Podcast
Questions and Answers
What is the minimum trans-membrane pressure (TMP) required to counterbalance the oncotic pressure of plasma proteins during ultrafiltration?
What is the minimum trans-membrane pressure (TMP) required to counterbalance the oncotic pressure of plasma proteins during ultrafiltration?
How is the ultrafiltration rate determined in modern hemodialysis machines?
How is the ultrafiltration rate determined in modern hemodialysis machines?
What might cause a negative trans-membrane pressure during dialysis?
What might cause a negative trans-membrane pressure during dialysis?
What is the Kuf value for the selected dialyzer used for a 30 kg dog assessed to be 7% overhydrated for the treatment?
What is the Kuf value for the selected dialyzer used for a 30 kg dog assessed to be 7% overhydrated for the treatment?
Signup and view all the answers
In older dialysis machines, what was primarily manipulated to achieve ultrafiltration?
In older dialysis machines, what was primarily manipulated to achieve ultrafiltration?
Signup and view all the answers
How does overhydration affect fluid removal rate in veterinary dialysis patients?
How does overhydration affect fluid removal rate in veterinary dialysis patients?
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?
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?
Signup and view all the answers
Which of the following statements about high-flux dialyzers is correct?
Which of the following statements about high-flux dialyzers is correct?
Signup and view all the answers
What is the primary disadvantage of using high efficiency dialyzers with large pores?
What is the primary disadvantage of using high efficiency dialyzers with large pores?
Signup and view all the answers
What does the KoA represent in the context of dialysis?
What does the KoA represent in the context of dialysis?
Signup and view all the answers
How is the extraction ratio for a solute calculated?
How is the extraction ratio for a solute calculated?
Signup and view all the answers
What is the definition of clearance in dialysis?
What is the definition of clearance in dialysis?
Signup and view all the answers
Which factors influence the KoA of a dialyzer?
Which factors influence the KoA of a dialyzer?
Signup and view all the answers
In the context of comparing the performance of dialyzers, what is a primary reason for assessing clearance rates?
In the context of comparing the performance of dialyzers, what is a primary reason for assessing clearance rates?
Signup and view all the answers
What is a potential outcome of using dialyzers with high Kuf?
What is a potential outcome of using dialyzers with high Kuf?
Signup and view all the answers
Why is comparing clearance rates critical to dialysis treatment?
Why is comparing clearance rates critical to dialysis treatment?
Signup and view all the answers
What primarily determines the diffusion rate during dialysis?
What primarily determines the diffusion rate during dialysis?
Signup and view all the answers
How does the velocity of a molecule in solution relate to its molecular weight?
How does the velocity of a molecule in solution relate to its molecular weight?
Signup and view all the answers
What variables can be adjusted to increase the flux per area in a dialysis process?
What variables can be adjusted to increase the flux per area in a dialysis process?
Signup and view all the answers
Which equation represents the relationship between solute flux and concentration difference?
Which equation represents the relationship between solute flux and concentration difference?
Signup and view all the answers
What does the KoA represent in the context of dialysis?
What does the KoA represent in the context of dialysis?
Signup and view all the answers
What factors contribute to the overall resistance to solute flow in dialysis?
What factors contribute to the overall resistance to solute flow in dialysis?
Signup and view all the answers
Which property of high efficiency dialyzers is crucial for effective solute clearance?
Which property of high efficiency dialyzers is crucial for effective solute clearance?
Signup and view all the answers
What is the effect of increasing the concentration gradient in regard to solute flux?
What is the effect of increasing the concentration gradient in regard to solute flux?
Signup and view all the answers
What does the ultrafiltration coefficient (Kuf) relate to primarily?
What does the ultrafiltration coefficient (Kuf) relate to primarily?
Signup and view all the answers
How is the transmembrane hydrostatic pressure (TMP) relevant to ultrafiltration rate?
How is the transmembrane hydrostatic pressure (TMP) relevant to ultrafiltration rate?
Signup and view all the answers
What equation describes the total resistance in a dialysis setup?
What equation describes the total resistance in a dialysis setup?
Signup and view all the answers
Which feature of a dialyzer contributes to its efficiency?
Which feature of a dialyzer contributes to its efficiency?
Signup and view all the answers
What limits the maximum clearance of a solute across a dialyzer?
What limits the maximum clearance of a solute across a dialyzer?
Signup and view all the answers
In the context of dialysis, what role does membrane thickness play?
