The accurate control of ultrafiltration.

An apparatus has been contructed to regulate ultrafiltration accurately during dialysis. The principle of the apparatus is that, per unit of time, exactly the same amount of dialysate is introduced into the dialyzer as is discharged from it. The apparatus consists of two isovolumetric pumps connected in line. The four compartments of the two pumps must change their functions at every pump stroke. This is a accomplished by a switching system. There is a continuously closed dialysate circuit. The fluid extracted from this circuit will be replenished from the blood compartment of the dialyzer. Ultrafiltration is regulated by a simple peristaltic pump, which sucks the fluid out of the closed dialysate circuit. The isovolumetric pumps and the switching system are driven by the elevated pressure of the dialysate (0.5--1.0 atm). The apparatus can be used in single pass dialysis. Dialysis in accordance with the Bergström principle can be simply performed. In over 5,000 dialyses with several types of dialyzers, ultrafiltration was always accurate within the measuring limits. Considerable improvement was noticed in the well-being of the patients; hypotension, nausea, vomiting and muscle cramps were not seen.