CVVH vs CVVHD Does it Matter? Patrick D. Brophy MD University of Michigan Pediatric Nephrology.
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Transcript of CVVH vs CVVHD Does it Matter? Patrick D. Brophy MD University of Michigan Pediatric Nephrology.
CVVH vs CVVHDCVVH vs CVVHDDoes it Matter?Does it Matter?
Patrick D. Brophy MDPatrick D. Brophy MDUniversity of Michigan University of Michigan Pediatric NephrologyPediatric Nephrology
OBJECTIVESOBJECTIVESDefinitionsDefinitions– CVVH vs CVVHDCVVH vs CVVHD
Mechanisms of actionMechanisms of action– Convective vs Diffusive clearanceConvective vs Diffusive clearance
Other Issues & Selective data review Other Issues & Selective data review – Drug Clearance, membranes & patients, anticoagDrug Clearance, membranes & patients, anticoag
Implementation of one modality over another-Implementation of one modality over another-RationaleRationale– Sepsis vs ARF vs Toxic ingestionsSepsis vs ARF vs Toxic ingestions– Advantages and Disadvantages, expertiseAdvantages and Disadvantages, expertise
DefinitionsDefinitions
Continuous Venous Venous HemofiltrationContinuous Venous Venous HemofiltrationMimics the process which occurs in the Mimics the process which occurs in the
mammalian kidneymammalian kidneyDescribes an almost exclusive convective Describes an almost exclusive convective
treatment with highly permeable membranestreatment with highly permeable membranesUltrafiltrate produced is replaced by a sterile Ultrafiltrate produced is replaced by a sterile
solution (High UF rates)solution (High UF rates)Patient weight loss results from the difference Patient weight loss results from the difference
between ultrafiltration and reinfusion ratesbetween ultrafiltration and reinfusion rates
DefinitionsDefinitionsContinuous Venous Venous HemodialysisContinuous Venous Venous Hemodialysis
Describes a predominantly diffuse treatment Describes a predominantly diffuse treatment in which blood and dialysate are circulated in which blood and dialysate are circulated either side of the dialysis membrane in either side of the dialysis membrane in countercurrent directions.countercurrent directions.
Dialysate may be custom or commercially Dialysate may be custom or commercially producedproduced
The ultrafiltration rate is approximately equal The ultrafiltration rate is approximately equal to the scheduled weight loss (lower UF rate).to the scheduled weight loss (lower UF rate).
DefinitionsDefinitions
Post-Dilution CVVH CVVHD
Pre-Dilution CVVH CVVHDF
Qb
Qb Qb
Qb
Qeff Qeff
QeffQeff Qd
Qd
Qr
Qr
Qr
Mechanisms of ActionMechanisms of Action
CVVHCVVHConvectionConvection
Solute is removed by “Solvent Drag”. The solvent Solute is removed by “Solvent Drag”. The solvent carries the solute (plasma water) through a semi-carries the solute (plasma water) through a semi-permeable membrane.permeable membrane.
The Roller Pump creates Hydrostatic Pressure, The Roller Pump creates Hydrostatic Pressure, which drives the solvent through the membrane.which drives the solvent through the membrane.
The membrane pore size limits molecular transferThe membrane pore size limits molecular transferMore efficient removal of larger molecules than More efficient removal of larger molecules than
diffusiondiffusion
Mechanisms of ActionMechanisms of Action
CVVHCVVHConvectionConvection
Since it mimics the mammallian kidney its thought Since it mimics the mammallian kidney its thought to be more “physiologic” and provides better to be more “physiologic” and provides better removal of middle molecules (500-5000 Daltons) removal of middle molecules (500-5000 Daltons) thought to be responsible for uremia.thought to be responsible for uremia.
With the advent of highly porous membranes need With the advent of highly porous membranes need to use larger markers (500-50000 Daltons) to to use larger markers (500-50000 Daltons) to determine “uremic clearance”.determine “uremic clearance”.
Enhanced clearance of autologous cytokines- Enhanced clearance of autologous cytokines- thought to be involved in Septic Inflammatory thought to be involved in Septic Inflammatory Response Syndrome (SIRS).Response Syndrome (SIRS).
