1. Dialysis removes waste and regulates fluids and electrolytes through diffusion, convection, and ultrafiltration. High efficiency and high flux dialyzers have higher clearance rates through larger surface areas and pore sizes. 2. Ultrafiltration is driven by hydrostatic pressure differences across the dialyzer membrane, regulated by transmembrane pressure. The ultrafiltration coefficient measures fluid removal rate per pressure change. 3. Different renal replacement therapies utilize different combinations of diffusion, convection, and ultrafiltration. Hemodialfiltration combines hemodialysis with hemofiltration to maximize all three processes.

1. PRINCIPLES OF DIALYSIS
Dr. Arun Varghese T
Nephrologist
Siva Hospital

2. • Principles?

3. Categorization of molecules

4. • High efficiency vs low efficiency
• High flux vs low flux
• KoA, Kuf
• Isolated ultrafiltration/Sequential dialysis
• Hemodiafiltration
• Hemofiltration

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

6. 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

9. Kidney Dialyzer
Urine Dialysate

10. 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

11. 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
diffusion
ultrafiltration

12. • Solution
• Semipermeable membrane

13. • Solution –mixture of solvent and solute
In dialysis
• Treated water- solvent
• Electrolytes and glucose – solute
• Solubility

14. • Membrane – thin layer of tissue

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
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18. Diffusion – Random Molecule Movement
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19. Diffusion – Random Molecule Movement
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20. Diffusion – Random Molecule Movement
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21. • example

22. • Tea bag

23. 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
diffusion
ultrafiltration

25. • Movement of fluid (solvent) across the
membrane
• Controlled fluid removal by manipulation
of pressure

26. • Filtration occure when fluid is pushed through
hydraulic pressure
• Fluid always moves from higher pressure to a
lower one

27. Ultrafiltration
A B

28. Ultrafiltration
A B

29. Basic Principals of Dialysis
• Principles related to solute removal
– Diffusion
– Convection
– ( KoA)
• Principles related to water removal
– Ultrafiltration
– Osmosis
– (Ultrafiltration coefficient-KUF)

31. • Convection is transfer of solutes by physical
circulation of a liquid

32. • Example

33. Ultrafiltration & Convection

35. Movement of FLUID across a
semipermeable from an area of LOWER
solute concentration to an area of HIGHER
solute concentration.

36. • In diffusion- solutes move
• In osmosis – solvent moves

37. • Application in Dialysis

39. • How to measure diffusion?
• KoA

40. • What are the factors determining diffusion?

41. MW of solute
Pore size
Pore number & distribution
Membrane thickness
Membrane surface area
Temperature on either side
Concentration gradient

42. Diffusion in dialysis
MW of solute
Pore size
Pore number & distribution
Membrane thickness
Membrane surface area – A
Temperature on either side
Concentration gradient
Ko

43. KoA
• The theoretical maximum clearance of the
dialyzer at infinite dialysate and blood flow
• Ko- permeability coefficient of the dialyzer
• A - surface area
• Expressed in ml/min

44. Mass transfer area coefficient KoA
Diffusive resistance
`

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

46. Diffusion in Dialyzer
For adequate diffusion
Dialysate flow 2-2.5 time blood flow

47. Effect of Blood Flow on Clearance

49. Distribution of pore size
A
B

50. Categorization of molecules

52. • What are the factors determining
ultrafiltration?

53. • Trans membrane pressure
• Hydraulic permeability of the membrane

54. ULTRAFILTRATION
Controlled fluid removal by manipulation of
hydrostatic pressure.
• Ultrafiltration uses both positive and negative pressure:
o Positive pressure
• pressure exerted by the blood flowing through the
dialyzer, Results from blood being pushed by blood
pump
o Negative pressure
• pressure applied to the dialysate side by the machine
• Pulls excess fluid from blood compartment to dialysate
compartment drain

55. Ultrafiltration
A B

56. Ultrafiltration
A B

57. Ultrafiltration
Transmembrane pressure
(TMP)
=
Positive pressure A - Negative pressure B
A B

58. • Hydraulic permeability
• Surface area
• Number and size of por

59. Ultrafiltration Coefficient (KUF)
• Milliliter of fluid per hour per mm Hg pressure
difference across the membrane
• Expressed in ml/hr/mmHg

60. • Flux
– Measure of ultrfiltration capacity
– Low or high flux dialyzers based on KUF

61. Low flux vs high flux
– Low flux - KUF < 10 ml/hr/mmHg
– High flux - KUF > 20 ml/hr/mmHg
– Low flux - B2 microglobulin clearance < 10 ml/min
– High flux - B2 microglobulin clearance > 20 ml/min

62. • Summarise

63. • High efficiency vs low efficiency
• High flux vs low flux
• KoA, Kuf
• Isolated ultrafiltration/Sequential dialysis
• Hemodiafiltration
• Hemofiltration

64. RRTs – Principles of Dialysis
Diffusion Convection Ultrafiltration
Conventional
Hemodialtsis
+++ + +
Hemofiltration - ++++ ++++
Hemodialfiltration +++ ++++ ++++

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

66. 1
• The blood dialysate flow configuration that
maintains the optimum blood dialysate
concentration gradient
A. Concurrent flow
B. Countercurrent flow
C. Crosscurrent flow
D. Recirculation flow

67. 2
• Ultrafiltration during hemodialysis is due to
A. Dialysate flow rate
B. Blood flow rate
C. Osmotic pressure gradient between blood and
dialysate
D. Hydrostatic pressure gradient between blood
and dialysate
E. None of above

68. 3
• Ultrafiltration coefficient (KUF) refers to
A. The resistance to water removal
B. Amount of water removed from blood per unit
time as a function of pressure difference
C. The amount of water removed per unit time
D. The resistance of dialyzer to solute removal

69. 4
• Mass transfer coefficient refers to
A. Amount of fluid removed per unit time
B. Amount of solute removed per unit time
C. The resistance offered to solute removal
D. The resistance offered to fluid removal
E. None of them

70. • Thank you

71. 5
• Sieving coefficient depends on all of following
EXEPT
A. Molecular weight cutoff the membrane
B. Ultrafiltration rate
C. Surface area
D. Diffusion

72. Sieving coefficient

73. Body water distribution
• In dialysis water and solutes can be removed
only from bloodstream

74. Fluid compartments

76. • Diffusion is greater for small molecules as
compared to larger molecules
• Low flux: molecular wt cut off = 10000
daltons
• High flux: molecular weight cut off = 30000
daltons

77. RRTs – Principles of Dialysis
Diffusion Convection Ultrafiltration
Conventional
Hemodialtsis
+++ + +
High Efficiency
HD
++++ + +
High Flux
Dialysis
+++ +++ +++
Hemofiltration - ++++ ++++
Hemodialfiltrat
ion
+++ ++++ ++++
Peritoneal
Dialysis
+++ - -

78. Urea kinetic modelling

79. Measuring dialysis adequacy
• Urea reduction ratio
• Kt/V