principles of dialysis combined
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Principles of Dialysis
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Hemodialysis
Dialysis Can
Remove wastes and excess fluid
Facilitate control of blood pressure Restore electrolyte and acid base balance
Cannot Replace hormones that the kidney no longer
produces Renin Erythropoeitin Calcitriol
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Goals of Hemodialysis
!anagement of some of the variousconditions that are a result of renal failure "remia Fluid overload Electrolyte imbalance
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Components of the Hemodialysis System
$he delivery system $he machine % dialysate
$he extracorporeal circuit Fistula needles &rterial bloodline 'enous bloodline Dialy(er )artificial kidney*
'ascular access
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Hemodialysis
Removes metabolic wasteproducts through diffusion
Removes excess fluidthrough ultrafiltration
,oth take place using asemipermeable membrane
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Principles of Hemodialysis
Definitions .emipermeable / allows passage of some
)but not all* substances and fluid
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Principles of Hemodialysis
.olutes / !olecules and electrolytes)particles* suspended in fluid the solids in asolution
Clearance / Rate of removal of specificsolutes Dialysate / a solution in which water is the
solvent and many dissolved substances such
as electrolytes and glucose are the solutes Electrolytes )34 Ca34 !g334 5a3* are present in
dialysate in concentrations similar to the levels inblood
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Principles of Hemodialysis
Definitions Diffusion / movement of solutes )particles*
through a semipermeable membrane from an
area of greater concentration to an area oflesser concentration
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Diffusion
$he movement ofparticles )solutes*through a
semipermeablemembrane from anarea of greater soluteconcentration to anarea of lesser soluteconcentration
semiermeable
membrane
dialysate
urea
bloodstream
creatinine
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Diffusion
Diffusion also depends
on: blood flow rate dialysate flow rate treatment time
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Diffusion
Salt particles pass
through cellophane
Solutions reach equal
concentration
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Principles of Dialysis
,oth osmosis anddiffusion can occur atthe same time across asemipermeable
membrane $he end result is that
movement continuesuntil the concentrationof moleculesequilibrates )becomese;ual* on both sides ofthe membrane
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Convection (Solute Drag)
<hen fluid crosses asemipermeable membrane ).=!*
some solutes are pulled along with it !ost effective way to remove large
solutes
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Principles of Hemodialysis
Adapted with permission of Amgen Inc.
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Principles of Hemodialysis
Diffusion occurs continuously in the patient>sbody as well as in the hemodialysis system 7nce dialysis has changed the chemical
concentrations of the blood4 that blood isreturned to the patient>s body where it slowlydilutes the rest of the blood
<aste products and electrolytes pass out ofthe patient>s cells and into the vascular system ? which in turn can be dialy(ed
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Factors Affecting Rate of Diffusion
$he nature of thesolution concentration
gradients molecular weight of the
solutes
temperature
$he nature of themembrane membrane
permeability surface area flow geometry
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Concentration Gradient
Difference in concentration of a given solutein a patient>s blood compared to fresh
dialysate Differences in concentration of solutes
between intercellular4 extracellular andvascular fluids
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Concentration Gradient
.olute movement can bein either direction
.olutes move toward thearea with lowerconcentration
$he larger the difference inconcentration across themembrane4 the higher therate of diffusion
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olecular !eight
.mallmoleculesmove fasterthan large
molecules
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"emperature
.olute particles
move faster athigher temperatures
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em#rane Permea#ility
@ow numerous are theporesA
@ow large are theporesA
@ow thinBthick is themembraneA
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Surface Area
s the amount ofmembrane in direct
contact with the bloodand dialysate
arger surface areasallow more diffusion
Range 9+ 22 .;uaremeters of surface area
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Flo$ Geometry
Countercurrent ,loodflows one way whiledialysate flows the
opposite way oal is to maintain a
concentration gradientand movement of
solute out of the blood
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Fluid Removal
"ltrafiltration <ater removal from the blood due to a
pressure gradient across a membrane "sed to remove excess water that has
accumulated in the tissue spaces betweendialysis treatments
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Filtration
$he movement of fluidthrough asemipermeablemembrane based on
the hydrostatic pressureexerted by the fluidagainst the membrane
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%ltrafiltration (%F)
$he removal of additionalfluid through asemipermeablemembrane as a result of
increasing the hydrostaticpressure differenceacross that membrane
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Fluid Removal
Adapted with permission of AmgenInc.
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%ltrafiltration
Pressure
Cellophane
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Positive Hydrostatic Pressure
=ositive pressure can be illustrated withan ordinary sprinkler hose =ositivepressure is exerted against the sides of
the hose as the water moves through it<ater is forced through the holes
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Fluid Removal
=ressure is exerted on the walls of themembrane on both sides of themembrane
,lood side pressure is positive Dialysate side pressure can be negative
or positive and is regulated by the dialysismachine
$he difference in pressure4 )blood sideminus dialysate side* is called the$ransmembrane =ressure or $!=
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Dialysis Concepts
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Principles of Hemodialysis
$he primary purpose of dialysis is to removewaste products4 remove excess fluid andmaintain a patient>s electrolyte balance
"nderstanding the principles of hemodialysiswill help us to do Gust that safely andeffectively
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Dialysis vs& Functioning 'idney
idney Functions <aste removal <ater removal Electrolyte balance
&cid base balance ,lood pressure control
Endocrine functions Erythropoietin Renin Calcitriol
@emodialysis H H H
H H )partially controlled with
ultrafiltration medicationsoften re;uired*
5o !ust be controlledusing medications