common terminology used and physiology in crrt jordan m. symons, md university of washington school...

Common Terminology Used and Physiology in CRRT

Jordan M. Symons, MD

University of Washington School of Medicine

Seattle Children’s Hospital

Seattle, WA - USA

8th International Conference On

Paediatric Continuous Renal Replacement Therapy (pCRRT)

16th - 18th July 2015Queen Elizabeth II Conference Centre, London, UK

Continuous Renal Replacement Therapy (CRRT)

• Extracorporeal circuit similar to IHD

• Runs continuously• Particle removal may

be by diffusion, convection or a combination

• Fluid removal by ultrafiltration

Rinse-O-Matic3000

Current Nomenclature for CRRT

SCUF: Slow Continuous Ultrafiltration

CVVH: Continuous Veno-Venous Hemofiltration

CVVHD: Continuous Veno-Venous Hemodialysis

CVVHDF: Continuous Veno-Venous Hemodiafiltration

C VV H

Basis for CRRT Nomenclature

Rate/Interval for Therapy

Blood Access

Method for Solute Removal

• SCUF

• CVVH

• CVVHD

• CVVHDF

UF

D

R

CRRT Schematic

Diffusion• Small molecules

diffuse easily• Larger molecules

diffuse slowly• Dialysate required

– Concentration gradient– Faster dialysate flow

increases mass transfer

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

H2O

H2O

H2O

H2O

Net Pressure

Effect of Pore Size on Membrane Selectivity

Creatinine 113 D

Urea 60 D

Glucose 180 D

Vancomycin~1,500 D

Albumin~66,000 D

IgG~150,000 D

Rate Limitations of Volume Removal

Vascular Compartment

Extra-Vascular Compartment

BP

Improved Volume Removal with Slower Ultrafiltration Rates

Vascular Compartment

Extra-Vascular Compartment

BP Stable

CRRT for Metabolic Control

0

20

40

60

80

100

120

Time

BU

N (

mg

/dL

)

IHD CRRT

Solution/Effluent Flow Rate is Limiting Factor in CRRT

QB 150ml/min

QD 600ml/hr

QR 600ml/hr

Effluent 1200ml/hr +

Solution/Effluent Flow Rate is Limiting Factor in CRRT

QB 150ml/min

QD 1000ml/hr

QR 1000ml/hr

Effluent 2000ml/hr +

Patient’s 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

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

Thank You for Your Attention