Renal Replacement Therapy Overview
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Renal Replacement Therapy Overview

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What is the minimum trans-membrane pressure (TMP) required to counterbalance the oncotic pressure of plasma proteins during ultrafiltration?

  • 25 mmHg (correct)
  • 10 mmHg
  • 75 mmHg
  • 50 mmHg

    • How is the ultrafiltration rate determined in modern hemodialysis machines?

  • By patient’s hematocrit levels
  • By measuring plasma protein concentration
  • By ultrafiltration pump controlling the TMP
  • By the difference in dialysate inflow and outflow volumes (correct)

    • What might cause a negative trans-membrane pressure during dialysis?

  • Increased ultrafiltration rate
  • Insufficient total protein concentration (correct)
  • Higher hematocrit levels
  • Excess blood clotting in the dialyzer

    • What is the Kuf value for the selected dialyzer used for a 30 kg dog assessed to be 7% overhydrated for the treatment?

    <p>15 mls/hr/mmHg</p> Signup and view all the answers

    In older dialysis machines, what was primarily manipulated to achieve ultrafiltration?

    <p>Trans-membrane pressure</p> Signup and view all the answers

    How does overhydration affect fluid removal rate in veterinary dialysis patients?

    <p>It limits the rate of fluid removal significantly</p> Signup and view all the answers

    For a dialysis treatment of a dog weighing 20 kg and assessed to be 8% overhydrated, what is the expected volume of fluid to be removed?

    <p>1.6 liters</p> Signup and view all the answers

    Which of the following statements about high-flux dialyzers is correct?

    <p>They should be used with machines equipped with special pumps</p> Signup and view all the answers

    What is the primary disadvantage of using high efficiency dialyzers with large pores?

    <p>They may expose blood to contaminants like pyrogens.</p> Signup and view all the answers

    What does the KoA represent in the context of dialysis?

    <p>The maximum clearance of a solute with infinite flow rates.</p> Signup and view all the answers

    How is the extraction ratio for a solute calculated?

    <p>By measuring the concentration in the inlet and outlet of the dialyzer.</p> Signup and view all the answers

    What is the definition of clearance in dialysis?

    <p>The plasma volume completely cleared of a solute.</p> Signup and view all the answers

    Which factors influence the KoA of a dialyzer?

    <p>The solute's molecular weight and membrane thickness.</p> Signup and view all the answers

    In the context of comparing the performance of dialyzers, what is a primary reason for assessing clearance rates?

    <p>To understand how efficiently different dialyzers remove various solutes.</p> Signup and view all the answers

    What is a potential outcome of using dialyzers with high Kuf?

    <p>Enhanced exposure to contaminants.</p> Signup and view all the answers

    Why is comparing clearance rates critical to dialysis treatment?

    <p>To optimize the dialysis process for patient-specific needs.</p> Signup and view all the answers

    What primarily determines the diffusion rate during dialysis?

    <p>Molecular size and concentration difference</p> Signup and view all the answers

    How does the velocity of a molecule in solution relate to its molecular weight?

    <p>Inversely proportional</p> Signup and view all the answers

    What variables can be adjusted to increase the flux per area in a dialysis process?

    <p>Increasing driving force or decreasing resistance</p> Signup and view all the answers

    Which equation represents the relationship between solute flux and concentration difference?

    <p>J = - (DA/X) ΔC</p> Signup and view all the answers

    What does the KoA represent in the context of dialysis?

    <p>The mass transfer coefficient for a solute</p> Signup and view all the answers

    What factors contribute to the overall resistance to solute flow in dialysis?

    <p>Blood resistance, membrane resistance, and dialysate resistance</p> Signup and view all the answers

    Which property of high efficiency dialyzers is crucial for effective solute clearance?

    <p>High urea KoA and large surface area</p> Signup and view all the answers

    What is the effect of increasing the concentration gradient in regard to solute flux?

    <p>Increases the flux</p> Signup and view all the answers

    What does the ultrafiltration coefficient (Kuf) relate to primarily?

    <p>Amount of fluid transferred per hour per pressure</p> Signup and view all the answers

    How is the transmembrane hydrostatic pressure (TMP) relevant to ultrafiltration rate?

    <p>Affects the rate of fluid transfer across the membrane</p> Signup and view all the answers

    What equation describes the total resistance in a dialysis setup?

    <p>RT = RB + RM + RD</p> Signup and view all the answers

    Which feature of a dialyzer contributes to its efficiency?

    <p>Large surface area for mass transfer</p> Signup and view all the answers

    What limits the maximum clearance of a solute across a dialyzer?

    <p>Blood flow and dialysate flow rates</p> Signup and view all the answers

    In the context of dialysis, what role does membrane thickness play?

    <p>Introduces resistance to solute flux</p> Signup and view all the answers

    What is a key benefit of using hemodiafiltration (HDF) compared to conventional hemodialysis?

