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Principle of

Hemo (dialysis)

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HEMODIALYSIS

Diffusion

HEMOFILTRATION :

Convection

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Principle of Hemodialysis

Dialysis removes nitrogenous(and other)

waste products, and corrects the electrolyte,

water, and acid baseabnormalities associatedwith renal failure.

It requires the use of semi-permeable

membrane which allow the passage ofwaterand small molecularweight solutes, but not

large molecules.

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Dialysis: General Principles

Diffusion

Movement of solutesfrom an area of greaterconcentration to lesser concentration

Osmosis

Movement of fluid from an area of lesser to an area ofgreater concentration of solutes.

Ultrafiltration (water & fluid removal)

Movement of fluid across a semipermeable membraneas a result of an artificially created pressure gradient.

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Diffusion

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Ultrafiltration

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Membrane

Membranet = 0

t = 0

t = equilibrium

t = later

Diffusion

Ultrafiltration

The Process of diffusion (top) and ultrafiltration (bottom)

A A

A A

B B

B B

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Hemodialysis Filter

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Mechanisms of Solute Removal

1. Diffusion

2. Convection

3. Diffusion + Convection

4. Adsorbtion

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Solute Clearance

MembraneBlood Dialysate/Ultrafitrate

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Diffusive Solute Clearance

MembraneBlood Dialysate/Ultrafitrate

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Diffusive Solute Clearance

MembraneBlood Dialysate/Ultrafitrate

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Convection

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ADSORPTION: molecular adherence to the surface

or interior of the membrane.

Adsorption

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ULTRAFILTRATION: The movement offluid through a membrane

caused by a pressure gradient.

Ultrafiltration

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Water movement during standard hemodialysis

Water movement

Intracellular fluid Extracellular fluid Dialyzer

Osmolality

320 mosm/kg

Loss of ureaand water

step1

step2

step3

280

Osmolality

320 mosm/kg

Falling to

290mosm/kg

as diffusion occurs

Compensatory refilling

d d li

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18

Air

Detector

Blood Leak

Detector

PT

PT = Pressure

Transducer

PT

Venous

clamp

Anticoagulant

Blood from Patient

Blood return toPatient

Dialysate In

Dialysate / UF Out (green

/ yellow)

Informational Display

A Standard HD Delivery System

PT

Mixing

System

Conductivity

Meter

Water, Acid Concentrate,

Bicarbonate Concentrate

In

Pre-mixed or

sorbent

regenerated

dialysate

Saline

Drip Chamber

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Solute Transfer & Ultrafiltration

C blood > C Dialysate

P blood P Dialysate

C blood > C Dialysate

P blood > P Dialysate

Blood Dialysate

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A semi-permeable membrane

Ur Cr

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Cr

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CrUr

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UrCr

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UrCr Cr

Cr

Ur

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UrCr

Cr

NO DIFFUSIONSOME DIFFUSIONSTART DIFFUSION

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A semi-permeable membrane

NO DIFFUSIONSOME DIFFUSIONSTART DIFFUSION

UrUr

Ur

Ur

Ur

Ur

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A semi-permeable membrane

Ur Cr

Ur Cr

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UrCrUr

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CrUr

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UrCr

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DIFFUSION DIFFUSION DIFFUSION

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A semi-permeable membrane

DIFFUSIONDIFFUSIONDIFFUSION

UrUr

Ur

Ur

Ur

Ur