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