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during lower GI procedures. Synthetic lipids have a larger molecular structure than natural lipids and are harder to clean. Carbohydrates are starches and sugars, which are used by the body for energy. They consist of ringed structures in single and multiple groupings. Compared to proteins and lipids, carbohydrates are relatively easy to clean since they are somewhat water soluble. Inorganic soils related to endoscopy include minerals introduced in saline and other flushing solutions, hard water contaminants such as calcium carbonate that may be in the water used to clean devices and metals like copper and iron (including rust).
Getting it all off The first general rule for effective soil removal and cleaning is to preclean the devices quickly and promptly; quickly because soil is easier to remove while it’s fresh and before it is allowed to dry on device surfaces, and promptly because processing delays can promote the prolif- eration of biofilms in moist, soiled chan- nels. Biofilms are complex communities of microorganisms that stick to each other and to surfaces. The biofilm is covered in a slimy extracellular layer (matrix) that acts like glue, making its removal extremely difficult, especially with traditional clean- ing chemistries. Biofilms can form very quickly, and once they do, additional cleaning steps with specialized products will be needed to remove them. For any type of soil, thorough cleaning requires a combination of soil breakdown and physical removal. So how do chemi- cals accomplish these functions?
Removal The term “removal” is often defined as mechanical actions (i.e., brushing or wiping) used during cleaning. However, cleaning chemistries also remove soils. They contain ingredients called surface active agents (surfactants) that function in several different ways. Surfactants provide wetting, suspending (emulsify- ing), solubilizing and anti-redeposition functions. They have a special structure with a hydrophilic (water-attracting) por- tion and a hydrophobic (water-repelling) portion, which allows them to line up at air/water and liquid/solid interfaces to perform their function.
Water does not wet surfaces well because of its surface tension. By lining
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up at the interface where the water meets the air, a surfactant lowers this surface tension, allowing the water to sheet over surfaces and flow into tight spaces like the narrow channels of endoscopes. Once the cleaning solution effectively wets all surfaces, surfactants then line up at the interface between the soil and the clean- ing solution to suspend soils so they can be rinsed away. Some surfactants are also able to pull soils completely into solution. Surfactants that provide effective suspen- sion and solubilization will also prevent soils that have already been removed from redepositing on other endoscope surfaces as the scope is being rinsed.
However, detergents with poorly for- mulated surfactant systems can compro- mise cleaning, especially in automated endoscope reprocessors (AERs). For example, a cleaning chemistry that foams too much can cause the recirculating pump to cavitate (create vapor bubbles), which lowers the system pressure and reduces overall cleaning effectiveness. Foam bubbles also introduce air into endoscope channels, which limits the cleaning solution’s contact with the chan- nel walls. Excess foaming can also inter- fere with rinsing and can require more flushing and time to adequately remove all detergent residue.
Breakdown
In addition to removing soils, cleaning chemistries help break soils down. They break large, water insoluble molecules such as proteins and lipids apart into smaller, more water-soluble pieces. Breakdown occurs because of hydrolysis, sequestration/chelation and surfactancy. Enzymatic cleaners break down tough
soils with protease enzymes and the enzymatic hydrolysis process. Protease enzymes only break down proteins. Hydrolysis uses water to break molecules
apart into smaller, more soluble pieces. Enzymes speed up the hydrolysis action. Enzymes are proteins themselves.
They function by holding the protein soil and water near each other to make them interact faster and more easily. The protease enzymes are not consumed by the reaction and will continue to work on protein soil as long as it is present on the dirty endoscope. This is especially help- ful for the manual endoscope cleaning process because enzymes help remove protein soils in areas of the devices (such as lumens and channels) that are difficult to reach and where mechanical cleaning action is minimal. The activity and efficacy of all enzymatic products also increases with temperature, but only to a certain point. Temperatures above 60°C (140°F) will start to denature the enzyme and prevent it from working. When enzymes denature, they start to unfold and lose their ability to speed the hydrolysis reaction.
Alkaline hydrolysis Hydrolysis can also be driven by alkalin- ity (the capacity of water to resist acidifica- tion). The reaction in alkaline hydrolysis is slightly slower, and it is effective against both protein and lipid soils. However, alkaline hydrolysis is more aggressive
– it does not discriminate between soils and device surfaces, and this can lead to potential material incompatibility issues and device damage. A controlled amount of alkalinity can help solubilize lipids and remove them.
Chelation
Sequestering/chelating ingredients can be beneficial to the cleaning process. Because of their ability to bind minerals and metals such as calcium, magnesium, iron, copper and zinc, chelants can control the hardness of tap water used for the
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hpnonline.com • HEALTHCARE PURCHASING NEWS • September 2021 37
Self-Study Test Answers: 1. C, 2. D, 3. D, 4. C, 5. B, 6. A, 7. B, 8. D, 9. B, 10. B
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