6:599 1995

Instead of exercising their patients and using the patient as his/her own control as per Ronco et al, these investigators selected patients with high and low cardiac indexes (CI) occurring spontaneously as measured by bioimpedance during hemodialysis. During a subsequent dialysis they found a significant difference, between the high and low CI groups, in rebound measured in each patient as the difference between single pool Kt/V and equilibrated Kt/V. The latter was measured using a 30-minute postdialysis BUN. They also found a significant correlation between the cardiac index and the difference in Kt/V. The difference was predicted by a model of urea kinetics that accounts for disequilibrium solely as a function of regional blood flow.

Comment: This study lends support to the concept that regional or organ blood flow is a major contributor to urea disequilibrium during hemodialysis. This effect is independent of solute diffusibility and should cause the same degree of disequilibrium for all solutes. (For poorly diffusible solutes the convective effect of differences in organ blood flow is predicted to accentuate diffusion-dependent disequilibrium.) Previous evidence suggested that most important determinant of urea disequilibrium is Kd/V. When Kd/V is constant, however, as it was in the high and low CI groups in this study, the effect of cardiac output could be seen. Although the rate equation predicts eKt/V fairly well as a function of Kd/V it would probably do better if CI were also included in the calculation. (Depner)

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Am Soc Nephrol
Basic hemodialysis : Adequacy, prescription, urea kinetics
Basic hemodialysis : Physiology