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Water Quality and Reprocessing Instruments
Water Quality and Reprocessing Instruments
by Herbert J. Kaiser, PhD; Gerald E. McDonnell, PhD; Jason F. Tirey, MA; andDaniel A. Klein, BS
While being one of the most important components of instrument reprocessingand sterilization, water is also one of the most ignored aspects in this entireprocess. Water is involved as the principal component in the cleaning, rinsing,and steam sterilization of stainless steel surgical instruments. It is very easyto determine the quality of the water used at a hospital or instrumentreprocessing facility.
Before proceeding, general water descriptions need to be defined. Make-upwater is defined as the water being used to make dilutions of detergents. Forexample, if a 1-ounce per gallon solution of a detergent was prepared, themake-up water is the water that is used to prepare that solution. Make-up wateris also the water used to make up lost water in the boiler. Final rinse water isdefined as the water used to rinse instruments prior to the instruments beingdried. Make-up water and final rinse water should be sampled as close to thepoint of use as possible when an analysis is being done.
Boiler water is defined as the water that is in the boiler in liquid form.Boiler water contains a wide variety of chemicals that have been added to it.These chemicals are added to prevent the boiler and steam lines from corroding,becoming scaled, foaming, etc. Boilers are operated by licensed personnel who gothrough extensive training in boiler maintenance and operation. The importanceof CS personnel establishing a good relationship with the boiler operatorscannot be stressed enough. Boiler operators take a great pride in the quality oftheir operations and the significant impact their services may have on theirfacility and the services they provide. With this in mind, care should be takenwhen addressing potential problems with boiler water. Sampling boiler water mustonly be done by the boiler operator. Samples of boiler water should be takenanywhere below the surface of the water in the boiler. Ideally, samples shouldbe taken immediately below the water level in the boiler and at the bottom ifthe boiler has these ports.
Condensate return water is defined as the steam that has condensed and isbeing returned to the boiler. Steam leaves the boiler in a facility and travelsthrough steam lines, performing whatever required functions it needs to. Whileit is traveling through the steam lines, it eventually cools and condenses. Thisis why it is called condensate return water. The water that condenses in thesteam lines is returned to the boiler. This water should be sampled before thewater reenters the boiler. If the steam lines in the facility are equipped withsteam coolers, samples should be taken as close to the point of use as possible.Sampling of condensate return water or steam must only be done by the boileroperator.
Carryover is defined as water and boiler chemicals that are transferred fromthe boiler to the steam system through foaming (also known as priming) or otherprocesses. The amount of carryover is what is being determined when condensatereturn water is analyzed. Blow down is the process by which solids in a boilerare controlled. Boiler operators use blow down to drain part of the residentwater in the boiler on a periodic basis. If this were not done on a regularbasis, the solids level in a boiler would increase to a point where the water inthe boiler would foam. When the boiler foams (or primes), boiler chemicals canbe transferred into the steam lines and subsequently deposited onto instrumentsin the sterilizers.
To understand water quality issues, a few concentration definitions need tobe established. Most components in water are described in terms of milligramsper liter (mg/L) or parts per million (ppm). Hardness and alkalinityconcentrations are typically expressed as an equivalent calcium carbonate (CaCO3)concentration. For example, while water hardness is primarily composed ofcalcium and magnesium carbonate, the magnesium carbonate portion is expressed ascalcium carbonate. This is done for ease of comparison among other analyses.Sometimes, water hardness will be described in terms of grains. One grain isequivalent to 17.1 ppm. In some water reports, the term "<LOQ"appears. This stands for "Less than Limit Of Quantitation." This meansthat the sample contains less than the lowest amount being determined.
Water quality reports often present water indexes. These indexes aremeasurements of various water tendencies. One such index is the CalciumSaturation Index. This is a calculated value that indicates whether calciumcarbonate will come out of solution (a value greater than zero) or stay insolution (a value less than zero). Based on various parameters of the water, itcan be predicted whether or not calcium carbonate hardness will form in thewater. The Calcium Saturation Index helps to calculate the probability ofcalcium carbonate precipitating from various waters rather than as anexperimental determination.
