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1. Physiological Principles
of Hemodialysis
Solve the Crosswords
Mohammed Abdel Gawad
Nephrologist
Alexandria – EGY
NephroTube Chairman
drgawad@gmail.com

3. To download the lecture contact me
drgawad@gmail.com
More lectures on
www.NephroTube.com

4. Solve the Crosswords

5. Talk Outline
• Diffusion – Convection Concept
• Concept of Clearance

6. Talk Outline
• Diffusion – Convection Concept
• Concept of Clearance

7. =

8. Dialysis
Solute composition of a solution A
(Blood), is altered
by exposing solution A
to a second solution B
(Dialysate),
through a semipermeable
membrane (Filter - Dialyzer)
Dialyzer
A
B

9. Dialyzer

10. Dialysis
Solute composition of a solution A
(Blood), is altered
by exposing solution A
to a second solution B
(Dialysate),
through a semipermeable
membrane (Filter - Dialyzer)
Dialyzer
A
B
BA
Dialyzer

11. Dialysis
Solute composition of a solution A
(Blood), is altered
by exposing solution A
to a second solution B
(Dialysate),
through a semipermeable
membrane (Filter - Dialyzer)
BA
Dialyzer Water molecules and LMW
solutes in the two solutions
can pass through the
membrane pores
Larger solutes (such as
proteins) cannot pass through
the semipermeable barrier

12. Dialysis
Solute composition of a solution A
(Blood), is altered
by exposing solution A
to a second solution B
(Dialysate),
through a semipermeable
membrane (Filter - Dialyzer)
BA
Dialyzer Water molecules and LMW
solutes in the two solutions
can pass through the
membrane pores
Larger solutes (such as
proteins) cannot pass through
the semipermeable barrier
Diffusion Ultra-Filtration
(Convection)
Hydrostatic Osmotic

13. Blood Dialyzate

14. Diffusion
Blood Dialyzate
Movement of solutes from a
compartment in which they
are in high concentration to
one in which they are in lower
concentration
The larger the MW of a solute,
the slower the diffusion

15. Large solutes can’t pass

16. Dialysis Solution
consists of sodium, potassium,
calcium, magnesium, chloride,
bicarbonate, and dextrose
added to highly purified water

17. Water
Treatment Unit
Dialysis Solution
consists of sodium, potassium,
calcium, magnesium, chloride,
bicarbonate, and dextrose
added to highly purified water

18. Blood Dialyzate

19. Ultrafiltration (Convection)
Hydrostatic UF
Blood Dialyzate
Solutes are swept through the
membrane pores along with
the water (a process called
“solvent drag”) in response to
a transmembrane pressure
gradient.
Water + Solute
(Solvent Drag)

20. Transmembrane
(Hydrostatic)Pressure
Hydrostatic pressure
gradient between the
blood and dialysate
compartments
Ultrafiltration (Convection)
Hydrostatic UF

21. Ultrafiltration (Convection)
Hydrostatic UF

22. Ultrafiltration Coefficient (KUF)
Number of milliliters of fluid per
hour that will be transferred across
the membrane per mmHg pressure
gradient across the membrane
1 mmHg 0 mmHg
1 Hour
?? ml of water
KUF
Vary and is a function of
membrane thickness and pore size

23. Ultrafiltration Coefficient (KUF)

24. Blood Dialyzate

25. Ultrafiltration (Convection)
Osmotic UF

26. Blood Dialyzate
Different types of Dialysis

27. Hemodialysis Hemofiltration
Diffusion (mainly)
+ Convection (ultrafiltration)
removing water accumulated during
the interdialytic period
Convection (ultrafiltration)
large amount of ultrafiltration
+ higher removal of larger, poorly
diffusible solutes
CRRT: CVVHD CRRT: CVVHF

28. Hemodialysis Hemofiltration
Diffusion (mainly)
+ Convection (ultrafiltration)
removing water accumulated during
the interdialytic period
Convection (ultrafiltration)
large amount of ultrafiltration
+ higher removal of larger, poorly
diffusible solutes
CRRT: CVVHD CRRT: CVVHF

29. Hemodiafiltration
Diffusion (HD)
+ High Convection (ultrafiltration) (HF)

30. Hemodiafiltration
Diffusion (HD)
+ High Convection (ultrafiltration) (HF)
CRRT: CVVHDF
If ultrapure dialysate
produced by the
dialysis machine as
replacement fluid
Online HDF
(OL HDF)

