Water is a vital component of dialysis. Compared to a healthy person who consumes around 2 liters of water daily, a hemodialysis patient is exposed to around 200 liters of water for every four-hour dialysis treatment. Water is also the major component of dialysate. Because of the huge volumes of water patients are exposed to, it is essential that dialysis water is maintained free of bacteria and contaminant.
Dialysis nurses and dialysis technicians play a central role in ensuring safe and quality water for dialysis. Policies and procedures for the maintenance and monitoring of water must be taken seriously to avoid patient complications, and to some extent, possible problems with the machines.
Why bacterial contamination of water and dialysate is a serious issue?
During the early years of dialysis, system-wide contamination of water resulted in wide-spread infections that often affected all patients within the center. Dialysis water-related infections were among the leading causes of morbidity and mortality among dialysis patients. Over the last 20 years, quality of dialysis water has improved significantly, particularly with the introduction of reverse osmosis (RO), ultrafiltation, UV filtration, and other sophisticated water purification methods.
While the bacteriological quality of dialysis water has considerably improved, the almost universal use of sodium bicarbonate instead of sodium acetate as buffer dialysate has also increased the risk of bacterial contamination of dialysate.
Compared to acetate, bicarbonate promotes the growth of specific microorganisms known to cause pyrogenic reactions among dialysis patients. Some of the commonly detected water-born microorganisms include the Pseudomonas species, including P. versicularis, P. maltophilia, and P. aeruginosa. There are also gram-negative bacteria that the dialysis water could harbor such as Moraxella, Alcaligenes species, and Corynebacteria. Likewise, dialysate has a nutrient-rich environment conducive for the growth of yeast and fungi. Severe contamination of dialysate can lead to pyrogenic reactions usually presenting as fever and cardiovascular instability.
Considering the favorable environment of dialysate, it is primordial to ensure that the dialysis water used for preparation of dialysate is free of any microorganism. Dialysis quality water is important now more than ever.
Focus on water treatment system
Due to the critical role of dialysis nurses and technicians in ensuring dialysis quality water, it is imperative that they understand what happens throughout the water treatment system.
Municipal water contains unwanted contaminants and bacteria that pose risk to patients and machines. So, before they are fed to the machines or used for preparing dialysate and reprocessing dialyzers, raw water passes through a systematic purification system – a series of devices, which filters out bacteria and contaminants.
The system is composed of three processes: the pre-treatment, water purification, and distribution. Through each process, monitors are in place to check water quality, water temperature, flow rates, and pressures. These monitors provide alarms if the condition does not meet the accepted limits. In addition, water sampling and testing is done periodically at each process.
The pre-filter process is composed of a series of devices that ensure adequate pressure, flow rate, and temperature is achieved. Blending valve mixes hot and cold water for an optimal temperature (77º F). Backflow preventer ensures water does not back up into the city water supply. A booster pump keeps the incoming water flow within the desired levels and prevents unwanted fluctuations. Components of the pre-filter and RO system require certain water pressure and flow rate to run efficiently.
The pre-treatment process comes with four filtration methods intended to remove specific contaminants. The multimedia or depth filter removes sand and silt in the water, as well as other solutes and substances. Once the water is free of micro-debris, it then passes through the water softener which removes magnesium and calcium. The softener works together with the brine tank to prevent scaling (accumulation of hard mineral deposits) in the RO membranes, which could potentially damage it. Carbon tanks (usually come in pairs) filter out chloramines/chlorine that is abundant in municipal water. Sample ports are located at the end of each tank to check the adequacy of removal of chloramines/chlorine. The carbon tanks also remove the finest debris and are the last process before the water enters the RO unit.
After the pre-treatment, water then passes through the RO membranes followed by an ultrafilter. The RO unit is contains a pump, semi-permeable membranes and quality monitors. It is a powerful purification method that removes bacteria, endotoxin, viruses, fine particles, and other solutes. It works by reversing the transport mechanism osmosis. The semi-permeable membrane allows water but not chemicals, microorganisms, and other un-dissolved substances. Product or treated water is then passes through the ultrafilter while the waste water is disposed to the drain. The ultrafilter is capable of removing bacteria, viruses and most endotoxin. It is also the last and final step before water is used for the machines, dialysate preparation and dialyzer reprocessing.
AAMI Dialysis Quality Water
The AAMI has set standards for maintaining dialysis quality water in all dialysis facilities. The recommended total viable microbial count should be lower than 200 CFU/mL and endotoxin concentration lower than 2 EU/mL. Action level for total microbial count is 50 CFU/mL and for endotoxin concentration, 1 EU/mL. Actions and corrective measures must be taken promptly in case treated water falls in the action level.
Periodic monitoring of the water bacteriology is essential to ensure patient safety. As dialysis nurse or dialysis technician, expect to check the water quality regularly.