The increasingly important decontamination standards have seen the greater adoption of validated ultrasonic cleaning baths in the CSSD environment.
Since the vCJD, or mad cow disease, scare swept across the UK, hospital sterile service departments (CSSD) have been under ever increasing pressure to provide higher standards of decontamination and traceability. Why?
Sterile service departments are responsible for the the reprocessing of reusable medical instruments that is cleaning, disinfecting and sterilising. Cleaning is the key step here as vCJD can be transferred via prions which require a more thorough cleaning process than other potential infections.
Because of government concern over the potential risk of vCJD and its potential for cross-infection a set of guidelines were introduced to cover the decontamination process. This document is called HTM2030 and covers every aspect of instrument reprocessing from procedures to equipment specifications and validation. It was designed to improve the whole process and tighten up on traceability, which it has achieved. It has also resulted in significant investment in the CSSDs to improve the service. This has meant purchase of new equipment, refurbishment of existing departments and new build CSSDs. Ultrasonic cleaning equipment has become an integral part of this process of improvement and investment due to its ability to clean difficult and complicated instruments.
Washer disinfectors have long dominated this market sector. They carry out a two stage process of cleaning and then disinfecting. The cleaning process is carried out by spray in a similar way to household dishwashers. This method of cleaning is really only effective for exposed areas of instruments and can be a time consuming. Spray cleaning means that areas like hinged mechanisms and serrated edges of instruments can retain contamination, as the water cannot effectively penetrate into these areas, meaning the instrument can potentially be still be contaminated at the end of the cleaning cycle. By then running the items through a high temperature rinse this could further the problem by baking the proteins onto the instrument instead of removing them, meaning they will require further cleaning before the sterilisation process. Pre cleaning with ultrasonic technology prior to the washer disinfector eliminates this problem. The reason for this is down to the nature of the ultrasonic cleaning process
The process itself works by using transducers to create sound energy on the bottom of the tank, which is then transferred through the water. The sound waves created are typically around 40KHz. They lead to the formation of millions of microscopic bubbles in the solution, a process called cavitation, which then expand until they are unable to support they own density, causing them to implode. During this implosion extremely high pressures occur. It is this that produces the cleaning action. The solution rushes in to fill the gap left as the bubble implodes and this creates a scrubbing motion on any surface it comes into contact with. It is effectively like millions of microscopic scrubbing brushes cleaning the surface area of the instrument. This process is ongoing throughout the entire cleaning section of the cycle with around thirty thousand bubbles occurring per second. However, unlike washer disinfectors, which can only clean exposed areas, ultrasonic cleaners have the ability to clean even unsighted areas. This is because the bubbles are small enough to form anywhere where water is present. This even includes the tiny gaps in between the hinged mechanisms on forceps and the serrated edges on scalpels in which water particles are small enough to fit into when the item is completely submerged.
Ultrawaves highly advanced Hygea 5000 has been specifically designed to clean hollow instruments such as rigid laproscopes. Although the process is the same, cleaning such instruments created the problem of how to clean the internals of the items. The Hygea 5000 has a number of attachments that can be hooked up to the different ports on the instruments to ensure flow of cleaning fluid through the instruments during the cleaning cycle. The presence of this cleaning fluid inside the instrument allows cavitation to occur within the hollow channel. Although the fluid is separated from the solution contained in the tank by the metal of the instrument the sound waves will pass through this and cause the bubbles to form inside the item. This results in the same level of cleaning on the inside of the instrument as is achieved on the outside, leaving the item completely contamination free.
Unlike the benchtop cleaners, this specialist hollow lumen cleaner has a fully automated three stage process of one wash and three rinse cycles each of which is drained after completion. The wash cycle starts with an automated fill, including automatic detergent dosing, which eliminates any operator error and ensures the correct temperature of cleaning fluid with the correct dose of detergent. The wash cycle then alternates between flushing the lumens with cleaning solution and timed ultrasonic intervals. This process provides the most effective cleaning of the internal lumen of the instrument. At the end of the cycle the contamination is drained away with the waste cleaning fluid. The first rinse cycle is a town water rinse that also includes lumen flushing and ultrasonic activity. This process ensures that any residual contamination from the wash cycle is removed. The final rinse can either be a second town water rinse or an RO water rinse. This final rinse ensure both the instruments and the tank are completely clean and ready for the next batch.
At present sites that use ultrasonic cleaners incorporate them as part of the decontamination process. Instruments are normally placed through and ultrasonic cleaning cycle, then through a washer disinfector before entering the clean room prior to sterilisation in an autoclave. Although this is an extra stage in the process it is essential for effective decontamination of difficult to clean items. The extra processing does not significantly effect overall reprocessing time, as the cycle time can be reduced through the washer disinfector as the instruments are already clean.
As featured in Clean Room Technology Magazine, Oct 2005
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