Ultrasonics in Infection Control

Ultrasonic cleaners provide an effective solution to the increasingly important question of the instrument reprocessing question. The quick cycle times, effective cleaning and validation possibilities make ultrasonic cleaning an essential part of the decontamination process.

As the technology used in operating procedures advances the need for cleaning processes to evolve is now a vital part of the surgical instrument reprocessing chain. Surgical instrument cleaning came under heavy scrutiny after the vCJD scare which swept through the UK and lead to the creation of decontamination guideline document HTM2030. Here we look at the process of ultrasonics and why it should be incorporated as an essential element of the infection control process, in order to achieve maximum decontamination standards.

In order to truly understand why ultrasonic cleaners are so effective for carrying out decontamination on soiled instruments it is important to understand how the process works.

An ultrasonic cleaner uses high frequency sound waves transmitted through a cleaning fluid in order to create a process called cavitation. To do this an electrical current is passed through a number of piezo ceramic transducers, which are bonded to the base of the bath. This causes the crystal elements to vibrate somewhere in the region of 40,000 times a second. These vibrations convert the electrical energy to sound energy, which is then transferred through the transducer element and into the liquid medium. As these sound waves pass through the liquid they cause the sequential formation of microscopic bubbles. Forced to expand by the moving sound waves they grow in size until they are unable to support their own density, causing them to implode: the process of cavitation. These implosions drag the surrounding fluid in to fill the gap created and leads to the occurrence of a cleaning action similar to a scrubbing brush, but on a microscopic scale. As this occurs millions of times a second it makes ultrasonic cleaning such a powerful decontamination process. Once an item is submerged into the water any area in contact with the cleaning fluid will be subjected to cavitation and therefore the cleaning action.

Many of the instruments used in today's operating procedures have complicated designs with difficult to clean areas which will require thorough cleaning after each use. It is ultrasonics ability to these difficult areas that has made it a vital element of the instrument decontamination process. This is best illustrated with hinged, serrated and hollow lumen instruments. If water can penetrate into the difficult area then ultrasonic activity can clean it, lifting off debris and contamination leaving it clean on a microscopic level.

Because of this ultrasonics has a definitive place as the foundation level cleaning method in the instrument reprocessing chain. Once an instruments use in theatre is complete they are transferred down to the dirty room of the hospital en-route to being sterilised. By placing them into an ultrasonic cleaner first it will ensure that the instruments are thoroughly cleaned prior to the disinfection stage.

An ultrasonic cleaner cycle is short, typically around ten minutes or less, meaning the time taken to decontaminate instruments can be reduced. This means the cycle time required in a washer disinfector can be reduced to just carry out the thermal disinfection stage and not the full cleaning cycle. With full cycle times for washer disinfectors being anything up to fifty minutes in length eradicating the need for them carry out a full cycle should increase the throughput of instruments, whilst achieving a higher level of decontamination.

There are a number of different ultrasonic cleaners available for use in decontamination. Current guidelines state that each stage of the cleaning cycle must be validated to allow for easy traceability.  Cardiff based company Ultrawave, have developed a series of units specifically to carry this out. Their range of Hygea ultrasonic cleaners come with fully in built validation as standard. This validation records and prints every aspect of the cleaning process and whether it was completed successfully. They offer two units for use in such environments. The Hygea 1250 is a benchtop cleaner which is ideal for smaller items such as scalpels and forceps and runs a very short cleaning cycle of a mere six minutes. The larger of the two units on offer is the Hygea 5000. This is a fully automated hollow lumen cleaner which has a series of connection ports where lumens are connected ensuring they are cleaned both internally and externally. Both record and validate each process allowing the user to guarantee that the cycle has been completed successfully prior to the items going into the washer disinfector.

First Published  The Operating Theatre Journal   Issue 184   January 2006   ISSN 1747-728X  www.otjonline.com