17-Oct-2005

Keep surgical instruments prion-free

Abstract

Since the BSE scare, hospital sterile service departments have looked to new standards of equipment decontamination. Edward Mant of Ultrawave describes how ultrasonic technology helps.

Today, hospitals use central sterile service departments (CSSDs) for cleaning, disinfecting and sterilising reusable medical instruments. And, because it is now believed that variant Creutzfeldt-Jakob disease (vCJD) the human form of BSE can be transferred from patient to patient via prions adhering to surgical instruments, such equipment requires more thorough cleaning.

Government concern over the risk of vCJD cross-infection led to the introduction of a set of guidelines in a document called HTM2030, which covers every aspect of instrument reprocessing from procedures to equipment specifications and validation and is designed to improve the whole process and tighten up on traceability, which it has consequently achieved. It has also resulted in significant investment in CSSDs in order to improve their services. This has meant purchase of new equipment, refurbishment of existing departments and new builds. Ultrasonic cleaning equipment has become an integral part of this investment process, due to its ability to clean complicated instruments.

Two-stage process Washer disinfectors have long dominated this market sector. They carry out a two-stage process of cleaning and disinfecting. The cleaning is carried out by sprays in a similar way to household dishwashers, but is only effective for cleaning exposed areas of instruments, and can be time-consuming. Spray cleaning also means that facets, such as hinged mechanisms and serrated edges of instruments, can retain contamination because the water cannot effectively penetrate these areas. Potentially, the instrument could still be contaminated at the end of the cleaning cycle. If this is the case, running the items through a high temperature rinse could worsen the problem by baking the proteins onto the instrument instead of removing them. Pre-cleaning with ultrasonic technology prior to the washer disinfector eliminates this problem. The process involves the use of transducers to create sound energy on the bottom of the tank, which is transferred through the water. The sound waves created are typically around 40kHz, and lead to the formation of millions of microscopic bubbles in the solution (a process called cavitation), which expand until they are unable to support their own density, causing them to implode. During this implosion extremely high pressures occur which produce the cleaning action. The solution rushes in to fill the gap left as the bubble implodes, creating a scrubbing action on any surface that it comes into contact with. This process is ongoing throughout the entire cleaning section of the cycle, with around 30,000 bubbles occurring per second.

Hidden areas cleaned Unlike washer disinfectors which clean only exposed areas, ultrasonics can clean unexposed areas. The bubbles are small enough to form anywhere that water is present when the item is completely submerged, even in the tiny gaps between the hinge mechanisms on forceps and the serrated edges on scalpels. Ultrawave's Hygea 5000 has been designed to clean hollow instruments such as rigid laproscopes. To do this it 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 instrument during the cleaning cycle. The presence of this cleaning fluid inside the instrument allows cavitation to occur within the hollow channel. Despite the fluid being separated by the metal of the instrument from the rest of the tank solution, the sound waves will pass through it and cause the bubbles to form inside. This results in the same level of cleaning on the inside of the instrument as on the outside, leaving it completely free of contamination. Unlike the benchtop cleaners, this 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.

Timed ultrasonic intervals The wash cycle then alternates between flushing the lumens with cleaning solution and timed ultrasonic intervals; this 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, which ensures that any residual contamination from the wash cycle is removed. The final rinse can be either a second town water rinse or a reverse osmosis (RO) water rinse to ensure that 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 put through an ultrasonic cleaning cycle, then through a washer disinfector before entering the cleanroom prior to sterilisation in an autoclave. Although this is an extra stage in the process, it is essential for effective decontamination of items that are difficult to clean. However, it does not significantly affect overall reprocessing time because the cycle time through the washer disinfector can be reduced as the instruments are already clean.

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