Infection Control Today - 11/2002: Cleaning Scopes

Cleaning Scopes: When Soap and Water Aren't Enough

By Joan Davis

Inorder to prepare endoscopes and other medical devices for reuse, they must becleaned and then either sterilized or exposed to high-level disinfection. Thefinal sterilization step will kill any microbes exposed to the sterilizationprocess. For devices that are thermosensitive, sterilization is accomplished bythe application of chemical sterilants such as glutaraldehyde. Microbes thatcome into contact with the chemical sterilant for the required time period arekilled. However, microbes that are trapped behind organic matter that isencrusted on or within the endoscope will not come into contact with thechemical sterilant and will not be killed. The device then would not be sterileand could transmit disease to patients and to healthcare personnel. The samesituation exists in the case of high-level disinfection. If the endoscope is notclean, then it cannot be effectively disinfected and could transmit disease.

The most important process before the sterilization or high-leveldisinfection step, therefore, is the removal of all soil and organic matter fromthe device. Removing all of the soil and organic matter from all surfaces willallow the chemical sterilant to reach, and thus kill, all of the microbespresent.

Pre-cleaning methods that require heat can damage the endoscope, as cancleaning products containing alkali. Alkali also has the disadvantage of notmigrating into "blind holes" in the medical devices. A properlyformulated cleaner should migrate into these recesses and remove the soil withinthem.

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

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

The types of enzymes used in enzymatic cleaning products vary, but a goodblend can consist of protease, lipase, amylase, carbohydrase and other enzymes.The reason that a well-chosen blend can be particularly effective is the variedand intimately mixed nature of the organic debris found in and on endoscopes andother medical devices. The membranes of blood and tissue cells, as well asassociated materials such as mucus, feces and other organic matter, containproteins, lipids and carbohydrates. Carbohydrates coat the outside of cells andfunction to bind the cells together into tissues. These components areintimately mixed and many are chemically bonded to each other. When protein ispartially digested by a cleaning product containing only protease, then thestarch, other carbohydrates and lipids in and around the cell membranes remain.The residual layers will cover the remaining protein, inhibiting the chance forthe protease enzyme to make contact with all the protein in the soil. Theintimate mixing of various types of organic matter is the reason that thesynergistic action of multi-enzyme products offers better performance thansingle-enzyme products provide.

The enzyme combinations in properly blended products effectively digest eachand 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 andlipid hydrolysis. Lipid digestion enables enhanced protein and carbohydratedigestion. Lipase is particularly valuable in endoscope cleaning because itdigests the fat, whereas surfactants may partially remove fat, but do not digestit or prevent its redeposition. Additional ingredients in enzymatic cleaningproducts include solubilizing agents, soil suspending agents and surfactantswith good wetting properties, chosen to enhance enzymatic action and contributeto the products' effectiveness.

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

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