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