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It’s Not the Washer-Disinfector, It’s How You Use It: Critical Insight into Loading Patterns

The validation or verification report of a washer-disinfector’s cleaning efficacy should clearly specify the test load. Modern cleaning machines are designed for the shortest possible cycle times to maximize instrument throughput. That need for speed leads to a situation where, in everyday use, even a relatively small difference in the way instruments are loaded may impact the result. It is therefore critical to think about the arrangement of instruments and accessories in the washer that reflect the type of load that is reprocessed on a daily basis. The closer we can simulate our regular load while testing, the more confident we can be about the final outcome.

Concave surfaces, holes, and crevices—perfect traps
The more complex the instrument, the more challenging the cleaning becomes. Let’s take the most obvious and hopefully hypothetical case of a bowl lying flat in the basket. During the first rinse when the concentration of contamination in the recirculating water is highest, this vessel will gradually fill up. It will fill up not only with water but with diluted contamination from all other instruments in this load. The same effect can be observed in dishwashers on the concave bottoms of wine glasses and cups. During the cycle, water is exchanged several times but that bowl will never drain. Contamination trapped inside becomes sediment and will be protected from the cleaning jets of consecutive stages of the cycle by a head of water that built up above it. Those cases are rare and we all know how to load bowls properly. The problem is that we have used the bowl to represent a phenomenon that is common to all concave surfaces, holes, and crevices we often see in regular and more complex surgical tools and accessories.

The mechanism of harboring contamination is the same as in the bowl but on a smaller scale. Instruments with such features must be positioned in a way that water drains out of those features with the aid of gravity. It also means that certain instruments may require dedicated accessories such as holders or organisers to position them properly in the washing chamber. 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. Such approach often helps with maximizing the washer’s capacity. Other instruments should be considered separately.

Shadowing—casting some light on it
This phenomenon is much more complex and to describe it properly, a brief explanation of the cleaning action is necessary. Cleaning is achieved when a cleaning medium (usually water with a chemical; e.g., detergent) reaches 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, basket, 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 altogether. This occurs often when instruments and accessories are stacked on top of each other. Examples of partial shadowing involve instruments being hidden from the direct cleaning action behind large surface objects, such as 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 to relocate instruments to mesh baskets and clean these accessories separately.

Conclusions
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. It goes without saying that testing cleaning performance is critical, but also 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 and load the washers more effectively.


Pawel de Sternberg Stojalowski, MSc, BSc, MBA, is an R&D engineer with passion for clever solutions. From his background in mechanical engineering, automation, robotics, and business stem innovations, Pawel has an interdisciplinary and cooperative approach to projects. He has been involved in R&D of equipment and technologies for decontamination and sterilization of complex surgical instruments since 2007. Today, Pawel leads an expert team researching, designing, prototyping, and evaluating innovative solutions aimed at solving challenges in decontamination of complex surgical instruments, contamination detection, and identification, as well as fluid dynamics and ultrasonic waves in washers.

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