The HTM says it does for sure. But we have a few questions and I’m sure you do too.
- What do we actually understand about the mechanics of proteins and bacteria removal and their adherence on to surgical equipment?
- What do we understand about the interface of the equipment we use in the removal of proteins and bacteria with the contamination itself?
- How do these devices actually work in this application?
The consistent removal of proteins and bacteria from surgical equipment should be a precision cleaning process and should not be confused with a more general cleaning application, where amounts of protein, grease or contaminant can be tolerated. In a sterile services context, only a very tight tolerance of the cleaning parameters should be acceptable, but let’s be fair, we’ve struggled to achieve this state and despite our hard work, dedication and best efforts, have been ‘flying by the seat of our pants’ since the HTM was introduced back in 2016.
The current methodology of using an ultrasonic system (sometimes) to remove the proteins followed by a thermal disinfection device to remove bacteria, followed by steam sterilization has been shown to be somewhat of a hit and miss process. So Why is this?
Let’s take a look at the process and try to analyze where and why we’ve been struggling to achieve consistent compliance to the HTM.
PROTEIN REMOVAL
This element of the process is arguably the most important aspect and for sure is the most difficult to achieve consistently. The problem is without doubt the erratic distribution of sound in ‘’general commercial grade’ ultrasonic cleaning systems.
Graph 1 below gives some indication of what is meant by ‘erratic dispersion’
Although the ‘spread’ of sound is only 17mV, in a precision cleaning application this is too much. In graph 1, the average mean voltage of 18.214mV and it can clearly be seen that there are both spikes and troughs of sound. While we should be mindful of the spikes, it is the troughs of sound that are concerning in this application, as these are areas where cleaning can be impaired or reduced. As can be seen is this example, over a 20 second snapshot, we have several troughs of varying lengths of time. Without doubt this is the reason for historical erratic protein removal via ultrasound. Also without doubt, if the proteins cannot be completely removed within stage one of the process, they will not be removed easily by either stage two or stage three.
Graph 2 below was taken from an advanced ultrasonic cleaning system which has been specifically designed for precision cleaning applications such as this.
Right away we can see that the spikes and troughs exist in the same way as in graph 1, however the size and amplitude has been dramatically reduced from 17mV to only 1.6mV. The chaos needed to clean is still present, but the application of the sound is more even, controlled, intense and effective.
Independent tests have shown that this intensity of controlled, advanced ultrasonics will remove all proteins to a very low level, well under the 5µg limit. In addition, it will do so in a very consistent manner.
HOW DOES THIS WORK?
Ultrasonics works via the process of cavitation. This is caused by flexure (NOT vibration) of the sides or base of a tank. The flexure is caused by the rapid expansion and contraction of transducers that are mechanically bonded to the tank. This flexure is very fast and can range from thousands up to millions of times per second. When fluid is introduced into the tank, microscopic vacuum chambers are created under the fluid on the downward flex and on the upward flex, these vacuums are pushed into the fluid in the form of vacuum bubbles. These bubbles rise-up through the tank fluid, growing all the time, until they hit the surface or an object, upon which they implode at high speed and pressure, creating a microjet that draws away the contamination.
The graphic below illustrates this process.
Phase 1 of this process is up to the formation of the micro-jet that gives rise to the very high temperature of 5000°K (4727°C). To enable precision cleaning via ultrasonics, these implosions and the subsequent high temperature pockets need to be tightly packed, homogenous and intense. Because of the uneven distribution of sound as found in a standard commercial grade device, the microscopic implosions and micro-jets are more sparsely spread, thus leading to uneven protein and bacteria removal.
PROCESS CHALLENGE DEVICES
The use of PCD’s to prove cleanliness in sterile services has been adopted by the sector for many years. Recently, Aseptium, an Inverness (UK) based company have introduced their Veritest PCD, which comprises 4 test strips, treated with a measured amount of Sheep Brain Homogenate that are set into a plastic frame designed to rigorously test any process. (PCD’s produced by other manufacturers are also available)
The below test sheet was taken at an NHS trust in February 2020 using a Medstar Compact Advanced Ultrasonic cleaning system. With a 15 minute cleaning cycle. The level and consistency of cleaning on this set of ‘Veritest’ PCD’s can clearly be seen.
BACTERIA REMOVAL
When our bubbles implode they also create temperatures of about 5000° Kelvin, (4727° Centigrade) Although only for a nano-second over a microscopic area, these temperatures are about 46 times hotter than boiling water, meaning that on a molecular level, any bacteria close to the imploding bubble will be ‘Cold Vapourized’. What is happening is that we are producing extremely small, high temperature pockets within a cold water matrix that will not materially increase the temperature of the said water by more than say 5°C over a standard 20 minute cleaning cycle.
The evenness and intensity of Advanced Ultrasonics has been independently shown to deliver a log reduction of 5.5 for heavily soiled instruments and a log reduction of 6.6 on lightly soiled instruments. This being achieved in 20 minutes in cold water. In essence therefore, what Advanced Ultrasonics delivers is a kind of ‘side effect disinfection’ and a ‘side effect sterilization’ through the control and intensity of the micro-jets as they implode on the surface of the instrument.
By actively tackling the removal of protein, we are getting a bonus in bacteria removal.
IN CONCLUSION
Is heat required to remove Protein and Bacteria?
Yes, but there are much better, consistent and efficient ways of delivering this heat other than with boiling water.
Applying the heat in a very precise and even manner has been shown to deliver startling results that far and away outstrip the requirements of the HTM01-01 (2016)
This can only be good for the decontamination sector and theatre bourn infection rates, with a positive impact on A&E departments and the general wellbeing and recovery of patients.
