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Infection Control Today - 08/2001: Instrumental Knowledge


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Cleaning: An Important Prerequisite for Instrument Sterilization and Disinfection

By Nancy S. Chu, MS and Martin Favero, PhD

Sterilization of instruments in hospitals has been an important part of preventing infections for more than 100 years. In the modern healthcare facility, instrument processing has evolved to a sophisticated science and one that has many components. The purpose of this article is to describe one of the most important components of instrument processing--instrument cleaning.

The cleaning process is the first step during reprocessing of reusable surgical instruments. Good cleaning is an important prerequisite of an optimal disinfection or sterilization procedure. If the cleaning process is deficient the sterilization and disinfection procedure can be significantly compromised.

In addition to removing microbial contamination (bioburden) that is present on surgical instruments after use, the cleaning process removes organic and inorganic matter that could react or interfere with disinfection or sterilization.

Instrument cleaning, as defined by the Association for Advancement of Medical Instrumentation (AAMI) in 1995, indicates that it is "the removal, usually with detergent and water, of adherent visible soil, blood, protein substances, and other debris from the surfaces, crevices, serrations, joints, and lumens of instruments, devices, and equipment by a manual or mechanical process that prepares the items for safe handling and/or further decontamination."1 There is currently no standard to define when a device is "clean," but it is generally accepted that a cleaning process to produce an aesthetically "clean" instrument should include the reduction of the microbial bioburden and removal of any organic and inorganic matter, so as to provide an instrument that can be effectively disinfected or sterilized.

A number of studies2-8 have shown that there is a wide range of bioburden present on surgical instruments immediately after use, and this level of microbial contamination is dependent on the surgery site. For example, the microbial load from a sterile body cavity is very different from that of the lower gastrointestinal (GI) tract, where a substantial microbial load of 1011 to 1012 CFU of aerobes and anaerobes per gram of feces can be found in 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 endoscopes used in the lower GI tract (i.e., colonoscopes). While the bioburden of gastroscopes2 is in the range of approximately 104, the bioburden of colonoscopes is less than 1010 after use.4 On the other hand, instruments used in other body regions, including sterile body cavities, have lower bioburden that is within the 101 to 103 range.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 and rinsing 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 insoluble and will precipitate out with time, causing scale and deposit problems in all equipment 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 because rust and water hardness crystals can occlude microbial spores, and can lengthen the sterilization process.12

After use, surgical instruments are often soaked immediately in enzymatic detergents. Flexible endoscopes are rinsed to flush out gross particulates, and then soaked. This is an important step that will prevent drying out of the instruments prior to cleaning. Organic matter in the form of blood, mucus, and tissue, if allowed to dry out on surgical instruments, is difficult to remove and requires additional time to rehydrate so that it can be removed.

The choice of cleaners can make a difference between a process that is efficient and effective and one that is not.13 Cleaning agents are formulated 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 pH agents are used for anodized aluminum or stainless steel surfaces that might be discolored or destroyed by acidic or alkaline detergents. Another effective choice is the use of enzymatic detergents, which are a combination of enzymes with detergent. The enzymes break down fat, protein, and carbohydrates.

Cleaning can be carried out either manually, automatically, or a combination of both methods. The basic method of manual cleaning uses a brush to create friction to remove soil; this method is very effective, especially for long narrow 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 with the brushing. Automated methods are generally used because they are consistently effective 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 one model or type of automated equipment will decontaminate all types of reusable surgical instruments14. Ultrasonic cleaning is a method usually used after gross soil has been rinsed or wiped from the surgical instruments. This method is useful in cleaning devices with joints and lumens that are difficult to reach manually.

Studies have shown that cleaning processes can reduce bioburden by approximately 4 logs in flexible endoscopes. Identification of the remaining microorganisms indicate that although the cleaning process itself removes the initial contaminants, there is a replacement of these microorganisms with waterborne and enteric microorganisms, which highlights the importance of sanitation in the device reprocessing areas. Studies with surgical instruments3-7 show that overall bioburden levels decrease after washing. In some instances the bioburden levels increased and this appeared to be related to the handling of the instruments during the washing procedure, with microbial contamination originating from human skin and rinse water containing waterborne bacteria such as pseudomonas.

The failure to remove organic and inorganic matter were shown in the 1950s and 1960s to cause sterilization processes, including ethylene oxide, formaldehyde gas sterilization, moist and dry heat to fail. Bacterial spores occluded by crystalline-type materials that were water soluble caused low temperature sterilization processes, i.e., vapor/plasma, vapor hydrogen peroxide, 100% ethylene oxide, and 12/88 ethylene oxide, to fail.15-19 These results were reconfirmed in the late 1990s by a study20 that showed the use of an artificial soil could sometimes create a technique induced sterilization failure. Jacobs et al.21 showed that microorganisms mixed with tissue culture fluid used as a surrogate body fluid actually formed physical crystals of NaCl, which protected the microorganisms used as a challenge. The results ostensibly showed that these carriers placed in ethylene oxide gas sterilizers and hydrogen peroxide gas sterilizers were not completely sterilized and a few of the carriers showed positive growth. In fact if the carriers were exposed for 60 seconds to non-flowing water the salts dissolved and the protective effect disappeared. Since any device would at least be 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 device manufacturers, so that future generations of surgical instruments can be easily and effectively cleaned. Surface finishes have also been shown to have an impact on the ability for the surface to be cleaned, since mirror finishes and smooth surfaces will result in less adherence of organic matter than rough finishes.21 Inaccessible locations on surgical instruments should be eliminated because if a surgical instrument cannot be cleaned, it cannot be effectively disinfected or sterilized.

Optimal cleaning conditions include good quality water, the correct type of detergent and mechanical cleaning system, well maintained and sanitized equipment, and consistent techniques when manual cleaning is used. Personnel handling surgical instruments, whether they are in the surgical suite or in the reprocessing areas, should be properly trained so that they recognize and understand the importance of each step of the reprocessing cycle that produces a "clean" surgical instrument. Coupled with surgical instruments that are designed for ease of cleaning, proper cleaning procedures will remove and/or reduce bioburden, organic, and inorganic matter. The end result will be a clean surgical instrument that can be effectively disinfected or sterilized.

Nancy S. Chu, MS, is a group leader in research and development. Martin Favero, PhD, is director of scientific and clinical affairs. Both work for Advanced Sterilization Products in Irvine, Calif.

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