Another water quality index is the Aggressive Index. This is a calculatedvalue that gives an indication of the aggressive nature of water. A value ofless than 10 means that the water is highly aggressive. A value between 10 and12 indicates that the water is moderately aggressive and a value greater than 12indicates that the water is nonagressive. This index allows us to predict thecorrosive nature of the water.
There are many definitions of various hardness qualities. In this article, wedefine distilled, deionized, or reverse osmosis water as water having a totalhardness value of less than 1 ppm. Soft water is defined as having a totalhardness value of less than 2.2 ppm. Water is considered to have a low hardnessif its total hardness concentration is less than 75 ppm. Medium hardness wateris defined as water having a total hardness of 76-150 ppm. High hardness wateris defined as water having a total hardness value greater than 150 ppm. Thesevalues vary widely depending upon the source of the water. They will also oftenvary from season to season. Some changes can be dramatic when communities changetheir water source during the year. For example, some communities receive theirwater from a reservoir for part of a year and then from a river during anotherpart of the year. Communities located between two rivers sometimes switchbetween rivers as their water source. Sometimes differences in water qualityexist within the same facility. This occurs because part of the facility may usemunicipal water while another part of the facility uses well water.
There are many methods of purifying water. These include reverse osmosis,deionization, and softening. Generally speaking, the purity of water producedthrough various processes can be considered to follow this trend: reverseosmosis> deionized water> softened water> tap.
In a water softener, only calcium and magnesium ions are removed from thewater. Water softening simply removes the water hardness. It does not remove anyother metal ions or organic contaminants. A water softener functions by passingwater through a resin bed. As the water flows through the resin bed, any calciumor magnesium in the water exchanges with sodium that is attached to the resinbed. Two sodium ions are exchanged for each calcium and magnesium ion in thewater. Eventually, the resin bed of the water softener becomes exhausted.Instead of purchasing a new resin bed, water softeners are regenerated. This isdone by passing a highly concentrated solution of salt through the resin bed.The sodium ions from the salt exchange with the calcium and magnesium ions thathave been absorbed on the resin bed. An important step in the regeneratingprocess is to rinse the resin before the water is used. This rinsing stepremoves the chloride from the resin bed. This is especially important in afacility that does instrument reprocessing and sterilization because chloride isone of the most harmful chemicals to which surgical instruments can be exposed.
Deionization removes all ionic species, not only the water hardness. In thedeionization process, ionic impurities are exchanged for hydrogen ions (H+)or hydroxide ions (HO-). Deionization by itself does not removeorganic contaminants. Typically, facilities will obtain deionization cartridgesfrom a reliable water treatment company. Deionization columns are typically notregenerated at the facilities.
Osmosis is the process by which solvent molecules (in this case water) passthrough a semi-permeable membrane. This occurs when a solution on one side ofthe membrane has a higher ionic strength than the solution on the other side ofthe membrane. The solution having the lower ionic strength tends to pass watermolecules through the membrane to dilute the solution having the higher ionicstrength. Given a suitable membrane, this osmosis occurs naturally. In reverseosmosis, as the name implies, the reverse occurs. The solvent molecules or waterfrom the solution with a high ionic strength passes through the membraneproducing pure water. The passage of the water through the membrane leaves theionic impurities on the far side of the membrane. This process occurs due topressure being applied that is greater than the osmotic pressure that wouldoccur naturally. Reverse osmosis removes nearly all of the ionic and organicimpurities originally present in the water. It is typical that prior to enteringthe reverse osmosis unit, the water is first deionized and passed through avariety of filters (to prevent clogging on the reverse osmosis membrane).
