Infection Control Today - 08/2001: Instrumental Knowledge
Cleaning: An Important Prerequisite for InstrumentSterilization and Disinfection
By Nancy S. Chu, MS and Martin Favero, PhD
Sterilizationof instruments in hospitals has been an important part of preventing infectionsfor more than 100 years. In the modern healthcare facility, instrumentprocessing has evolved to a sophisticated science and one that has manycomponents. The purpose of this article is to describe one of the most importantcomponents of instrument processing--instrument cleaning.
The cleaning process is the first step during reprocessing of reusablesurgical instruments. Good cleaning is an important prerequisite of an optimaldisinfection or sterilization procedure. If the cleaning process is deficientthe sterilization and disinfection procedure can be significantly compromised.
In addition to removing microbial contamination (bioburden) that is presenton surgical instruments after use, the cleaning process removes organic andinorganic matter that could react or interfere with disinfection orsterilization.
Instrument cleaning, as defined by the Association for Advancement of MedicalInstrumentation (AAMI) in 1995, indicates that it is "the removal, usuallywith detergent and water, of adherent visible soil, blood, protein substances,and other debris from the surfaces, crevices, serrations, joints, and lumens ofinstruments, devices, and equipment by a manual or mechanical process thatprepares the items for safe handling and/or further decontamination."1There is currently no standard to define when a device is "clean," butit is generally accepted that a cleaning process to produce an aesthetically"clean" instrument should include the reduction of the microbialbioburden and removal of any organic and inorganic matter, so as to provide aninstrument that can be effectively disinfected or sterilized.
A number of studies2-8 have shown that there is a wide range ofbioburden present on surgical instruments immediately after use, and this levelof microbial contamination is dependent on the surgery site. For example, themicrobial load from a sterile body cavity is very different from that of thelower gastrointestinal (GI) tract, where a substantial microbial load of 1011to 1012 CFU of aerobes and anaerobes per gram of feces can be foundin the colon.9-11 Flexible endoscopes used in the upper GI tract (i.e.,gastroscopes) show a range of bioburden that is less than that of endoscopesused in the lower GI tract (i.e., colonoscopes). While the bioburden ofgastroscopes2 is in the range of approximately 104, thebioburden of colonoscopes is less than 1010 after use.4 Onthe other hand, instruments used in other body regions, including sterile bodycavities, have lower bioburden that is within the 101 to 103range.3,5,7
Water is one of the most important components of instrument reprocessing,because in addition to being the principle medium used in the cleaning andrinsing of soiled surgical instruments, it is used during steam sterilization.Water quality varies with the season and the locality. Community supplied (tap)water contains minerals including calcium and magnesium salts that are insolubleand will precipitate out with time, causing scale and deposit problems in allequipment associated with water, e.g., steam autoclaves and washers.Other detrimental effects of poor rinse-water quality include spotting, pitting,and rusting of instruments. Steam sterilization also can be compromised becauserust and water hardness crystals can occlude microbial spores, and can lengthenthe sterilization process.12
After use, surgical instruments are often soaked immediately in enzymaticdetergents. Flexible endoscopes are rinsed to flush out gross particulates, andthen soaked. This is an important step that will prevent drying out of theinstruments prior to cleaning. Organic matter in the form of blood, mucus, andtissue, if allowed to dry out on surgical instruments, is difficult to removeand requires additional time to rehydrate so that it can be removed.
The choice of cleaners can make a difference between a process that isefficient and effective and one that is not.13 Cleaning agents areformulated to break down and remove soil and debris. Detergents with low pH(acidic) are more effective for inorganic soil while high pH (alkaline)detergents are more effective for organic soils like fat or protein. Neutral pHagents are used for anodized aluminum or stainless steel surfaces that might bediscolored or destroyed by acidic or alkaline detergents. Another effectivechoice is the use of enzymatic detergents, which are a combination of enzymeswith detergent. The enzymes break down fat, protein, and carbohydrates.
