Principle of dialy
Principle of dialysis
, If two solutions of different composition are placed on different side of a permeable membrane, solutes will move by diffusion from the solution with the highest concentration (blood) to the solution with the lowest(dialysate) .
In hemodialyzer , arterial blood flows through the lumen of a hollow fiber dialyzer where water and small waste metabolites, mainly urea, creatinine, uric acid and phosphate ions, pass through the hollow fiber membrane walls from blood to the dialyzing fluid which is an osmotically balanced solution of electrolytes and glucose
The rate of movement with depend on the concentration gradient between blood and the dialysate, the permeability of the membrane, and the surface area of the membran. The maximum rate of solute transfer occurs initially when the concentration gradient is greatest (Ultrafiltration), as for substances removed from blood the concentration of the substances leaving will be less than the entering and for substances added to blood the concentration in blood leaving will be higher than the entering .
Hemodialysis membranes are often grouped into three categories, (a) cellulose membranes (most often cuprophane), (b) modified cellulose such as acetate, cellulose triacetate, and hemaphan, (C) synthetic membrane such as polyacrylonitrile, polymethylmethacrylate, ethylene – vinyl alcohol copolymer, polyamide and polysulfone.
Eighty percent of the dialyzers used were made of cellulose materials which have excellent permeability for low molecula substances, but due to their strength and excellent blood compatibility, synthetic polymer membranes have replaced the cellulose membranes(3).