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Water Treatment for Hemodialysis: What You Must Know to Keep Patients Safe.

Water is a risk for individuals on hemodialysis (HD). Dialysate is primarily composed of water, and water that is not adequately treated to remove contaminants can cause injury and death to patients on HD.

Is our drinking water safe? For drinking, yes. However, contaminates harmless in drinking water can be toxic when present in dialysate. Substances like aluminum, chlorine, and fluoride, which are purposefully added to drinking water, are toxic when present in any substantial quantity in dialysate.

What makes use of drinking water unsafe for use in HD?

* Exposure is huge. The average person consumes about 2 liters of liquids (in various forms) each day. To create dialysate, treated water is mixed with acid and base concentrates in a defined ratio. Dialysate is more than 90% water. People on HD are exposed to 90 to 192 liters of water each treatment (see Figure 1) (Medical Education Institute [MEI], 2017).

* Exposure is unprotected. When liquids are consumed, the liquid is processed through the digestive tract. Liquids are absorbed into the bloodstream, with that blood going immediately to the liver, which filters out contaminates. The blood of individuals on HD is directly exposed to that huge volume of water across the very thin membrane of the dialyzer, which is only selective to the size of the molecule.

* Little to no kidney function. The kidneys of healthy individuals are able to process and excrete contaminates that may be ingested in water or food. Individuals who depend on HD do not have sufficient kidney function to perform this process.

Risks to Individuals of Exposure to Improperly Prepared Water or Dialysate

Exposure to improperly treated water or substandard dialysate can cause patients to experience both acute and chronic problems. These problems include anemia, alterations in blood pressure and acid-base balance, neurological compromise, chronic inflammation, bone disease, hemolysis, fever, and more (Association for the Advancement of Medical Instrumentation [AAMI], 2014c).

A more complete list of clinical symptoms seen when patients on HD are exposed to inadequately purified water or contaminated dialysate is shown in Table 1. While acute reactions can be quite dramatic and deadly, it is likely that many reactions to inadequately purified water or improperly prepared dialysate go unreported because symptoms of such exposure often mimic problems that result from chronic kidney disease (CKD) with its attendant chronic inflammation.

Standards and Regulations Related to HD Water

AAMI sets standards for HD water and dialysate. The standards developed by AAMI are considered "consensus standards," which means they are developed by agreement of a group of volunteers representing the industry (providers and manufacturers) and government agencies. The AAMI Committee for Renal Disease and Detoxification (RDD) includes representatives from the industry (e.g., AmeriWater, BBraun, Baxter, DaVita, Dialysis Clinics Incorporated, Fresenius, MarCor, NxStage, RPC), professional associations (e.g., the American Nephrology Nurses Association [ANNA], the National Renal Administrators Association [NRAA]), and federal agencies (e.g., the Food and Drug Administration [FDA], the Centers for Medicare & Medicaid Services [CMS], and the Centers for Disease Control and Prevention [CDC]); as well as other companies and independent consultants. AAMI develops voluntary standards and has no regulatory authority.

The American National Standards Institute (ANSI) approves AAMI standards and acts as the United States National Committee to the International Standards Organization (ISO). ANSI and ISO seek to "harmonize" standards, meaning they strive to make their standards congruent around the world to provide a consistent expectation for manufacturers and users. The current standards are referred to as ANSI/AAMI Standards, but an updated version is expected to be finalized in late 2018 and will carry the endorsement of an AAMI/ISO standard. See Table 2 for a crosswalk from past to present and future standards.

The FDA (2018) is responsible for ensuring that drugs, vaccines, and other biological products and medical devices intended for human use are safe and effective. HD water purification systems and HD machines are considered Class II medical devices by the FDA (2014). Class II devices require the manufacturer to track critical components and maintain a complaint investigation system. Manufacturers of HD machines and water treatment components must have FDA approval to market their products.

CMS issues regulations for HD facilities that accept Medicare payment for the treatment of individuals requiring outpatient HD. In 2008, CMS adopted ANSI/AAMI RD52:2004 Dialysate for Hemodialysis as part of the Conditions for Coverage (CfC), the end stage renal disease (ESRD) regulations to guide water treatment and dialysate preparation (CMS, 2008b). The CfC are the Medicare regulations (i.e., rules) that outpatient HD facilities must follow to be eligible to receive reimbursement for care of Medicare beneficiaries. Adopting the AAMI document as regulation made meeting that specific ANSI/AAMI standard a requirement for outpatient HD facilities. Since 2008, the AAMI standards for water and dialysate have been updated multiple times. CMS, however, has not updated their regulations or adopted a more current standard. CMS allows the use of more current standards as long as the newer recommendations are equal to or more stringent than the CMS rule. This article will reference the most current standards, and point out any differences between those and the CMS regulations that outpatient HD facilities must meet.

What about acute HD? What standards/regulations must providers of acute HD follow? Acute HD services are surveyed by state agencies and accreditation organizations (AO) based on hospital CMS regulations and AO standards, which in most cases, do not specifically address HD. While the ESRD regulations do not apply to acute programs, state surveyors may apply knowledge of the safety standards in those regulations when surveying acute programs. State and AO surveyors may use standards from the AAMI, the ISO, and the CDC, as well as policies and procedures of the hospital and acute services (Maltais & Payne, 2014).

Water Supply

The first step to understanding water treatment is to understand water sources. Municipal suppliers use two sources of water: ground water and surface water. Ground water comes from underground chambers, such as wells and springs, and is generally lower in organic materials but higher in inorganic ions, such as iron, calcium, magnesium, and sulfate. Surface water comes from lakes, ponds, rivers, and other surface reservoirs. Surface water is generally more contaminated with organisms and microbes, industrial wastes, fertilizers, pesticides, and sewage. Some municipalities rely primarily on surface water most of the year, and then blend in well water when the supply of surface water falls. If the source of water varies over the course of the year, HD facilities will need to design their water treatment systems to handle the worst case scenario.

The Environmental Protection Agency (EPA) regulates all public water systems (i.e., those having at least 15 service connections or serve at least 25 people for at least 60 days a year). These regulations require the public water systems to comply with the Safe Drinking Water Act, which sets the maximum allowable level of contaminants in drinking water (EPA, 2004).

Municipalities or public water suppliers process both surface and ground water, and depending on the quality of the supply water, they may add chemicals to handle problems or potential problems. Chemicals added can include:

* Alum--To cause particles to "clump" together and sink to the bottom of the settling pond.

* Chlorine and/or chloramines--To control bacterial growth.

* Fluoride--To prevent dental cavities.

Each of these chemicals will harm patients on HD if not removed to safe levels in the water used for treatment. Unfortunately, there is little to no control on the amounts of these chemicals that may be added. A comparison of the maximum allowable levels of contaminants in water set by AAMI (for HD water) and the EPA (for drinking water) is shown in Table 3.

The EPA requires municipal water supply companies to monitor and test the water on a periodic basis. The quality of the water can change from season to season and even day to day. This variability in the quality of tap water places an extra burden on nephrology professionals working to deliver the purest water feasible to persons on HD.

Source Water and Acute HD Programs

Some hospitals treat their water supply, softening the water or adding chemicals, such as disinfectants or descaling agents. Acute HD programs should determine if the hospital is treating the water supply and take steps to ensure water used for HD is safe. Open communication with responsible hospital staff members is critical to ensure the HD program is notified of changes or additions to any hospital-based water treatment systems.

Emergency Preparedness Requirements

In 2016, CMS added a new CfC to ESRD regulations. This Condition of Coverage: Emergency Preparedness requires HD facilities to make preparations for emergencies that might interrupt services to their patients. There are four key elements to this CfC:

* Emergency plan, including a risk assessment.

* Policies and procedures to address potential emergencies.

* Communication plan.

* Training and testing for patients and staff (CMS, 2016).

Water and dialysate are critical to the function of every HD facility, and an interruption in the ability to provide safe water or dialysate must be considered in the emergency plan. Emergency preparedness includes having a back-up plan for an alternate source for electricity and water in the event these services are interrupted or if there is a sudden change in incoming water quality. Policies and procedures should address actions to take in the event of failure of a critical component of the system (e.g., carbon tank, reverse osmosis [RO] system, circulation pump). Training and testing of personnel would include ensuring staff members understand the plan related to the water supply and how to access the communication plan to contact support for making connections to alternate sources for water and power.

Contingency Plan

An HD facility must develop a contingency plan regarding actions to take if the electrical or water supply to the facility is lost or if there is a failure of a critical component of the system (e.g., carbon tank, RO system, or circulation pump). This includes a backup plan in the event the water supply or electrical power is interrupted. The plan should also address sudden changes in incoming water quality (AAMI, 2014d; CMS, 2008a). CMS regulations also require that an HD facility should have an agreement with a back-up facility where patients can receive HD treatments if the facility cannot be made operational.

Water Treatment Systems

Labeling and Schematics

The FDA and AAMI, as well as CMS, require certain information be available to the operator of the HD water treatment and dialysate preparation systems. This includes labels on each component and the tubing, as well as a schematic diagram of the system. The labels for all water treatment devices must include (AAMI, 2014e; CMS, 2008b):

* The type of device, how it functions, and what to monitor.

* The manufacturer's name and address with phone number.

* Model and serial number.

* Appropriate warnings for use.

* Identification of methods to prevent improper connections.

* Prominent warnings if the component contains germicides.

Flow schematics and diagrams of the system should be displayed in the water treatment room and updated as necessary. Having directional arrows on the piping and clearly labeling valves are also expected by CMS and will assist staff in identifying any issues. CMS requires the operator to know the purpose and operating parameters of the different components. Listing the expected readings for various gauges and monitors on the water treatment log sheet will facilitate this process and serve as a ready reference. Some of these parameters will vary from system to system and should be set based on the facility's unique situation and upon manufacturer's recommendations. Parameters that may vary in different systems include pressure readings, flow readings, and conductivity measurements at various points in the system. Expected operating parameters should be determined during the initial validation process when a new system is installed (AAMI, 2014d).

Water Treatment System Components

This section describes water treatment system components, including ancillary components, pretreatment components, and treatment components (e.g., RO and deionization [DI] systems), post-treatment components, and distribution systems. Components chosen will vary depending upon an analysis of the source water quality and philosophy of the medical director, staff, or organization. Typically, every component described here will not be needed in each HD water treatment system. Components are discussed in the order that they are most likely to be placed in a HD water treatment system (see Figure 2). Note: When the word "must" appears, compliance is required by CMS regulations (mandatory) for outpatient HD facilities. Following the description of each component is a statement as to whether the component is mandatory or optional based on CMS regulations for outpatient HD. Regardless of that status, if a component is installed as part of the water system, monitoring that component is mandatory.

Ancillary Components

Ancillary components include back-flow preventers, temperature blending valves, and booster pumps.

Back-flow preventer. Back-flow preventers are required to protect the city water supply from potential contamination by disinfectants and cleaners used in the HD water treatment system. All water treatment systems, including water systems for acute HD, require a form of back-flow prevention.

Local codes dictate the type of back-flow preventer that can be used, and these codes vary. Some codes may require a break tank for water treatment systems used for acute HD. A break tank uses an air gap to separate the water supply from the water treatment system. Back-flow prevention devices should never be placed in the purified water loop piping because they can potentially contaminate the product water with bacteria, disinfectants, and metals. Most back-flow preventers are of a type known as reduced pressure devices (RPDs). These devices have areas of stagnant water, which can promote the growth of bacteria and make it very difficult to rinse out disinfectants used in maintaining the system. Most back-flow preventers are made of brass, which would readily leach metals, such as copper, into HD water. The cost of stainless steel back flow preventers is prohibitive, and their use would not resolve the stagnation issue. Back flow prevention is only necessary at the very beginning of the water treatment system to provide a means to prevent contamination of the city water supply.

If back flow from the HD treatment system were to occur, back-flowing fluid would flow into the drain rather than back into the city supply lines. Discharge of spent water and dialysate in the acute care setting should be into an appropriate floor drain or standpipe connection. If these are not available, a sink may be used as long as there is an air gap between the end of the tubing carrying the spent fluids to prevent contaminated effluent from back flowing into the HD machine, and the sink is not used for any other purpose during the treatment.

