Welcome to Dialysis Patient Care!

Tuesday, October 19, 2010

Scientific Principles Used in Dialysis


Sections of Scientific Principles Used in Dialysis

SOLUTIONS

• A solution is a mixture of a solvent and a solute.
• The solvent is a fluid.
• The solute is any substance that can be dissolved into the solvent.
• Example: Salt water - water is the solvent and salt is the solute.
• Dialysate is the solution that is used during dialysis.
• Water is the solvent.
• The solutes are electrolytes (e.g., potassium, calcium, sodium, magnesium, and chloride ions) and glucose (sugar)
• Electrolytes levels in the dialysate closely match the levels in human blood.
• This reduces the loss of these electrolytes out of the blood and into the dialysate during dialysis.


SEMIPERMEABLE MEMBRANE
• A semipermeable membrane is a type of thin, flexible filter - a barrier that allows only particles smaller than  a certain size to pass through it.
• In dialysis, the semipermeable membrane's holes allow small molecules, such as water and urea, to pass through easily.
• The small size of the pores keeps larger molecules and blood cells from passing through the membrane.


DIFFUSION
• Diffusion is the process by which atoms, molecules, and/or other particles move from an area where they are in high concentration to an area where they are in concentration.
• Diffusion can occur in solids, gases, or liquids, such as blood.
• In dialysis, diffusion occurs across an artificial semipermeable membrane


Source: advancedrenaleducation.com

Factors Affecting Diffusion: the Nature of the Solution

1. Concentration Gradient: How concentrated is the fluid on each side of the membrane?
     • Solutes can move through a membrane in either direction, but always toward the area of lesser concentration..
     • As the concentration gradient increases, solute movement increases too.
     • Diffusion stops when the concentrations on both sides of the membrane are equal.
     • Concentration gradient allow dialysate to remove wastes from a patient's blood and to balance electrolytes in the blood with electrolytes in the dialysate.

2. Molecular weight of the solutes: How large are the dissolved particles?
     • Smaller particles (urea and salts) diffuse more easily and quickly than larger ones (such as RBcs, WBCs, albumin, platelets, viruses and bacteria.

3. Temperature: How warm is the fluid?
     • Molecules move faster at higher temperatures, so warmer fluids allow faster diffusion.
     • Dialysis temperature is controlled during dialysis forpatient safety, comfort and faster diffusion.

Factors Affecting Diffusion: the Nature of the Membrane
1. Membrane permeability: How plentiful and large are the pores?
     • More pores allows faster diffusion
     • Larger pores allow larger molecules to pass through

2. Surface area of the membrane: How big is the membrane?
     • Surface area is the amount of membrane in direct contact with the blood and dialysate
     • Larger surface areas allow more diffusion

3. Flow geometry: How do the fluids flow?

• In dialysis, blood flows one way while dialysate flows the opposite way.
• This countercurrent flow of blood to dialysate speeds up diffusion, because with this arrangement, a high concentration gradient between the blood and dialysate cm be maintained throughout the length of the dialyzer

A concurrent flow -would occur if blood and dialysate moved in the same direction


Only molecules smaller than the pores will
pass through. Source: http://www.fmqai.com/library/attachment-library/4scientificprinciples.pdf




OSMOSIS
• Osmosis is movement of a sol vent through a semipermeable membrane from an area of lower solute concentration toward an area of higher solute concentration.
• The difference in concentration is called an osmotic pressure gradient.
•  Osmotic pressure can be overcome by hydraulic pressure using a pump, gravity, or other means.
Hydraulic pressure is pressure created naturally (such as from gravity) or artificially (such as a pump).
• Hydraulic pressure affects the amount of water thai is removed from the patient during dialysis.


Source: advancedrenaleducation.com


FILTRATION AND ULTRAFILTRATION
• Filtration - is the movement of fluid through a filter as the result of hydraulic pressure.
• Ultrafiltration-water removal from blood due to a pressure, gradient across a membrane.


Source: toltecint.com


CONVECTION
• The transfer of heat and solutes by physical circulation or movement of the parts of a liquid or gas.
• Also called 'solute drag'



FLUID DYNAMICS

• A fluid is a liquid or gas that changes shape at a steady rate when acted upon by a force.
• The field of "dynamics" addresses the motion and equilibrium of systems.
• Fluid dynamics applies to dialysis, because it describes how two fluids (blood and dialysate) are pumped through tubing.
• Several factors affect the movement, or flow, of fluid through tubing:
     • Flow rate - the amount of fluid that flows through the tubing in a given period of time (e.g., 10ml/min)
     •  Flow velocity -is the speed at which the fluid moves through a given length of tubing.
     • Velocity is based on the rate of flow and the area of a cross section of the tube.
• If the flow rate is held constant but the cross section of the tube is reduced by half, the flow velocity will double.





Scientific Principles Used in Dialysis - Related Hemodialysis Article



0 comments:

Post a Comment

Latest Article

 

hemodialysis,peritoneal dialysis, dialysis machine, kidney dialysis, dialyse, dialyzer, dialyse tubings, complications of dialysis, dialyzer reprocessing, protein dialysis, kidney transplant, hemodialysis diet, renal nurse, renal failure, hollow fiber membranes, minerals and electrolytes, kidney treatment, dialysis treatment