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