Calculation of Standard Kt/V (stdKt/V) with Corrections for Postdialysis Urea Rebound

Recent work has shown that postdialysis urea rebound and equilibrated Kt/V (eKt/V) for short daily therapies, either hemodialysis (HD; Leypoldt et al, 2002 ASN meeting) or hemofiltration (HF; Jaber et al, this meeting), cannot be predicted by the Daugirdas-Schneditz rate equation. We derived a modified rate equation that accurately predicts eKt/V from single-pool Kt/V (spKt/V) and used it to derive nomograms for calculating stdKt/V from spKt/V for therapies containing an arbitrary number (N) of either short (2 hr) or long (8 hr) treatments per week. The modified rate equation was derived using multiple linear regression from measured spKt/V and eKt/V values during conventional (4 hr) HD (n = 21), short (2 hr) HD (n = 21) and short (2–3 hr) HF (n = 33). Values of stdKt/V were calculated using a fixed-volume kinetic model: stdKt/V = 168*(1-exp-[-eKt/V])/t/((1-exp [-eKt/V])/(eKt/V)+ 168/N/t-1), where t = treatment time in hrs. Measured values of spKt/V ranged from 0.38–1.89 and treatment rate (K/V) from 0.10–0.63/hr. The derived modified rate equation was: eKt/V = 0.927*spKt/V− 0.255*K/V. Prediction of eKt/V from this equation was high (r2 = 0.986, p < 0.0001), and calculated relationships between stdKt/V per week and spKt/V per treatment are as shown in the figures below. We suggest that stdKt/V can be predicted from spKt/V values using a modified rate equation and a fixed-volume kinetic model.