1
• Dialyzer clearance is expression of
A. The performance of a dialyzing process
B. The volume of blood totally cleared of a
given substance per unit time
C. The blood solute flux rate per minute
D. Both A & B
E. Both B & C
2
• Which one of the following does not
influence dialyzer urea clearance
A.
B.
C.
D.
E.
Blood flow rate
Dialysate flow rate
Membrane permeability
Surface area of the dialyzer
Blood concentration of urea
3
• Factors affecting the rate of diffusion in
hemodialysis include all of these EXCEPT
A.
B.
C.
D.
E.
Surface area of dialyzer
Membrane size
Hydrostatic pressure in blood compartment
Membrane pore size distribution
Concentration gradient between blood and
dialysate
4
• Diffusive resistance include all of the
following EXEPT
A.
B.
C.
D.
Blood film layer thickness
Membrane permeability
Dialysate film thickness
Solute drag
5
• The blood dialysate flow configuration
that maintains the optimum blood
dialysate concentration gradient
A.
B.
C.
D.
Concurrent flow
Countercurrent flow
Crosscurrent flow
Recirculation flow
6
• 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
7
• 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
8
• Mass transfer coefficient refers to
A.
B.
C.
D.
E.
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
9
• Sieving coefficient depends on all of
following EXEPT
A.
B.
C.
D.
Molecular weight cutoff the membrane
Ultrafiltration rate
Surface area
Diffusion
10
• Factors affecting the net flux include
A.
B.
C.
D.
E.
Membrane surface area
Membrane permeability
Blood dialysate flow configuration
A&B
All of the above
Functions of the Kidneys
• Excretory
– Excretion of waste products
• Regulatory
– Fluid
– Electrolytes
– Acid base
• Hormonal
– Rennin
– Erythropoietin
– 1,25 OH D3
• Metabolic
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
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)
Principles of Dialysis
What is Diffusion ?
• Movement of the solute through semi
permeable membrane from one side to
the other on the basis of concentration
gradient
Diffusion – Random Molecule Movement
`
Diffusion – Random Molecule Movement
Diffusive resistance
`
Diffusion – Random Molecule Movement
Diffusive resistance
`
Diffusion – Random Molecule Movement
Diffusive resistance
`
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
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
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: 59-74 1855
Ultrafiltration
A
B
Ultrafiltration
A
B
Ultrafiltration
Transmembrane pressure
(TMP)
=
Positive pressure A + Negative pressure B
Ultrafiltration Pressure
(UFP)
=
TMP – Oncotic Pressure A
A
B
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
Ultrafiltration & Convection
Osmosis
Osmosis & Convention
Kidney
Urine
Dialyzer
Dialysate
Diffusion- KoA
Diffusive resistance
`
Diffusion in Dialyzer
Diffusive force = Concentration gradient
Blood
Dialysate
Countercurrent
& Concurrent
Js= KoA x log mean concentration gradient
Membrane
Countercurrent Blood-Dialysate
Flow
Diffusive force
Blood
Membrane
Dialysate
Diffusion in Dialyzer
Diffusive force
Blood
Dialysate
Membrane
Diffusion in Dialyzer
For adequate diffusion
Dialysate flow 2-2.5 time blood flow
Js= KoA x log mean concentration gradient
Dialysate Flow Unstirred layer
effect
Effect of Dialysate Flow Rate on
Membrane Diffusion
Blood Flow & Diffusion
Wide blood channel
Blood Flow & Diffusion
Blood Flow & Diffusion
Slow Blood Flow
Membrane Limited Diffusion
Flow Limited Diffusion
Effect of Blood Flow on Clearance
Dialyzer design
Older hollow fiber dialyzer
Dialysate out
Dialysate out
Blood out
Blood & dialysate flow geometry
Blood in
Header
Dialysate out
Hollow fiber
Casing or jacket
Dialysate in
Dialysate
Blood out
Blood flow velocity
Header modification
Blood flow and dialysate flow rate
Improved header design
Spiral blood flow inlet
Smooth cut vs rough cut surface
Blood flow velocity
Placement of fibers, straight fibers
Placement of fibers - Mourie Design
Space yarn between fibers
Comparison of dialysate flow
The densitometry profiles achieved in the three
different hemodialyzers are graphically reported (top
panels).
Claudio Ronco et al. JASN 2002;13:S53-S61
Clearances
Wavy (undulated fibers) vs straight
OLDER DIALYZER
Dialysate entry port
Dialysate entry port
Pores size and distribution
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
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
–
–
–
–
–
of Dialyzer for
Surface area-number of pores
particular salute
Size of pores
ie. KoA urea
Distribution of pores
At particular blood and dialysate
flow rate
Thickness of membrane
Temperature of solution
Dialyzer KoA
Calculated from clearance, blood flow, dialysate flow
Qb.Qd Ln
KoA =
Qb - Qd
1-Kd/Qb
1-Kd/Qd
Kd: Dialyzer clearance
Qb: Blood flow
Qd: dialysate flow
KoA: Mass transfer area coefficient
• Diffusion is greater for small molecules
as compared to larger molecules
• Low flux: molecular wt cut off = 10000
deltons
• High flux: molecular weight cut off =
30000 deltons
Distribution of pore size
A
B
Categorization of molecules
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
Sieving coefficient
• Depends on
– Molecular weight cutoff of the membrane
– Ultrafiltration rate
– Membrane surface area
Sieving coefficient
Dialysance
Rate of removal
Dialysance =
Concentration gradient
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
Concentration
Outflow
Concentration
Dialysance
Dialysate
Blood flow
Ml/min
Sodium
Urea
Sodium
On line urea clearance = Sodium dialysance
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
Dialysance
Dialysate
Blood flow
Ml/min
Sodium Potassium
Sodium Potassium
Calcium
Calcium
Bicarbonate
Magnesium
Bicarbonate
Magnesium
Shift of solute per minute = Blood flow per minute (Inflow – outflow concentration)
Difference of concentration in blood & dialysate
Effect of Pore Distribution & Solute
MW on KoA
A = Low flux cellulose membrane,
B= High flux membrane
Low Flux Cellulose Membrane
High Flux Membranes
Erythrocyte Diffusion Barriers
Urea
Creatinine
Phosphate
Effect of Hematocrit on Clearance
Effect of Flow on Membrane
Filtration
• Flux
– 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
• Efficacy
• Related to urea clearance of dialyzer
urea clearance – KoAurea
– Low efficacy – KoAurea < 500 ml/min
– High efficacy – KoAurea > 600 ml/min
RRTs – Principles of Dialysis
Diffusion
Convection
Ultrafiltration Osmosis
Conventional
Hemodialtsis
+++
+
+
+
High
Efficiency HD
++++
+
+
+
High Flux
Dialysis
+++
+++
+++
+
Hemofiltration
-
++++
++++
-
Hemodialfiltra
tion
+++
++++
++++
+
Peritoneal
Dialysis
+++
-
-
++