Mod 1: Principles of CRRT
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Questions and Answers

What occurs when the filtration fraction (FF) is higher than 25%?

  • Lower protein levels on the filter
  • Decreased risk of filter clotting
  • Less fluid removal
  • Decreased permeability of the filter (correct)

    • In Continuous Renal Replacement Therapy (CRRT), the blood flow is generally less than the therapy fluid rate.

    False

    What does K represent in the estimation of Kt/V?

    Clearance rate of solutes

    In intermittent hemodialysis (IHD), if the blood flow is slow, the blood is completely cleared of _______.

    <p>solute</p> Signup and view all the answers

    Which of the following accurately describes the relationship between blood flow rate (Qb) and solute clearance in IHD?

    <p>Higher Qb can lead to less thorough clearance</p> Signup and view all the answers

    Match the clearance mechanisms to their definitions:

    <p>Diffusion = Movement of solute from high to low concentration Ultrafiltration = Fluid movement driven by pressure gradients Convection = Solute movement due to drag from flowing fluid Hemodiafiltration = Combination of diffusion and convection for solute removal</p> Signup and view all the answers

    Hemodiafiltration balances the benefits of both diffusive and convective modes.

    <p>True</p> Signup and view all the answers

    What is the typical effluent rate for adult CRRT therapy at 2 L/hr?

    <p>33 ml/min</p> Signup and view all the answers

    What is the main factor that determines the convective flux in ultrafiltration?

    <p>Ultrafiltration rate</p> Signup and view all the answers

    In pre-filter dilution, the hemoconcentration and clotting are decreased significantly.

    <p>True</p> Signup and view all the answers

    What does FF stand for in the context of filtration?

    <p>Filtration Fraction</p> Signup and view all the answers

    The formula for calculating the Filtration Fraction (FF) is FF* = (QUF/Qp) x 100, with the calculated value indicating whether it is too ______ or not.

    <p>high</p> Signup and view all the answers

    Match the types of dilution with their characteristics:

    <p>Pre-Filter Dilution = 30-40% decreased efficiency compared to postdilution Post-Filter Dilution = Shorter filter life due to clotting</p> Signup and view all the answers

    Which of the following is a disadvantage of post-filter dilution?

    <p>Decreased solute transfer</p> Signup and view all the answers

    What is the primary purpose of a semipermeable membrane in therapy?

    <p>To allow selective passage of solutes</p> Signup and view all the answers

    Fouling refers to solutes sticking to the membrane and enhancing its permeability.

    <p>False</p> Signup and view all the answers

    Solutes are concentrated against the membrane on the effluent side during filtration.

    <p>True</p> Signup and view all the answers

    What is the primary benefit of having a higher ultrafiltration rate?

    <p>Enhanced solute movement out of red blood cells</p> Signup and view all the answers

    What is the role of transmembrane pressure (TMP) in solute removal?

    <p>TMP drives the movement of solutes across the membrane.</p> Signup and view all the answers

    The equation for calculating Filtration Fraction is FF = (QUF / (Qb x [1- HCT])) x 100, which relates ______ flow to ultrafiltration.

    <p>plasma</p> Signup and view all the answers

    The primary mechanism used in ultrafiltration is _____ pressure.

    <p>transmembrane</p> Signup and view all the answers

    What happens if the filtrate velocity is fastest in the center of the hollow fiber?

    <p>Cells sludge against the membrane</p> Signup and view all the answers

    Match the following solute removal mechanisms with their descriptions:

    <p>Diffusion = Movement due to concentration gradient Convection = Movement driven by fluid flow Adsorption = Solutes stick to the membrane surface Ultrafiltration = Fluid removal driven by pressure</p> Signup and view all the answers

    Which of the following represents continuous therapies?

    <p>High volume hemofiltration</p> Signup and view all the answers

    Larger molecules achieve higher clearance during typical operating situations with CRRT.

    <p>False</p> Signup and view all the answers

    What is the effect of concentration polarization on solute removal?

    <p>It creates a gradient that can enhance diffusion but may impair solute clearance for higher molecular weight solutes.</p> Signup and view all the answers

    In hemodialysis, solute removal is primarily achieved through _____ and _____ mechanisms.

    <p>diffusion, convection</p> Signup and view all the answers

    Which therapy requires an arterial and venous catheter?

    <p>HD</p> Signup and view all the answers

    Dispersion can occur when polymers accumulate by the membrane, creating a uniform solution.

    <p>False</p> Signup and view all the answers

    What does the sieving coefficient indicate in the context of convection?

    <p>The sieving coefficient indicates how effectively solutes are removed from blood during ultrafiltration.</p> Signup and view all the answers

    Continuous therapies like _____ use a blood pump to set flow speeds.

    <p>CVVH</p> Signup and view all the answers

    What is the concentration gradient in the context of diffusion?