Monitoring. Back flow preventers are inspected at installation and annually. These must be installed by a licensed plumber and inspected annually by a qualified person.

Mandatory or optional? Mandatory due to national and local codes.

Temperature blending valve (tempering valve or mixing valve). Temperature blending valves bring water to the optimal temperature for most efficient RO function (~77[degrees]F or 25[degrees]C). The temperature blending valve mixes hot and cold water to achieve this temperature. The valve works like the handle in a shower, which is turned to adjust the temperature of the water. These valves are called thermostatic valves, and contain a spring that controls how much hot and cold water flow through them. Once the desired temperature is set, the valve maintains that temperature even if the temperature of the water feeding them varies. When the blended water is too warm, the spring expands and reduces the flow of hot water and increases the flow of cold water. If the water is too cold, the spring contracts and allows more hot water in and less cold water. If the water feeding the RO below 25[degrees]C, the RO will produce less water; each 1[degrees]C drop in temperature drop equals a 3% decrease in product water volume. Mixing valves are widely used on large central RO systems in geographical areas that are likely to have cold incoming water (e.g., they are more common in Minnesota than in Arizona).

If blending hot and cold water together from a faucet for an acute HD treatment, a temperature gauge must be in place with an audible alarm. High temperatures may damage the RO membranes and could harm the patient if the HD machine temperature alarm fails to place the dialysate flow in bypass.

Temperature-blending valves must be sized to accommodate the anticipated range of flow and must be fitted with a means to prevent backflow into the hot or cold water lines. To validate that the valve is working and to set the temperature to the desired level, a temperature gauge is normally placed after the blending valve, and the reading is recorded daily.

Monitoring. Tempering valves are monitored by observing the blended water temperature. This temperature should be documented daily on the RO log sheet and readings monitored for any trend. A temperature that fluctuates from day to day could indicate an eminent failure of the blending value, which could then be replaced proactively.

Mandatory or optional? Optional.

Booster pump. Booster pumps provide a constant water pressure and flow to the entire water treatment cascade to allow successful operation. HD facilities often experience fluctuating or decreased incoming water flow and pressure, and back flow preventers and temperature blending valves may substantially lower the pressure of the feed water. To compensate, a pump to boost the water pressure may be placed next in the water treatment cascade.

Monitoring. Pressure gauges before and after the booster pump are used to monitor the function of the pump. Gauges should be read daily, and readings recorded. In many systems, the post-booster pump (low) pressure should be recorded when the pump turns on, and the (higher) pressure when the pump turns off. In newer RO systems, the booster pump is a variable speed pump that simply speeds up or slows down to maintain a consistent pressure.

Mandatory or optional? Optional.

Pretreatment Components

Pretreatment components include chemical injection systems, sediment filters, water softeners, and carbon filters. These may be used to "pre-treat" the incoming water, to remove contaminates and adjust the chemical make-up prior to the water entering the primary treatment component.

Chemical injection systems. Chemical injection systems are used to change the pH of the incoming water to improve the function of water treatment components. The ideal incoming water pH should be 5.0 to 8.5 to allow the RO to operate properly and the carbon tanks to remove chlorine/chloramine effectively. In many areas of the country, the source water pH is higher than 8.5. Water with a pH higher than 8.5 with chloramines present will cause the carbon to be less effective at removing chlorine and chloramine, and cause the RO membrane performance to degrade, resulting in poor water quality (Luehmann, Keshaviah, Ward, Klein, & Thomas, 1989). When this is the case, a chemical injection system may be incorporated into the design of the pretreatment system to lower the pH, especially when chloramine is present in the source water. Chemical injection systems meter a small amount of a strong mineral acid, such as muriatic acid, also known as hydrochloric acid (HCl), or sulfuric acid into the feed water system. The use of an organic acid, such as acetic acid, is not recommended because those acid types are nutrient-rich and can encourage the growth of bacteria.

Chemical injection systems may also be used to reduce chloramines in the incoming water in situations when the usually sufficient carbon tanks alone are not adequate to do the job. Sodium bisulfite and ascorbic acid are two chemicals that may be injected into the water treatment system to aid in the reduction of chloramines (AAMI, 2014e).

Any chemicals used in an injection system must be compatible with all components of the water treatment system in all operation modes. For instance, if the RO system were to go into emergency back-up and the HD facility had to use DI for its primary treatment, additives should not create a toxic chemical when combined with the deionization resin.

Chemical injection devices consist of a reservoir that contains the chemical to be injected, a metering pump, and a mixing chamber. These devices are located in the incoming water line, after the booster pump. The device should be able to tightly control the addition of chemicals and have a control system that allows chemicals to be injected in proportion to the water flow through the pretreatment tanks, or a pH monitor that automatically adjusts the injection of chemicals.

Chemical injection systems should be placed before the sediment filter because the lower pH will cause dissolved metals like aluminum and some salts in the feed water to precipitate. The sediment filter following the injection system can then capture most of the solidified particles.

Monitoring. Continuous monitoring of the pH of the water is required (AAMI, 2014d). When a chemical injection system is used, there must also be a means to verify that the chemical additive and its byproducts are decreased to a safe level before the product water is used for patients, or evidence that the chemicals in use do not cross into the bloodstream during HD. All material safety data sheets (MSDS) and Occupational Safety and Health Administration (OSHA) requirements must be followed for the safe handling of the chemicals used.

Mandatory or optional? Optional.

Sediment filters. Sediment filters remove sediment from the source water. Many source waters, despite their apparent clarity, contain large amounts of suspended particulate matter that can adversely affect the water treatment system. Large particulates of 10 microns or greater, such as dirt, silt, and colloidal matter, will cause the source water to be turbid or cloudy, and may be removed by sediment filtration. If not removed, these particles can clog the carbon and softener tanks, destroy the RO pump, and foul the RO membranes.

Part of the evaluation of the source water prior to designing the water treatment system for a facility should include a silt density index (SDI) test. An SDI measures and evaluates how rapidly a special-sized screen becomes clogged from a particular water source. Most RO membrane manufacturers recommend the feed water SDI not exceed a value of 5.0

Sediment filters are typically placed at the beginning of the pretreatment cascade and can be cartridge type filters, single media filters, or multimedia filters. Multimedia filters contain layers of various media ranging in size from gravel to sand that physically trap particles as the water is filtered downward through the tank. Each tier is composed of a different-sized media so not all the particulates are collected at the top, but rather, distributed through the media bed. By using a stratified bed, increasingly smaller particles are captured, the entire bed is used, and the filter is not rapidly clogged.

An automatic multimedia filter is routinely backwashed on a preset time schedule (when the water treatment system is not in use) so the media is cleansed and redistributed regularly. By directing the water flow from the bottom of the tank upward (backwashing), the tightly packed bed is lifted so the lighter particulate matter floats to the top and out the drain. The media, chosen for its size and density, then resettles in its ordered layers when the process is complete. The frequency of backwashing depends on the number of particulates in the supply water and the pressure drop through the tank.

Monitoring. Sediment filters are monitored by comparing the readings on pressure gauges placed on the inlet and outlet of the filter. If the difference (Delta) in the pressure in the gauge before the filter is greater than a set value (e.g., 10 pounds per square inch [PSI]) in the gauge after the filter, then it is time to backwash (multimedia type) or replace (cartridge type) the filter. Readings for both gauges should be recorded daily, along with the calculated delta pressure.

Mandatory or optional? Optional.

Timing devices. Timing devices allow an automatic process to occur unattended. Sediment filters are one of several components that may use a timing device for automatic backwashing or recharging. Any timer should be visible to the operator of the system and the time displayed recorded daily.

Monitoring. The time displayed should match the time of day the device is read, unless there is a posted notice that the time is off set to allow sequential backwashing of multiple components. Newer treatment systems often have integrated timer heads that do not require such off sets. Situations, such as power failures, can result in a delay in backwashing and subsequent operation occurring during patient treatment. When backwashing is in progress, water flow to the RO is interrupted, and this could result in delays in patient treatment. This underscores the importance to monitor and document the times displayed on the timers.

Mandatory or optional? Optional.

Water softener. Water softeners protect the RO from scaling and extend the life of the DI (see Figure 3). Hard water containing calcium and magnesium forms scale or mineral deposits on RO membranes and eventually fouls the membranes, resulting in a decline in the product water quantity and quality. Mineral scale can become permanent and decrease the life expectancy of RO membranes if not cleaned. Some source waters can foul RO membranes within hours if a softener is not used, with scale that turns the membranes literally to stone. This scale is formed because calcium carbonate is not very soluble in water. When up to 50% or more of the feed water crosses to the permeate side of the RO membrane, the calcium carbonate, which remains on the concentrate side, exceeds its solubility level, comes out of solution, and scales the RO membrane.

Softeners turn hard water into "soft" water by removing the hardness and exchanging it for sodium (see Figure 4). Resin beads within the tank have a high affinity for the cations calcium and magnesium (both divalent bonds) that are present in the source water. Resin beads release two sodium ions (monovalent bond) for each calcium or magnesium molecule captured. Sodium chloride is highly soluble and does not deposit scale on the RO membranes, and is rejected by the RO quite readily to the drain.

Hardness is measured in grains per gallon or mg/L. Softeners are sized in grains of capacity. A source water analysis that states the level of the hardness as CaC[O.sub.3] is important in determining the size of the softener needed.

The softener can be placed before or after the carbon tanks. If the softener is placed before the carbon tanks, decreased softener resin life may occur if the resin is exposed to detrimental levels of chlorine or chloramines in the incoming water. If the softener is placed after the carbon tanks, the water processed by the softener will not contain chlorine/ chloramines, which can allow microbial growth within the softener, increasing the bacterial bioburden within the softener and downstream to the RO membrane. Most facilities place the softener prior to the carbon tanks because protecting the system from bacterial growth is more important than the expense of periodically replacing the softener resin.

The softener needs regenerating on a routine basis with concentrated sodium chloride solution (brine) before the resin capacity is exhausted. Like multimedia filters, during normal operation, the water flows downward and can tightly pack the resin. Before the regeneration process, the resin is backwashed to loosen the media and rinse away any particulates. After the backwashing step, the brine solution is drawn into the tank to regenerate the resin. During regeneration, the calcium and magnesium ions are overwhelmed by the number of sodium ions and forced off the resin bead sites. Next, the excess salt solution is rinsed out of the tank.

Regeneration is usually performed every day or every other day the softener is used at a time when the water treatment system is not in use. High water flow and pressure are required for backwashing; therefore, one pretreatment component or tank is backwashed at a time. Most HD facilities use a permanent softener that incorporates a brine tank and control head to execute the automatic regeneration cycle. Automatically regenerated softeners must be fitted with a regeneration lock-out device to prevent the regeneration process from occurring during patient treatments, averting the possibility of highly concentrated sodium levels being transported to the patients (AAMI, 2014a).

Portable exchange softeners (softeners that are regenerated off-site) are sometimes used in areas that regulate the amount of sodium chloride discharged to drain. In this case, the softener tank will be replaced on a routine basis and will not have a control head or brine tank. This type of softener may also be used on single patient portable RO systems in acute HD settings for quick turn-around and ease. Many acute HD programs do not use softeners on portable ROs due to the size and weight of the softener tanks. While this may mean the RO membranes will need replacement earlier, the RO will reject the calcium and magnesium so the patient is not adversely affected. If portable exchange softeners are used, the water treatment vendor is expected to ensure the empty tank is disinfected and rinsed before it is filled with the regenerated resin, and care must be taken to keep medical use and nonmedical use resins separated during processing (AAMI, 2014a).

