The application of sound into fluid to deliver an efficient cleaning process has been around for many years and has been utilised to great effect. However, there is clean and then there is clean. So, what do we actually mean when we use this word? Certainly, the requirements for general commercial and industrial cleaning are far removed from what is required in the decontamination sector.

Historically, ultrasonics have been used in an attempt to remove proteins from surgical equipment prior to processing in a thermal device. The results, however, were erratic – leading the sector, in many cases, to discard the process altogether through uncertainty of the results achievable with the equipment provided. Nevertheless, the fact remains, if set up correctly in a controlled manner, with complete focus on the application of sound, ultrasonic technology can achieve exceptional levels of precision cleaning capable of meeting the high demands of the healthcare and medical sector.

How does fluid-based ultrasonic cleaning technology work?

Transducers bonded to the base or side of a tank are excited by high frequency electricity, causing them to expand and contract at very high rate. This mechanical action causes high speed flexure of the radiating tank face(s). The speed of this movement is too fast for the fluid in the tank to follow, resulting in the production of vacuum chambers. On the upward flexure the vacuum is released in the form of a vacuum bubble that rises up through the fluid until it hits an object, (or the surface of the fluid) upon which the bubble implodes under high pressure, creating a micro-jet that draws away any contamination that may be on the surface of the object. This in a nutshell is how the technology works. However, there are limitations as to how effective and efficient the cleaning action will be in isolation.

Attaining and maintaining ‘zero’

Alphasonics took up this challenge in 2013, having operated predominantly in a sector that required regular, precision cleaning of very delicate components without causing damage. It was pondered if the same technology could provide the elusive ‘zero’ that the decontamination sector was striving for.

The fundamental question is what are we actually trying to achieve – zero what? Zero bacteria or zero protein? From the research and development carried out over the past eight years, it has become clear that one cannot be achieved without the other. Zero bacteria will never be consistently reached if there is protein remaining on the instrument as bacteria can exist on, in or under an area of protein, so to get at the bacteria, the protein has to be completely and consistently removed.

But here lies the problem: as others have found out, protein is extremely difficult to remove and becomes more tenacious when heat is applied. This fact alone makes it incredibly difficult to consistently remove the protein fully in any thermal device. I am not saying that it cannot be done, as others have shown (unpublished), but the inclusion of heat simply makes the task much more difficult.

Obtaining ‘zero’ has always been the goal. It took some time to understand the issue fully and of course the potentially devastating consequences of failure. The real breakthrough came in 2014 when a ProReveal device was purchased. This investment enabled a ‘test and measure’ regime to be quickly established that yielded great progress.

Our research found that the removal of protein is easier in cold water with the optimum temperature being between 17° to 20°C. By 2016 before the launch of the revised HTM0101, the point had reached whereby complete and consistent removal of protein had been achieved well into the ng range (as measured with a validated ProReveal device).

Then came the Health Technical Memorandum (HTM), that alongside other things stipulated that the ultrasonic activity should be validated on a very regular basis. This threw a spanner into the works as how could this be achieved? With a foil test? Surely not. As no technology existed at that time to measure ultrasonic cavitation, a sub-project was embarked on to develop a device that would accurately and consistently validate the ultrasonic activity in a tank of fluid.

Two years later and with collaboration with a University, the world’s first device to measure electrical activity caused by cavitation and, as such provide a measure of the cavitation itself, was developed. This piece of equipment opened several doors and enabled full compliance with the HTM.

The development of the Cavitation Validation Device (CVD), coupled with a methodology of applying sound into fluid, delivered startling results and provided a major breakthrough in striving for ‘zero’ as not only were the levels of cleanliness achievable, but more importantly consistently delivered.

Natural dispersion

The natural dispersion of high frequency sound when applied into fluid is of a somewhat erratic nature. Fine for cleaning jewellery or spectacles, but not for achieving consistent precision cleaning that is required for healthcare. It is this natural dispersion of sound that is at the heart of the failure of successive manufacturers of surgical equipment cleaning systems to produce devices that consistently deliver what the sector needs.

The graphs 1 and 2 (see below), featured in this article, give some indication of what is meant by ‘erratic dispersion’. Graph 1 shows the cavitation activity in a system that historically has been used to clean surgical equipment. It can be noted that there are both ‘spikes’ and troughs’ of sound about a mean. In surgical instrument cleaning settings, the spikes of sound are of little consequence, but the size and duration of the troughs of sound are of great concern and where we need to focus our attention.

The CVD device that produced these graphs achieves its results via 9 sets of readings, each of 20 seconds duration, with 10 individual readings per second, meaning 1800 individual readings overall. The section ‘readings 1-3’ gives us the average size of the spikes and troughs across the whole 1800 individual readings and it is noted that in this set the mean voltage was 19.254mV and the min reading was 13.4mV.

A 5.85mV variance does not sound like a lot, but when cleaning at this level on a contaminant that is extremely difficult to remove, it is too much and trials carried out between 2014 and 2016 proved this conclusively. What is also of concern is the length of time that a trough can last. In this graph, we can clearly see a trough of sound (in green) that is 2 seconds in duration, plus a further 2 seconds while the power fell before recovering again. This highlights a period of 4 seconds where cleaning can be impaired.