    <p>HDF allows for the online preparation of ultrapure replacement fluids.</p> Signup and view all the answers

    Which principle underlies the removal of uremic toxins in native kidneys?

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

    What does the variable 'J' represent in the equation J = - (DA/X) ΔC?

    <p>The rate of solute transfer</p> Signup and view all the answers

    How does increasing ultrafiltration impact convective clearance?

    <p>It maximizes convective clearance.</p> Signup and view all the answers

    What limitation does the cost of sterile solution impose on treatment options?

    <p>It limits the option to optimize convective clearance.</p> Signup and view all the answers

    Which of the following dialysis techniques is characterized by continuous venovenous hemodiafiltration?

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

    What does the variable 'Kuf' measure in the context of dialysis?

    <p>The volume of fluid transferred per hour per mm Hg of transmembrane pressure.</p> Signup and view all the answers

    Why is having a large surface area in modern hemodialyzers beneficial?

    <p>It minimizes the extracorporeal blood volume needed.</p> Signup and view all the answers

    What is the primary aim of renal replacement therapy?

    <p>Restore homeostasis in patients with acute kidney injury</p> Signup and view all the answers

    Which type of dialysis is associated with the highest efficacy?

    <p>Intermittent hemodialysis</p> Signup and view all the answers

    What characteristic is NOT associated with continuous renal replacement therapy (CRRT)?

    <p>Does not require constant patient monitoring</p> Signup and view all the answers

    What is the role of the dialyzer in hemodialysis?

    <p>To act as a semipermeable membrane where blood and dialysate meet</p> Signup and view all the answers

    Which substance is NOT typically part of dialysate composition?

    <p>Acetylsalicylic acid</p> Signup and view all the answers

    In which type of dialysis is solute removal achieved through draining dialysate fluids?

    <p>Peritoneal dialysis</p> Signup and view all the answers

    What happens to dialysate after it has been exposed to blood in hemodialysis?

    <p>It is eliminated as waste following a single pass</p> Signup and view all the answers

    What is a significant benefit of ultrapure dialysate?

    <p>Enables hemodilafiltration</p> Signup and view all the answers

    What method is employed to manage water contaminants before it is used for dialysate?

    <p>Reverse osmosis treatment</p> Signup and view all the answers

    Which feature distinguishes modern dialyzers from older versions?

    <p>Use of synthetic polymers instead of cellulosic membranes</p> Signup and view all the answers

    Which process is primarily used for concentration of solutes in blood during dialysis?

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

    What significant drawback does peritoneal dialysis have compared to other methods?

    <p>Lower overall effectiveness in solute removal</p> Signup and view all the answers

    What is the primary function of the blood circuit in hemodialysis?

    <p>To transport blood to and from the patient through the dialyzer</p> Signup and view all the answers

    Which condition would most likely necessitate the use of hemodialysis?

    <p>Acute kidney injury</p> Signup and view all the answers

    Study Notes

    Renal Replacement Therapy

    • Renal replacement therapy encompasses various artificial blood purification methods.
    • Aims to restore homeostasis in patients with acute kidney injury.
    • Includes removal of nitrogenous waste, correction of acid-base balance, electrolytes, and fluid imbalances.
    • Involves the prescription and delivery of treatment at an appropriate schedule.

    Types of Renal Replacement Therapy

    • Intermittent Hemodialysis (IHD): Highly effective, performed thrice weekly.
    • Continuous Renal Replacement Therapy (CRRT): Less effective than IHD, patients receive continuous treatment.
    • Peritoneal Dialysis (PD): Least effective, solute removal achieved by injecting and draining dialysate fluids into the peritoneal space at specific intervals.

    Factors Affecting Choice of RRT

    • Efficacy: IHD > CRRT > PD
    • Training: IHD >>> CRRT > PD
    • Maintenance: PD is very easy, CRRT is relatively easy, IHD is relatively intense.
    • Cost: IHD > CRRT > PD
    • Long-term Outcomes: IHD > CRRT > PD

    Dialysis Components

    • Dialyzer: Acts as an artificial kidney.
    • Blood Circuit: Begins at the vascular access, blood is drawn into the arterial line, processed in the dialyzer, and returned to the patient via the venous line.
    • Dialysate Circuit: Dialysate solution is pumped through compartments into the dialyzer. Dialysate is discarded after passing through the dialyzer (single pass).

    Dialysate

    • Generated from purified water and concentrates:
      • Acid concentrate
      • Bicarbonate concentrate
    • In CRRT, dialysate is provided in sterile bags.
    • Dialysate composition determines blood composition at the end of treatment.
    • During a single IHD treatment, patients are exposed to 120-200 liters of dialysate.

    Water Purification

    • Water undergoes multiple purification steps:
      • Particulate filters
      • Carbon sorbents for organic solutes
      • Water softeners to reduce minerals
      • Deionization beds to remove inorganic ions
      • Reverse osmosis to remove residual contaminants
    • Some systems utilize ultraviolet light to kill microorganisms, potentially increasing LPS concentrations.
    • Ultrapure dialysate generated within dialysis machines decreases chronic inflammation and enables hemodilafiltration.

