Mohammed Abdel Gawad Nephrology Specialist Kidney & Urology Center (KUC) Alexandria – EGY drgawad@gmail.com

1. Physiological Principles
of Hemodialysis
Solve the Crosswords
Mohammed Abdel Gawad
Nephrology Specialist
Kidney & Urology Center (KUC)
Alexandria – EGY
drgawad@gmail.com

2. Solve the Crosswords

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

4. 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

5. 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

6. 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

7. 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

8. Blood Dialyzate

9. 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

10. Large solutes can’t pass

11. Blood Dialyzate

12. 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)

13. 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

14. Ultrafiltration Coefficient (KUF)

15. Blood Dialyzate

16. Ultrafiltration (Convection)
Osmotic UF

17. Blood Dialyzate
Different types of Dialysis

18. 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

19. 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
Hemodiafiltration
Diffusion (HD)
+ High Convection (ultrafiltration) (HF)
CRRT: CVVHD CRRT: CVVHF

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

21. CRRT: SCUFHemofiltration, CRRT: CVVHF

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

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

24. 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

25. Dialyzer Clearance is “KD”

26. Dialyzer Clearance is “KD”

27. 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

28. 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

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

30. 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

31. 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

32. Dialyzer flux
The ability of a dialyzer to remove
very large molecules such as β2-
microglobulin

33. Dialyzer flux
The ability of a dialyzer to remove
very large molecules such as β2-
microglobulin

34. Adsorption

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

36. 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)

37. Gawad
Thank You