Module 3: Principles Of Dialysis

Principles Of Dialysi
Created Sep 18, 2010
by ameyer08
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Dialysis replaces 3 main kidney functions
Removing wastes from the blood Removes excess fluid from the blood Keeping electrolytes in...
Solutions
a mixture of a solvent and a solute
Solvent
Fluid
Solute
any substance that can be dissolved into the solvent
Dialysate
the solution that is used during dialysis Solvent: Water Solute: Electrolytes (potassium,...
Electrolyte Levels in Dialysate
closely match the levels in the human blood. This reduced the loss of these electrolytes out...
Controlling pts blood electrolyte levels
can be controlled by changing the dialysate. Adding an electrolyte to the dialysate at a level...
Semipermeable Membrane
a type of thin, flexible filter- a barrier that allows only particles smaller than a certain...
Dialysis semipermeable membrane
In dialysis, the semipermeable membrane's holes allow small molecules, such as water and urea,...
Diffusion
the process by which atoms, molecules, and/or other particles move from an area where they...
Energy for Diffusion
Energy for the movement comes from the molecules themselves, and does not depend on outside...
Factors affecting diffusion: The nature of the solution
Concentration Gradients Molecular weight of the solutes Temperature
Concentration Gradients
Solutes move through a semipermeable membrane from an area of greater concentration to an area...
Molecular weight of the solution
Smaller molecules diffuse more easily and quickly than larger ones. Large blood components...
Temperature
Molecules move faster at higher temperatures, so warmer fluids allow faster diffusion. Dialysate...
Factors Affecting Diffusion: The Nature of the Membrane
Membrane permeability Surface area of the membrane Flow geometry
Membrane permeability
A membrane with more pores allows faster diffusion. Larger pores allow larger molecules to...
Surface area of the membrane
Surface area is the amount of membrane in direct contact with the blood and dialysate. Larger...
Flow geometry
In dialysis, blood flows one way while dialysate flows the opposite way. This countercurrent...
Osmosis
In diffusion, solutes move. In osmosis, the solvent moves across the membrane. Osmosis is...
Osmotic Pressure Gradient
The difference in concentration  
Hydraulic pressure
Osmotic pressure can be overcome by hydraulic pressure using a pump, gravity or other means....
Reverse osmosis water treatment devices
Hydraulic pressure can reduce or overcome osmotic pressure. This principle is the basis for...
Filtration
the movement of fluid through a filter as the result of hydraulic pressure. Fluid will always...
Ultrafiltration (UF)
Water removal from blood due to a pressure gradient across a membrane. In dialysis, UF is used...
Convection
transfer of heat and solutes by physical circulation or movement of the parts of a liquid or...
Solvent drag
as a solvent crosses a semipermeable membrane, it drags along smaller solutes
Fluid
a liquid or gas that changes shape at a steady rate when acted upon by a force
Dynamics
addreses the motion and equilibrium of systems
Fluid dynamics
describes how two fluids-blood and dialysate-are pumped through tubing. Several forces affect...
Flow rate
amount of fluid that flows through the tubing in a given period of time
Flow velocity
speed at which the fluid moves through a given length of tubing. Velocity is based on the...
Pressure in any fluid system
the pressure in any fluid system is always related to the flow and the resistance; the greater...
Fluid compartments
The human body is made mostly of fluids. Fluids are found in 3 compartments: Intracellular...
Pressure gradients in fluid compartments
Differences in the level of sodium and electrolytes between compartments (gradients) cause...
Dialysis and body compartments
During dialysis, only fluid from the intravascular compartment can be removed
Extracorporeal Circuit
Outside the body Together, the tubing and dialyzer are called the extracorporeal circuit
Fluid intake
Food Beverages Intravenous fluids
Fluid Output
Respiration Stool Perspiration adn skin water loss Dialysate loss Residual urine Vomiting
Fluid dynamics in dialysis
blood pump speeds the flow of blood from the pt. Blood passes through the needle-the first...
Resistance in the blood pump
The tubing The tiny hollow fibers in the dialyzer The small opening of the venous blood return...
Resistance in the blood pump creates:
positive pressure inside the lines and dialyzer fibers. As blood passes through these resistances,...
Venous pressure
The pressure measured after blood leaves the dialyzer (venous pressure) is the lowest positve...
Positive hydraulic pressure
The average pressure of blood entering and leaving the dialyzer fibers is the true amount of...
Countercurrent flow.
dialysate flows through the dialyzer and around the hollow fibers in one direction. Blood flows...
Transmembrane pressure (TMP)
The machine can control the pressure differential between the blood and dialysate compartment...
Diffusion in dialysis
The hollow fibers in the dialyzer are the semipermeable membrane. Blood passes through the...
Electrolyte balance in dialysis
is also maintained with diffusion. It is vital to pts health to keep the right level of electrolytes...
Diffusion occurs continuously in the pts body
as clenased blood is returned to the pt, it slowly dilutes the rest of the blood. The drop...
UF in dialysis
UF requires pressure to force fluid through the membrane. The dialysis machine can create a...
Convection in dialysis
As water (a solvent) moves from the blood compartment to the dialysate compartment, molecules...
Osmosis in dialysis
the pressure of UF pushes fluid out of the blood nad into the dialysate. But osmotic forces...
Example of FIltration and UF
Soak a sponge in water. Hold the sponge over a bucket of water and watch the sponge filter...


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