The basics of hemodialysis equipment

The hemodialysis (HD) machine pumps the dialysate as well as the patient’s blood through a dialyzer. The blood and dialysate are separated from each other by a semipermeable membrane permitting solute and water transfer as governed by laws of physics. In practice, however, this procedure is somewhat more complex. The operational system of the HD machine represents a complex array of detectors, controllers, monitors, and safety devices to ensure a safe operation. This integrated system allows the operator the ability to control the blood and the dialysate circuits as well as monitor important variables like ultrafiltration (UF) rate, adequacy, dialysate composition, and circuit pressures. Although such advances make patient management somewhat easier for the nephrologist, they do not change the basic tenet of patient care—first to do no harm. Consequently, it is extremely important for the practicing nephrologist to recognize and understand the terminology, significance, and management of the basic operational mechanics of HD machines. This article will focus on essential principles of HD equipment that are necessary for ensuring a safe, standard HD procedure (the description of equipment for other specialized procedures like hemofiltration is beyond the scope of this review). From a practical point of view, it is often useful to divide the HD process into two main parts, that is, the blood circuit and the dialysate circuit. The standards for HD equipment in the United States are set by the AAMI (Association for the Advancement of Medical Instrumentation). GENERAL GUIDELINES GOVERNING THE USE OF HD EQUIPMENT