In the context of dialysis, what role does membrane thickness play?
Signup and view all the answers
What is a key benefit of using hemodiafiltration (HDF) compared to conventional hemodialysis?
What is a key benefit of using hemodiafiltration (HDF) compared to conventional hemodialysis?
Signup and view all the answers
Which principle underlies the removal of uremic toxins in native kidneys?
Which principle underlies the removal of uremic toxins in native kidneys?
Signup and view all the answers
What does the variable 'J' represent in the equation J = - (DA/X) ΔC?
What does the variable 'J' represent in the equation J = - (DA/X) ΔC?
Signup and view all the answers
How does increasing ultrafiltration impact convective clearance?
How does increasing ultrafiltration impact convective clearance?
Signup and view all the answers
What limitation does the cost of sterile solution impose on treatment options?
What limitation does the cost of sterile solution impose on treatment options?
Signup and view all the answers
Which of the following dialysis techniques is characterized by continuous venovenous hemodiafiltration?
Which of the following dialysis techniques is characterized by continuous venovenous hemodiafiltration?
Signup and view all the answers
What does the variable 'Kuf' measure in the context of dialysis?
What does the variable 'Kuf' measure in the context of dialysis?
Signup and view all the answers
Why is having a large surface area in modern hemodialyzers beneficial?
Why is having a large surface area in modern hemodialyzers beneficial?
Signup and view all the answers
What is the primary aim of renal replacement therapy?
What is the primary aim of renal replacement therapy?
Signup and view all the answers
Which type of dialysis is associated with the highest efficacy?
Which type of dialysis is associated with the highest efficacy?
Signup and view all the answers
What characteristic is NOT associated with continuous renal replacement therapy (CRRT)?
What characteristic is NOT associated with continuous renal replacement therapy (CRRT)?
Signup and view all the answers
What is the role of the dialyzer in hemodialysis?
What is the role of the dialyzer in hemodialysis?
Signup and view all the answers
Which substance is NOT typically part of dialysate composition?
Which substance is NOT typically part of dialysate composition?
Signup and view all the answers
In which type of dialysis is solute removal achieved through draining dialysate fluids?
In which type of dialysis is solute removal achieved through draining dialysate fluids?
Signup and view all the answers
What happens to dialysate after it has been exposed to blood in hemodialysis?
What happens to dialysate after it has been exposed to blood in hemodialysis?
Signup and view all the answers
What is a significant benefit of ultrapure dialysate?
What is a significant benefit of ultrapure dialysate?
Signup and view all the answers
What method is employed to manage water contaminants before it is used for dialysate?
What method is employed to manage water contaminants before it is used for dialysate?
Signup and view all the answers
Which feature distinguishes modern dialyzers from older versions?
Which feature distinguishes modern dialyzers from older versions?
Signup and view all the answers
Which process is primarily used for concentration of solutes in blood during dialysis?
Which process is primarily used for concentration of solutes in blood during dialysis?
Signup and view all the answers
What significant drawback does peritoneal dialysis have compared to other methods?
What significant drawback does peritoneal dialysis have compared to other methods?
Signup and view all the answers
What is the primary function of the blood circuit in hemodialysis?
What is the primary function of the blood circuit in hemodialysis?
Signup and view all the answers
Which condition would most likely necessitate the use of hemodialysis?
Which condition would most likely necessitate the use of hemodialysis?
Signup and view all the answers
What is the definition of clearance in hemodialysis?
What is the definition of clearance in hemodialysis?
Signup and view all the answers
What factors influence clearance in hemodialysis?
What factors influence clearance in hemodialysis?
Signup and view all the answers
What is diffusion, and what influences it?
What is diffusion, and what influences it?
Signup and view all the answers
What is convection in the context of hemodialysis?
What is convection in the context of hemodialysis?
Signup and view all the answers
What are first-order kinetics in hemodialysis?
What are first-order kinetics in hemodialysis?
Signup and view all the answers
What is the Ultrafiltration Coefficient (Kuf)?
What is the Ultrafiltration Coefficient (Kuf)?
Signup and view all the answers
Which of the following are characteristics of high-efficiency dialyzers?
Which of the following are characteristics of high-efficiency dialyzers?
Signup and view all the answers
What methods are used in water purification for dialysis?
What methods are used in water purification for dialysis?
Signup and view all the answers
Dialysis is an inflammatory process.
