Abstract: SA-PO667

Calculation of Weekly Standard Kt/V by Urea Mass Removed During Hemodialysis Results in a Simple Equation

Session Information

Category: Dialysis

  • 604 Home and Frequent Dialysis

Authors

  • Leypoldt, J. Ken, None, San Clemente, California, United States
  • Vonesh, Edward F., None, San Clemente, California, United States
Background

Accurate calculation of weekly urea standard Kt/V (stdKt/V) during hemodialysis (HD) requires first calculating sequentially single-pool and equilibrated Kt/V (Daugirdas et al, Kidney Int 2010), but this approach can be intimidating to clinicians. We explored whether an alternative approach to calculating stdKt/V based on urea mass removed would lead to a simple equation with approximately equivalent accuracy for both conventional and more frequent HD.

Methods

Theoretical consideration of urea mass balance during HD treatments derived the following equation for stdKt/V, namely stdKt/V = N * (URR + UFV/V)/(1 - N * t / 10080) where N is number of treatments per week, URR is urea reduction ratio per treatment, UFV is ultrafiltration volume per treatment, V is post-dialysis urea distribution volume and t is treatment time in minutes. The URR requires correction for post-dialysis rebound (Tattersall et al, Kidney Int 1996). The numerator of this equation represents the fractional urea mass removed from V, and the denominator corrects for intradialytic urea generation. We compared the accuracy of this novel equation for calculating stdKt/V with the conventional approach (Daugirdas et al, Kidney Int 2010) by simulations using a two-compartment model of urea kinetics. Model simulations were performed for patients with V of 20-50 L, weekly UFV of 0-14 L, treatment times of 2-8 hours, 5 different dialyzer urea clearances; this generated 350 different treatment conditions for HD performed 3, 4, 5 and 6 times per week.

Results

Results are tabulated as the absolute value of differences between approximation equations and the numerically simulated stdKt/V.

Conclusion

The urea mass removed and Daugirdas et al equations compute values of stdKt/V that are clinically equivalent. This work provides a novel, simple equation for calculating stdKt/V during HD and strengthens the theoretical understanding of stdKt/V.

Treatments per weekStatisticDaugirdas et al equationsUrea mass removed equation
3Mean ± SD0.019 ± 0.0160.014 ± 0.017
Median (IQR)0.017 (0.009-0.023)0.008 (0.003-0.018)
4Mean ± SD0.024 ± 0.0220.072 ± 0.029
Median (IQR)0.020 (0.011-0.030)0.069 (0.051-0.090)
5Mean ± SD0.080 ± 0.0490.076 ± 0.082
Median (IQR)0.075 (0.047-0.105)0.041 (0.015-0.110)
6Mean ± SD0.086 ± 0.0540.022 ± 0.028
Median (IQR)0.080 (0.049-0.113)0.014 (0.008-0.022)

SD = standard deviation; IQR = interquartile range