Principles Dialysis 12-09-3

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  • Principles of Dialysisp y

  • Objecti esObjectives

    U d t d th f ti f l Understand the functions of a normal kidney in relationship to the artificial kidkidney

    Understand the transport mechanisms of dialysis

    Understand the components of the artificial pkidney

    Understand the components of dialysateUnderstand the components of dialysate

  • Functions of the Kidneys

    R remove R regulateR regulate E endocrine

  • Functions of the KidneysFunctions of the Kidneys

    Removal of wasteRemoval of waste products

    Urea breakdown of Urea - breakdown of protein in the diet

    Creatinine - endCreatinine - end product of creatine metabolism, ,skeletal/muscle breakdown

  • Functions of the Kidneys (cont)Functions of the Kidneys (cont) Regulation ofRegulation of

    Fluid balancel l b l Electrolyte balance

    Sodium, potassium, calcium, phosphate, magnesiummagnesium

    Acid/base balance P t t b li id i Prevents metabolic acidosis

  • Functions of the Kidneys (cont) Endocrine

    Functions of the Kidneys (cont)Endocrine Production of Renin

    Enzyme that controls blood pressure by affecting y e t at co t o s b ood p essu e by a ect gNa+ and fluid volume

    Erythropoietin formation controls red blood cell production in the bone

    marrow

    S i l i f Vi i D i Stimulates conversion of Vitamin D to its active form calcitriol a hormone that enhances absorption of calcium from theenhances absorption of calcium from the intestine

  • Renal FailureRenal Failure

    Renal failure occurs when something Renal failure occurs when something -disease, injury, malformation - prevents the kidneys from performing their manykidneys from performing their many essential tasks.Kid i h h b d h Kidneys are so important that the body has a built-in backup - an extra kidney

    Only one working kidney is needed to maintain health

  • Understanding Dialysis

    To understand Dialysis you must know what kidney functions are replaced by y p ydialysis: Removal of waste products from the bloodRemoval of waste products from the blood Regulation of fluid balance by removing

    excess fluid from the blood Regulation of electrolyte and acid/base balance

    in the blood

  • Further Understanding

    Scientific Principles of dialysis include the following:g Solvents SolutesSolutes Semipermeable membranes Transport mechanismsTransport mechanisms

  • Solutions and Membranes

    Solutions Solvent is a fluid (water)Solvent is a fluid (water) Solute is a substance that can be dissolved in a

    solvent: Potassium, Sodium and Calcium are examples

    Semi-Permeable membranesSe e eab e e b a es A thin layer of material with pores or openings that

    allow some substances to pass through freely, while keeping other substances out.

  • Transport Mechanisms

    Necessary to move fluid and solutes through the semi-permeable membraneg p

    Mechanisms used in dialysisOsmosis Osmosis

    DiffusionFiltration Filtration

    Ultrafiltration

  • Osmosis

    Movement of FLUID across a semipermeable b f f LOWER l tmembrane from an area of LOWER solute

    concentration to an area of HIGHER solute concentration.

  • DiffusionM t f di l d ti l (S l t ) Movement of dissolved particles (Solutes) across a semipermeable membrane from an

    HIGHER l t t ti tarea HIGHER solute concentration to an area of LOWER solute concentration

    Removes waste products from the blood BUN and Creatinine

  • Principles of HemodialysisPrinciples of Hemodialysis

    Adapted with permission of Amgen Inc.

  • Factors that Affect the Rate ofFactors that Affect the Rate of Diffusion

    Molecular Size small molecules move faster than larger g

    molecules Membrane Permeability

    pore size, number, thickness, design Surface Area

    th t th f f th the greater the surface area of the semipermeable membrane, the more rapidly diffusion occurs

  • Factors that Affect the Rate ofFactors that Affect the Rate of Diffusion (cont)

    Temperature molecules move faster as temperature

    iincreases Concentration Gradient

    difference in the concentration of solutes of the difference in the concentration of solutes of the two different fluids

    Flow Geometryy countercurrent flow in dialysis blood flows

    one direction while dialysate flows the opposite way which increases the rate of diffusionway which increases the rate of diffusion

  • Principles of HemodialysisPrinciples of Hemodialysis

    Osmosis and DiffusionOsmosis and Diffusion The end result of both is that movement will

    continue until the concentration of moleculescontinue until the concentration of molecules equilibrates (becomes equal) on both sides of the membrane

    Concentrations do not equilibrate during dialysis as dialysate passes through the dialyzer once on the way to the drain

  • Filtration

    Process of passing fluid through a filter or semipermeable membrane. p Filtration is controlled by hydrostatic pressure. Fluid always moves from an area of higherFluid always moves from an area of higher

    pressure to an area of lower pressure Regulates fluid balance in the bloodRegulates fluid balance in the blood

  • Ultrafiltration

    Controlled fluid removal by manipulation of hydrostatic pressure. Ultrafiltration uses both positive and negative pressure: Positive pressure = pressure exerted by the blood

    flowing through the dialyzerflowing through the dialyzer Results from blood being pushed by blood pump

    Negative pressure = pressure applied to the dialysateNegative pressure pressure applied to the dialysate side by the machine

    Pulls excess fluid from blood compartment to dialysate compartment drain

  • Fluid RemovalFluid Removal

    Adapted with permission of Amgen Inc.

