1. Principles of dialysis
Prof Tahir Shafi

2. Dialyzer clearance is expression of1
Dialyzer clearance is expression of
The performance of a dialyzing process
The volume of blood totally cleared of a given substance per unit time
The blood solute flux rate per minute
Both A & B
Both B & C

3. 2
Which one of the following does not influence dialyzer urea clearance
Blood flow rate
Dialysate flow rate
Membrane permeability
Surface area of the dialyzer
Blood concentration of urea

4. 3
Factors affecting the rate of diffusion in hemodialysis include all of these EXCEPT
Surface area of dialyzer
Membrane size
Hydrostatic pressure in blood compartment
Membrane pore size distribution
Concentration gradient between blood and dialysate

5. 4 Diffusive resistance include all of the following EXEPT
Blood film layer thickness
Membrane permeability
Dialysate film thickness
Solute drag

6. 5
The blood dialysate flow configuration that maintains the optimum blood dialysate concentration gradient
Concurrent flow
Countercurrent flow
Crosscurrent flow
Recirculation flow

7. 6 Ultrafiltration during hemodialysis is due to Dialysate flow rate
Blood flow rate
Osmotic pressure gradient between blood and dialysate
Hydrostatic pressure gradient between blood and dialysate
None of above

8. 7 Ultrafiltration coefficient (KUF) refers to
The resistance to water removal
Amount of water removed from blood per unit time as a function of pressure difference
The amount of water removed per unit time
The resistance of dialyzer to solute removal

9. 8 Mass transfer coefficient refers to
Amount of fluid removed per unit time
Amount of solute removed per unit time
The resistance offered to solute removal
The resistance offered to fluid removal
None of them

10. 9 Sieving coefficient depends on all of following EXEPT
Molecular weight cutoff the membrane
Ultrafiltration rate
Surface area
Diffusion

11. 10 Factors affecting the net flux include Membrane surface area
Membrane permeability
Blood dialysate flow configuration
A&B
All of the above

12. Functions of the Kidneys
Excretory
Excretion of waste products
Regulatory
Fluid
Electrolytes
Acid base
Hormonal
Rennin
Erythropoietin
1,25 OH D3
Metabolic

13. Functions of the Kidneys
Excretory
Regulatory
Electrolytes
Acid base
Fluid
Hormonal
Renin
Erythropoiten
1,25 OH D3
Metabolic
Solute removal or solute shift
Water removal

14. Basic Principals of Dialysis
Principles related to solute removal (mass transfer)
Diffusion
Convection
(Clearance, dialysance, net flux, KoA, sieving coefficient)
Principles related to water removal
Ultrafiltration
Osmosis
(TMP, Ultrafiltration coefficient-KUF)

15. Principles of Dialysis
Diffusion

16. What is Diffusion ?
Movement of the solute through semi permeable membrane from one side to the other on the basis of concentration gradient

17. Diffusion – Random Molecule Movement`

18. Diffusion – Random Molecule Movement
Diffusive resistance `

19. Diffusion – Random Molecule Movement
Diffusive resistance `

20. Diffusion – Random Molecule Movement
Diffusive resistance `

21. Mass transfer area coefficient KoA
Diffusive resistance
- MW of solute
Pore size, number &
distribution
- Temperature on either side
Membrane thickness
Diffusive resistance
Membrane surface area – A
Concentration gradient Ko `

22. KoA
The rate at which the solutes diffuse through the membrane – overall permeability -transport coefficient expressed as cm2/minute – Ko
KoA is Ko x surface area –
Mass transport area coefficient – ml/min

23. Net flux Js = KoA ( C ) Js = Rate of solute movement in mg/min
also called as net Flux
Ko = Membrane and solute specific constant cm2/min
A = membrane area cm2
C = Concentration gradient
Ficks A, Annals Physiol 95:
Ann Physiol

24. Ultrafiltration
and
Convection

25. Ultrafiltration A B

26. Ultrafiltration A B

27. A B Ultrafiltration Transmembrane pressure (TMP) =
Positive pressure A + Negative pressure B
Ultrafiltration Pressure
(UFP) =
TMP – Oncotic Pressure A A B

28. Ultrafiltration Coefficient (KUF)
Hydraulic permeability of the membrane X UFP.
Hydraulic permeability
Surface area
Number and size of pores
UFP = TMP-Oncotic pressure
Expressed as milliliter of fluid moved per hr per mmHg of ultrafiltration pressure

29. Convection

30. Ultrafiltration & Convection

31. Osmosis

32. Osmosis

33. Osmosis & Convention

34. Diffusion in moving
solutions

35. Kidney
Dialyzer
Urine Dialysate

36. Diffusion- KoA
Diffusive resistance `

37. Diffusion in Dialyzer Diffusive force = Concentration gradient Blood
Membrane
Dialysate
Countercurrent
& Concurrent
Js= KoA x log mean concentration gradient

38. Countercurrent Blood-Dialysate Flow
Diffusive force
Blood
Membrane
Dialysate

39. Diffusion in Dialyzer
Diffusive force
Blood
Membrane
Dialysate

40. Diffusion in Dialyzer For adequate diffusion
Dialysate flow time blood flow
Js= KoA x log mean concentration gradient

