Figure 15

The hemodialysis membrane. Most membranes are derived from cellulose. (The earliest clinically useful hemodialyzers were made from cellophane sausage casing.) Other names of these materials include cupraphane, hemophan, cellulose acetate. They are usually sterilized by ethylene oxide or gamma irradiation by the manufacturer. They are relatively porous to fluid and solute but do not allow large molecules (albumin, vitamin B12) to pass freely. There is some suggestion that cupraphane membranes sterilized by ethylene oxide have a high incidence of biosensitization, meaning that the patient may have a form of allergic reaction to the membrane. Polysulfone, polyacrylonitrile, and polymethylmethacrylate membranes are more biocompatible and more porous (high flux membranes). They are most often formed into hollow fibers. Blood travels down the center of these fibers, and dialysate circulates around the outside of the fibers but inside a plastic casing. Water for dialysis must meet critical chemical and bacteriologic standards. These are listed in Figures 1-6 and 1-7.


Concentration (mg/L)


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