Mechanisms of ActionMechanisms of Action
CVVHCVVHConvectionConvection
Sieving Coefficient- clearance coefficient for Sieving Coefficient- clearance coefficient for hemofiltration defined by UV/Phemofiltration defined by UV/P
U= Filtrate ConcentrationU= Filtrate ConcentrationV= VolumeV= VolumeP= Mean plasma concentration over the clearance periodP= Mean plasma concentration over the clearance period
SC is 1 for molecules that pass through the SC is 1 for molecules that pass through the membrane easily & 0 for those that do notmembrane easily & 0 for those that do not
Mechanisms of ActionMechanisms of Action
CVVHDCVVHDDiffusion (predominantly)Diffusion (predominantly)
Solute diffuses down an electrochemical gradient Solute diffuses down an electrochemical gradient through a semi-permeable membrane in response through a semi-permeable membrane in response to an electrolyte solution running counter current to to an electrolyte solution running counter current to the blood flow through the filter.the blood flow through the filter.
Diffusive movement occurs via Brownian motion of Diffusive movement occurs via Brownian motion of the solute- smaller molecules (ie urea) have the solute- smaller molecules (ie urea) have greater kinetic energy and are preferentially greater kinetic energy and are preferentially removed based on the size of the concentration removed based on the size of the concentration gradientgradient
Mechanisms of ActionMechanisms of Action
CVVHDCVVHDDiffusion (predominantly)Diffusion (predominantly)
Some convection occurs due to prescribed UF and Some convection occurs due to prescribed UF and if High flux filters are utilizedif High flux filters are utilized
Solute removal is proportional to the concentration Solute removal is proportional to the concentration gradient and size of each moleculegradient and size of each molecule
Dialysate flow rate is slower than BFR and is the Dialysate flow rate is slower than BFR and is the limiting factor to solute removallimiting factor to solute removal
Solute removal is directly proportional to dialysate Solute removal is directly proportional to dialysate flow rate flow rate
Mechanisms of ActionMechanisms of Action
CVVHDCVVHDDiffusion (predominantly)Diffusion (predominantly)
Diffusion Coefficient- clearance coefficient for Diffusion Coefficient- clearance coefficient for hemodialysis defined by UV/Phemodialysis defined by UV/P
U= Dialysate (+Filtrate) ConcentrationU= Dialysate (+Filtrate) ConcentrationV= VolumeV= VolumeP= Mean plasma concentration over the clearance P= Mean plasma concentration over the clearance
periodperiod
Principle same as for SC with 1= to optimal Principle same as for SC with 1= to optimal clearance and 0= to no (minimal clearance)clearance and 0= to no (minimal clearance)
Other IssuesOther Issues
The greatest difference between The greatest difference between modalities is likely the impact of the modalities is likely the impact of the membrane utilized and their specific membrane utilized and their specific characteristics.characteristics.
There are no data available assessing There are no data available assessing patient outcomes using diffusive (CVVHD) patient outcomes using diffusive (CVVHD) and convective (CVVH) therapiesand convective (CVVH) therapies
Other IssuesOther Issues
Low molecular weight solutesLow molecular weight solutes
Middle/High molecular weight solutesMiddle/High molecular weight solutes
Drug/Toxin ClearanceDrug/Toxin Clearance
Impact on Adsorptive membrane Impact on Adsorptive membrane characteristicscharacteristics
AnticoagulationAnticoagulation
Patient CharacteristicsPatient Characteristics
Low Molecular Weight SolutesLow Molecular Weight Solutes
Relative equivalence of convective and Relative equivalence of convective and diffusive clearances (membrane variation diffusive clearances (membrane variation and design)and design)
Solute Molecular Weight Solute Molecular Weight and clearanceand clearance
Jeffrey Jeffrey et al.,et al., Artif Organs 1994 Artif Organs 1994
Solute (MW) Sieving Coefficient Diffusion Coefficient
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
Diffusive & Convective Solute Diffusive & Convective Solute Clearances During CRRTClearances During CRRTBrunet et.al AJKD 34:1999Brunet et.al AJKD 34:1999
Evaluated convective & dialysate Evaluated convective & dialysate clearance of :clearance of :
UREAUREACreatinineCreatininePhosphatePhosphateUratesUrates
BB22microglobulinmicroglobulin
Variety of UF & Dialysate Flows with Multiflow60 Variety of UF & Dialysate Flows with Multiflow60 &100 membranes&100 membranes
CVVH vs CVVHD continuedCVVH vs CVVHD continued
