Chap 9'

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Chap 9. Artificial Kidney Devices
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Haemodialysis

• The most common method of treating end stage
  renal failure
• introduction in the 1960s
• Improved composition of the dialyser and
  dialysate, but little change in the main design
• Still complicated and expensive method of
  treatment
• Introduction of continuous ambulatory peritoneal
  dialysis (CAPD) in 1975
• With or without hemodialysis
• Increased at a steady rate
• cheaper, easier and less demanding therapy
• a number of factors to consider

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Ideal Artificial Kidney

• Efficient removing waste products
• Water
• Small priming volume
• Small resistance to flow
• inexpensive, easy to use
• Reliability, safety
• Low cost
• Nontoxic, blood-compatible

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Haemodialysis
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Haemodialysis

• approximately 3 sessions/week with sessions
  lasting 4-5 hours (depending on the patient)
• dialysed at home but usually in a hospital or
  satellite patient care centre
• Heparin to reduce the amount of blood clotting
• the principle of osmosis
• uses a large surface area to transfer waste
  products and fluid as fast as possible.
• Between dialysis, a strict diet with a reduced
  fluid intake
• requires access to the vascular system and thus
  there is a risk of infection.
• The access point must be periodically changed. 

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Peritoneal Dialysis

• A tube-like catheter is inserted to fill the
  abdomen with dialysis solution.
• The peritoneum is used to transport waste and
  fluid.
• usually takes 30-40 minutes
• The dwell time (time when the fluid is in the
  abdominal cavity) usually takes 4-6 hours with 4
  exchanges per day (depending on the patient.)
• Continuous ambulatory peritoneal dialysis most
  common and does not require the assistance of a
  machine.
• Assisted peritoneal dialysis using a machine
  (cycler) to fill and drain the abdominal cavity
  (usually while sleeping)
• may use a combination of the two methods
  depending on the patient
• The dwell time is dependant on the patients
  ability to transport fluids and waste over time.

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• Peritoneal dialysis a freer lifestyle than
  haemodialysis but can be problematic if the
  patient skips treatments.
• The dialysate can be changed by the patient
  almost anywhere
• Infection the biggest problem due to bacteria
  which can cause peritonitis.
• In a basic setup the main equipment is the
  transfer set and the dialysate.
• Dialysate bags are usually heated to body
  temperature before being used with most cyclers
  having a built in heating unit.

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• Haemodialysis a high clearance rate over a
  short period of time
• Peritoneal dialysis a low clearance but is
  continuous
• more effective removal of urea with peritoneal
  dialysis
• Peritoneal dialysis generally for younger
  patients
• Both methods have similar problems in terms of
  the patients overall health.
• Anaemia due to the lack of red blood cells.
• Renal osteodystrophy affects 90 of dialysis
  patients and causes a patients bones to become
  brittle and malformed.
• Sleep disorders as well as deposits of proteins
  on joints and tendons causing pain

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TYPES OF DIALYZERS

• to provide controllable transfer of solutes and
  water across a semi permeable membrane separating
  flowing blood and dialysate streams.
• The transfer processes are diffusion (dialysis)
  and convection (ultrafiltration).
• Three basic dialyzer designs
• coil
• parallel plate
• hollow fiber

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Coil dialyzer

• The blood compartment consisted of one or two
  long membrane tubes placed between support
  screens and then tightly wound around a plastic
  core.
• Non-uniform dialysate flow distribution across
  the membrane.

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Parallel Plate Dialyzer

• Sheets of membrane are mounted on plastic support
  screens, and then stacked in multiple layers
  ranging from 2 to 20 or more.
• multiple parallel blood and dialysate flow
  channels with a lower flow resistance
• The physical size of the parallel plate dialyzers
  has been greatly reduced since their
  introduction.

• There have been major improvements
• thinner blood and dialysate channels with
  uniform dimensions,
• minimal masking or blocking of membranes on the
  support,
• minimal stretching or deformation of membranes
  across the supports

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Hollow Fiber Dialyzer

• most effective design for providing low-volume
  high efficiency devices with low resistance to
  flow.
• fiber bundle
• The fibers are potted in polyurethane at each end
  of the fiber bundle in the tube sheet, which
  serves as the membrane support.

Ultra filtration

• All excess fluid must be removed from the
  bloodstream as the patient's blood flows through
  the dialyzer.
• The process of water removal from the bloodstream
  is called ultra filtration, and the amount of
  fluid removed is the ultra filtrate.