Monitoring. Done by testing water hardness post-softener and observing pressure gauges pre- and post-softener. A hardness test using an ethylene-diaminetetracetic acid (EDTA) titration test, or dip and read test strips on the effluent softened water should be done at least once, at the end of the day and recorded (AAMI, 2014d). Testing at the end of the day is done to validate the softener removed hardness all day. While doing an additional test at the beginning of the day is optional, this would determine whether the softener was regenerated adequately during the night. Hardness test results should be less than 1 grain per gallon (gpg) hardness (less than 17.5 mg/L) and performed on water just processed, not water that has been in the tank an extended period of time. Start the water treatment system approximately 15 minutes prior to drawing the sample. A shorter interval is acceptable for the smaller portable systems. If the hardness test reads above 1 gpg, the softener may need regenerating before use. Check the timer in the control head to see that it displays the correct time, and read and record the pressure from the gauges pre- and post-softener daily to assure the softener is not clogged (CMS, 2008b).

Mandatory or optional? Optional.

Brine tank. Brine tanks provide a concentrated salt solution for use in recharging the softener. The brine tank contains the salt pellets and water used to create the super-saturated salt solution (brine) used for softener regeneration. Fifteen pounds of salt are required to regenerate one cubic foot of resin (30,000 grain capacity). Only refined, pellet-shaped salt should be used. Salt designated as rock salt may contain too many impurities, such as dirt, that may damage or clog the brine tank and softener control head (AAMI, 2014d). Use of rock salt can allow the formation of a "salt bridge." If a salt bridge has formed, the salt above the bridge will not dissolve into solution, preventing the softener from regenerating to full capacity and decreasing the time the softener will function.

Monitoring. Visually inspect the salt level in the tank daily. The tank should be at least half-full of salt. Record the level of salt in the tank daily

Mandatory or optional? Mandatory for systems using a regenerated softener.

Anion exchange resin tanks (or organic scavenger tanks). Anion exchange tanks remove organic material from the source water that would mask adsorption sites of the carbon media. Organic scavenger tanks can increase the life of the carbon tank when placed before the carbon tanks. A test on the supply water for high levels of tannins (a plant chemical from decomposing leaves), lignines (a complex polymer in plant cell walls and wood), and total organic or oxidizable carbon (TOC) will determine whether an organic scavenger is necessary in a system. Seasonal changes will affect levels of TOC, lignines, and tannin in the source water.

Anion exchange tanks work on a similar basis as softeners, but instead of exchanging sodium, a cation, they swap chloride, an anion, for organic matter. These tanks are backwashed to relieve any compacting and remove sediment, but the backwash cycle does not regenerate the anion exchange media. Once an anion exchange tank is exhausted, it needs to be regenerated. If the tank does exhaust, the trapped organics will be released and could mask the carbon resin, causing it to fail.

Monitoring. An inline TOC monitor can detect when organic chemicals are breaking through, or a water sample can be sent to a laboratory for analysis. The most cost-effective plan is to regenerate the tank routinely according to the manufacturer's recommended schedule, based on an analysis of the source water. The tank should also be equipped with a visible timer and pre- and post-pressure gauges to be read and recorded daily. If portable anion exchange tanks are used, the tanks must be disinfected and rinsed before refilling, and a separate process for resins used for biomedical purposes must be in place at the exchange facility (AAMI, 2014e).

Mandatory or optional? Optional.

Carbon filters. Carbon filtration is the primary tool used to remove total chlorine. Chlorine and chloramines are added to the city water supply to disinfect the potable water and reduce the risk of bacterial contamination in the city water distribution system. Both can be harmful to patients if not reduced to safe levels in the water used for HD. The maximum allowable level for chlorine is 0.5 ppm, and the allowable level for chloramine is 0.1 ppm. To simplify testing, it is recommended that a test that checks for both chlorine and chloramine be used (i.e., test for total chlorine), with a maximum allowable level of 0.1 ppm. Recognize that the test result must be less than 0.1 ppm for the water to be safe for patient use. While not required, the use of a low-level test (i.e., a test that detects levels of total chlorine between 0.0 and 0.1 ppm) alerts the user of the need for action prior to reaching the maximum allowable level.

These additives allow us to drink water with minimal risk of becoming ill from a parasite or pathogenic bacteria. However, there are some drawbacks to the disinfectants themselves. For instance, chlorine can combine with other organic chemicals to form trihalomethanes, which are known carcinogens. For this reason, chloramines, a combined chlorine that cannot combine with other chemicals, has become a major disinfectant of drinking water. However, as compared to chlorine, a longer contact time is required for chloramine to be removed by carbon filtration. Since the initiation of chloramine use, there have been more reported incidents where patients suffered hemolysis and other symptoms related to chloramine exposure compared to similar reported instances with chlorine (Ackerman, 1988; FDA, 1988; Luehmann et al., 1989).

In addition to serious risks exposure to chlorine or chloramines present to patients, neither chlorine nor chloramines are effectively removed by RO, and either can actually damage the thin film-type RO membranes. Therefore, chlorine and chloramines must be removed from the water before the water enters the RO system. In a DI system, chloramines must be removed before DI because there is a possibility that carcinogenic nitrosamines may develop if non-carbon filtered water enters the DI bed (Kirkwood, Dunn, Thomasson, & Simenhoff, 1981).

Carbon filtration removes chlorine and chloramines by adsorption and a chemical reaction called catalytic reduction. Adsorption occurs as the incoming water flows down through the granular activated carbon (GAC), and solutes diffuse from the water into the pores of the carbon and become attached to the GAC structure (see Figure 5).

An additional mechanism of GAC reduction of total chlorine is a chemical reaction. Contact with the activated carbon reduces the chlorine into a non-oxidative chloride ion. While this reaction removes free chlorine very rapidly, it takes much longer to remove chloramines because that reaction is a two-step process (DeSilva, 2000, Gaur, 2013). GAC also adsorbs a wide variety of naturally occurring and synthetic organic compounds, such as herbicides, pesticides, and industrial solvents (Luehmann et al, 1989).

GAC can be made of many different organic materials, such as bituminous coal, coconut shells, peach pits, wood, bone, and lignite that have been exposed to excessive temperatures without oxygen so it does not burn. GAC is then acid washed to remove the ash and etch the carbon to increase its porosity and adsorbency. Acid washing prevents leaching of metals, such as aluminum, from the GAC. Non-acid-washed carbon may be used but should be rinsed thoroughly before the first use (AAMI, 2014d).

GAC is rated in terms of an iodine number that measures the ability of the GAC to adsorb low molecular weight, small organic substances such as iodine, chlorine, and chloramines. The higher the iodine number, the more chlorine and chloramines will be adsorbed. An iodine number of 900 (i.e., each gram of carbon will adsorb 900 mg of iodine) or greater is considered optimal for chlorine and chloramines removal (AAMI, 2014e).

Though not required, another rating to consider with GAC is the abrasion number. The higher the abrasion number, the more durable the carbon. A higher abrasion number may allow carbon to last longer, as frequent backwashing of the carbon tanks can be wearing on the carbon.

Regenerated carbon that is reburnt and reused by the manufacturer, must not be used for HD; only virgin carbon may be used (AAMI, 2014e). Carbon adsorption is used in many toxic applications, and when regenerated, the reused carbon can retain impurities that may be toxic to patients. Mesh size refers to the actual size of the carbon particles. It is recommended that GAC have a mesh size of 12 x 40 or smaller to provide a large surface area, but not too small, or the smaller particles will compact, and flow will be impeded through the bed (Luehmann et al., 1989). Simply stated, this means carbon particles will fit through a mesh screen that has 12 evenly sized holes per linear inch, but not fit through a mesh screen with 40 evenly sized holes per linear inch. New carbon must be rinsed before the first use by flushing water thoroughly through the tank to remove the ash and carbon fines (small pieces of carbon), or these will damage the RO pump and membrane.

At least two carbon beds must be used in a series configuration (where the water exiting the first tank feeds the next tank), and there must be a sample port after the first tank, and another sample port after the second tank (see Figure 6). Sometimes tanks are arranged as a series-connected pair (the water stream is split and feeds into two or more parallel sets of carbon tanks) so each tank can be smaller. Whether arranged in series or in parallel, each tank or group of tanks must provide five minutes of empty bed contact time (EBCT) for a total of at least 10 minutes EBCT at the maximum anticipated flow rate, and the water flow through the tanks should be equal. A five-minute exposure time of the water through the first tank or set of carbon tanks is required to assure the total chlorine level in the water leaving the tank is reduced to less than 0.1 mg/L (AAMI, 2014c) with the second tank (or set of tanks) providing an equal level of removal. The contact time can be calculated using the input flow rate (Q) in gallons per minute (gpm) and the volume of carbon media in cubic feet (V). Use the following formula to calculate EBCT (AAMI, 2014d):

EBCT = (V/Q) x 7.48 (7.48 is the number of gallons in a cubic foot of water)

where V = volume of carbon and Q = flow rate in gallons per minute

Portable single-patient systems used in the acute or home care setting are allowed to meet the requirement to reduce the chlorine level to below 0.1 mg/L with less than a 10-minute EBCT. Usually, this means using carbon block technology. Solid block activated carbon (SBAC) is a densely compacted block of GAC powder that provides a large surface area in a compact size. A single patient carbon filtration system may use a GAC tank and an SBAC as the polisher, or may use two SBACs in series. The manufacturer of the SBAC is required to show results equivalent to a 10-minute EBCT; that is, the block carbon technology is capable of achieving the required reduction of total chlorine.

GAC has a finite capacity and will eventually be exhausted. The ability of the carbon to remove chlorine and chloramines is affected when other substances mask the reactive sites of the GAC when the pH of the water increases or the temperature decreases. These variables make it impossible to predict when the carbon may exhaust and make frequent testing mandatory. The total chlorine level must be checked before every patient shift, or if there is no definite patient shift, every four hours (CMS, 2008a).

Monitoring. Carbon tank monitoring is accomplished by testing the chlorine level as it leaves the first or "worker" tank. The N,N-diethyl-p-phenylene-diamine (DPD)-based test kits or equivalent (dip and read test strips) are recommended. There are low-level dip and test strips available that allow determination of lower levels of total chlorine, enabling identification of an upward trend and the ability to proactively replace the carbon filters. Quality control procedures, such as testing meters or strips against known standards, are important with any method chosen.

If the total chlorine level after the first tank (or group of tanks) rises to 0.1 mg/L or above (a positive test result), total chlorine must be immediately checked after the second tank (or group of tanks). As long as the test is less than 0.1 mg/L after the second tank, HD treatments may resume, with arrangements made to change out the first tank(s) within a 72-hour period, and more frequent total chlorine testing (e.g., testing every 30 minutes to two hours) per facility policy (CMS, 2008a). If the test result after the second carbon filter(s) reaches 0.1 mg/L or greater, all treatments must be stopped immediately to protect patients from harm.

When replacing the carbon, if practical, the used second carbon tank may be placed in the first position, and the new tank put in the second spot. If it is not possible to switch the position of the tanks, both tanks should be rebedded or replaced. Bypass valves to allow the feed water to completely bypass the carbon tanks should not be placed on the piping to the carbon tanks because this could present a patient safety issue. If any bypass valves are present, they should be labeled with warnings and locked in the open position (e.g., via zip tie or cinch plastic tie) so the valve cannot be accidentally repositioned.

Inherent problems with carbon tanks are channeling (when water follows the same path through the tank because water tends to flow in the path of least resistance), compaction resulting in smaller carbon fines, and biological fouling because carbon is an organic medium. These issues cause the carbon surface area to be underutilized. To avoid these issues, carbon tanks are backwashed on a routine basis to "fluff" the bed, clean the debris out, and expose unused binding sites of the carbon. Backwashing does not remove adsorbed chlorine or regenerate the carbon. When the carbon adsorption sites are exhausted, the carbon must be replaced.

Cartridge or exchange carbon tanks may be used. These are not back-washable and must be replaced on a more frequent basis. In all cases, the emptied tank must be disinfected and rinsed before repacking with new GAC.

