Separation Technology in Dialysis

1
Separation Technology in Dialysis

• Allan P. Turner M.D.
• February 17,2006

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Kidney Function
3
Kidney Function
4
Terms Used in Dialysis

• Diffusion
• Convection
• Ultrafiltration
• Clearance

100 ml/min 100mg/dl
100 ml/min 50 mg/dl
Clearance50 ml/min
100 ml/min 100mg/dl
100 ml/min 10 mg/dl
Clearance90 ml/min
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Options for RRT

• Hemodialysis
• 3X a week for 3-4 hours
• diffusive clearance with ultrafiltration of water
• faster blood flow ratesless hemodynamic
  stability
• CRRT(Hemodiafiltration)
• a continuous process
• used on critically ill patients in US
• more convective clearance
• lower blood flow rates and smaller filtergreater
  hemodynamic stability
• Peritoneal Dialysis
• peritoneal membrane used as semipermeable
  membrane
• batch process

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Description of Hemodialysis

• Primarily diffusion
• Dialysate
• looks like blood of healthy patient
• 3X week for 3-4 hours
• Blood and dialysate flows are fast
• QB500 ml/min
• QD800 ml/min

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Membrane(Dialyzer)

• Hollow Fiber Design
• Biologic vs synthetic
• Reuse
• Terms
• Biocompatibility
• High efficiency
• High flux

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Access

• Difficult
• Trade Offs
• rapidity of use
• chance of infection
• patient comfort
• need for addl procedures

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Access(PermCath)

• Use immediately
• No needle sticks
• High infection rate
• High recirculation

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Access(AV Graft)

• Use in 2-3 weeks
• Some infection risk
• 2 needle sticks
• low recirculation
• numerous interventions to keep open

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Access(AV Fistula)

• 3-18 months to use
• Minimal infection risk
• Can last a lifetime

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Anticoagulation

• Blood clots
• Heparin
• discovered in 1926
• Partial clotting
• limits diffusion
• reduces surface area
• Access must stop bleeding
• Calcium
• required for clotting

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Dialysis Machine

• Blood Circuit
• anticoagulate
• deliver blood to membrane
• safely return blood to patient
• Dialysate Circuit
• deliver dialysate at proper temperature,
  concentration, and pH
• control ultrafiltration

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Dialysis Machine(Blood Circuit)

• Roller pump
• Heparin syringe pump
• 2 air traps
• Air detector
• Venous line clamp

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Dialysis Machine(Dialysate Circuit)

• Warm, deaerate, mix concentrates, monitor
  conductivity and pH, pump
• Detect blood leaks
• Generate and monitor ultrafiltration

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Dialysis Machine
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Dialysis Machine
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Dialysate
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Urea Clearance

• ?Urea uremic toxin?
• Diffusion
• Urea MW60 (small)
• KoA
• Clearance of urea of 250ml/min
• Native kidneys provide urea clearance of about
  90-110ml/min

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Urea Clearance
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Clearance of Other Solutes

• Urea(MW 60), creatinine(MW 113), B12 (MW1355),
  ß2 microglobulin (MW11,800), albumin (MW80,000)
• Middle molecules
• Diffusion not effective

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Hemofiltration

• Convection to clear larger molecules
• Replacement fluids without removed solute
• Costly

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Continuous Renal Replacement Therapy(CRRT)

• Critically ill ICU patients
• low BP
• cant tolerate large QB or large filter
• often cant be systemically anticoagulated
• Continuous
• low clearances but runs 24/7
• Anticoagulation
• regional anticoagulation instead of systemic
• Combine hemodialysis and hemofiltration
• hemodiafiltration
• increases clearances even of middle molecules
• continuous venovenous hemodiafiltration(CVVHDF)

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CRRT vs Hemodialysis
Dialysate 40ml/min(2500ml/hr)
Replacement fluid 1000ml/hr
CRRT
QB 150ml/hr
Dialysate Ultrafiltration Replacement fluid
Dialysate 800ml/min(48,000ml/hr)
Hemodialysis
QB 500ml/hr
Dialysate Ultrafiltration
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CRRT Citrate Anticoagulation
Tri-Sodium Citrate
Blood
C
C
From
C
C
C
C
patient
D
Liver
I
A
Citrate HCO3
L
C
Y
Calcium
Z
C
C
E
R
Blood
To
C
C
C
C
C
C
patient
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CRRT
V
Gambro Prisma
with
Gambro Prisma
with
V
Patient
M60 AN69 Filter
M60 AN69 Filter
Q
B
iCa
2
1.1-1.3
100-150
mL
/min
mmol
/L
(actual Q
Q
Q
)
B
B, machine
R
Q
Q
Q
Q


E
R
FR
D
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CRRT
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Peritoneal Dialysis(PD)

• Salmon dialysis
• Peritoneal membrane
• Capillaries
• Diffusion, ultrafiltration( ie osmosis),
  convection, and absorption

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PD Membrane

• Pd Membrane
• surface areaBSA1-2 m2
• heteroporus, heterogeneous semipermeable membrane
  with complex physiology
• Blood Flow
• approx. 50-100 ml/min
• 3 pore model
• large pores(macromolecules like proteins)
• small pores(small solutes)
• ultrapores(aquaporins)(water without solute)

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PD Ultrafiltration

• Dextrose(3 concentrations) added to provide
  gradient for UF(osmosis)
• Glucose diffuses into blood and diminishes
  gradient
• Absorption of dialysate occurs limiting UF
• Newer agents

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PD Clearance

• High Transporters
• dialyze well
• ultrafilter poorly
• ? Icodextran ?
• best with freq. short dwells
• High Avg/Low AVG transporters
• Low Transporters
• ultrafilter well
• dialyze poorly
• best with longer short dwells
• Options
• CAPD
• CCPD

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Future

• Which separation techniques improve mortality
• Less expensive RRT as population grows
• Improve patients quality of life
• Biological systems