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Thomas Graham Origins of dialysis

• Thomas Graham, Professor of Chemistry at
  Anderson's University in Glasgow, coined the term
  dialysis in 1861.
• Extraction of urea from urine

The introduction of haemodialysis

• In 1913, Abel, Rowntree, Turner and colleague
  constructed the first artificial kidney.
• Never used to treat a patient.

• George Haas from Germany performed the first
  successful human dialysis in 1924.
• lasted for 15 minutes, and no complications
  occurred.

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WJ Kolff and H Berk

• developed the first practical human haemodialysis
  machine was developed by from the Netherlands in
  1943.
• This rotating drum artificial kidney consisted of
  30-40 metres of cellophane tubing in a stationary
  100-litre tank.

One of Kolff's first artificial kidneys (1946)
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Alwall dialyser

• The dialysis tubing was wound around the
  vertically mounted screen.
• Dialysate circulated round this at variable
  pressure.

The Kolff-Brigham dialyser (1950)
An Alwall dialyser in the 1950s.
a modified version of the original rotating drum
kidney
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• In 1946 Nils Alwall produced the first dialyser
  with controllable ultra-filtration.
• 10-11 metres of cellophane tubing wrapped around
  a stationary, vertical drum made of a metal screen

the Kolff-Brigham kidney

• successfully used to treat renal failure in a few
  centres in the early 1950s, and in the Korean war.

Modified Kolff twin coil kidney (Royal Infirmary
of Edinburgh)

• In 1956 Kolff and Watschinger developed the "twin
  coil" artificial kidney, a modification of the
  "pressure cooker" dialyser developed by Inouye
  and Engelberg in 1952.

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Dialysis using a domestic washing machine
Nose and colleagues in Japan (1961)
Kolff at the Cleveland Clinic, USA (1965)
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Peritoneal Dialysis

• Tenckhoff described home peritoneal dialysis
  using the repeated puncture technique.
• 20-22h (60l) of dialysis under local anaesthetic.
  
• Tenckhoff and colleagues later developed a soft
  tunnelled catheter, making peritoneal dialysis
  viable.

The beginnings of renal transplantation

• In 1933, the first recorded human cadaveric
  transplant took place in Russia.
• The first human kidney transplant from an
  allograft in 1936, by U Voronoy.
• the 1st successful kidney transplant between
  identical twins in 1954
• The first successful kidney transplant using an
  organ taken from a cadaver was in 1962 (Haeger K,
  1989), made possible by the development of the
  first effective drug to prevent rejection,
  azathioprine.

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Dialysis Passive diffusion through a membrane
Objective  Understanding the kidney as a part
of the excretory system Understanding the mass
transfer process Illustrating an artificial
organ Getting acquainted with techniques for
chemical concentration measurement
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Kidney

• the most important organs of the excretory
  system.
• clean from the blood substances not needed in the
  body.
• a complex filter, where active and passive
  mechanisms are involved as well as several
  complex control mechanisms

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The Artificial Kidney

• two major functions solute and water removal.
• the semi-permeable membrane.
• If blood is in contact with the membrane and
  dialysate is on the other side, solutes will be
  removed from the blood and pass to the dialysate
  side.

• a counter current system
• The average concentration difference across the
  membrane is larger.

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• As blood is pushed through the blood compartment
  in one direction, suction or vacuum pressure
  pulls the dialysate through the dialysate
  compartment in a countercurrent, or opposite
  direction.
• These opposing pressures drain excess fluids out
  of the bloodstream and into the dialysate, a
  process called ultrafiltration.
• Diffusion moves waste products in the blood
  across the membrane into the dialysate
  compartment.
• Electrolytes and other chemicals in the dialysate
  solution can cross the membrane into the blood
  compartment.

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Blood Components
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Hemodialysis System

• Pumps
• heaters
• temperature controls
• pressure and flow meters
• bubble detectors to avoid blood cell destruction
• etc

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Hollow Fiber Dialyzers
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Hemodialysis Systems
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Hemodialysis Systems
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Embedded Pentium 586 ??
Embedded Pentium 586? Serial ?? ??
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Specification of Flow Unit
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Fluid Unit
Heat Exchanger, Adjustable Regulator, Air Removal
System, Concentrate Supply System, Equalizer
System, Ultrafiltration System etc
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Concentrate Supply System
Acetate ??
Bicarbonate ??
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Air Removal System ???