Monitoring the carbon tanks also includes documenting pre- and post-tank pressures, and checking the clock on the backwash timer for the correct time so the timer does not begin a backwash cycle while treatments are occurring. Records should document when the carbon tanks have been exchanged or re-bedded, and include the grade of carbon used and the length of time the new carbon is rinsed before use. EBCT should be calculated during the initial validation of a newly installed water treatment system, after carbon beds have been replaced, and any time flow rates in the RO system have changed.

Mandatory or optional? Mandatory.

Reverse Osmosis Systems

RO systems are composed of several parts, including cartridge prefilters, RO pump and motor assembly, RO membranes, and quality monitors.

Cartridge prefilter. Prefilters are used to protect the RO from particulates. These filters are positioned after all pretreatment components and immediately before the RO pump and membranes. Carbon fines, resin beads, and other debris exiting the pretreatment components can destroy the pump and foul RO membranes. Typically, prefilters range in pore size from 1 to 5 microns. The housing of the prefilter must be opaque to deter algae growth (AAMI, 2014e).

Monitoring. Gauges are used to monitor the filter inlet and outlet pressures. If the delta pressure increases by approximately 8 PSI or greater over the difference in pressures when the filter was new, the filter is clogged and needs replacement. Prefilters are inexpensive insurance against damaging more expensive items downstream in the system, so changing these on a set schedule (e.g., monthly) is a good practice. When removing the old filter, inspect the filter's center tube for soiling. If dirt is present, the filter was overburdened and should have been replaced sooner. Read and record pre- and post-filter pressures and the delta pressure daily.

Mandatory or optional? Mandatory with RO systems.

RO pump and motor assembly. The RO pump (the noisy thing you hear in the RO room) increases water pressure across RO membranes to make pure water. RO systems typically operate with pressures between 200 to 250 PSI.

RO pumps must be made of high-grade stainless steel, inert plastics, or carbon graphite-wetted parts. Pumps containing brass, aluminum, copper, and other metals will leach contaminants into the water and are not compatible with peracetic acid-type disinfectants. Operating RO pumps dry will cause irreparable damage.

Monitoring. Monitor the inlet and discharge pressures continuously and record daily.

Mandatory or optional? Mandatory with RO systems.

RO membranes. The RO membrane is the heart of the system. These membranes produce the purified water by the process of reverse osmosis (see Figures 7 and 8). Osmosis is a natural process where water moves across a semi-permeable membrane from a solution with a lower solute level to a solution with a higher solute level. This can be restated as a process where water moves from a solution with a higher water concentration to a solution with a lower water concentration. Dissolved solutes take up space, so a solution with more solutes contains less water (Hellebrand, Allen, & Hoffman, 2017; Lodish et al., 2000).

RO is the opposite of osmosis in that hydraulic pressure is used to overcome osmotic pressure, causing water to flow in the opposite or unnatural direction from a compartment with more concentration of solutes across a semi-permeable membrane to the compartment with less concentration of solutes (see Figure 9, in which the circles represent solutes). Natural osmotic flow is reversed, and pure water passes through the membrane, leaving the dissolved solids (salts, metals, etc.) and other solutes behind on the concentrated (or waste) side. In an RO system, hydraulic pressure overpowers osmotic pressure. Depending on how much product water is needed, the RO system will have one or more membranes.

RO membranes are the tightest membrane used in HD--they have pores that are much smaller than those in a dialyzer membrane. RO membranes reject to the drain dissolved inorganic elements, such as ions of metals, salts, chemicals, and organics, including bacteria, endotoxin, and viruses. Approximately 95% to 99% of charged ionic particles are rejected, while contaminants that have no charge (such as organics) are sieved out if they are larger than 200 molecular weight. Ionic contaminants are highly rejected compared to neutrally charged particles, and polyvalent ions are more readily rejected than monovalent ions. Incoming water pH and damage to the membranes will alter the function of the RO and its rejection characteristics.

Thin film (TF) RO membranes made of polyamide (PA) are the most common type used in HD. These membranes are made with a thin, dense, semi-permeable membrane over a thick, porous substructure for strength and are spiral-wound around a permeate collecting tube. The spiral design allows a large surface area to be created in a small space. The incoming water stream will split into two streams--one of purified water that has crossed the membrane and the other a waste or "reject" stream used to carry rejected solutes to the drain. This is known as cross flow filtration.

TF RO membranes will degrade when exposed to oxidants, such as chlorine/chloramines, and therefore, must be preceded by carbon adsorption. Bleach cannot be used to sanitize TF RO membranes. Care must be taken with the use of peracetic acid products for disinfection because they will oxidize the RO membrane if used above a 1% dilution, if left in contact with the membrane longer than 11 hours, or if iron deposits and other metals are present on (or within) the RO membrane. Other factors that can influence RO membrane performance and water quality include incoming water temperature and pH, adequate pretreatment, and cleanliness of the RO membrane surface (Dow Chemical 1998b).

TF membranes have a wide pH tolerance from 2 to 11, with an optimum pH range of 5.0 to 8.5. High alkalinity increases potential for scaling, or deposition of substances on the membrane surface, reducing the available surface area (Dow Chemical 1998a).

Monitoring. RO membrane performance is measured by percent rejection. Final product water quality is measured by conductivity and displayed as either micro-Siemens/cm or total dissolved solids (TDS). TDS is sometimes displayed as mg/L and sometimes as parts per million (PPM), which are equivalent terms (there are 1 million milligrams in a liter). Either percent rejection or permeate water quality monitors must be used and continuously displayed, and must have audible and visual alarms when quality set points are exceeded. The biomedical technician supporting the facility should know this set point and be able to explain to a surveyor when the quality alarm will sound. When an RO is the final treatment component, the audible alarm must be able to be heard and seen in the patient care area. To prevent potential patient harm, if a predetermined set point is violated, the water for use should divert to drain. Small portable RO systems are exempt from the divert-to-drain standard because one-to-one monitoring usually exists. If the quality of water produced by a portable system falls below the set quality limit, the treatment must be discontinued and the medical director notified (AAMI, 2014d).

Percent rejection alone only measures membrane performance. For example, if the source water is relatively pure, containing 100 PPM dissolved solids (metals, salts, etc.), and the percent of those dissolved solids that are rejected to waste equals 95%, the final water quality measure would display 5 TDS mg/L or PPM (i.e., have 5 PPM of dissolved solids). However, if the source water had as much as 1,000 PPM dissolved solids and the percent rejection continued to be 95%, the final water quality measure would then be 50 PPM (i.e., have 50 PPM of dissolved solids). In each scenario, the percent rejection is the same 95%, but the final quality of the water is significantly different. Recognize that the onsite measurements for TDS or PPM cannot tell you what contaminants are included in that rise in dissolved solids. An AAMI chemical analysis is the only way to know what levels of each contaminant remain in your treated water. CMS requires that an AAMI water chemical analysis be done at least annually and if the treated water quality falls below a 90% rejection rate; some state regulations require more frequent testing. If the water quality falls below the preset quality limits, the medical director must be notified to determine whether to continue treatments (CMS 2008b). It is important to note that CMS states: "The use of water outside of AAMI standards should be extremely rare, considered only when no other option is available to provide desperately needed HD, and limited to one treatment per patient" (CMS, 2008a).

AAMI has determined the maximum allowable levels of contaminants that can safely be in the water for HD without causing harm (see Table 2). Usually, RO systems can produce water that meets the AAMI standards if the source water is drinking water that meets EPA guidelines. A two-stage RO, in which product water from one RO is fed into a second RO, is sometimes used for extra purification. Deionization may also be used to polish RO water when the product water from the RO does not meet the quality standard.

RO systems, pumps, HD machines, and other equipment each require a minimum flow rate and pressure to operate properly without damage. RO system pressure gauges typically measure the inlet water supply, pump, reject water (or waste), and product water pressures, which are displayed as pounds per square inch (PSI) or in actual gallons per minute (GPM) using flow monitors. Percent recovery (not to be confused with percent rejection) of a large RO system is generally set between 50% to 75%, meaning that if the RO has a flow of 8 GPM and a 50% recovery, half (4 gallons) of the incoming water is being made into product water and the other half (4 gallons) will go to the drain or be recycled back into the feed water line. With 75% recovery, 75% of the water entering the RO is made into product water, and 25% goes to the drain or recycle. Many RO systems will recycle some of the reject stream to increase the flow into the RO and to conserve water (called "waste recycle"). Most RO distribution systems will return the unused purified product water back to the system to decrease water wastage (Dow Chemical, 1998b; Hedlund & Robertson, 2015).

All gauges and flow meters should be maintained within the manufacturer's specifications, and readings should be recorded daily. Water quality (conductivity or TDS) should be within the limits defined for the facility, checked against an independent device routinely (e.g., weekly or monthly, per facility policy), and recorded at least daily. Percent rejection should be above 90% and documented daily. While it is true for all measurements on a water treatment system, it is especially important to include the expected parameters for water quality on the log sheet. These parameters should be consistent with the manufacturer's recommendations. Every application is unique; thus, these parameters should be determined during the initial system validation performed at installation. Trend analysis is vital for monitoring water treatment systems. Monitoring trends allows the user to be more proactive and to see a problem arising, rather than "putting out fires."

Scale deposits, such as calcium and magnesium salts, silt, metals, organics, and dirt, will accumulate on and eventually foul the exterior surface of the RO membrane. Routine cleaning, usually quarterly, will strip off the scale and silt build up. High pH cleaners will remove the silt and dirt slime layer, and low pH cleaners strip the mineral scale and metal build up.

Disinfection regimens vary widely, but at least once a month is routine for the central RO (AAMI, 2014d). A method to prevent disinfectant from being delivered to patients (e.g., disinfection lock-out) must be provided by the manufacturer (AAMI, 2014e). Portable RO systems should be disinfected according to the manufacturer's instructions, and more frequently if the equipment is not operated for several days or if test results indicate the disinfection schedule is not sufficient to allow compliance with AAMI microbiological quality requirements (AAMI 2014c).

The potential for bacterial proliferation can be diminished by operating the equipment for at least 15 minutes each day, regardless of whether or not a treatment is being performed. Another approach would be to add a bacteriostatic agent (e.g. sodium bisulfite) to reverse osmosis systems that are to be stored. If a bacteriostatic agent is used, the machine should be clearly labelled to indicate the presence of that agent (AAMI, 2014d, p. 79).

Mandatory or optional? Either an RO or a DI system is mandatory. A quality monitor is mandatory.

Deionization Systems

DI is seldom used as a primary water treatment method for in-center HD, but it may be used as a back up. Facilities that use DI as an emergency back up to the RO may have the tanks offline in a "dry" stage ready for use as needed, or have an agreement with a DI vendor to deliver the tanks quickly in case of an emergency. DI is sometimes required to 'polish' the water when RO alone cannot reduce the contaminants to levels within AAMI standards.

DI is more frequently used in acute or home settings for individual patients. With the advent of portable RO systems, use of DI in those settings is declining. NxStage Pure Flow (an individual patient HD system with a disposable water treatment system) uses DI as the primary water treatment component (NxStage Medical, Inc., 2015).

DI tanks contain resin beads that remove both cations and anions from the water in exchange for hydroxyl (O[H.sup.-]) and hydrogen ([H.sup.+]) ions. The ions released combine to form pure water ([H.sub.2]O) (see Figure 10). DI tanks can be either dual bed or mixed-bed varieties. Dual bed setups require at least two tanks because one tank contains all cation-attracting resin beads, and the second tank has all anion-attracting resin beads. The water flows in series from one tank to the second to remove the unwanted ions. Mixed-bed deionizers contain both cation and anion-attracting ions in one tank and produce a higher quality of water than dual beds. Dual beds may be used as long as the dual beds are followed by at least one mixed-bed DI tank. It is recommended that when DI is in place, at least two mixed beds are used in a series configuration so that if the first tank exhausts, it can be taken offline and the second one used for a short time, with constant monitoring, until the first DI is replaced (AAMI, 2014e).