    Dialysate Composition

    • Final solute concentration is determined by the type of acid concentrate and prescription.
    • Na+ and bicarbonate are directly programmed into the dialysis machine.
    • Other solutes are added using different acid concentrates or directly to the acid component.

    Dialyzer

    • The dialyzer is where blood and dialysate meet.
    • Blood flows into the dialyzer through the header and is distributed through capillaries (fibers) contained within a bundle.
    • Dialysate flows around the fibers.
    • Early dialyzers were made of cellulosic membranes, which triggered complement activation.
    • Modern synthetic polymer-based dialyzers lack hydroxyl groups, resulting in reduced complement activation.
      • Polysulfone
      • Polyamide
      • Polyacrylonitrile

    Solute Removal Mechanisms

    • Diffusion: Follows a concentration gradient, driven by solute size, temperature, pressure, and concentration difference.
    • Convection: Fluid flow from high to low pressure, transporting solutes with it.
    • Adsorption: Minimal contribution, involves the binding of solutes to the dialyzer membrane.

    Diffusion

    • Based on random molecular movements.
    • Driven by: Solute size, temperature, pressure, and concentration gradient.
    • Temperature and pressure are relatively constant during dialysis, making solute size and concentration difference the primary determinants of diffusion rate.
    • Velocity of molecules is inversely proportional to molecular weight.
    • Diffusion occurs from high to low concentration until equilibrium is reached.
    • Equilibrium results in bidirectional exchange of solute with no net diffusion.
    • Rate of diffusion is linearly related to the concentration difference.
      • J = - (DA/X) ΔC
        • J: Solute flux (mg/min)
        • ΔC: Concentration gradient
        • A: Membrane area (cm2)
        • X: Membrane thickness (cm)
        • D: Constant (cm2/min)

    Mass Transfer Coefficient (Ko) and Area (A)

    • KoA: Measures the maximum clearance of a solute across the dialyzer when blood and dialysate flow are infinite.
    • KoA: Constant for a given dialyzer, determined by the solute, dialyzer membrane, and pore size.
    • Can be calculated from basic transport values if blood and dialysate flow rates are known.

    Resistance to Solute Exchange

    • Solute must overcome resistance within the blood, membrane, and dialysate.
      • RB: Blood resistance
      • RM: Membrane resistance
      • RD: Dialysate side resistance

    Membrane Resistance

    • Determined by the thickness and diffusivity of the membrane.
    • Vary based on the chemical composition of the membrane.
    • High efficiency dialyzers have high KoA values (>600-700 mL/min).
    • To be advantageous, high efficiency dialyzers require large surface area and high blood and dialysate flow rates.

    Ultrafiltration

    • Rate of fluid removal.
    • Determined by:
      • Transmembrane hydrostatic pressure (TMP)
      • Hydraulic permeability
      • Surface area of the membrane.

    Ultrafiltration Coefficient (Kuf)

    • Represents the amount of fluid transferred per hour for each 1 mmHg of TMP.
    • Units: mL/hr/1 mmHg.
    • Influenced by hematocrit and total protein concentration.
    • Minimum TMP of 25 mmHg is needed to overcome oncotic pressure.
    • UF rate may change during treatment due to blood clotting or changes in hematocrit.

    Ultrafiltration Control

    • Older machines used pressure control, leading to potential inaccuracies in volume removal.
    • Modern machines use volumetric control, measuring dialysate inflow and outflow directly to determine UF.

    Dialyzer Classifications

    • Low-flux: Lower Kuf values.
    • High-flux: Higher Kuf values, requiring specialized pumps to control UF rate.

    Hemodiafiltration (HDF)

    • Maximizes convective clearance by increasing ultrafiltration and replacing fluid with a pre- or post-filter solution.
    • Facilitates removal of larger molecular weight solutes.
    • Meta-analysis of RCTs show benefits of online post-dilution HDF over HD in reducing mortality.

    Key Concepts

    • Diffusion: The primary mechanism of solute removal in the native kidney.
    • Kuf: Measure of a dialyzer's fluid removal capacity.
    • High efficiency dialyzers: Characterized by large surface area and efficient solute removal.
    • KoA: Measures the maximum clearance of a solute across the dialyzer when blood and dialysate flow are infinite.
    • Clearance: Represents the plasma volume completely cleared from a solute.

    Summary

    This text provides a comprehensive overview of principles and techniques employed in renal replacement therapy, emphasizing crucial factors for optimizing treatment and understanding dialysis mechanics, specifically addressing solute removal, membrane properties, filtration dynamics, and the advantages of HDF.

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    Description

    This quiz covers the essential aspects of renal replacement therapy, including its purpose, types, and factors influencing treatment choices. Explore the differences between intermittent hemodialysis, continuous renal replacement therapy, and peritoneal dialysis. Discover how each method helps restore homeostasis in patients with acute kidney injury.

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