Dialysis is an inflammatory process.
Signup and view all the answers
Which dialysis type runs continuously for over 24 hours?
Which dialysis type runs continuously for over 24 hours?
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)
- J = - (DA/X) ΔC
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.
Clearance in Hemodialysis
- Clearance is the volume of plasma cleared of a specific solute per unit time (ml/min).
- Clearance is influenced by blood flow rate, dialysate flow rate, and KoA (mass transfer area coefficient).
- KoA represents the dialyzer's capacity for transferring mass and is determined by membrane properties like pore size and surface area.
Diffusion in Hemodialysis
- Diffusion is the movement of solutes from high concentration to low concentration across a semi-permeable membrane.
- It's the primary removal mechanism for small solutes like urea and creatinine.
- Factors affecting diffusion include concentration gradient, molecular size, membrane surface area, membrane thickness, and temperature.
Convection in Hemodialysis
- Convection is the movement of solutes along with water flow across the membrane, driven by solvent drag during ultrafiltration.
- It's effective at removing larger molecules that diffusion cannot handle.
- Factors influencing convection include transmembrane pressure, solvent drag, molecule size, and membrane pore size.
Zero-Order vs First-Order Kinetics
- First-Order Kinetics: The rate of solute removal is directly proportional to the solute concentration.
- Zero-Order Kinetics: The rate of solute removal is constant, regardless of solute concentration.
- Most solutes in hemodialysis follow first-order kinetics, so removal is faster when concentrations are higher.
Ultrafiltration Coefficient (Kuf)
- Kuf is a measure of a dialyzer’s fluid removal ability.
- It is the amount of fluid (ml) removed per hour per mmHg of transmembrane pressure.
- Determinants of Kuf include membrane composition, pore size, thickness, and oncotic pressure.
High-Efficiency vs. High-Flux Dialyzers
- High-Efficiency Dialyzers: Optimized for removing small solutes like urea and creatinine; less effective for middle-sized molecules.
- High-Flux Dialyzers: Optimized for removing middle-sized molecules and toxins; have larger pores and higher Kuf.
Hemodialysis Types
- Intermittent Hemodialysis (IHD): Highly effective for acute and chronic kidney failure; provides flexibility in scheduling; removes small solutes.
- Continuous Renal Replacement Therapy (CRRT): Less effective than IHD; runs continuously for critically ill patients; removes solutes slower than IHD.
- Peritoneal Dialysis (PD): Involves dialysate inserted into the peritoneal cavity; least effective; typically used for home management of CKD.
Solute Removal Mechanisms in Hemodialysis
- Diffusion: Solutes move from high to low concentration areas across the semi-permeable membrane.
- Convection: Water movement carries solutes with it (solvent drag) driven by transmembrane pressure.
- Ultrafiltration: Fluid removal driven by transmembrane pressure.
- Adsorption: Minimal role in dialysis; some solutes adhere to the membrane surface.
Dialyzer Structure & Function
- Modern dialyzers use synthetic polymers (polysulfone, polyamide, polyacrylonitrile).
- Dialyzers have thousands of hollow fibers where blood and dialysate flow in opposite directions, separated by a membrane.
Key Dialyzer Terms
- KoA (Mass Transfer Area Coefficient): Describes the dialyzer's maximum solute clearance capacity.
- Ultrafiltration Coefficient (Kuf): Defines the dialyzer's fluid removal capacity per mmHg of transmembrane pressure.
Water Treatment for Dialysis
- Water is purified through particulate filters, carbon sorbents, and deionization.
- Reverse Osmosis (RO) is essential for removing contaminants.
- Ultrapure dialysate reduces chronic inflammation and enables hemodiafiltration.
Principles of Solute Removal: Diffusion
- Driven by random molecular movement (molecular kinetics) that follows the law of probability.
- Influenced by the concentration gradient, molecular size, and membrane area.
Clearance and Solute Removal
- Higher concentration gradients lead to faster clearance rates.
- Clearance is also influenced by membrane thickness, pore size, and blood/dialysate flow rates.
Membrane Resistance in Dialyzers
- Overall resistance in a dialyzer is influenced by blood resistance, membrane resistance, and dialysate resistance.
- Efficiency is improved by reducing the largest resistance.
- High-efficiency dialyzers have high KoA values (over 600-700 ml/min).
- Low blood flow rates decrease clearance, so high-flow dialyzers are preferred in these cases.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
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.
