Hemodialysis is a life-sustaining procedure for patients who have non-functioning kidneys. This form of treatment substitutes the role of healthy kidneys of the human body. Without healthy kidneys, we can’t eliminate the naturally-accumulated bodily wastes and excess fluids from our bodies. A complete dialysis system consists of a dialysis machine, a dialyzer, a disposable blood tubing set and an array of chemicals for formulating a dialysate solution used within the dialyzer. The dialyzer acts as the filter, separating wastes from the blood. It has a highly-porous membrane located within its closed plastic housing, which also separates the blood compartment and a dialysate compartment. The blood drawn by the dialysis machine passes through the disposable blood tubing set and the blood side of the dialyzer. On the other hand, the dialysate solution prepared by a dialysis technician from the chemicals prior to treatment is transported through the dialysate side of the dialyzer. Since the pores of the dialyzer’s membrane are so tiny, wastes from the blood that passes through it are filtered by way of osmosis. Vital components from the dialysate still pass through the opposite direction of the membrane and into the blood. This simple transfer of wastes into the dialysate effectively cleanses the blood, allowing the desired components from the dialysate to circulate into the bloodstream.
What is priming?
Blood drawn from the patient’s body, as well as blood cleansed by dialysis pass through a disposable blood tubing set. The blood tubing set and the dialyzer act as a closed extracorporeal route through which the patient’s blood travels. Each set consists of an arterial line connected to an arterial receptacle for drawing blood from the patient, and a venous line connected to a venous receptacle for returning blood to the patient. Blood tubing sets also have a variety of other lines for connecting the blood pump and the dialyzer between the arterial and venous receptacles. Before the blood tubing and the dialyzer can be utilized in any dialysis treatment, both should be primed by the dialysis technician. Priming is the process of removing air from the tubing or dialyzer by allowing sterile saline solution to flow through it. New tubing and dialyzers, whether they’re new or reused, are filled with air. Without priming, excess air may lead to clotting of dialyzer fibers during treatment, which can negatively affect the patient. Once primed, the sterile saline solution is recirculated through the blood tubing set and the dialyzer to produce a steady flow and remove remaining trapped air from within the system. The process of priming and recirculating also cleans the dialyzer, flushing its membrane of any debris and remaining chemicals from previous usage.
How Priming is Done by a Dialysis Technician
Reused dialyzers must be cleaned with a sterilant solution by the dialysis technician. However, that doesn’t mean that the sterilant solution itself shouldn’t be cleaned from the dialyzer before each dialysis treatment. This cleaning procedure effectively occurs when the dialyzer undergoes priming and recirculation. When being primed, the dialyzer is flushed with saline solution which gets rid of most of the sterilant. Typically, dialysis machines require that the steps for priming and recirculation are done separately. A priming sequence on a traditional machine requires that the dialysis technician connect the outlet of the machine, the venous line, to a saline source. The dialysis technician will then operate the machine in reverse to fill the circuit with saline. At the beginning, the priming solution passes through the dialyzer and, because of the reverse flow, exits the circuit through the dialysis machine’s input line, which is the arterial line. A waste bin is used by the dialysis technician to dispose of the priming solution. The first priming solution is ideally discarded since it may contain significantly high amounts of sterilant when the dialyzer was sterilized and reused following a previous dialysis treatment. After priming the blood tubing and dialyzer, the dialysis technician will disconnect the venous and arterial lines of the blood tubing set from the saline source and waste bin subsequently. The venous and arterial lines are then connected. By this time, the dialysis technician will switch the machine from its reverse operation, and operate it normally to recirculate the saline solution through the extracorporeal circuit. Of the two separate procedures of priming and recirculating, recirculating the saline requires more time than first priming the circuit with saline. The entire process takes approximately 15 minutes to complete. However, when a significant amount of air is introduced into the circuit, priming and recirculating should be started over at the expense of machine down-time and a new bottle of sterile saline solution.
The Importance of Proper Priming
Priming removes air and sterilant from the bloodlines and dialyzer. When air bubbles enter the venous bloodstream, the patient’s pulmonary blood flow can be substantially blocked, causing complications. Similarly, when these small bubbles are introduced into the arterial side, death by blockage of coronary and/or cerebral arteries may be possible. The signs and symptoms of air embolism typically vary depending on what vessel is affected. For instance, an embolism in a blood vessel to the lungs causes chest pain and shortness of breath. Consequently, an embolism affecting the arteries to the brain will cause immediate loss of consciousness and often causes convulsions. While the chemicals used as sterilants are designed to destroy a wide range of pathogens that may be present in the dialyzer, they can be harmful to humans. When sterilant enters the patient’s bloodstream due to the poor priming done by the dialysis technician, blood poisoning may occur in varying degrees. During recirculation, any sterilant left is discarded with the help of ultrafiltration and diffusion. The sterilant moves from the blood side of the dialyzer to the dialysate side, then down the drain. Lastly, proper priming warms the saline so the patient does not get too cool when the treatment is initiated.