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Separation Technology in Dialysis Allan P. Turner M.D. February 17,2006.

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Presentation on theme: "Separation Technology in Dialysis Allan P. Turner M.D. February 17,2006."— Presentation transcript:

1 Separation Technology in Dialysis Allan P. Turner M.D. February 17,2006

2 Kidney Function


4 Terms Used in Dialysis Diffusion Convection Ultrafiltration Clearance 100 ml/min 100mg/dl 100 ml/min 50 mg/dl Clearance=50 ml/min 100 ml/min 100mg/dl 100 ml/min 10 mg/dl Clearance=90 ml/min

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

6 Description of Hemodialysis Primarily diffusion Dialysate –looks like blood of healthy patient 3X week for 3-4 hours Blood and dialysate flows are fast –Q B =500 ml/min –Q D =800 ml/min

7 Membrane(Dialyzer) Hollow Fiber Design Biologic vs synthetic Reuse Terms –Biocompatibility –High efficiency –High flux

8 Access Difficult Trade Offs –rapidity of use –chance of infection –patient comfort –need for addl procedures

9 Access(PermCath) Use immediately No needle sticks High infection rate High recirculation

10 Access(AV Graft) Use in 2-3 weeks Some infection risk 2 needle sticks low recirculation numerous interventions to keep open

11 Access(AV Fistula) 3-18 months to use Minimal infection risk Can last a lifetime

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

13 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

14 Dialysis Machine(Blood Circuit) Roller pump Heparin syringe pump 2 air traps Air detector Venous line clamp

15 Dialysis Machine(Dialysate Circuit) Warm, deaerate, mix concentrates, monitor conductivity and pH, pump Detect blood leaks Generate and monitor ultrafiltration

16 Dialysis Machine


18 Dialysate

19 Urea Clearance ?Urea = uremic toxin? Diffusion Urea: MW=60 (small) KoA Clearance of urea of 250ml/min Native kidneys provide urea clearance of about ml/min

20 Urea Clearance

21 Clearance of Other Solutes Urea(MW 60), creatinine(MW 113), B12 (MW=1355), ß2 microglobulin (MW=11,800), albumin (MW=80,000) Middle molecules Diffusion not effective

22 Hemofiltration Convection to clear larger molecules Replacement fluids without removed solute Costly

23 Continuous Renal Replacement Therapy(CRRT) Critically ill ICU patients –low BP –cant tolerate large Q B 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)

24 CRRT vs Hemodialysis Q B 150ml/hr Dialysate + Ultrafiltration +Replacement fluid Replacement fluid 1000ml/hr Dialysate 40ml/min(2500ml/hr) Q B 500ml/hr Dialysate + Ultrafiltration CRRT Hemodialysis Dialysate 800ml/min(48,000ml/hr)

25 CRRT Citrate Anticoagulation D I A L Y Z E R Blood From patient Blood To patient C C C C CC Calcium C C C CC C CCC Liver Citrate HCO3 Tri-Sodium Citrate

26 CRRT V Q B Q E = Q R + Q FR + Q D Dialysate: 4 L bag Na + 140mEq/L Cl mEq/L HCO 3 25mEq/L K + 4.0mEq/L Mg 1.16mEql/L Rate: mL/hr Q D mL/min (actual Q B = Q B, machine – Q R ) Patient Ca 2+ Gluconate 78mEq/L (20 g/L) in NS Rate: 80mL/hr PF iCa 2+ ( mmol/L) iCa mmol/L Gambro Prisma with M60 AN69 Filter Q R Prefilter Fluid: 4L bag 0.67%Trisodium Citrate 3- 23mM/L Na + 140mEq/L Rate: mL/hr 24mmol/h citrate Gambro Prisma Pre-Pump Pre- Dilution Set V


28 Peritoneal Dialysis(PD) Salmon dialysis Peritoneal membrane Capillaries Diffusion, ultrafiltration( ie osmosis), convection, and absorption

29 PD Membrane Pd Membrane –surface area=BSA=1-2 m 2 – heteroporus, heterogeneous semipermeable membrane with complex physiology Blood Flow –approx ml/min 3 pore model –large pores(macromolecules like proteins) –small pores(small solutes) –ultrapores(aquaporins)(water without solute)

30 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

31 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

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

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