Infection Control Today - 11/2002: Cleaning Scopes

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Cleaning Scopes: When Soap and Water Aren't Enough

By Joan Davis

In order to prepare endoscopes and other medical devices for reuse, they must be cleaned and then either sterilized or exposed to high-level disinfection. The final sterilization step will kill any microbes exposed to the sterilization process. For devices that are thermosensitive, sterilization is accomplished by the application of chemical sterilants such as glutaraldehyde. Microbes that come into contact with the chemical sterilant for the required time period are killed. However, microbes that are trapped behind organic matter that is encrusted on or within the endoscope will not come into contact with the chemical sterilant and will not be killed. The device then would not be sterile and could transmit disease to patients and to healthcare personnel. The same situation exists in the case of high-level disinfection. If the endoscope is not clean, then it cannot be effectively disinfected and could transmit disease.

The most important process before the sterilization or high-level disinfection step, therefore, is the removal of all soil and organic matter from the device. Removing all of the soil and organic matter from all surfaces will allow the chemical sterilant to reach, and thus kill, all of the microbes present.

Pre-cleaning methods that require heat can damage the endoscope, as can cleaning products containing alkali. Alkali also has the disadvantage of not migrating into "blind holes" in the medical devices. A properly formulated cleaner should migrate into these recesses and remove the soil within them.

Enzymatic cleaners, in particular, can be extremely effective in removing soil and organic matter. Like any standard mild detergent product containing surfactants and having a near-neutral pH, they are not corrosive to the endoscopes. Well-formulated enzymatic cleaners also will migrate into "blind holes" in the instruments.

Enzymatic products have an advantage over standard detergent products; they biochemically break down the soil, digesting it so it will be easily washed away. If organic matter is stuck inside the channels of an endoscope, standard detergents products may not be able to remove it. Later treatment with glutaraldehyde may fix the material in place, rendering it even more difficult to remove and trapping microbes behind it. Enzymatic products, however, can digest the soil, breaking it down so it can be washed away. The balanced blends of enzymes and other ingredients in some of these products have synergistic effects on combined protein-fat-carbohydrate soils, to digest and remove all of them. After pre-cleaning with the appropriate enzymatic cleaner, the endoscope is free from all soil and organic matter. It then is truly clean and ready for effective sterilization or high-level disinfection.

The types of enzymes used in enzymatic cleaning products vary, but a good blend can consist of protease, lipase, amylase, carbohydrase and other enzymes. The reason that a well-chosen blend can be particularly effective is the varied and intimately mixed nature of the organic debris found in and on endoscopes and other medical devices. The membranes of blood and tissue cells, as well as associated materials such as mucus, feces and other organic matter, contain proteins, lipids and carbohydrates. Carbohydrates coat the outside of cells and function to bind the cells together into tissues. These components are intimately mixed and many are chemically bonded to each other. When protein is partially digested by a cleaning product containing only protease, then the starch, other carbohydrates and lipids in and around the cell membranes remain. The residual layers will cover the remaining protein, inhibiting the chance for the protease enzyme to make contact with all the protein in the soil. The intimate mixing of various types of organic matter is the reason that the synergistic action of multi-enzyme products offers better performance than single-enzyme products provide.

The enzyme combinations in properly blended products effectively digest each and all of the intertwined components of the organic soil "matrix." Hydrolysis of protein enhances the degradation of fats and carbohydrates. Digestion of carbohydrates likewise allows faster and more complete protein and lipid hydrolysis. Lipid digestion enables enhanced protein and carbohydrate digestion. Lipase is particularly valuable in endoscope cleaning because it digests the fat, whereas surfactants may partially remove fat, but do not digest it or prevent its redeposition. Additional ingredients in enzymatic cleaning products include solubilizing agents, soil suspending agents and surfactants with good wetting properties, chosen to enhance enzymatic action and contribute to the products' effectiveness.

The digestion and removal of all organic soil in the pre-cleaning step is the best preparation for sterilization or high-level disinfection of endoscopes and other medical devices. Enzymatic cleaning products that are balanced to digest combined protein-fat-carbohydrate soils can remove organic matter more effectively than can other types of cleaning products, leaving the endoscopes and medical devices clean and ready for sterilization or high-level disinfection.

Joan Davis served as a polymer chemist, nuclear magnetic resonance spectroscopist and adjunct professor at Medgar Evans College. She also served as a chemist at Ruhof Corporation.

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