What quality of water is good enough? The answer to this question depends onthe water's intended use. If the water is being used as make-up water, anyquality of water is sufficient if and only if the detergent that is used toclean the instruments can sufficiently chelate the water hardness and metalsthat are present. A chelating agent essentially reacts with water hardness andmetals in the water preventing them from interfering with the cleaning process.Many commercially available detergents contain chelating agents. The ideal waterfor use as a final rinse for stainless steel surgical instruments is reverseosmosis water. If reverse osmosis water is not available, then deionized wateror at least softened water should be used as a final rinse. Untreated tap watershould never be used as a final rinse for stainless steel surgical instrumentsthat will be steam or gas sterilized.
There are many signs of insufficient chelation during the cleaning process.The primary signs are white spots or a film on the instruments and also insidethe washer itself. These white spots or film are either the water hardnessprecipitating out of solution or a combination of the water hardness with thedetergent being used. Other signs are metal deposits on either the instrumentsor the inside of the washer. These metal deposits can form due to high levels ofiron or copper present in the water.
There are also many signs when a poor quality rinse water is used. Again,white deposits can form on the instruments prior to sterilization. These whitedeposits occur simply because of dry down of the water and concentration of thehardness content on the surface of the instruments. Rust deposits may alsoappear on the instruments prior to sterilization. This can occur due to poorquality rinse water corroding the instruments. Gold tints on instruments aftersterilization typically mean that the instruments were exposed to high chloridelevels, which can come from improper regeneration of a water softener orcarryover of boiler chemicals into the steam system. Pitting of instrumentsafter sterilization can also mean that the instruments were exposed to highlevels of chloride either in the rinse water or the steam.
In addition, sterilization may be compromised. Experiments have beenconducted to investigate this. Both Bacillus subtilis and Bacillusstearothermophilus were individually mixed with various soils, and killcurves were determined for steam sterilization. It was shown in our laboratoriesthat crystals of both iron oxide/hydroxide (rust) and calcium carbonate (waterhardness) significantly inhibited steam sterilization. These results can belinked to possible clinical situations.
Spore Survival Experiments
Many previous efforts have explored the use of agents to indicate theeffective sterilization of a given technique. A more recent study showed that B.stearothermophilus could survive within 18 different crystals for over sevenyears.3 These attempts showed that the occlusion of spores withincrystals did significantly inhibit sterilization in all types of apparatus.However, crystals were thought to be unrepresentative of the clinicalenvironment. This is simply not the case for calcium carbonate and ironoxide/hydroxide occluded spores that can be readily related to clinicalexperiences. This was demonstrated in the lab.
Calcium carbonate and iron oxide/ hydroxide occluded spores were prepared bysuspending the spores in a 10% solution of either calcium chloride or ironchloride. The final concentrations of the spores in the solutions were 108 cfuper mL. A solution of 10% sodium carbonate (for calcium) or sodium hydroxide(for iron) was added to the spore suspension to cause precipitation. Theprecipitate/solution was vortexed for five minutes to aid the suspension of thespores within the forming crystals. After precipitation was complete, thecrystals were centrifuged. The supernatant was poured off, and the crystals wererinsed with sterile water. The crystals were centrifuged again, and thensuspended in sterile water. Stainless steel coupons were inoculated with 10ÂµLof the crystal suspension. The coupons were dried overnight at 90ÂºC.
The coupons were placed in a small glass petri dish with a lid. The petridish was placed in the center of the autoclave, and the autoclave was run forthe desired amount of time at 121ÂºC with a five minute drying time. Thetemperature build-up time was neither monitored nor controlled. The petri disheswere removed from the autoclave immediately following the completion of thecycle. After cooling, the coupons were recovered in five mL of distilled water.The samples were sonicated for five minutes to disrupt the crystals and vortexedfor at least 30 seconds prior to plating. The pour plate method was used withtryptic soy agar. Incubation was done at 35ÂºC for B. subtilis, and 57ÂºCfor B. stearothermophilus.