Particles without an electrical charge are not removed by DI, which means DI does not remove non-ionized substances like bacteria and endotoxin, plus the DI resin provides a conducive environment for microbial growth. Because of the potential for bacterial contamination, DI must be followed by an ultrafilter so the downstream components are not contaminated and patient safety is not compromised (AAMI, 2014e). Even when DI is coupled with an ultrafilter, it is unable to remove low molecular weight bacterial by-products such as microcystins (toxins from blue-green algae) that can be deadly to patients. Carbon filtration must precede DI; otherwise, carcinogenic nitrosamines can develop when water that is not carbon filtered contacts the resin beads (AAMI, 2014e; Kirkwood et al. 1981; Luehmann et al., 1989).

DI resins retain all ions' accumulated contaminants until the resins reach an exhaustion point. Before this occurs, the DI tank must be exchanged for a new one. If a DI is used past its point of exhaustion (measured by less than 1 meg-ohm/cm resistivity, equal to a conductivity less than 1 microsiemen/cm), the resins will release mass quantities of the more weakly attracted ions to accommodate ions with higher attraction. Weakly attracted ions like aluminum and fluoride would be among the first "dumped" (see Figure 11). In essence, an exhausted DI tank can serve as a "multiplier" of contaminants. For example, if the incoming water has 10 PPM of fluoride, when the DI tank exhausts, as much as 1,000 PPM of fluoride could be dumped at once into the product water. Patient injuries and deaths have occurred when DI was used past the point of exhaustion (Luehmann et al., 1989).

When the DI bed is exhausted, the resin must be replaced with medical (or potable water) designated resins (AAMI, 2001; FDA 1996; Luehmann et al., 1989). DI is used for many industrial applications, such as in chrome plating factories, which can leave the resin full of toxins and heavy metals. These industrial resins could harm patients and should be regenerated separately from resins used for HD. As with other components, the emptied tanks should be disinfected at the time of regenerating to prevent pyrogenic episodes in patients.

With all the risks that DI presents, it is not recommended as the sole treatment component for multiple patients.

Monitoring. DI must be monitored continuously with a temperature-compensated audible and visual resistivity alarm that can be heard and seen in the patient care area. DI must also have a divert-to-drain mechanism to prevent patient exposure to unsafe water by automatically sending water to the drain if it does not meet the quality set point (AAMI, 2014e).

Resistivity, which is the inverse of conductivity, must be monitored continuously, should read above 1 meg-ohm/cm, and be recorded twice daily (AAMI, 2014e). Pre- and post-DI tank pressure readings should be read and recorded daily. DI tanks should be exchanged on a regular basis even if the resin is not exhausted due to the microbiological fouling potential.

Mandatory or optional? Optional if an RO system is in use.

Post-Treatment Components

Post-treatment components include ultraviolet irradiators, endotoxin retentive filters, submicron filters, and ultrafilters.

Ultraviolet (UV) irradiator. UV is a low-pressure mercury vapor lamp enclosed in a transparent quartz sleeve that emits a germicidal 254 nm wavelength, delivering a dose of radiant energy in order to control bacteria proliferation. The UV is able to penetrate the cell wall of the bacterium and alter the DNA to either kill it or render it unable to replicate (Byrne, 2015).

It is possible for some species of bacteria to become resistant to the UV irradiation, which is more of an issue if bacteria are exposed to sub-lethal doses. To prevent this, the irradiator must be equipped with a calibrated ultraviolet intensity meter that delivers a minimum dose of radiant energy at 16 milliwatt-sec/[cm.sup.2] and activates a visual alarm that indicates the lamp needs to be replaced. If the UV is not equipped with an intensity meter, the dose of radiant energy delivered must be at least 30 milliwatt-sec/[cm.sup.2]. As the UV kills the bacteria, it may increase the level of endotoxin in the water as a result of the destruction of the gramn-egative bacteria (endotoxin-producing) cell wall where endotoxins harbor. To trap the endotoxin, UV must be followed by ultrafiltration (AAMI, 2014e).

UV irradiation may also be placed on the feed side of the water treatment system after all pre-treatment components (e.g., post-carbon tank) and before the RO. This will diminish the bacteria exiting from the tanks and reduce the bioburden to the RO membranes. An appropriately sized UV for the expected water flow and an easy-to-clean quartz sleeve would increase the effectiveness of the UV in this position.

Monitoring. Record daily the output of the radiant monitor and readings of any pressure gauges associated with the UV. Regular maintenance of the UV device includes replacing the lamp when the radiant output indicates or at least annually (or every 8,000 hours operation). Biofilm, a protective slime coating that bacteria secrete when they attach themselves to a surface, will decrease the effectiveness of UV. Routine cleaning of the quartz sleeve will remove the biofilm.

Mandatory or optional? Optional.

Endotoxin retentive filters, submicron filters, and ultrafilters. Endotoxin-retentive filters, submicron filters, and ultrafilters reduce the level of bacteria/endotoxin in the final product water. A submicron filter reduces the level of bacteria in the final product water, whereas an ultrafilter or endotoxin retentive filter removes both bacteria and endotoxin. Each are membrane filters that can be cross flow types with a feed stream, product stream, and reject stream (like RO membranes), or a dead-ended design with one stream (see Figure 12).

It is recommended that any submicron, endotoxin-retentive filters, and ultrafilters used in water treatment systems be validated for medical use. There are "nominal" and "absolute" ratings for ultrafilters and submicron filters in the industry. "Nominal" generally means "as stated on the label." Absolute ratings are more appropriate for HD applications because they are derived from a validation process. Filters that are not for medical use may contain preservatives that require 500 to 1,000 gallons of water to thoroughly rinse. One incident occurred in New York in 1989 that was caused by the use of a commercially available, non-medical filter. Sodium azide, a desiccant and preservative, was inadequately rinsed from the filter, and this exposure caused nine patients to experience life-threatening hypotension, blurred vision, abdominal pain, headache, and loss of consciousness shortly after treatments began (FDA, 1989).

Whenever DI or UV is used, ultrafilters must follow these devices. Ultrafilters give added benefit when placed at points of use, such as at the source for reuse water, bicarbonate fill station, and in the dialysate flow path of each HD machine (Cappelli, 1991).

Submicron, endotoxin-retentive filters, and ultrafilters, even though they eliminate microbes, are targets for bacteria infestation if not routinely cleaned and disinfected or replaced. Membranes can become fouled with bacteria that can actually grow through the membrane, contaminating the product water.

Monitoring. The pressure differentials pre- and post-filter should be monitored continuously and documented at least daily. There should be some difference between the inlet and outlet pressures. If these pressures are the same, it is possible that the water is flowing around the filter rather than through the membrane. On the other hand, too great a difference ("delta") between the inlet and outlet pressures indicates the membrane is clogged. Filters operated in the cross flow design should be fitted with a flow meter to monitor the waste stream.

Mandatory or optional? Mandatory if using DI or UV; otherwise, optional.

Water Distribution System

Product water distribution systems can be grouped into two categories: direct feed and indirect feed. A direct feed system "directly" delivers the product water from the final treatment component to the product water loop for distribution (see Figure 13). DI systems do not include a return loop. With an RO system, unused product water is usually re-circulated back into the RO unit to reduce water wastage. An indirect feed system involves a storage tank that accumulates the product water and delivers it to the distribution loop (see Figure 14). Unused portions of the product water are typically sent back into the storage tank. The RO will stop and start filling the tank based on the high and low level switches in the storage tank.

Water storage. The water storage system is used to store product water until needed for HD. Water storage and distribution systems contain large amounts of water that no longer include chlorine or chloramine to prevent microbial growth. The larger volume and surface area increases the potential for biofilm formation. The storage tank should be designed to minimize the growth of bacteria by having a conical or bowl-shaped bottom to allow for complete emptying and have a tight-fitting lid that is vented to air through a hydrophobic 0.45 m air filter to prevent microbes from entering the tank. The tank should be designed for easy, frequent disinfection and rinsing with an internal spray mechanism. Storage tanks must be made of inert materials that do not leach contaminants into the purified water, and the size of the tank should be in proportion to meet the facility's peak demands, no larger (AAMI, 2014e; FDA, 1996; Luehmann et al., 1989). Storage tanks require a recirculation pump made of inert, non-leaching materials that can withstand the higher velocities of flow needed to supply water to a group of HD machines. The recirculation pump operates continuously, 24 hours per day, seven days per week.

Monitoring. Bacteria and endotoxin levels must be monitored after the storage tank, and the air vent filter should be replaced routinely. Record pre- and post-pressures of the distribution pump(s) daily.

Mandatory or optional? Optional.

Water distribution piping systems. Water distribution piping systems carry product water to the point of use. A continuous loop design where the water returns to the storage tank or to the RO unit will conserve water and is recommended. No deadends or multiple branches should exist in the distribution system because these allow water to stagnate and bacteria and biofilm to grow.

Highly purified water is very aggressive and will leach metals and chemicals from materials with which it comes in contact. Polyvinyl chloride (PVC) is the most common piping material used in the United States for HD because of its low cost and relatively inert nature. Other substances that may be used include, but are not limited to, chlorinated PVC (CPVC), polyvinylidene fluoride (PVDF), polyethylene (PE), cross-linked polyethylene (PEX) polypropylene (PP), and stainless steel (SS). Though these materials may be more inert than PVC, they tend to be more expensive. That said, the use of materials other than PVC is becoming more common. Extreme attention to detail in installing the distribution system is imperative: if the system is plumbed improperly, many problems can result, wasting time and money, and potentially placing patients at risk of harm. Copper, brass, aluminum, lead, zinc, or other toxic substances must not be used in the piping, and the piping must not contribute bacterial contamination. The inner surfaces of the joint connections should be as smooth as possible to avoid microbiological adhesion; smooth, beveled edges should be used in connections (rather than hacksawn edges); simple wall outlets with the shortest possible fluid path and minimum pipe fittings are recommended (Luehmann et al., 1989).

The ANSI/AAMI RD 52 document (AAMI, 2004) included a recommendation that the flow velocity in the distribution system be maintained at 1.5 feet/second for direct feed systems, and 3.0 feet/second in indirect feed systems. Because there is no evidence that a certain velocity will prevent biofilm formation, the current ANSI/AAMI standard (AAMI, 2014e) does not specify a recommended flow velocity in the distribution system.

Monitoring. The distribution system should be evaluated routinely (e.g., quarterly) and the loop visually inspected (when possible) for incompatible materials that may have been inadvertently added. Loop repairs should be performed by trained personnel or a reputable plumber, and all materials used should be inspected for compatibility. Disinfection should always follow any invasive repair to the system. Bacteria and endotoxin testing should be done routinely on the loop (AAMI, 2014b; FDA, 1996; Luehmann et al., 1989).

Mandatory or optional? Mandatory unless an integrated system HD machine is used.

Disinfection of Water Systems

Routine disinfection of water treatment and distribution systems is critical to keep patients safe. Biofilms are communities of microorganisms attached to surfaces. Once bacteria and other microorganisms attach to a surface, they excrete biofilm, an extracellular polymer or glycocalyx that will both protect them from chemicals and supply nutrients to maintain life (Meltzer, 1997). Anywhere non-sterile water flows, biofilm will form. Biofilms offer bacteria and other microbes an endless supply of food and protection against most disinfectants. Even with routine chemical disinfection, biofilm can form. Biofilms form faster in slow-moving water and have a more difficult time attaching themselves in fast-moving water, but will eventually take hold.

Bleach and ozone are the most effective means for reducing or removing biofilms (AAMI, 2014d). Once a biofilm has firmly established itself, it is nearly impossible to eradicate. Many times, entire water treatment systems and distribution piping have had to be replaced to eliminate a biofilm problem.

Ozone disinfection. Ozone is a very powerful oxidizing agent in the form of a gas, O3 that is formed from oxygen being put through an electrical generator placed onsite. The ozone generated is then injected into the water. With sufficient exposure time, ozone can sometimes eradicate existing biofilms.

