Physiological Principles of Hemodialysis

Solve the Crosswords

Mohammed Abdel GawadNephrology Specialist

Kidney & Urology Center (KUC)Alexandria – EGY

drgawad@gmail.com

Solve the Crosswords

Talk Outline

• Diffusion – Convection Concept

• Concept of Clearance

DialysisSolute composition of a solution A

(Blood), is altered by exposing solution Ato a second solution B

(Dialysate), through a semipermeable

membrane (Filter - Dialyzer)

Dial

yzerA

B

DialysisSolute composition of a solution A

(Blood), is altered by exposing solution Ato a second solution B

(Dialysate), through a semipermeable

membrane (Filter - Dialyzer)

Dial

yzerA

B

BA Dial

yzer

DialysisSolute composition of a solution A

(Blood), is altered by exposing solution Ato a second solution B

(Dialysate), through a semipermeable

membrane (Filter - Dialyzer)

BA Dial

yzer

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

DialysisSolute composition of a solution A

(Blood), is altered by exposing solution Ato a second solution B

(Dialysate), through a semipermeable

membrane (Filter - Dialyzer)

BA Dial

yzer

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 barrierDiffusion Ultra-Filtration

(Convection)

Hydrostatic Osmotic

Blood Dialyzate

DiffusionBlood 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

Large solutes can’t pass

Blood Dialyzate

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)

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

Ultrafiltration Coefficient (KUF)

Blood Dialyzate

Ultrafiltration (Convection)Osmotic UF

Blood Dialyzate

Different types of Dialysis

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

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

Hemodiafiltration

Diffusion (HD)+ High Convection (ultrafiltration) (HF)

CRRT: CVVHDF

If ultrapure dialysate produced by the

dialysis machine as replacement fluid

Online HDF (OL HDF)

CRRT: SCUFHemofiltration, CRRT: CVVHF

Talk Outline

• Diffusion – Convection Concept

• Concept of Clearance

Extraction ratio

The extraction ratiois the percentage reduction of urea (or any other solute)

across the dialyzer

Extraction RatioEffect 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

Dialyzer Clearance is “KD”

Dialyzer Clearance is “KD”

Dialyzer Clearance is “KD”

At very high Qb, the clearance will plateau → theoretical maximum clearance of a

dialyzer at infinite blood anddialysate flow rates

( )

Removal efficiency falls at higher Qb, and so the

clearance does not increase with QB in a 1:1 ratio

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

Mass Transfer Area Coefficient “ ”

when QB is low (~200 mL/min), dialyzers in the

800–1,600mL/min

K0A range have ~ similar

clearances

Dialyzer efficiency The ability of a dialyzer to remove

small solutes.Represented by K0A for urea

Dialyzer fluxThe ability of a dialyzer to remove very large molecules such as β2-

microglobulin

Dialyzer fluxThe 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

Dialyzer fluxThe ability of a dialyzer to remove very large molecules such as β2-

microglobulin

Dialyzer fluxThe ability of a dialyzer to remove very large molecules such as β2-

microglobulin

Adsorption

Concept of ClearanceExtraction Ratio (ER)

Dilayzer Clearance (KD)

Mass Transfer Area Coefficient (K0A)

Dialyzer Efficiency Dialyzer Flux

Solve the Crosswords1 A method of RRT that uses diffusion

parallel with high volume of ultrafiltration as a main mechanism for solute transport with a

replacement fluid2 Approved filter by FDA to treat dialysis

related amyloidosis3 A method of RRT that uses diffusion as a

main mechanism for solute transport5 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 flux9 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)

GawadThank You