The resistance of the spores in crystals dried at 90ÂºC differed from thosedried at 37ÂºC. This is because the drying of the samples at 37ÂºC, and at roomtemperature, does not remove all the water from the sample. When this sample isplaced in the autoclave, and the temperature is raised, the water remaining inthe sample and the spores is also heated. The presence of the water, now at ahigh temperature, within the sample kills the spores more rapidly. Drying at90ÂºC significantly changes the environment of the spores in the crystals. Thisdrying increases the resistance to steam sterilization. Drying at 90ÂºC removesmost, if not all, of the unbound water (along with its heat content) present inthe crystals. This means that the steam must pass through and rehydrate thesoils before it can reach the actual spore and kill it.
This presents a potentially serious problem within the clinical setting. Inmany, if not all, of the automated washers used in CS units in hospitals, thereis a drying cycle at the end of the washing cycle. The temperatures in thesedrying cycles are often somewhere between 100ÂºC and 140ÂºC. If the final rinseof the instruments is done with hard water, hard water deposits could form onthe instruments. Calcium carbonate (water hardness) displays inverse solubility.Therefore, as the temperature increases, calcium carbonate becomes less soluble.In extreme hard water areas, thermal rinses could cause precipitation ofhardness crystals. If spores were to be trapped within highly concentrated hardwater deposits, it is possible that those spores could survive steam or gassterilization.
Prevention of this scenario is fairly easy. First, all rinse cycles should bedone with either reverse osmosis, deionized, or at least softened water.Secondly, inspection of the instruments should be done before use. Any hardwater deposits or rusing should disqualify an instrument from use in an invasiveprocedure. These instruments should then be reprocessed using appropriate waterconditions. Thirdly, the use of detergents containing agents to preventprecipitation of water hardness onto the instruments is recommended.
Steam quality is a measurement of the amount of moisture in steam. Steam usedin sterilization processes is typically a mixture of steam and moisture. Thesteam content should be greater than or equal to 95% but less than 100%. Thismeans that steam should contain less than 5% liquid. It is important for steamto contain a slight amount of moisture to be effective as a sterilant. Steampurity is a measurement of the amount of contaminants in steam. This measurementis usually that of the chemicals being used in the boiler. For example, if thereis moisture present in the steam, that moisture will contain those chemicalsfound in the boiler. An excessive amount of these chemicals (carryover) in thesteam will cause staining, spotting, and corrosion of surgical instruments.There are many signs of carryover. Stained wraps occur when boiler chemicals aredeposited on the wraps as the steam penetrates the wraps to reach theinstruments within. A purple rainbow color on the instruments is also anindication of carryover. This is typically caused by having excessiveneutralizing amines in the steam. Black deposits on instruments or wraps aretypically caused by high sulfate or sulfite content in the steam. Again, thesulfate/sulfite is a result of carryover from the boiler. A heavily stainedsterilizer chamber is a good indication of a problem with carryover. Pitting ofinstruments is typically caused by high chloride levels in the steam due tocarryover.
The Association for the Advancement of Medical Instrumentation (AAMI)indicates that there is no approval process for boiler water additives intendedfor use in steam sterilization. However, AAMI references the lists in 21 CFR173.310 and 21 CFR 100.11 as appropriate chemicals for use in boilers. Theselists include compounds that are allowed for use in steam where food contactwill occur.
Water impurities, such as alkali metal, metal, and chloride ions adverselyaffect surgical instruments, both in their appearance and functionality. Sendinga sample of your water to a testing facility can help you get the results youneed to troubleshoot problems that may be occurring in your process. It can alsohelp you in maintaining the quality of your process by knowing the quality ofthe water that is being used.
For a list of references, clickhere.
Herbert J. Kaiser, Ph.D., Jason F. Tirey, M.A., Gerald McDonnell, Ph.D.,and Daniel A. Klein, B.S., are employed at STERIS (St. Louis, Mo).For a complete list of references click here