3 Factors influencing the effectiveness of Ultrasonic Cleaners

What determines the result of instruments cleaned in an ultrasonic cleaner? Some factors determine the cleaning effectiveness of the cleaner. Of more importance, however, is the physical properties of the cleaning solution through which the ultrasonic waves propagate.

The electrical power applied to the transducers is in direct proportion to the magnitude of the ultrasonic waves. The amplitude of these waves and the electrical power both have to exceed a minimum threshold value for cavitation to take place.

The properties of the cleaning solution, which include its temperature, viscosity, density, vapor pressure, and surface tension, cause this threshold value to vary such that changes in any one of these properties can influence cleaning effectiveness.

Apart from helping in the removal of patient debris from contaminated instruments, detergents boost cleaning effectiveness by decreasing the surface tension of the water. This effect increases cleaning effectiveness by facilitating the transmission of the ultrasonic waves through the detergent solution, lowering the minimum amount of ultrasonic energy necessary for cavitation to take place, and reducing the resistance to the flow of the detergent solution through the instrument’s narrow lumens and orifices.

Some of the factors influencing the effectiveness of ultrasonic cleaners include;

Instrument arrangement

The method of instrument arrangement in the processing chamber affects cleaning effectiveness as much as the choice of the detergent. Ultrasonic energy travels in one direction from the transducer through the cleaning liquid. This potential shortcoming can be solved by proper arrangement of the contaminated instruments in the processing tray to ensure maximum exposure to and contact with the ultrasonic waves.

Laying the contaminated instrument’s most heavily soiled surface towards the bottom of the cleaner’s processing basin improves chances of achieving cleaning effectiveness.

Additionally, rotating the instrument and repeating the ultrasonic cleaning cycle to expose all of its surfaces to the ultrasonic energy may help if the instrument is heavilysoiled.

Energy distribution and intensity

Most of the quantitative methods for assessing the cleaning effectiveness of ultrasonic cleaners can be very hectic and take up a lot of time, and often need at least some subjective interpretation of the results.

However, a few methods may be of significant help in approximating their cleaning effectiveness. For instance, the “aluminum foil erosion test” examines both the intensity and distribution of the cleaner’s ultrasonic energy.

New sheets of aluminum foil are placed vertically in the middle of the ultrasonic cleaner’s processing tray filled with water. (Detergent is not necessary since the purpose of the test is to assess the intensity and distribution of the ultrasonic energy and not the effectiveness of cleaning.) After several cycles, the sheets are inspected for patterns of damage or corrosion.

The power and uniformity of the intensity and distribution of the cavitation are shown by the significance and uniformity of damage to the foil sheets.

The presence of air bubbles

The presence of air bubbles in the cleaning solution also affects cleaning time. Ultrasonic waves, unlike sound waves, require a liquid medium for effective transmission. Hence, the surfaces of instruments dotted with air bubbles cannot be cleaned effectively by ultrasonic energy.

Neither can instruments be properly cleaned by ultrasonic energy if pockets of air remain between them. In the same way, detergent solutions containing air bubbles can affect the proper transmission of ultrasonic waves, affecting cleaning effectiveness.

However, when the ultrasonic cleaning cycle is started, the removal of air and other gases from the detergent solution and any other liquid medium is then possible.

Also, numerous tests have been proposed to assess the effectiveness of ultrasonic cleaners. Physical observation of the extent to which patient soil is removed from a contaminated instrument, though subjective, can be a trusted measure of cleaning effectiveness. More quantitative tests may evaluate cleaning effectiveness by measuring and comparing the levels of a radioactively-tagged material like blood, before and after ultrasonic cleaning.


Apart from enhancing the productivity of reprocessing staff and reducing the staff’s exposure to contaminated instruments, ultrasonic cleaners have been proven to be more effective and thorough than manual scrubbing, which is usually tiresome and whose results are often unpredictable and faulty.

Other overlooked advantages of ultrasonic energy include its improvement of the sporicidal properties of liquid chemical sterilants. At a time when low-temperature sterilization processes are gaining more preference, more emphasis and significance should be placed on improving the effectiveness of the cleaning process to make up for the low sterility assurance levels of low-temperature sterilization processes in comparison to thermal sterilization.

The development of instrument designs that facilitate cleaning and are not damaged by the rigors of cavitation is recommended to minimize the possibility of cross-infection.