Ozone has a very short half-life of about 25 minutes at 20C in highly purified water. In the presence of organic and inorganic impurities, ozone will degrade more rapidly. Exposure to UV irradiation will quickly remove ozone. Ozone must always be rinsed out of the system, and its absence verified prior to the water being used for patient treatment with a test method capable of detecting ozone levels down to 0.1 ppm (mg/L), such as use of an indigo trisulfonate colorimetric test or the equivalent (Tarrass, Benjelloum, & Benjelloum, 2010). Strips and DPD tests are available for this level.

By-products of ozone in the presence of impurities (e.g., biofilm) are safe and include carbon dioxide, carboxylic acids, filterable solids, and neutralized organics (such as inactivated endotoxin). Ozone has been classified by the FDA as generally recognized as safe (GRAS). The OSHA maximum exposure level for ambient ozone is 0.1 ppm over a time-weighted average of eight hours in a five-day period (shorter exposure time to higher levels [e.g., 0.3 for 15 minutes] is acceptable). To prevent ozone from getting into the air, it is recommended that the storage tank system and piping remain closed when ozone is in use (Tarrass et al., 2010).

Ozone is not recommended for RO disinfection because the powerful oxidant will destroy the membranes. Chemical disinfection must continue to be used for the RO unit. Ozone is easy to make (using air and an ozone generator) and does not require a lengthy rinse time; thus, it is convenient to use for the storage tank and distribution piping.

All distribution piping systems are different, so each system must be evaluated for compatibility with ozone. Ozone, for example, is listed as being incompatible with PVC, the material used in most distribution pipes. However, at low levels used for disinfection purposes, between 0.3 to 0.7 ppm, the PVC is not significantly affected. Bleach is also not compatible with many materials, but at low concentrations, does not harm those materials. Ozone can be destructive to ultrafilters made of polysulfone, so ultrafilter and endotoxin retentive filter materials must be considered when deciding to use ozone (Amato & Curtis, 2002; Meltzer, 1997; Murphy, 1998).

A test based on indigo trisulfonate or an equivalent (e.g., DPD with a conversion factor) will indicate the absence of ozone in the water. An ambient air ozone test should be performed routinely to comply with OSHA-permissible exposure limits (AAMI, 2014d).

Hot water disinfection systems. The use of hot water disinfection is well known in the HD industry because many HD machines use this method for routine disinfection. In the past, hot water disinfection was not commonly used in the United States for water treatment system disinfection because heat is not compatible with PVC piping. Current practice is seeing many new facilities installing water system distribution systems that are heat-tolerant.

Generally, a minimum of 80[degrees]C for a 10-minute exposure time will perform a more than adequate disinfection of a distribution loop (and ROs with heat-compatible membranes). The temperature and contact time need to be established and validated by the manufacturer of the system. The temperature of the water in the system during disinfection is expected to be monitored and recorded at a point most distal from the water heater. Demonstration of reaching the correct temperature for the right amount of time is considered a successful disinfection (AAMI, 2014d).

When disinfecting the water and dialysate delivery systems, it is important to disinfect the incoming water line to the HD machine (Amato, 1995; Bland & Favero, 1989). This line should be disinfected with the distribution system and care taken to ensure the disinfectant is rinsed completely after an adequate exposure time is provided. During chemical disinfection of an RO system (or water holding tank), if the HD machine is turned on, this will pull the disinfectant into the HD machine through the incoming water line. This same method may be used during heat disinfection of a distribution loop, but not with ozone.


Purpose and Function

Dialysate is composed of product water mixed with acid and bicarbonate concentrates. These concentrates are available in liquid and powder forms. Liquid forms can be directly mixed with product water, while the powdered forms must first be mixed with product water.

Mixing ratio. Table 4 lists the various mixing ratios available for proportioning dialysate concentrates with product water. To reduce the potential for errors, all concentrates in a facility should be of the same mixing ratio. Note that each ratio is represented by a specific symbol: the symbol should be included in labeling of concentrate containers and machine site outlets of centrally delivered acid.

Acid Concentrate

Along with electrolytes and glucose, acid concentrate includes acetic acid to lower the pH, so when it is proportioned with water and bicarb solution (which has a pH of about 8.25), the dialysate pH will be near neutral. Liquid acid concentrate is available in gallon jugs, in 55-gallon barrels, and via tanker truck delivery. It is important that the person receiving the supply of acid concentrate check the contents of the delivery against the order, and if transferring to a storage tank, that the exact formulation of the delivery "match" the order and the labeling on the storage tank (e.g., 2 K/2.5 calcium transferred into a storage tank labeled 2K/2.5 calcium). Also in the interest of reducing the risk of errors, a limited range of acid concentrates should be available, and that "spiking" (i.e., adding a concentrated electrolyte powder to the acid solution to increase that electrolyte) be prohibited in the chronic setting and used rarely in the acute setting. Any spiking must be done by a registered nurse with specific education and training for that task. CMS has some specific regulations related to spiking in outpatient facilities, which include careful labeling of the container with the final concentration of the added electrolyte.

When acid concentrate is mixed on site from powder, it is important the manufacturer's directions are followed exactly, and any required testing is done and verified prior to the release of the mixture for storage or use. Recognize that pH testing is not reliable as a test for concentrate mixing because large variations in concentration do not produce significant changes in pH.

Bicarbonate Concentrate

Bicarbonate concentrate is available in liquid or powder for onsite mixing with product water. The shelf life of an opened bottle of liquid or mixed bicarbonate is limited due to the risk of bacterial growth and loss of CO2. Most manufacturers require discard within 24 hours of opening the liquid or mixing the powder with product water.

If mixing bicarbonate from powder, follow the directions of the powder's manufacturer, including any required testing. Beware of overmixing bicarbonate because this can result in release of carbon dioxide, altering the chemical makeup of the mixture. If a significant amount of C[O.sub.2] is lost, the solution becomes sodium carbonate, with a potential pH of 12. This change in pH causes the calcium and magnesium in the dialysate to precipitate out of solution, with potential ill effects for patients (Myron-L Company, 2012).

Integrated HD Systems

This label applies to HD systems that incorporate water treatment and dialysate preparation for single patient use. As of early 2018, there were two integrated HD systems on the market in the United States: "System One" by NxStage and "Tablo" by Outset.

NxStage Medical, Inc. (2015) provides a smaller, user-friendly HD machine with disposable blood path including the pressure monitoring system. A separate module, known as "PureFlow," is composed of a disposable water treatment system that uses carbon block technology for chlorine removal and DI as the treatment component. Redundant alarms and shutdown mechanisms protect the patient when water treatment components exhaust. Because calcium will precipitate out of mixed bicarbonate dialysate, NxStage uses lactate rather than bicarbonate as a buffer in the dialysate. This allows use of premixed, ready-to-use dialysate in 5-liter bags or a concentrate diluted by the user with AAMI-quality water in batches of 30 to 50 liters. The batch is sufficient for one to three treatments.

Outset Medical, Inc. provides a user-friendly HD machine, "Tablo," that includes an RO system as the water treatment component and carbon block technology for chlorine removal. It has a unique component that pasteurizes the RO product water to minimize bacterial growth. The Tablo uses containers of conventional acid and bicarbonate, mixing these concentrates online in real time. There are redundant alarms and shutdown mechanisms for patient safety. The touch screen user interface provides the operator with set up instructions and advice for resolving alarms (Neumann, 2016).

CMS included specifications for the use of integrated HD machines in the 2008 ESRD regulations. Under the CfC Water and Dialysate Quality, the regulation requires that the system's FDA-approved labeling is followed for machine use and monitoring of the water and dialysate quality with preconfigured, FDA-approved HD systems (CMS, 2008a). The CMS interpretive guidance allows use of this type of machine in-center and for home patients if approved by the FDA. Differences in monitoring integrated HD systems may result when following the manufacturer's directions. For example, for machines that prepare a "batch" of dialysate for more than one treatment, testing of total chlorine before the first use of each batch is sufficient. Quarterly cultures and endotoxin testing of water/dialysate produced by integrated systems are allowed.

Keeping Patients Safe from Bacteria and Endotoxins

Purpose and Function

Water and dialysate can be a source of infection or pyrogenic reactions in patients on HD. It is critical that proactive steps are taken to decrease the potential for patient harm. Routine testing of multiple sites, monitoring results for any trends, recognition of bacteria or endotoxin test results above action levels, and action to promptly correct causes must be included in every facility's program of oversight of water treatment and dialysate preparation. One purpose of water treatment components we have just discussed is to remove bacteria and endotoxin. Once the product water moves into the distribution system, risks for bacterial contamination increase. While the acid concentrate will not support bacterial growth, liquid bicarbonate is a rich nutrient for bacteria. It is imperative and required that routine monitoring for bacterial contamination of the water and dialysate distribution system be done diligently and action taken to reduce risks of patient harm.

The major change in the updates of the ANSI/AAMI standards is adoption of recommendations of lower bacterial and endotoxin levels (see Tables 5 and 6). While CMS has not yet adopted these newer standards, many HD companies have adopted the lower levels in their policies and practice. Because using the lower levels as targets is considered as more stringent than the CMS regulation, facilities would not be cited for choosing to follow the newer standards.

Bacteria Testing of Product Water

The 2014 ANSI/AAMI standards set the maximum allowable bacteria level in water used for HD at 100 colony-forming units/ml (CFU/mL), with an action level 50% of that level, or 50 CFU/mL (AAMI, 2014c). If the action level is violated, the facility must show it is taking some action (e.g., disinfection, re-assaying) to address the potential problem. At a minimum, bacterial levels should be tested monthly. Weekly bacteria assays are recommended for new systems until a pattern of compliance with the allowable level is established (e.g., one to two months) (AAMI, 2014d).

At a minimum, water samples should be collected from the first and last outlets of the water distribution loop, water entering any reprocessing equipment, water used to prepare concentrates, and water exiting the DI, ultrafilters, UV, and storage tank systems (as applicable). The outlet should be allowed to flow for 60 seconds before obtaining the sample. Sample ports should not be disinfected with bleach or betadine because the residual disinfectant will kill any potential bacteria in the sample. Alcohol may be used to clean the ports if rinsed completely (if used inside the port) or allowed to dry completely (if used on the outside of the ports) before samples are taken (AAMI, 2014d).

Bacteria Assaying Technique

Samples that cannot be assayed within four hours can be refrigerated for up to 24 hours after collection but should not be frozen. Total viable counts must be obtained using the membrane filter technique (where a known volume of water is filtered through a membrane, and the membrane is then aseptically transferred to an agar plate) or the spread plate technique (an inoculum of at least 0.1 to 0.3 mL of sample is spread over the agar). Use of a calibrated loop to apply the sample is prohibited; this method is not sensitive enough for HD bacteria testing because the sample used is too small. The 2014 ANSI/AAMI standard allows the use of either of the following culture methods for standard HD water and dialysate:

1) Tryptone glucose extract agar (TGEA) or Reasoner's 2A supplemented with 4 % sodium bicarbonate, or equivalent. Blood or chocolate agar shall not be used. Incubation temperatures of 17[degrees]C to 23[degrees]C, and an incubation time of 168 h (7 d); or

2) Trypticase soy agar (TSA, a soybean casein digest agar) or standards method agar and plate count agar (also known as TGYE), incubated at 35[degrees]C for 48 hours (AAMI 2014a).

Note: This is the method endorsed by ANSI/AAMI:RD52:2004, adopted by CMS as regulation.

Culture media must not include blood or chocolate agar because these are too nutrient-rich and will kill bacteria being tested. Colonies should be counted using a magnifying device (AAMI, 2014b). The current ANSI/ AAMI standard does not allow the use of Millipore samplers for water or dialysate cultures (AAMI, 2014d).

Endotoxin Testing of Product Water

The current ANSI/AAMI standards require a lower endotoxin level than the CMS-adopted ANSI/AAMI RD52:2004 standards. According to the ANSI/AAMI 11663:2014 standard, endotoxins in the water used for HD purposes must not exceed 0.25 EU/mL (endotoxin units/mL), and action must be taken when the level exceeds 0.125 EU/mL. Endotoxin testing is done with the Limulus Amebocyte Lysate (LAL) assay using either a kinetic assay or a gel-clot assay (AAMI, 2014a). The kinetic assay is more reliable and sensitive than the gel-clot method because it uses computer-driven spectrophotometry that calculates the amount of endotoxin. The gel-clot assay only renders a negative or positive result at a given concentration. At a minimum, two tubes should be run each time the gel-clot method is used--one for control and one for testing the sample. When drawing the water samples for endotoxin, the same techniques apply as for bacteria sampling, as long as these follow the recommendations of the test manufacturer or the laboratory, and endotoxin-free sample collection tubes are used (AAMI, 2014b).