Cleaning can be carried out either manually, automatically, or a combinationof both methods. The basic method of manual cleaning uses a brush to createfriction to remove soil; this method is very effective, especially for longnarrow lumens. However, many variances associated with this method can occur,such as the number of times it is brushed, and the force that is associated withthe brushing. Automated methods are generally used because they are consistentlyeffective and they minimize personnel exposure to microbial contamination.Automatic systems are designed to clean and sanitize, clean and pasteurize,clean and thermally or chemically disinfect, and clean and sterilize. No onemodel or type of automated equipment will decontaminate all types of reusablesurgical instruments14. Ultrasonic cleaning is a method usually used after grosssoil has been rinsed or wiped from the surgical instruments. This method isuseful in cleaning devices with joints and lumens that are difficult to reachmanually.
Studieshave shown that cleaning processes can reduce bioburden by approximately 4 logsin flexible endoscopes. Identification of the remaining microorganisms indicatethat although the cleaning process itself removes the initial contaminants,there is a replacement of these microorganisms with waterborne and entericmicroorganisms, which highlights the importance of sanitation in the devicereprocessing areas. Studies with surgical instruments3-7 show thatoverall bioburden levels decrease after washing. In some instances the bioburdenlevels increased and this appeared to be related to the handling of theinstruments during the washing procedure, with microbial contaminationoriginating from human skin and rinse water containing waterborne bacteria suchas pseudomonas.
The failure to remove organic and inorganic matter were shown in the 1950sand 1960s to cause sterilization processes, including ethylene oxide,formaldehyde gas sterilization, moist and dry heat to fail. Bacterial sporesoccluded by crystalline-type materials that were water soluble caused lowtemperature sterilization processes, i.e., vapor/plasma, vapor hydrogenperoxide, 100% ethylene oxide, and 12/88 ethylene oxide, to fail.15-19These results were reconfirmed in the late 1990s by a study20 thatshowed the use of an artificial soil could sometimes create a technique inducedsterilization failure. Jacobs et al.21 showed thatmicroorganisms mixed with tissue culture fluid used as a surrogate body fluidactually formed physical crystals of NaCl, which protected the microorganismsused as a challenge. The results ostensibly showed that these carriers placed inethylene oxide gas sterilizers and hydrogen peroxide gas sterilizers were notcompletely sterilized and a few of the carriers showed positive growth. In factif the carriers were exposed for 60 seconds to non-flowing water the saltsdissolved and the protective effect disappeared. Since any device would at leastbe exposed to water for a short period of time during any washing procedure,these "protective" results have no clinical relevance.
Design considerations for ease of cleaning should be incorporated by devicemanufacturers, so that future generations of surgical instruments can be easilyand effectively cleaned. Surface finishes have also been shown to have an impacton the ability for the surface to be cleaned, since mirror finishes and smoothsurfaces will result in less adherence of organic matter than rough finishes.21Inaccessible locations on surgical instruments should be eliminated because if asurgical instrument cannot be cleaned, it cannot be effectively disinfected orsterilized.
Optimal cleaning conditions include good quality water, the correct type ofdetergent and mechanical cleaning system, well maintained and sanitizedequipment, and consistent techniques when manual cleaning is used. Personnelhandling surgical instruments, whether they are in the surgical suite or in thereprocessing areas, should be properly trained so that they recognize andunderstand the importance of each step of the reprocessing cycle that produces a"clean" surgical instrument. Coupled with surgical instruments thatare designed for ease of cleaning, proper cleaning procedures will remove and/orreduce bioburden, organic, and inorganic matter. The end result will be a cleansurgical instrument that can be effectively disinfected or sterilized.
Nancy S. Chu, MS, is a group leader in research and development. MartinFavero, PhD, is director of scientific and clinical affairs. Both work forAdvanced Sterilization Products in Irvine, Calif.
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