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Post-Dilution CVVH. CVVHD. Q r. Q b. Q b. Q eff. Q eff. Q d. Q r. Q r. Q b. Q b. Q eff. Q eff. Q d. Pre-Dilution CVVH. CVVHDF. Solute Mass Transfer in CRRT Garred et al., AJKD 1997. Mechanisms of Solute Removal: IHD vs CRRT Clark and Ronco, Kidney Int 1998. IHD CRRT

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solute mass transfer in crrt garred et al ajkd 1997

Post-Dilution CVVH

CVVHD

Qr

Qb

Qb

Qeff

Qeff

Qd

Qr

Qr

Qb

Qb

Qeff

Qeff

Qd

Pre-Dilution CVVH

CVVHDF

Solute Mass Transfer in CRRTGarred et al., AJKD 1997
mechanisms of solute removal ihd vs crrt clark and ronco kidney int 1998
Mechanisms of Solute Removal: IHD vs CRRTClark and Ronco, Kidney Int 1998

IHD CRRT

Small Solutes Diffusion* Diffusion** (CVVHD)(mw < 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

Large Proteins Convection Convection(mw > 50,000)

* Determinants: flow rates, membrane thickness** Determinants: effluent dialysate flow rate

solute clearance in crrt

QP

(

)

QP +QR

Solute Clearance in CRRT

Concentration in effluent dialysate

(

)

E =

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

Concentration in blood

Concentration in filtrate

(

)

S =

Concentration in blood

dialytic solute removal mechanisms
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
urea clearance in pre dilution cvvh brunet et al ajkd 1999

33.9

28.7

 = -15%

QUF (mL/h)

Urea Clearance in Pre-Dilution CVVHBrunet et al., AJKD 1999

Clearance (mL/min)

effect of dialysate flow rate on small solute clearances in cvvhd bonnardeaux et al ajkd 1992
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)

effect of dialysate flow rate on solute equilibration in cvvhd bonnardeaux et al ajkd 1992

D/P Ratio

Urea

Creatinine

Inlet QD (mL/min)

Effect of Dialysate Flow Rate onSolute Equilibration in CVVHDBonnardeaux et al., AJKD 1992
components of small solute clearance in crrt sigler et al ajkd 1987
Components of Small Solute Clearance in CRRTSigler et al., AJKD 1987

Urea clearance, cc/min

Ultrafiltration, (QF)cc/min

urea and creatinine kinetic parameters in arf patients leblanc et al ajkd 1998
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

effect of solute molecular weight on equilibration jeffrey et al artif organs 1994
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**

*P<0.05 vs sieving coefficient**P<0.01 vs sieving coefficient

factors influencing rrt dose in arf

Factor CRRT vs IHD

K . t Favors CRRT (due to “t”)

Anticoagulation Favors IHD

Hypotension Favors CRRT

Compartment Effects Favors CRRT

Access Recirculation Favors CRRT

“Down-Time” Favors IHD

Defined Target Favors Neither

Factors Influencing RRT Dose in ARF
prescribed vs delivered rrt in arf
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
effect of cvvh on hemodynamic parameters in septic patients de vriese et al jasn 1999
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)

effect of filter pore size on survival in experimental sepsis lee et al crit care med 1998

8

7

6

5

4

Number of Animals Alive

3

2

1

0

0

12

24

36

48

60

72

84

96

108

120

132

144

156

168

180

192

Survival Time (hr)

Effect of Filter Pore Size on Survivalin Experimental SepsisLee et al., Crit Care Med 1998