Transcript Symons-TermsInCRRTx

8th International Conference On
Paediatric Continuous Renal Replacement
Therapy (pCRRT)
16th - 18th July 2015
Queen Elizabeth II Conference Centre, London, UK
Common Terminology Used
and Physiology in CRRT
Jordan M. Symons, MD
University of Washington School of Medicine
Seattle Children’s Hospital
Seattle, WA - USA
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
Current Nomenclature for CRRT
SCUF:
CVVH:
Slow Continuous Ultrafiltration
Continuous Veno-Venous
Hemofiltration
CVVHD: Continuous Veno-Venous
Hemodialysis
CVVHDF: Continuous Veno-Venous
Hemodiafiltration
Basis for CRRT Nomenclature
C VV H
Rate/Interval
for Therapy
Blood
Access
Method for
Solute Removal
CRRT Schematic
R
• SCUF
• CVVH
D
UF
• CVVHD
• CVVHDF
Diffusion
• Small molecules
diffuse easily
• Larger molecules
diffuse slowly
• Dialysate required
– Concentration gradient
– Faster dialysate flow
increases mass
transfer
H2 O
Net Pressure
•
•
H2 O
H2 O
•
H2 O
•
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
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
BP
Extra-Vascular
Compartment
Vascular
Compartment
Improved Volume Removal with
Slower Ultrafiltration Rates
BP
Stable
Extra-Vascular
Compartment
Vascular
Compartment
CRRT for Metabolic Control
120
BUN (mg/dL)
100
80
60
40
20
0
Time
IHD
CRRT
Solution/Effluent Flow Rate is
Limiting Factor in CRRT
QR 600ml/hr
QB 150ml/min
QD 600ml/hr
Effluent 1200ml/hr +
Solution/Effluent Flow Rate is
Limiting Factor in CRRT
QR 1000ml/hr
QB 150ml/min
QD 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