01-11-2012, 06:05 PM
Hemodialysis and the Artificial Kidney
Hemodialysis.ppt (Size: 4.36 MB / Downloads: 126)
What sort of things are excreted?
Urea - 30 g/day
Creatinine - 2 g/day
Salt - 15 g/day
Uric Acid - 0.7 g/day
Water - 1500 mL/day
Unknown
Kidney failure
accumulation of waste
acidosis, edema, hypertension, coma
Kidney Structure and Function: Nephrons
Functional units of the kidney
1.2 million per kidney
Filtration and removal of wastes
Reabsorption of water, proteins, other essentials into the blood
Actively Secreted Substances
Hydroxybenzoates
Hippurates
Neutrotransmitters (dopamine)
Bile pigments
Uric acid
Antibiotics
Morphine
Saccharin
What does this mean in terms of dialysis?
Purpose - removal of wastes from the body
Kidney should be the ideal model for hemodialysis
Water retention / removal
Salt retention / removal
Protein retention
Artificial Kidney
Removes waste products from the blood by the use of an extracorporeal membrane process
Waste products pass from the blood through the membrane into the dialysate
Mechanisms of Transport through the Membrane
Diffusion (true dialysis)
movement due to concentration gradient
If concentration is higher in the blood and the species can pass through the membrane, transport occurs until the concentrations are equal
Slow
If dialysate concentration is higher, the flow goes toward the blood
Membrane Materials
Wettability - usually hydrophilic for transport of dissolved materials
Permeability
Mechanical strength
Blood compatibility
Design Considerations
Should be:
Efficient in removing toxic wastes
Efficient in removing water (ultrafiltration or osmosis)
Small priming volume (<500 mL)
Low flow resistance on blood side
Convenient, disposable, reliable, cheap
Hemofiltration
Cleansing by ultrafiltration
Materials removed from the blood by convection
Analogous to glomerulus of natural kidney
Features
Same equipment as hemodialysis
Leaky membrane required
Water lost is replaced either before or after filter (physiologic solution)
No dialysate needed
Clearance less dependent on molecular weight - better for middle molecules
Generally faster than hemodialysis