  • Transmembrane Pressure (TMP)Transmembrane Pressure (TMP) The pressure difference across the semipermeable p p

    membrane is called the TMP Highest positive pressure is found post pump in the arterial

    header of the dial erheader of the dialyzer Lowest pressure is found in the venous header as the blood

    leaves the dialyzer Water molecules in the blood can pass through the

    membrane as long as the pressure exerted by the blood is greater than that of the dialyzeris greater than that of the dialyzer

    TMP was used to determines how much water crosses the membrane until the advent of UF control systemsthe membrane until the advent of UF control systems

  • Electrolyte

    An electrolyte is any substance that, in a solution, conducts an electrical current. , In water, the molecules of many substances

    ionize, or separate into particles called ions, , p p ,which carry electrical charges.

    Electrolytes in the blood are necessary for y ythe body to send signals to the nerves and muscles.

  • Two Types of Electrolytes

    Anions (-) negatively charged particles.

    Cations (+) positively charged particles.

    Chloride Sulfates

    h h

    Potassium Sodium

    l i Phosphates Bicarbonate (Acetate)

    Calcium Magnesium

  • Functions of Electrolytes

    Maintain fluid balance Conduct nerve impulsesConduct nerve impulses Cause muscle contraction

    Aid i l i ( l i ) f bl d Aid in coagulation (clotting) of blood

  • The Artificial KidneyThe Artificial Kidney Also called a dialyzerAlso called a dialyzer It contains two compartments:

    Bl d d di l t Blood and dialysate Compartments are separated by a semi-

    permeable membrane Hollow fibers

    Compartments are encased in a clear plastic cylinder which acts a support for the fibersy pp

  • DialyzersDialyzersDesign Blood

    Semipermeable membrane

    In

    Dialysate Support Structure Internal Compartments

    Blood

    OutOuter Casing

    Blood Dialysate Membrane

    Potting

    Bl d

    Dialysate Ing

    Material

    Blood Out

  • What is a semi-permeable pmembrane?

    A thin layer of material with pores that allow smaller molecules to pass through but notsmaller molecules to pass through but not larger molecules

    Blood cells are too large to pass through Blood cells are too large to pass through Waste products, excess chemicals, and excess

    fl id th hfluid can pass through

  • What is Biocompatibility?What is Biocompatibility?

    Compatible with living tissueCompatible with living tissue Patients must be able to tolerate the dialyzer

    membrane it must be biocompatible with themmembrane it must be biocompatible with them When blood is exposed to a foreign material,

    immune cells in blood react to defend the bodyimmune cells in blood react to defend the body All dialysis membrane materials react to some

    degree with immune cells in blooddegree with immune cells in blood Effects may be subtle or life threatening

  • HemodialyzersHemodialyzers

    Synthetic membranes are considered to beSynthetic membranes are considered to be more bio-compatible Examples of synthetic membranep y

    Polysulfone Polyacrylonitrile (PAN)y y ( )

    Note: Patients can develop sensitivity (allergic-type reaction) to any membrane

  • MembranesMembranes Conventional

    small surface area small surface area removes small molecular size particles well KUF 2-7mL/hr/mmHgg

    High Efficiency removes small to middle size molecules wellremoves small to middle size molecules well KUF 7-15mL/hr/mmHg

    High FluxHigh Flux removes small, middle, and larger molecular size

    particles KUF - > 15mL/hr/mmHg

  • DialysateDialysate

    Composed of concentrated electrolytes Composed of concentrated electrolytes, bicarbonate and treated water

    El t l t t ti i th di l t Electrolyte concentration in the dialysate determine what is removed or given to the patient

    Tailored to each patients needs based on blood Tailored to each patient s needs based on blood chemistries

    Regulates electrolyte and acid/base balance in Regulates electrolyte and acid/base balance in the blood

  • Dialysate

    Enables the removal of Waste productsWaste products Excess fluid

    P l f Prevents excess removal of Essential electrolytes Excessive fluid depletion

  • Dialysis Prescription

    Contains physician orders for the dialysate necessary to meet the needs for each patient

    C l i P i d S di Calcium, Potassium and Sodium Contains physician orders for the dialyzer necessary to

    meets the needs for each patientmeets the needs for each patient Surface area available for dialysis is related to dialyzer

    size Contains physician orders for a target weight and length of

    dialysis treatment Contains physician orders for a blood flow rate Contains physician orders for a blood flow rate

  • Understanding the Principles ofUnderstanding the Principles of Dialysis

    Means you understand the need for each i di l i h di l dpatient to dialyze using the dialysate and

    dialyzer ordered by the patient's physician

  • QUESTIONS?