Historical background

Thomas Graham, a London chemist, reported the principles of the semipermeable membrane in 1861 and gave the process of selective diffusion the name dialysis. Then, in 1913, Abel, Rowntree, and Turner devised an apparatus for the dialysis of blood, using a number of collodion tubes, through which flowed blood while a saline solution bathed the outsides of the tubes (Fig. 7-1). This device was used successfully to treat animals with uremia. Later, Kolff and Berk developed the first clinically successful artificial kidney, after the development of heparin for anticoagulation and the ready availability of cellulose in the form of cellophane tubing. They employed a rotating drum of wood slats around which a spiral of cellophane tubing was wrapped. The lower portion of the drum was immersed in a bath of dialysis fluid, while the blood was propelled along the tubing by rotating the drum. In 1948 Skeggs and Leonards developed a parallel plate dialyzer; the first disposable dialyzer was the Travenol twin-coil unit, marketed in 1956. About 1965 Gambro began production of disposable parallel plate devices, while at the same time hollow-fiber artificial kidneys were developed in the U.S.

Figure 7-1 Vividiffusion apparatus of Abel, Rowntree, and Turner.

(Adapted from Nosé Y: Manual on artificial organs, vol 1, The artificial kidney, St. Louis, 1969, Mosby.)

Solute transfer

How does the semipermeable membrane function in hemodialysis?

The patient’s blood is passed through a compartment formed by the semipermeable membrane. Dialyzing fluid surrounds this compartment. Red blood cells, white blood cells, platelets, and most plasma proteins are too large to pass through the pores of the membrane. Water and small particles, such as electrolytes, cross by diffusion (Fig. 7-2), as do urea (60 Da), creatinine (113 Da), and glucose (184 Da).

Figure 7-2 Semipermeable membrane.

What is diffusion?

Diffusion, or conductive transport, may be defined as the movement of solutes from an area of greater concentration of solutes to an area of lesser concentration of solutes. Molecules in solution are in constant motion and seek to spread uniformly throughout the solution. The rate of spread depends on the concentration, size, and electric charge of the particles. Diffusion of particles across a semipermeable membrane is the basis of dialysis. Diffusion will occur until equilibrium is reached (Fig. 7-3).

Figure 7-3 Typical hemodialysis system. Toxin-laden blood from the patient diffuses across the membrane within the dialyzer into the dialysis fluid. Clean blood is returned to the patient.

(From Black JM, Hawks JH, Keene AM: Medical-surgical nursing: clinical management for positive outcomes, ed 7, Philadelphia, 2005, Saunders.)