    <p>The difference between the solute concentrations on either side of the membrane</p> Signup and view all the answers

    Study Notes

    Principles of CRRT

    • CRRT stands for Continuous Renal Replacement Therapy
    • CRRT is used for critically ill, hemodynamically unstable patients over an extended period.
    • Hemoperfusion started as a mistake in 1977, Germany
    • A femoral vein catheter was mistakenly placed in the femoral artery
    • CRRT started as a purely convective therapy, later a blood pump was added
    • It took 10 years to treat the first neonate, in 1985

    Methods of Solute Removal

    • Diffusion: Solutes move from high concentration to low concentration
    • Convection: Solutes move due to fluid flow.
    • Ultrafiltration: Removal of fluid by applying pressure.
    • Adsorption: Solutes stick to the membrane

    Semipermeable Membrane

    • TMP = (Pin + Pout)/2 - Peff
    • Fouling: proteins stick to membrane causing decreased permeability

    Types of Therapy

    • Continuous Therapies are intended for critically ill, hemodynamically unstable patients over an extended period of time.
    • Prolonged Intermittent Therapies are evolved for more efficient use of time

    Blood Flow

    • Arteriovenous: Requires arterial and venous catheters, arterial pressure determines blood flow speed.
    • Venovenous: Requires dual lumen catheters or two venous catheters, requires a blood pump, operator sets blood flow speed

    Abbreviations

    • C refers to continuous
    • AV refers to arteriovenous,
    • V refers to venovenous,
    • H means hemofiltration
    • HD means hemodialysis
    • HDF means hemodiafiltration

    CAVH

    • CAVH (Continuous Arteriovenous Hemofiltration)
    • A diagram showing the flow of replacement fluid, access, return, and effluent

    CVVH

    • CVVH (Continuous Venous Hemofiltration) Post Filter: A diagram showing the flow of replacement fluid, access, pump, return, and effluent

    CVVHDF

    • CVVHDF (Continuous Venous Hemofiltration with Diafiltration) Post Filter: A diagram showing the flow of replacement fluid, access, pump, return, and effluent

    SCUF

    • SCUF (Slow Continuous Ultrafiltration): A diagram showing the flow of replacement fluid, access, pump, return, and effluent

    Modalities of RRT

    • Different ways to perform renal replacement therapy.

    High Volume Hemofiltration

    • Larger volume of fluid removal/replacement
    • Replacement fluid composition determines blood concentrations.
    • No phosphate

    Convective Clearance

    • "Solvent Drag": Every ml of effluent = 1 ml plasma clearance
    • Convective flux determined by ultrafiltration rate, blood solute concentration and membrane siiving properties.
    • Less dependent on molecular size.

    Fluid Flow Characteristics

    • Velocity fastest in center
    • Resistance to flow at edges near walls
    • Cells and proteins sludge against membrane on blood side
    • Solutes concentrated against membrane on effluent side
    • Blocks pores, causing decreased diffusion and convection efficiency
    • Unstirred layer decreases diffusion efficiency

    Pre-filter Dilution

    • Advantages include decreased hemoconcentration, reduced clotting, mass transfer alterations, reduced RBC and protein concentration, and increased flow through the blood compartment.
    • Increased membrane shear rate enhances solute movement.

    Post-Filter Dilution

    • Advantages include maximal efficiency.
    • Disadvantages include hemoconcentration inside the filter, clotting, decreased solute transfer, and decreased filter life.

    Filtration Fraction

    • FF is the proportion of plasma filtered across the membrane.
    • Target FF<25% for hemoconcentration. Higher FF leads to a higher risk of filter clotting and more protein on the filter membrane, thus decreasing permeability.

    Definitions

    • QNetUF = net patient fluid removal
    • QUF = all fluid removed (QR + QPBP + QNetUF)
    • PBP = pre-blood pump

    Diffusion

    • IHD (Intermittent Hemodialysis) uses dialysate in excess of blood flow (Qd = 500 ml/min) with blood flow rate (Qb = 50-300 ml/min)
    • CRRT (Continuous Renal Replacement Therapy): Blood flow (Qb) exceeds therapy fluid, (Qd + Qr + QNetUF) 2 L/hr = 33 ml/min typical adult, 10L/hr = 166 ml/min max. Qb = 50-180 ml/min.

    Diffusive Clearance Rates

    • clearance values given for IHD and CRRT

    Hemodiafiltration - CVVHDF

    • Balances good and bad of diffusive and convective modes.
    • New machines can perform predilution and postdilution simultaneously

    Estimating Kt/V

    • Formulas for various CRRT methods.

    Comparing CRRT to IHD

    • CRRT is not blood flow dependent, whereas IHD is.
    • Higher blood flow rates in CRRT reduce clotting.

    Bacteriological Safety of Therapy Fluid

    • Dialysate and Replacement Fluids (prepackaged) are essentially sterile.
    • More expensive than dialysate made by the dialysis machine, which requires water purification.
    • Endotoxins can cause inflammation

    Wrap-Up Questions

    • List methods of clearance (solute removal)
    • Define CVVH, CVVHD, CVVHDF, SCUF in regards to clearance methods
    • Define filtration fraction
    • What are the advantages and disadvantages of pre vs post-filter dilution?
    • What determines “dose” in CRRT?

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