Conclusions:Conclusions:At QAt QUFUF with predilution (2L/hr) FRF 15-20% reduction with predilution (2L/hr) FRF 15-20% reduction
in urea, urates & creatininein urea, urates & creatinine
SC= 1 for all small molecules for CVVH-both filtersSC= 1 for all small molecules for CVVH-both filters
M100>M60 (QM100>M60 (QDD 1.5-2.5L/hr) diffusive clearance with 1.5-2.5L/hr) diffusive clearance with
the difference increasing as molecular weight the difference increasing as molecular weight increasedincreased
QQDD > 1.5L/hr poor diffusive middle molecule > 1.5L/hr poor diffusive middle molecule
clearance (both membranes); whereas increasing clearance (both membranes); whereas increasing nonlinear clearance occurred with convection as Qnonlinear clearance occurred with convection as QUFUF
increased for both filtersincreased for both filters
CVVH vs CVVHD continuedCVVH vs CVVHD continued
No additive effect with combination No additive effect with combination dialysate & FRF therapy for middle dialysate & FRF therapy for middle molecule clearancemolecule clearance
Authors conclude:Authors conclude:– ““Convection more efficient than diffusion in Convection more efficient than diffusion in
removing mixed- molecular- weight solutes removing mixed- molecular- weight solutes during CRRT”during CRRT”
Drug & Toxin ClearanceDrug & Toxin Clearance
Drug/Toxin ClearanceDrug/Toxin Clearance– Molecular WeightMolecular Weight– Protein BindingProtein Binding– VdVd– Membrane compositionMembrane composition
As MW increases diffusive drug clearance As MW increases diffusive drug clearance declines more than convective clearancedeclines more than convective clearance
Adsorptive Membrane Adsorptive Membrane CharacteristicsCharacteristics
Biocompatible membranes appear to have Biocompatible membranes appear to have greater adsorptive properties than less greater adsorptive properties than less biocompatible membranes (PAN>Polysulfone)biocompatible membranes (PAN>Polysulfone)Filter Characteristics for small molecule removal Filter Characteristics for small molecule removal include: pore size distribution & density and include: pore size distribution & density and surface area and at conventional flow rates (in surface area and at conventional flow rates (in adults-2L or less) clearance is flow rate adults-2L or less) clearance is flow rate dependent. dependent. As molecular size increases: hydraulic As molecular size increases: hydraulic permeability & adsorption capacity become permeability & adsorption capacity become important.important.
Adsorptive Membrane Adsorptive Membrane CharacteristicsCharacteristics
No specific Membrane recommendations No specific Membrane recommendations as no studies to definitively prove superior as no studies to definitively prove superior performance under specific modalityperformance under specific modality
AnticoagulationAnticoagulation
Citrate use- centers relatively confined to Citrate use- centers relatively confined to diffusive therapy (works well with diffusive therapy (works well with CVVHDF)CVVHDF)– Citrate: multiple protocols for CVVHDCitrate: multiple protocols for CVVHD
Few for CVVH (Niles et.al. 2002-CRRT abstract) Few for CVVH (Niles et.al. 2002-CRRT abstract) where citrate included in FRFwhere citrate included in FRF
Heparin- both CVVH & CVVHDHeparin- both CVVH & CVVHD
Patient CharacteristicsPatient Characteristics
Etiology underlying the patient’s can help Etiology underlying the patient’s can help determine choice of therapydetermine choice of therapy– Speculative benefit of CVVH in Sepsis, Toxin Speculative benefit of CVVH in Sepsis, Toxin
removal (although filter impact very important)removal (although filter impact very important)– For ARF & Fluid overload little difference is For ARF & Fluid overload little difference is
likely likely
No Definitive demonstration of superiority No Definitive demonstration of superiority of one over the otherof one over the other
Final Thoughts & SummaryFinal Thoughts & Summary
Currently- no data to prove outcome Currently- no data to prove outcome superior with either modalitysuperior with either modality
Best to use what each center is most Best to use what each center is most comfortable withcomfortable with
Acute Dialysis Quality Initiative (ADQI) Acute Dialysis Quality Initiative (ADQI) Guidelines reflect these ongoing study Guidelines reflect these ongoing study requirements and recommendationsrequirements and recommendations
Plenty of work to do!!!!Plenty of work to do!!!!
ACKNOWLEDGEMENTSACKNOWLEDGEMENTS– MELISSA GREGORYMELISSA GREGORY– ANDREE GARDNERANDREE GARDNER– JOHN GARDNERJOHN GARDNER– THERESA MOTTESTHERESA MOTTES– TIM KUDELKATIM KUDELKA– LAURA DORSEY & BETSY ADAMSLAURA DORSEY & BETSY ADAMS
(p. brophy)