Bacteriology of Dialysate

The same assaying techniques described above for water samples are used for dialysate samples. Routine bicarbonate concentrate sampling for bacteria is unnecessary unless it is believed to be the source of a problem. If testing of bicarbonate is needed, the concentrated sample will need to be diluted to be tested (AAMI, 2004). AAMI has set standards for three categories of dialysate purity: conventional dialysate, ultra-pure dialysate, and dialysate for infusion (see Table 6).

Conventional (Standard) Dialysate

The maximum allowable microbial level for conventional dialysate is less than 100 CFU/mL, with an action level of 50 CFU/mL. The endotoxin level should be less than 0.5 EU/mL, with an action level of 0.25 EU/mL. While the bacterial standard is the same for product water, the allowable level of endotoxins in conventional dialysate is higher than the allowable level in HD water in recognition that the components (i.e., powders) used to constitute concentrates may contribute endotoxins (AAMI, 2014c). If the action levels are violated, steps should be taken to address the issue, such as disinfection of the HD machine and/or resampling.

AAMI and CMS regulations require that dialysate samples should be collected from at least two machines per month, making sure all machines are tested within a year (CMS 2008b). Some states require all machines to be sampled within each calendar quarter. Machines tested are to be viewed as a sample of all machines; a pattern of positive test results should result in action taken to address all machines. Dialysate samples must be drawn where the fluid enters the dialyzer (AAMI, 2014d), from the Hansen connector or a port in the dialysate line for this purpose.

Assays should be repeated if bacteria or endotoxin levels in the dialysate violate the action level. For new systems, weekly testing should be performed until bacteria and endotoxin in the dialysate are within acceptable limits. If a patient exhibits an endotoxin reaction or septicemia, dialysate and water sampling should be done as close to the event as possible, along with blood cultures and other tests the medical director may dictate. If the endotoxin reaction arose due to endotoxin build up in a reprocessed dialyzer, it may be difficult to confirm. This is because LAL testing may be negative in this instance because a protein carrier, like blood, is necessary to draw out the endotoxin from the dialyzer. In facilities that practice reuse of hemodialyzers, close attention must be paid to water used for reprocessing dialyzers, and reuse practices should be evaluated with any patient reactions potentially related to exposure to endotoxin.

Ultrapure Dialysate

The case for ultrapure dialysate. Though fluid and solutes mainly flow from the blood side of the dialyzer into the dialysate and down the drain, dialyzers with highly permeable membranes, such as high-flux dialyzers, can have back-filtration and back-diffusion occurring due to their large pore size. This allows water and solutes to flow from the dialysate into the blood side of the dialyzer (Leypoldt, Schmidt, & Gurland, 1991). This may allow endotoxins and endotoxin fragments, which are small enough to cross the high-flux porous membrane, to cause acute and/or long-term symptoms in patients.

Several research papers conclude that long-term effects of exposure of patients on HD to endotoxin and other cell fragments from gram-negative bacteria result in a chronic inflammatory response. AAMI has, therefore, taken a step toward more strict standards in dialysate. Chronic endotoxin exposure from dialysate at a level lower than that which causes an acute pyrogenic reaction (e.g., temperature spike, chills, rigors, hypotension) can stimulate pro- and anti-inflammatory activities, resulting in decreased transferrin, increased beta-2 microglobulin, and amyloidosis, leading to carpal tunnel syndrome and accelerated atherosclerosis (Canaud, Bosc, Leray, Morena, & Stec, 2000). Elevated C-reactive proteins (CRP) levels from the acute phase inflammatory response can predict mortality and morbidity in patients on HD, and have been linked to malnutrition, resistance to erythropoietin, and when combined with cholesterol and triglyceride levels, increased cardiovascular risk (Panichi et al., 2000).

Ultrapure dialysate should have a viable microbial count less than 0.1 CFU/mL and an endotoxin level lower than 0.03 EU/mL. The pour plate method, described above, is not adequate to test for this low level of bacteria. The membrane filter technique and use of lower temperatures and longer incubation time are required to achieve this level of sensitivity. For users committed to providing ultrapure dialysate, if these levels are violated, action must be taken to correct the situation. The user is responsible for developing a monitoring plan, including testing frequency, to keep microbial and endotoxin levels within the standard. Dry powder bicarbonate cartridges that are mixed with product water online during treatment are frequently used to achieve the low microbial standard because bulk bicarbonate is more easily contaminated with microbes and endotoxin (AAMI, 2004). The use of inline ultrafiltration of the dialysate may also be necessary to achieve the low microbial/endotoxin standard.

Dialysate for Infusion

In the United States, convective therapies, where a large volume of an electrolyte solution (20 to 70 L) is infused into the patient's blood as replacement fluid, is not commonplace. Hemodiafiltration and hemofiltration therapies require sterile replacement fluids. In Europe, some commercially available machines will produce the sterile solution online from conventional dialysate by sequential ultrafiltration through ultrafilter membranes. Dialysate for infusion must be sterile and non-pyrogenic (AAMI, 2014c). The manufacturer of the equipment must validate the ability of the equipment to consistently produce water that meets these requirements. The user must then follow the manufacturer's guidelines for use, monitoring, and maintenance so the equipment used will continue to meet specifications through an established process (AAMI, 2014c).

New HD Fluid Standards

With the growth of multinational corporations with interest in HD, AAMI collaborates with ISO to develop and update standards used worldwide. These standards are currently being updated, and the numbering changed for greater clarity. It is anticipated these updated standards will be released late in 2018 and will be recognized as AAMI/ISO standards. See Table 2 for a crosswalk from previous to current and future standards.

As mentioned earlier, the major difference in the standards adopted by CMS as regulation and the current standards are the lower levels for bacteriology and endotoxin tests results. Until CMS revises the CfC, surveyors will use the older standards as the minimum requirement facilities must meet. This time should be used by facilities to develop methods to assure the new standards can be met to improve the quality of care for patients and to be prepared when CMS adopts the new standards. Because the newer standards are more stringent than the older standards, a facility that chooses to adopt the newer standards and follows those requirements would be considered in compliance with CMS requirements. CMS also requires staff members to follow the facility's policies and procedures. If your facility has adopted the newer AAMI standards, surveyors will expect you to meet those more stringent requirements.

It is important to understand that monitoring of microbiological contamination in HD water systems should focus on establishing a routine that prevents the development of growth in the system. Testing should validate that scheduled disinfections are maintaining the system in a way that contains microbiological contamination below action levels. A protocol that uses monitoring to retroactively decide when to disinfect a system will inevitably result in test results that exceed the bacterial purity standards.


Water treatment and dialysate preparation are complex but can be fascinating topics. By understanding water treatment system operation, dialysate purity issues, the nuances of patient reactions, and communicating with technicians, nephrology nurses can protect patients from unsafe water and dialysate and contribute immensely to long-term positive outcomes for patients.

Improving Your Water Treatment Vocabulary

It often seems that water treatment professionals speak a different language. Here are a few terms that may not be common to everyone.

Action level: Concentration of a contaminant at which steps should be taken to interrupt the trend toward higher, unacceptable levels.

Adsorption: A process by which molecules or particles adhere to a surface.

Anion: A negatively charged ion.

Backwash: Reverse flow through a component; may be used to flush trapped particles to drain or to prevent channeling.

Bacteria: Microscopic, single-celled organisms that can cause disease.

Bacterial bioburden: The number of bacteria living on a surface that has not been sterilized.

Biofilm: Coating on surfaces that consists of microcolonies of bacteria embedded in a protective extracellular matrix. The matrix, a slimy coating secreted by the cells, protects the bacteria from antibiotics and chemical disinfectants.

Brine: A concentrated salt solution used to flush the resin bed of a water softener. This recharges the softener with sodium chloride ions which will be exchanged for calcium and magnesium to soften the water.

Buffer: A substance that maintains the pH of a solution at a constant level, even if an acid or base is added to the solution. Bicarbonate is a buffer used to keep the pH of dialysate at the desired rate.

Cation: A positively charged ion.

Channeling: "Pathways" worn through the media within a component due to water flowing along the same routes repeatedly. Channeling reduces expected contact time and can be relieved by backwashing.

Colony forming unit (CFU): The number of living bacteria per milliliter in water or dialysate.

Concentrate: Electrolyte solution (acid or bicarbonate), which after dilution (or being mixed) with product water becomes dialysate. Also refers to the reject stream of an RO, in which the dissolved solids from the feed water are concentrated.

Conductivity: The extent to which a solution allows an electric current to move through it. It is an indirect method of measuring the electrolyte concentration of a solution.

Contact time: The amount of time a fluid is in contact with a process, such as the time water is in contact with a carbon filter.

Contaminate: An undesired chemical or microorganism.

Deionization: Use of positively and negatively charged resins to remove unwanted ions from water used for dialysis by exchanging the unwanted ions for Hydrogen and Hydroxyl, which combine to form H2O.

Delta p or Delta pressure: A term used to refer to a difference in the pressure measured before and after a component, often represented by the symbol A.

Dialysate: A precise mixture of product water and electrolytes and, usually, dextrose, to allow exchange of solutes with the patient's blood during hemodialysis.

Diffusion: Movement of particles (solutes) across a membrane to create equilibrium in a given area. In dialysis the solutes move across a semipermeable membrane from an area of higher concentration to an area of lower concentration until the concentrations on both sides of the membrane are equal.

Disinfectant: A chemical or thermal (e.g. heat) process that destroys or slows the growth of harmful microorganisms (e.g., bacteria, viruses).

Downstream: Following a specified component, as in "The RO is downstream of the carbon filter."

Effluent: The output exiting any component of the water treatment system.

Electrolyte: Ion capable of transferring or exchanging electrons. In dialysate, the electrolytes are the charged ions that result from dissociation of the salts dissolved in water. These charged ions are responsible for the conductive property of dialysate.

Empty bed contact time: The amount of time the feed water stays in contact with the charcoal bed in a carbon tank to allow removal of chlorine and chloramines.

Endotoxin: A harmful toxin that is present inside a bacteria's cell wall and is released when the cell dies. Endotoxin exposure can cause pyrogenic (fever) reactions.

Exhaustion: The point at which the resin can no longer exchange additional ions, or carbon can no longer effectively remove chlorine.

Feed water: The input entering any component of the water treatment system.

Filters: Devices that remove particles, solutes, and other substances of a given size range by use of media such as gravel, sand, cartridges or carbon.

Filtration: The process of passing water through a filter.

Flocculants: Agents that cause sediment to "clump" into larger groupings and fall to the bottom of a settling pool.

Foul: To make dirty; pollute. In the case of an RO membrane, to make less efficient.

Germicide: Agent that kills microorganisms.

Ground water: Water beneath the earth's surface found in wells and springs.

Hydraulic pressure: Water pressure created naturally (such as by gravity) or artificially (such as by use of a pump).

Ion: Atom or group of atoms that carry a positive or negative electrical charge.

Limulus amoebocyte lysate test (LAL test): Assay used to detect and quantify the amount of endotoxin.

Osmosis: Movement of fluid across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration until the concentration of solutes on both sides of the membrane are equal.

Pathogenic: A disease producing agent or microorganism.

Permeable: Allows a substance to pass through.

pH: An expression of the hydrogen ion (acid) concentration of a solution. A solution with a pH above 7 is alkaline (a base), while a solution with a pH below 7 is an acid.

Pores: Holes; in a RO membrane, the size of the pores allow some particles to pass through, while preventing passage of particles which are too large.

Permeate: The output of the RO, also known as product water.