41. Dialysate Flow Unstirred layer effect

42. Effect of Dialysate Flow Rate on Membrane Diffusion

43. Blood Flow & Diffusion
Wide blood channel

44. Blood Flow & Diffusion

45. Blood Flow & Diffusion
Slow Blood Flow

46. Membrane Limited Diffusion

47. Flow Limited Diffusion

48. Effect of Blood Flow on Clearance

49. Dialyzer design

50. Older hollow fiber dialyzer
Dialysate out
Blood out

51. Blood & dialysate flow geometry
Blood in
Header
Dialysate out
Dialysate in
Hollow fiber
Casing or jacket
Dialysate
Blood out

52. Blood flow velocity

54. Header modification

55. Blood flow and dialysate flow rate

56. Improved header design
Spiral blood flow inlet

58. Smooth cut vs rough cut surface

59. Blood flow velocity

60. Placement of fibers, straight fibers

61. Placement of fibers - Mourie Design

62. Space yarn between fibers

63. Comparison of dialysate flow

64. The densitometry profiles achieved in the three different hemodialyzers are graphically reported (top panels).
Figure 7. The densitometry profiles achieved in the three different hemodialyzers are graphically reported (top panels). These curves were obtained by analysing a cross-sectional segment at half-length of the dialyzer. Values are expressed in Hounsfield units. (Bottom panels) the dotted line describes the average dialysate flow velocity in each hemodialyzer, and the bars describe the regional flow velocities in selected regions of the bundle (central and peripheral). For the standard configuration, the difference in velocity between the peripheral regions (peak velocity) and the central region (lowest velocity) demonstrate the uneven flow distribution. The pattern achieved with the Moiré design is definitely superior among the three configurations.
Claudio Ronco et al. JASN 2002;13:S53-S61

65. Clearances

66. Wavy (undulated fibers) vs straight

67. Dialysate entry port
OLDER DIALYZER

68. Dialysate entry port

69. Pores size and distribution

71. Mass transfer area coefficient-KoA of Dialyzer
Product of overall mass transfer coefficient (Ko) for a given solute x dialyzer surface area (A)
Expressed as ml/min

72. Diffusion in Hollow Fiber Dialyzer
Concentration gradient
Blood flow rate – channel width
Dialysate flow rate - channel width
Directions of blood and dialysate flow
Molecular weight of solute
Shape, size of molecule
Membrane property
Surface area-number of pores
Size of pores
Distribution of pores
Thickness of membrane
Temperature of solution
KoA
of Dialyzer for
particular salute
ie. KoA urea
At particular blood and dialysate flow rate

73. Dialyzer KoA Calculated from clearance, blood flow, dialysate flow
1-Kd/Qb
1-Kd/Qd
Qb.Qd
Qb - Qd Ln
KoA =
Kd: Dialyzer clearance
Qb: Blood flow
Qd: dialysate flow
KoA: Mass transfer area coefficient

74. Diffusion is greater for small molecules as compared to larger molecules
Low flux: molecular wt cut off = deltons
High flux: molecular weight cut off = deltons

75. Distribution of pore sizeA B

76. Categorization of molecules

77. Sieving coefficient
It refers to the amount of solute removed by convection
A sieving coefficient =
Concentration in the ultrafiltrate
Concentration in blood
A sieving coefficient of 0.5 for a solute means that 50% of that solute will pass through membrane during ultrafiltration

78. Sieving coefficient Depends on Molecular weight cutoff of the membrane
Ultrafiltration rate
Membrane surface area

79. Sieving coefficient

80. Dialysance
Rate of removal Dialysance = Concentration gradient

81. Clearance & Dialysance
Rate of removal Clearance = mean of inflow & outflow concentration
Rate of removal per min=
Blood flow x (inflow concentration - outflow concentration
Blood flow
Ml/min
Inflow Outflow
Concentration Concentration

82. Dialysance Dialysate Urea On line urea clearance = Sodium dialysance
Blood flow
Ml/min
Sodium
Urea
Sodium
On line urea clearance = Sodium dialysance

83. Functions of the Kidneys
Excretory Solute removal (Urea,creatinine etc.)
Regulatory
Electrolytes
Acid base
Fluid
Hormonal
Renin
Erythropoiten
1,25 OH D3
Catabolic
Solute shift
Water removal

84. Dialysance Dialysate Blood flow Ml/min
Sodium Potassium Calcium Bicarbonate
Magnesium
Sodium Potassium Calcium Bicarbonate
Magnesium
Shift of solute per minute = Blood flow per minute (Inflow – outflow concentration)
Difference of concentration in blood & dialysate

85. Effect of Pore Distribution & Solute MW on KoA
A = Low flux cellulose membrane, B= High flux membrane

86. Low Flux Cellulose Membrane

87. High Flux Membranes

88. Erythrocyte Diffusion Barriers
Urea
Creatinine
Phosphate

89. Effect of Hematocrit on Clearance

90. Effect of Flow on Membrane Filtration

91. Flux Permeabilty Measure of ultrfiltration capacity
Low or high flux dialyzers based on KUF
Low flux when KUF < 10 ml/hr/mmHg
High flux when KUF > 20 ml/hr/mmHg
Permeabilty
Related to middle molecular clearance
Low & high permeability=B2 microglobulin clearance < 10 and > 20 ml/min

92. Related to urea clearance of dialyzer urea clearance – KoAurea
Efficacy
Related to urea clearance of dialyzer urea clearance – KoAurea
Low efficacy – KoAurea < 500 ml/min
High efficacy – KoAurea > 600 ml/min

93. RRTs – Principles of Dialysis
Diffusion
Convection
Ultrafiltration
Osmosis
Conventional Hemodialtsis
+++ +
High Efficiency HD
++++
High Flux Dialysis
Hemofiltration -
Hemodialfiltration
Peritoneal Dialysis ++