The validation report of a Washer-Disinfector clearly specifies the test load. Modern cleaning machines are designed for the shortest possible cycle times to maximise instrument throughput and save energy. Because of that, even a relatively small difference from the way the test load was used may result in a “failed” cycle. It is therefore critical to arrange instruments and accessories in such a way that cleaning performance is not compromised.
Concave surfaces, holes and crevices – perfect traps
The most obvious case is a bowl lying flat that fills up during the cycle. During the first rinse when the concentration of proteins in the recirculating water is highest this vessel gradually fills up. Contaminated water is not drained out and is carried on through all the washing stages. It is not the single bowl that should be reprocessed but the entire load. Once such a bowl is filled up to the top the heavier particles sediment on its bottom, while water creates a protective layer over it.
Exactly the same mechanism can be observed on some more complex instruments or accessories with concave surfaces, holes and crevices. Instruments with this type of feature must be positioned so that water drains out of them with the aid of gravity. It also means that certain instruments may require a dedicated accessory to position them properly. Attention should be also paid to the lighter, usually plastic, elements that may be easily flipped over or relocated by the jets of water from spray-arms or nozzles.
Correct orientation of instruments is also critical for effective drying as efficiency of drying is directly proportional to the water surface area exposed to the hot dry air. Therefore, flat surfaces should not be placed horizontally to avoid puddles of standing water. In the case of bowl shaped elements it is best to orient them vertically or at a steep angle. This also helps with maximising the washer’s capacity. Other instruments should be considered separately.
Shadowing – casting some light on it
This phenomenon is much more complex and in order to describe it properly a brief explanation of the cleaning action is necessary. Cleaning results from a cleaning medium (usually water with a chemical e.g. detergent) reaching the contaminated surface of the instrument and through a combination of mechanical and chemical processes removing unwanted content.
Shadowing occurs when an instrument or a part of its surface area is covered by another object (usually another instrument or accessory) that limits exposure to the cleaning medium. The extreme case is when flat surfaces are put against each other and through surface tension, stick together preventing access of the cleaning medium. This occurs when instruments and accessories are stacked. Examples of partial shadowing involve instruments being hidden from the direct cleaning action behind large surface objects like bowls or lids and also larger instruments.
Accessories like storage boxes, cassettes and dedicated enclosures require special attention. On many occasions these items were not designed with cleaning performance in mind. In some cases it may be better therefore to relocate instruments to mesh baskets and clean these accessories separately.
A Washer-Disinfector is just a sophisticated tool. The end result depends on how it’s used and the loading process has a significant impact on the final outcome. So next time you load the machine pause for a moment and notice where the water comes from and how it reaches your instruments. This exercise will allow you to eliminate shadowing and trapping contamination inside instruments and accessories.
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