Potable water: Water that is safe to drink.

Proportioning system: Apparatus that proportions product water and hemodialysis concentrates (acid and bicarbonate) to create dialysate.

Pyrogen: Fever-producing substance.

Pyrogenic reaction: Reaction caused by pyrogens. Symptoms include chills, fever, shaking, low blood pressure, vomiting, and muscle pain.

Reject stream: The waste water and concentrated ions and other contaminants "rejected" by the RO.

Scaling: Coating of membranes or filter media by solutes which come out of solution and become solids.

Sediment: Matter that settles to the bottom of a liquid.

Semipermeable membrane: A material with tiny holes, or pores, that allows the passage of small particles (solutes) but prevents the passage of large particles. The membrane's permeability depends on the size and number of the pores, and the thickness of the membrane.

Silt density index (SDI): The amount of particulate matter present in water.

Solutes: Particles dissolved in fluid, creating a solution.

Source water: The source of water feeding the water treatment system; also used to refer to the water feeding a single component, or the water feeding the municipal water treatment system.

Spent water/dialysate: Water or dialysate that has been used.

Surface water: Water that comes from ponds, lakes, reservoirs, and rivers.

Total dissolved solids (TDS): Sum of all solutes in a solution.

Turbidity: Cloudiness in the water caused by a suspension of small particles.

Water treatment cascade: All the components in the water treatment system.

Water treatment system: Collection of water treatment devices and associated piping, pumps, valves, gauges, etc., that together produce water for dialysis.

The Philadelphia Incident

Even though there have been many more recent incidences with chloramine poisoning of patients, the most noted example remains the "Philadelphia Incident' of 1987 because so many factors led to adverse patient outcomes.

Initially, a nurse in the facility noticed an unusually large number of hematocrit values that were lower than normal. Patients also complained of headaches and malaise, and were hypotensive. After two to three days of symptoms, it became apparent that chloramine was the culprit causing hemolysis. Forty-four of the 107 patients required transfusions, and 10 were sent to the emergency department for additional treatment. Fortunately, thanks to careful clinical monitoring, no patients died during this event (Ackerman, 1988; FDA, 1988).

Investigation of this incident revealed that the water requirements for the facility had increased, and a water vendor added more RO membranes without increasing the size of the pretreatment carbon filters to accommodate the higher flow rate. The staff person monitoring the system recorded the chloramine levels accurately as they climbed to toxic levels (AAMI maximum level is 0.1 mg/L), but the staff member was not aware this was a dangerous level and did not report the results to a supervisor. In addition, no written policy was in place to guide the testing of total chlorine levels, and double checks with signatures were not standard procedure. Finally, staff erroneously believed that backwashing the carbon would regenerate the tank (Ackerman, 1988; FDA, 1988).

This incident illustrates the need for education for clinical staff members, choosing reputable water vendors, developing and implementing clear policies and procedures, and re-evaluating the entire water treatment system whenever any component is changed.


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Glenda M. Payne, MS, RN, CNN, is the Cofounder and Principal of the National Dialysis Accreditation Commission and a member of the Association for the Advancement of Medical Instrumentation (AAMI) Renal Disease and Detoxification Committee. She previously worked as a State and Federal surveyor for thirty years, served as a primary author of the Texas End Stage Renal Disease (ESRD) Licensing Rules and the Federal ESRD Interpretive Guidance, and member of the core faculty for surveyor training and tool development from 1989-2011. Glenda is a charter member of ANNA's Dallas Chapter, and has served as Southeast Vice President, National Secretary, and President of ANNA.

Jim Curtis is a Managing Partner of Jim Curtis & Associates, LLC. Jim is a co-founder of Outset Medical and is a Past President of the National Association of Nephrology Technicians (NANT). He was previously a voting member of both the AAMI Renal Disease and Detoxification and the AAMI Medical Devices in Home Applications Committees. Jim was the editor of Water Treatment for Dialysis, published by the National Association of Nephrology Technicians/Technologists (NANT) in 2015.

Editor's Note: This article is an update of two previous NNJ articles (Amato, 2005; Layman-Amato, Curtis, & Payne, 2013).

Statement of Disclosure: The authors reported no actual or potential conflict of interest in relation to this continuing nursing education activity.

Note: The Learning Outcome, additional statements of disclosure, and instructions for CNE evaluation can be found on page 169.

Caption: Figure 1: Comparison of the Weekly Water Exposure of Individuals Not on Dialysis (Bottles to the Left) with Individuals on Dialysis (Crates to the Right)

Caption: Figure 2: Typical Pretreatment System

Caption: Figure 3 Water Softener

Caption: Figure 4 Softener Ion Exchange

Caption: Figure 5: Carbon Filters

Caption: Figure 6: Paired Carbon Filters

Caption: Figure 7: Basic Reverse Osmosis Element

Caption: Figure 8: Reverse Osmosis Membrane

Caption: Figure 9: Reverse Osmosis

Caption: Figure 10: Deionization (DI) Ion Exchange Process

Caption: Figure 11 Deionization (DI) Ion Exchange--DI Exhausted

Caption: Figure 12: Endotoxin Filter

Caption: Figure 13: Indirect Feed Design

Caption: Figure 14 Direct Feed Design
Table 1

Signs and Symptoms and Possible Water
Contaminant-Related Causes

Symptom           Possible Water Contaminants

Anemia            Aluminum, chloramine, copper, zinc

Bone disease      Aluminum, fluoride

Hemolysis         Copper, nitrates, chloramine

Hypertension      Calcium, sodium

Hypotension       Bacteria, endotoxin, nitrates

Metabolic         Low pH, sulfates

Neurological      Aluminum

Nausea and        Bacteria, calcium, copper, endotoxin, low pH,
vomiting          magnesium, nitrates, sulfates, zinc, Microcystins
                  (from blue-green algae)

Death             Aluminum, fluoride, endotoxin, bacteria, chloramine,

Visual            Microcystins

Liver failure     Microcystins

Note: Revised from FDA (1989).

Table 2

Relationship Between previous AAMI Standards for Hemodialysis Fluids,
Current ANSI/AAMI Standards, and Future ANSI/AAMI/ISO Standards
(Effective in 2019)

Content              Previous           Current       Future Standard
                     Standard          Standard

User guidance     ANSI/AAMI RD52*   ANSI/AAMI         AAMI-ISO 23500-
on achieving      Dialysate for     23500:2014        1 Guidance for
compliance with   Hemodialysis      Guidance for      The Preparation
fluid quality     (part)            the Preparation   and Quality
standards                           and Quality       Management of
                                    Management of     Fluids for
                                    Fluids for        Haemodialysis
                                    Hemodialysis      and Related
                                    and Related       Therapies: Part
                                    Therapies         1 General

Water treatment   ANSI/AAMI         ANSI/AAMI         AAMI-ISO 23500-
equipment         RD62** Water      26722:2014        2: Part 2 Water
                  Treatment         Water Treatment   Treatment
                  Equipment for     Equipment for     Equipment for
                  Hemodialysis      Hemodialysis      Haemodialysis
                  Applications      and Related       Applications
                  (part)            Therapies         and Related

Water quality     ANSI/AAMI         ANSI/AAMI         AAMI-ISO 23500-
standard          RD62** Water      13959:2014        3: Part 3 Water
                  Treatment         Water for         for
                  Equipment for     Hemodialysis      Haemodialysis
                  Hemodialysis      and Related       and Related
                  Applications      Therapies         Therapies

Production of     ANSI/AAMI         ANSI/AAMI         AAMI-ISO 23500-
dialysate         RD61**            13958:2014        4: Part 4
concentrates      Concentrates      Concentrates      Concentrates
                  for               for               for
                  Hemodialysis      Hemodialysis      Haemodialysis
                                    and Related       and Related
                                    Therapies         Therapies

Dialysate         ANSI/AAMI RD52*   ANSI/AAMI         AAMI-ISO 23500-
quality           Dialysate for     11663:2014        5: Part 5
standard          Hemodialysis      Quality of        Quality of
                  (part)            Dialysis Fluid    Dialysis Fluid
                                    for               for
                                    Hemodialysis      Haemodialysis
                                    and Related       and Related
                                    therapies         Therapies

* Adapted by CMS as regulation outpatient HD.

** Parts of these documents referenced in RD52 were adopted as
regulation by CMS for outpatient HD.

Table 3

AAMI and EPA Maximum Allowable Levels of Contaminants in Water

Contaminant       EPA Maximum for    AAMI Maximum      Concentration
                  Drinking Water     Concentration    Associated with
                      (mg/L)              for          Hemodialysis
                    (Condensed       Hemodialysis      Toxicity (mg/
                  List) July 2002     Water (mg/L           L)

Calcium            Not regulated     2 (0.1 mEq/L)         88.00
Magnesium          Not regulated     4 (0.3 mEq/L)
Potassium          Not regulated     8 (0.2 mEq/L)
Sodium             Not regulated    70 (3.0 mEq/L)        300.00
Antimony               0.006            0.0060
Arsenic                0.005            0.0050
Barium                 2.000            0.1000
Beryllium              0.004            0.0004
Cadmium                0.005            0.0010
Chromium               0.100            0.0140
Lead                  0.015**           0.0050
Mercury                0.002            0.0002
Selenium               0.050            0.0900
Silver                 0.100            0.0050
Aluminum           0.05 to 0.2*         0.0100             0.06
Chloramines           4.000*            0.1000             0.25
Free Chlorine         4.000*            0.5000
Copper                1.300**           0.1000             0.49
Fluoride            2.0* to 4.0         0.2000             1.00
Nitrate (as           10.000            2.0000             21.00
Sulfate              250.000*          100.0000           200.00
Thallium               0.002            0.0020
Zinc                  5.000*            0.1000             0.20

Unenforceable maximum contaminant level goal (secondary standard).

**Action level at 90th percentile.

Source: Adapted from AAMI, 2014c; EPA, 2004.

Table 4

Concentrate Mixing/Proportioning Ratios

Concentrate Type   Acid Proportioning Ratio   Geometric Symbol

35 X                        1:34 *                 Square
36.83 X                   1:35.83 *                Circle
45 X                        1:44 *                Triangle
36.1 X                     1:35.1 *               Hexagon

*Acid: bicarbonate and water.

Source: Adapted from AAMI, 2014b.

Table 5

Comparison of Maximum Allowable Levels of Bacteria and Endotoxin in
Standard HD Water According to ANSI/AAMI 13959:2014 and ANSI/AAMI

Contaminant                    ANSI/AAMI      ANSI/AAMI
                               Max Level     Action Level

Total viable bacteria count   < 100 CFU/mL    50 CFU/mL
Endotoxin                     < 0.25 EU/mL   0.125 EU/mL

Contaminant                    CMS/RD 52      CMS/RD 52
                               Max Level     Action Level

Total viable bacteria count   < 200 CFU/mL    50 CFU/mL
Endotoxin                      < 2 EU/mL       1 EU/mL

Sources: AAMI, 2004, 2014c.

Table 6

Comparison of Maximum Allowable Levels of Bacteria
and Endotoxin in Dialysate According to AAMI/ANSI RD52:2004
and ANSI/AAMI/ISO 11663:2014

                                           Bacteria Limit/Action
                                              Level (CFU/mL)

ANSI/AAMI RD52:2004   Standard                   < 200/50

ANSI/AAMI/ISO         Standard                   < 100/50
11663:2014            Ultrapure                    < 0.1
                      Substitution Fluid          Sterile

                                           Endotoxin Limit/Action
                                               Level (EU/mL)

ANSI/AAMI RD52:2004   Standard                     < 2/1

ANSI/AAMI/ISO         Standard                   < 0.5/0.25
11663:2014            Ultrapure                    < 0.03
                      Substitution Fluid       Non-pyrogenic

Sources: AAMI, 2004, 2014a.
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Title Annotation:CNE: Continuing Nursing Education
Author:Payne, Glenda M.; Curtis, Jim
Publication:Nephrology Nursing Journal
Article Type:Report
Date:Mar 1, 2018
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