What is a dialyzer?
A dialyzer consists of a container that contains a semipermeable membrane that separates the dialysate from the blood that has been removed from the patient.
A hollow fiber dialyzer, the type most commonly used today, consists of a cylinder that contains more than 10,000 hollow fibers that are made of a semipermeable material.
To maximize the diffusion that takes place between the blood and dialysate, blood travels through the hollow fibers, and dialysate flows around the outside of these hollow fibers in a countercurrent direction from the blood.
The size of the dialyzer is measured by the surface area of the semipermeable membrane and is expressed in square meters. Most adult hemodialysis membranes have a surface area between 1.5 and 2.5 m 2 ; pediatric dialyzers are often less than 1 m 2 . A number of different materials are used for the semipermeable membranes. These materials vary in the degree to which small and middle molecules can pass through the membrane, which, in turn, is determined by the number and size of the pores in the dialyzer membrane. In the United States, most membranes are composed of either semisynthetic or synthetic materials that allow for the removal of larger molecules to some degree. Typical dialyzer membranes consist of polysulfone, polyethersulfone, cellulose acetate, biacetate or triacetate, or polyamides.