• ??? ? ?? ??
• Dialyzer? ??, ??? ??, Flow Rate? ???, ??? ??
• Mixing Chamber A
• Degassing Pump
• Mixing Chamber B
• ???? ??? ? ??? ??? ??? ????, ????? ?? Degassing
  Chamber ? ???? ??? Chamber ??? Air Valve? close

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Flow Equalizer system

• Dialyzer? ???? ?? ???? ?? ??? ?? ???? ?? ???
  ????? ??? ??
• 2-Way ?? ??? ??
• Valve1, Valve4 open
• ? Valve5, Valve8 open,
• Valve2, Valve3 open
• ? Valve6, Valve7 open

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Ultrafiltration system

• Pre Equalizer? ?? ???? Dialyzer? ??? ? Post
  Equalizer? ???? ?? ??? UF Pump? ??
• Pre Equalizer? ??? ????
• ???? ??? Monitoring
• Post Equalizer? ??? ???? Post Equalizer? ???
  Monitoring

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Blood Unit
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Blood Pump System

• Peristalic Pump? ??? ??, ??? ??? ???? ??? ?? ??

AV Chamber Level Adjustment System

• ??? ??? ???? Chamber ?? ?? ??? ?? ??
• ?? ??? Blood Line? Saline? ?????, Chamber? ??? ??

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Touch Screen
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GUI(Graphics User Interface)
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Modeling of film-type dialyzer
Assume, same partition coefficient
At Steady state (no accumulation of solute in any
region), the same fluxes through both films and
through the membrane
Assuming
(1) linear concentration profiles (2) Zero bulk
flow (3) No electrical potential gradients (4)
Constant diffusivity
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The overall concentration difference
or
Thus,
or
K Overall mass transfer coeff.
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Expressions for the Overall Mass Transfer Rate
The mass transfer
integrating
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Total mass transferred in the dialyzer
Thus,
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Analogy with Heat Transfer
Hot fluid
2
1
cold fluid
Hot fluid
2
1
cold fluid
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log mean temperature difference (LMTD)
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Expressions for Dialysance, Clearance, and
Extraction Ratio

• Dialysance D
• performance of the dialyzer
• (Total mass transfer) / (unit conc difference)

• Clearance C
• Equivalent amount of inlet blood (eg. ml/min) to
  clear all solute at the that mass transfer rate

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Expressions for Dialysance, Clearance, and
Extraction Ratio

• Extraction ratio E
• Amount of solute concentration change for
  complete equilibrium with large amount of
  dialysate with conc CDi

If

• As membrane area and the amount of dialysate used
  is increased, E approaches 1.

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For a cocurrent dialyzer,
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or
where
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For a countercurrent dialyzer,
or
where
Fig. 9.8, 9.9, 9.10
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Modeling of the Patient-Artificial Kidney Systems
For high dialysate flow rates,
irrespective of dialyzer types
0 (fresh dialysate with no solute)
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Modeling of the Patient-Artificial Kidney Systems
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Prediction of Required Treatment Time
For a flat plate dialyzer

• When first connected to the patient, BUN(blood
  urea nitrogen) is 150 mg, what will be BUN in
  the blood returning to the patient

• What is clearance value for urea?

Removes urea at a rate equivalent to completely
cleaning 113cc/min of blood
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Prediction of Required Treatment Time
For a flat plate dialyzer

• To complete the patients BUN 50 mg, how long
  will it take, neglecting urea production in the
  body during dialysis?

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Mass Transfer and Clearance
In the dialysis process, water and solutes are
removed.
Overall Mass Transfer
Overall Mass Transfer is the fractional depletion
of a given solute in the blood as it passes
through the dialyzer. Assuming no water
filtration, the mass transfer rate under steady
state conditions is where CBi, CBo, CDi and
CDo (mol/ml) are blood input, blood output,
dialysate input and dialysate output
concentrations respectively.
QBo and QDo (ml/min) are the blood and dialysate
output flow rates, respectively.
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Solute Removal
Solute Removal for the artificial kidney can be
characterized by the clearance C (ml/min).
Again, assuming no water filtration, clearance
is defined as the mass transfer rate divided by
the initial concentration difference This can
be written two ways Clearance is a function
of blood flow. It varies only between 0 and the
blood flow. We therefore define extraction
fraction as the normalized clearance with respect
to blood flow
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Filtration

• Water is removed from the blood by
  ultrafiltration.
• Clinically, the blood is usually subject to
  higher pressure than the dialysate resulting in
  ultrafiltration.
• Ultrafiltration can be enhanced by increasing the
  resistance to blood flow at the dialyzer output,
  subjecting the dialysate to negative pressure or
  using membranes that are more permeable to water.
  
• Ultrafiltration (ml/min) (blood inflow)
  (blood outflow), corresponding to the water
  removed from the patient per minute When
  there is ultrafiltration, clearance can now be
  written as