Solute Mass Transfer in CRRT Garred et al', AJKD 1997

1
Solute Mass Transfer in CRRTGarred et al., AJKD
1997
2
Mechanisms of Solute Removal IHD vs CRRTClark
and Ronco, Kidney Int 1998
IHD CRRT Small Solutes Diffusion Diffusion
(CVVHD)(mw lt 300) Convection (CVVH) Middle
Molecules Diffusion Convection(mw
500-5,000) Convection Diffusion LMW
Proteins Convection Convection(mw
5,000-50,000) Diffusion Adsorption Adsorption L
arge Proteins Convection Convection(mw gt
50,000) Determinants flow rates, membrane
thickness Determinants effluent dialysate
flow rate
3
Solute Clearance in CRRT

• CVVHD K E . QD
• Post-Dilution CVVH K S . QUF
• Pre-Dilution CVVH K S . QUF .

Concentration in effluent dialysate
(
)
E
Concentration in blood
Concentration in filtrate
(
)
S
Concentration in blood
4
Dialytic Solute Removal Mechanisms

• 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 rate determined by ultrafiltration
  rate (pressure gradient) and membrane sieving
  properties
• importance directly proportional to solute size

5
Urea Clearance in Pre-Dilution CVVHBrunet et
al., AJKD 1999
Clearance (mL/min)
6
Effect of Dialysate Flow Rate onSmall Solute
Clearances in CVVHDBonnardeaux et al., AJKD 1992
Dialysate Out
Urea
Clearance or Flow Rate (mL/min)
Creatinine
Ultrafiltration
Inlet QD (mL/min)
7
Effect of Dialysate Flow Rate onSolute
Equilibration in CVVHDBonnardeaux et al., AJKD
1992
8
Solute Equilibration in CVVHDBrunet et al., AJKD
1999
Clearance (mL/min)
QE (mL/h)
9
Components of Small Solute Clearance in
CRRTSigler et al., AJKD 1987
Urea clearance, cc/min
Ultrafiltration, (QF)cc/min
10
Urea and Creatinine Kinetic Parameters in ARF
PatientsLeblanc et al., AJKD 1998
nPCR (gm/kg/d) 1.75 0.82 Creatinine Index
(mg/kg/d) 13.7 4.7 LBM (kg) 38.3 11.9 LBM/BW
() 49.5 14.0
11
Effect of Solute Molecular Weight on
EquilibrationJeffrey et al., Artif Organs 1994
Solute (MW) Sieving Coefficient (HF) Diffusion
Coefficient (HD) Urea (60) 1.01 0.05 1.01
0.07 Creatinine (113) 1.00 0.09 1.01
0.06 Uric Acid (168) 1.01 0.04 0.97
0.04 Vancomycin (1448) 0.84 0.10 0.74
0.04 Plt0.05 vs sieving coefficientPlt0.01
vs sieving coefficient
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Factors Influencing RRT Dose in ARF
13
Prescribed vs Delivered RRT in ARF

• CRRT
• Down-time procedures, filter changes
• Decline in filter performance ? SC or CDo/CBi,
  UFR
• Access recirculation
• IHD
• Failure to achieve prescription (QB, time)
• Compartment effects (rebound)
• Access recirculation

14
Effect of CVVH on Hemodynamic Parametersin
Septic PatientsDe Vriese et al., JASN 1999
Cardiac output (l/min)and PAOP (mm Hg)
Systemic Vascular Resistance(dyne.s/cm5)
Time (hours)
15
Effect of Filter Pore Size on Survivalin
Experimental SepsisLee et al., Crit Care Med 1998