Graph 2 shows the activity in a system, where the incoming sound has been manipulated to greatly reduce the size of the spikes and troughs, while still creating the chaos required to deliver an effective clean. Again, looking at ‘readings 1-3’, we can see that the mean in this set of readings was 27.828mV and the min voltage was 27.2mV, showing a variance of only 0.628mV across 1800 individual readings.

The readings taken with this device are done so across three levels within the fluid depth and from side to side. In essence, these results are unique, extremely accurate and deliver a never-seen-before insight into the activity of high frequency sound when applied into fluid. Readings such as this have been taken in tanks 5m in length that delivered very similar results.

It is a simple fact that if something can be measured, it can be improved. This has been the case with the CVD, as apart from being able to look at competitor equipment and having a product to sell, we have also been able to insert this probe into our own equipment, enabling several unique modifications to be made to further enhance the performance, efficiency and capability of the cleaning system.

Foil test

This erratic dispersion of sound is clearly highlighted when conducting a foil test. It is a misconception that when holes are created in the tin foil, it is an indication of good ultrasonic activity – in fact, it is quite the opposite. The holes created in the tin foil are as a result of the spikes of sound as shown in graph 1 and as such, clearly demonstrate erratic dispersion. If spikes are present, there will inevitably be troughs, leading to potentially poor cleaning. Where ultrasonic activity is homogenous, there should be pummelling in the tin foil, but no holes. If holes are present, the system should be considered as not fit for purpose at this level.

Through intense experimentation and great assistance from several eminent colleagues, technology is now available that delivers complete protein removal.

Bacteria

But what about bacteria? It was decided in 2018 to engage an outside laboratory to look for and measure any residual bacteria that may still linger on the instrument after processing.

The results obtained came as bit of a shock and a further leap in understanding of the relationship between bacteria and protein. The results matrix (Figure 1) highlights what is achieved in terms of bacteria removal following processing in an advanced ultrasonic cleaning system. The laboratory used their own heavily soiled instruments and removed them for measuring immediately after a 20-minute cycle at 20°C.

What this table of results clearly indicates is that once the protein is completely removed, it is a relatively easy job to remove bacteria with the right chemistry in an Advanced Ultrasonic tank with homogenous activity.

While disinfection cannot be claimed as the device does not have a thermal disinfection cycle, the results clearly speak for themselves. A log reduction of 5.5 in cold water. ‘Side effect disinfection’ is disinfection that is achieved, not as the primary aim of the equipment but as a ‘side effect’ of the protein removal process.

Further trials were carried out on ‘lightly soiled’ instruments that returned an average log reduction figure of 6.65, giving further proof of the efficiency of this technology. Several articles have been written about cold sterilisation. Figure 2 shows that it is indeed possible.

What do we mean by advanced ultrasonics?

No matter how good, even or aggressive the distribution of sound is, this in itself will not deliver the consistency required for this application. More is needed. The core technology used in the contamination removal process must be supplemented by a suite of additional technologies to ensure that the consistency and performance of the device is maintained. Furthermore, every aspect of the system has to be monitored as much as possible from start to finish not only to ensure compliance, but to reduce theatre bourn infections and reduce the risk to life.

With this in mind, every aspect of the device should be monitored to ensure that the system is functioning as it should, with appropriate alarms in place to warn and also cut the electrical supply to the machine if required.

One such aspect, although not stipulated within the HTM 01-01, is the control of biofilm and the negative impact this can have on cleaning performance. During the many trials carried out between 2013 and 2016, it was noted that the first trial carried out after a weekend always rendered poor results. It was concluded that this was in fact caused by biofilm settling on the walls and base of the tank over the weekend (even with the lid closed). We found it astounding that such a small element could affect cleaning in such a way, even after such a short length of time. What this highlighted was that every aspect of the device needed to be exactly right before cycle start if system, and consequently output control, were to be achieved. Recognition and attention to biofilm is a critical requirement in any cleaning device that hopes to deliver the desired results.

To avoid the use of foil tests as a means of gauging the ultrasonic output it is important that in some way the core cleaning technology itself should be self-monitoring, with suitable safeguards in place to take corrective action should the generator tuning drift, or a transducer fail for example. This feature comes into play where lumens and rigid endoscopes are to be cleaned, alongside standard surgical instruments.

When validating the ultrasonics, where should the parameters and limits be set? Outside the lumen or inside the lumen? Measuring the ultrasonic activity down the inside of the lumen is an impossibility with a foil test. However, with a CVD, experiments have been undertaken to determine the losses through the wall of a lumen/rigid endoscope that enable the generator output control system to be set to accommodate this.

There are several other inherent features that need to be included within a successful device, which although not directly linked to HTM compliance itself, enable the conditions for compliance. For example, we have known for a long time that ultrasound when applied into a fluid, actually works at its best during something called the ‘de-gassing phase’. De-gassing of the tank fluid can take a few seconds or several minutes, depending on the watts per litre of sound applied. Active cavitation is a technology that greatly assists with cleaning performance and consistency. Betasound is another technology that delivers the ultimate in even distribution of sound into a tank of fluid.

Protein removal system

Ultimately, after eight years of R&D, the result is a fully compliant, robot cleaning device for surgical instruments, lumens and rigid endoscopes. The design and functionality of Medstar 3 renders instruments and lumens completely protein free to both inside and outside surfaces and has several patented features that enhance the performance and enable compliance with the HTM. It has also been designed to accept robotic instruments.

During this period, many discoveries were made which have ultimately led to the development of equipment and technologies that will help improve patient safety and patient outcomes.

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