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Pediatric CRRT: Terminology and Physiology Jordan M. Symons, MD University of Washington School of Medicine Seattle Childrens Hospital.

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Presentation on theme: "Pediatric CRRT: Terminology and Physiology Jordan M. Symons, MD University of Washington School of Medicine Seattle Childrens Hospital."— Presentation transcript:

1 Pediatric CRRT: Terminology and Physiology Jordan M. Symons, MD University of Washington School of Medicine Seattle Childrens Hospital

2 CRRT: What is it? C ontinuous R enal R eplacement T herapy Strict definition: any form of kidney dialysis therapy that operates continuously, rather than intermittently More common definition: continuous hemofiltration technique, often used for hemodynamically unstable patients

3 Current Nomenclature for CRRT SCUF:Slow Continuous Ultrafiltration CVVH: Continuous Veno-Venous Hemofiltration CVVHD:Continuous Veno-Venous Hemodialysis CVVHDF: Continuous Veno-Venous Hemodiafiltration

4 C VV H Basis for CRRT Nomenclature Rate/Interval for Therapy Blood Access Method for Solute Removal

5 Solute Removal Mechanisms in RRT Diffusion –transmembrane solute movement in response to a concentration gradient –importance inversely proportional to solute size Convection –transmembrane solute movement in association with ultrafiltered plasma water (solvent drag) –mass transfer determined by UF rate (pressure gradient) and membrane sieving properties –importance directly proportional to solute size

6 Diffusion

7 Convection

8 Clearance: Convection vs. Diffusion

9 SCUF CVVH CVVHD CVVHDF UF D R CRRT Schematic

10 Rate Limitations of Volume Removal Vascular Compartment Extra-Vascular Compartment BP

11 Improved Volume Removal with Slower Ultrafiltration Rates Vascular Compartment Extra-Vascular Compartment BP Stable

12 CRRT for Metabolic Control

13 Hollow Fiber Hemofilter

14 Hemofiltration Membranes Capillary Cross Section Blood Side

15 Hemofilter Characteristics Pore size –High Flux vs. High cut-off Surface area; porosity –Effects on maximum ultrafiltration capacity Membrane material –polysulfone, PAN, etc.; modifications Adsorption Prime volume

16 Effect of Pore Size on Membrane Selectivity Creatinine 113 D Urea 60 D Glucose 180 D Vancomycin ~1,500 D IL-6 ~25,000 D Albumin ~66,000 D

17 Effect of Pore Size on Membrane Selectivity Creatinine 113 D Urea 60 D Glucose 180 D Vancomycin ~1,500 D Albumin ~66,000 D IL-6 ~25,000 D These effects are maximized in convection

18 Other Membrane Characteristics: e.g., Charge Negative charge on membrane: Negatively charged particles may be repelled, limiting filtration

19 Other Membrane Characteristics: e.g., Charge Negative charge on membrane: Negatively charged particles may be repelled, limiting filtration Positively charged particles may have increased sieving

20 Other Membrane Characteristics: e.g., Charge Negative charge on membrane: Negatively charged particles may be repelled, limiting filtration Positively charged particles may have increased sieving Charge may change adsorption

21 Blood Flow and Dialyzer Have Major Impact on Intermittent HD Clearance Dialyzer 2: Higher K 0 A Dialyzer 1: Lower K 0 A Dialysate flow rate (Q D ) always exceeds Q B

22 Solution/Effluent Flow Rate is Limiting Factor in CRRT Q B 150ml/min Q D 600ml/hr Q R 600ml/hr Effluent 1200ml/hr +

23 Solution/Effluent Flow Rate is Limiting Factor in CRRT Q B 150ml/min Q D 1000ml/hr Q R 1000ml/hr Effluent 2000ml/hr +

24 Patients Chemical Balance on CRRT Approximates Delivered Fluids Diffusion: blood equilibrates to dialysate Convection: loss is isotonic; volume is replaced Consider large volumes for other fluids (IVF, feeds, meds, etc.) Watch for deficits of solutes not in fluids

25 Diffusion Small molecules diffuse easily Larger molecules diffuse slowly Dialysate required –Concentration gradient –Faster dialysate flow increases mass transfer

26 Convection Small/large molecules move equally Limit is cut-off size of membrane Higher UF rate yields higher convection but risk of hypotension May need to Replace excess UF volume H2OH2O H2OH2O H2OH2O H2OH2O Net Pressure

27 Kramer, P, et al. Arteriovenous haemofiltration: A new and simple method for treatment of over- hydrated patients resistant to diuretics. Klin Wochenschr 55:1121-2, First CAVH Circuit

28

29 CRRT Machines

30 Pediatric CRRT Terminology and Physiology: Summary CRRT comes in several flavors –SCUF, CVVH, CVVHD, CVVHDF Solute transport: diffusion/convection UF approximates 1-compartment model Membrane characteristics affect therapy Fluid composition, rates drive clearance Advancing technology provides more options

31 One of the first infants to receive CRRT Vicenza, 1984


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