1. Dialyzer Math

2. The Math Terms of Hemodialysis
Kuf
Efficiency
Flux
Performance
KoA
Kt/V
URR
Recirculation

3. KUf Permeability of Water mL of water per hour per mm Hg
KUf = Volume/hrs / (transmembrane gradient)

5. KUf Questions
What Transmembrane Pressure (TMP) is needed to ultrafilter 3 L of fluid over 3 hours with an F-40 filter?
50 mmHg
What Transmembrane Pressure (TMP) is needed to ultrafilter 3.5 L of fluid over 3 hours with an 8L filter?
103 mmHg

6. Self-Assessment KUf Question
Pre-HD weight in a patient on chronic HD is 2.4 kg above dry weight. He is usually dialyzed for 4 hours. If the KUf of the dialyzer is 3, what is the TMP in mmHg required to bring his weight down to the dry weight?

7. Self-Assessment KUf Question
Pre-HD weight in a patient on chronic HD is 2.4 kg above dry weight. He is usually dialyzed for 4 hours. If the KUf of the dialyzer is 3, what is the TMP in mmHg required to bring his weight down to the dry weight?

8. Clearance K
K = f (KoA, QD, QB)

9. Self-Assessment Question
The solute transport of a dialyzer is dependent on all of the following except:
KoA QB QD
Priming volume of the dialyzer

10. Self-Assessment Question
The solute transport of a dialyzer is dependent on all of the following except:
KoA QB QD
Priming volume of the dialyzer

11. Efficiency - KoA Dialyzer Mass Transfer Area Coefficient
KoA = f (Ko, surface area)
Ko = f (pore size, membrane thickness)
mL/min
Usual efficiency:
High efficiency: > 700

12. Using KoA
Once KoA of a dialyzer is known, the clearance (K) of urea can be calculated given the QD and the QB
Charts or Graphs available for each dialyzer

13. Getting the K from Graphs

14. Using the dialyzer with KoA of 400 shown below, what’s the clearance of urea at a QD of 500 mL/min and a QB of 350 mL/min?

15. So What’s Flux, Performance & Efficiency?
Efficiency: KoA
Performance: Clearance
Flux: KUf

16. Flux Refers to size of pores High Flux is KUf > 20 mL/hr/mmHg
Urea Clearance
Same for high-flux vs high efficiency
Beta-2 Microglobulin
More clearance with high-flux

18. Ways to Measure Adequacy
URR
Kt/V

19. URR The Urea Reduction Ratio
(Pre BUN – Post BUN ) / Pre BUN
R = 1- URR

20. Simple Kt/V
R = e – Kt/V
R = 1 – URR

21. Kt/V Calculations Good: Kt/V = -ln(R) Better: Kt/V = -ln(R-0.008 * t)
Better Yet: Kt/V = -ln (R * t) (spKt/V) + ( * R) * UF/W
Best: In-line monitoring

22. spKt/V Formula Breakdown
Urea
generation
during dialysis
-ln (R * t) + ( * R) * UF/W
Raw Urea
Reduction
Adjustment
For
Volume
Removed

23. Problem
A new patient weighing 60 kg comes in with newly discovered ESRD. The BUN is For the first run, you choose to drop the BUN no more than 20% using a small surface area dialyzer with K of 250 mL/min.
A: How long should the treatment be?
B: What’s the URR?
33 min

24. Tougher Problem
A new patient weighing 25 kg comes in with newly discovered ESRD. The BUN is For the first run, you choose to drop the BUN no more than 20% using an F-40 filter at a QB of 200 mL/min and QD of 500 mL/min.
A: What’s the Urea Clearance (K)?
B. How long should the treatment be?
20 min

25. All the following are true of high/low flux hemodialyzers except:
A. Conventional HD uses high-flux membranes
B. High efficiency HD refers to a rapid removal of small solutes
C. Low flux HD is good for urea clearance
D. High flux HD uses membranes with large pore size

26. All the following are true of high/low flux hemodialyzers except:
A. Conventional HD uses high-flux membranes
B. High efficiency HD refers to a rapid removal of small solutes
C. Low flux HD is good for urea clearance
D. High flux HD uses membranes with large pore size

27. Recirculation
Running the same blood through the dialyzer over and over
Overestimates adequacy
Easiest Measure: 3-Sample Method
Peripheral (P)
Arterial from Dialyzer (A)
Venous from Dialyzer (V)
(P-A) / (P-V) = Recirculation
Accepted Recirc % is ~ 12%

28. Recirculation Question
A 16 year old being dialyzed daily in the PICU via a Shiley in the PICU has pre-dialysis BUN of 120 mg/dL and post-HD BUN of 30 mg/dL despite restriction of protein and no evidence of catabolism. You suspect recirculation. What samples do you ask to be drawn?

29. Recirculation Question
Pre-Dialyzer BUN:
Post-Dialyzer BUN:
Peripheral Venous BUN: 115
(115 – 100 )
= = 30 %
( )