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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?
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