31. CRRT: SCUFHemofiltration, CRRT: CVVHF

32. CRRT

33. Talk Outline
• Diffusion – Convection Concept
• Concept of Clearance

34. Extraction ratio
The extraction ratio
is the percentage reduction
of urea (or any other
solute) across the dialyzer

35. Extraction Ratio
Effect of Erythrocytes
Plasma
RBC
U
U
U
U
U
U
Dialysis
Machine
Plasma
RBC
U
U
Urea equilibrate quickly
Increased Ht% will minimally
or not affect Urea ER
C
C
C
C
C C
C
C
Cr and Phosphate
equilibrate slowly
Increased Ht% decreases ER

36. Extraction Ratio
Effect of Blood Flow Rate (Qb)
Low flow, More
time to be
cleaned
Per one Cycle
Flow rate over time
length of HD
session is more
important

37. Dialyzer Clearance is “KD”
The extraction ratio for molecules larger
than urea will be less than that of urea

38. Dialyzer Clearance is “KD”

39. Dialyzer Clearance is “KD”
At very high Qb, the clearance
will plateau → theoretical
maximum clearance of a
dialyzer at infinite blood and
dialysate flow rates
( )
Removal efficiency falls at
higher Qb, and so the
clearance does not increase
with QB in a 1:1 ratio

40. Mass Transfer Area Coefficient “ ”
The theoretical maximum clearance of a dialyzer
(for a given solute) at infinite blood and dialysate
flow rates (mL/min)
the permeability coefficient of
the dialyzer membrane for a
given solute
the total effective surface area
of the membrane in the
dialyzer
Increased by making the
membrane thinner, by adjusting its
porosity & other factors

41. Mass Transfer Area Coefficient “ ”
when QB is low
(~200 mL/min),
dialyzers in the
800–
1,600mL/min
K0A range have
~ similar
clearances

42. Dialyzer efficiency
The ability of a dialyzer to remove
small solutes.
Represented by K0A for urea
Dialyzer flux
The ability of a dialyzer to remove
very large molecules such as β2-
microglobulin

43. Dialyzer flux
The ability of a dialyzer to remove
very large molecules such as β2-
microglobulin
Water permeability (KUF) is used to specify
the flux
High-flux dialyzers will have a water
permeability > 15–20 mL/hr/mm Hg

44. Adsorption

45. Concept of Clearance
Extraction Ratio (ER)
Dilayzer Clearance
(KD)
Mass Transfer Area
Coefficient (K0A)
Dialyzer Efficiency

46. Solve the Crosswords
1 A method of RRT that uses diffusion
parallel with high volume of ultrafiltration as
a main mechanism for solute transport with a
replacement fluid
2 Approved filter by FDA to treat dialysis
related amyloidosis
3 A method of RRT that uses diffusion as a
main mechanism for solute transport
5 Movement of solutes from a compartment in which they are in high
concentration to another compartment in which they are in lower
concentration7 The ability of a dialyzer to remove large sized
molecules and it is specified by water flux
9 Qb X Extraction ratio
10 A method of RRT that uses convection as
a main mechanism for solute transport with a
replacement fluid
8 A mechanism by which solutes are swept
through the membrane pores along with the
water in response to a transmembrane
pressure gradient or osmotic pressure
11 Molecule that its extraction ration is
affected by changes in Ht% level
12 The percentage reduction of urea (or any
other solute) across the dialyzer
17 The ability of a dialyzer to remove small
solutes, represented by K0A for solute18 Modality of CCRT that uses convection as
a main mechanism for solute transport
without replacement fluid (abbreviation)
4 Molecule that
its extraction ration
is slightly or not
affected at all by
changes in Ht% level
6 Movement of water from area of solute
low concentration gradient to an area of
higher concentration gradient of the same
solute
13 The pressure in the blood compartment
minus the pressure in the dialysate
compartment (abbreviation)
14 A method of RRT that uses diffusion
parallel with high volume of ultrafiltration as
a main mechanism for solute transport with
an ultrapure dialysate produced by the
dialysis machine as replacement fluid
(abbreviation)
15 The theoretical maximum clearance of a
dialyzer (for a given solute) at infinite blood
and dialysate flow rates (mL/min)
(abbreviation)
16 Number of milliliters of fluid per hour
that will be transferred across the membrane
per mmHg pressure gradient across the
membrane (abbreviation)

47. Thank You