Guide to Ultrasonic Cleaning
What is Ultrasonic Cleaning?
Sonication (or ultrasonic) technology uses mechanical vibrations (sound waves) in a liquid as a cleaning method in a process known as cavitation. Essentially, the generation of sound waves in the liquid produces bubbles that collapse (burst or implode) on contact with surfaces, which aids in the removal of soil from surfaces. When designed correctly, ultrasonic cleaning can be particularly useful for cleaning of hard to reach areas on a device, but can also be gentle on delicate instruments such as microsurgical and ophthalmology devices.
Important Variables in Ultrasonic Cleaning
Ultrasonic cleaning systems can provide cleaning using a combination of effects that are important for a controlled cleaning process over time. These variables include:
- Cavitation, based on the ultrasonic power
- Detergent activity
- Flow (for lumened devices, when applicable).
The optimization of these combined effects provides an efficient cleaning system for delicate and difficult to clean devices such as Minimally Invasive Surgical (MIS) instruments, laparoscopic devices and robotic surgical attachments.
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The efficiency of the cavitation process is dependent on the design of the ultrasonic system and particularly on the ultrasonic power (measured in kilohertz, kHz). A comparison of cavitation at 40 and 132 kHz power in water is shown below:
Although both processes can aid in cleaning, the higher power process (132kHz) is considered more efficient for cleaning surfaces, in particular for penetration of smaller spaces. A further way to optimize sonication cleaning is to use two alternating sonication powers, such as 58/132 kHz, to provide a more efficient process. Both these can create more implosions in tighter surface spaces that are typical of complex instruments/devices.
How the sonication is generated (using transducers) in the system is also important. For example, older technology uses metal transducers that could sometimes cause problems with metal instruments, while newer designs use ceramic transducers that are gentler on devices.
Immersion, Detergents and Rinsing
Immersion has the benefit of soaking the device in the designated detergent to allow for the cleaning activity, in particular enzymatic activity (when used) under controlled conditions. The choice of cleaning chemistry is important. These detergent based products should be designed to provide efficient cleaning, be effective over a range of different water qualities, not be harmful to the device, protect the device from damage over time, and be easy to rinse. The controlled conditions for cleaning will include temperature, detergent concentration, exposure time, and rinsing. Rinsing is important to ensure that no toxic or interfering residual substances remain on the device before further processing (disinfection/sterilization). Note that adequate rinsing may require one or more rinses with fresh water to ensure the removal of harmful residue. Rinsing may be done manually, in accordance with device manufacturer's instructions, or as part of an automated cycle, as validated by the device and/or sonication system manufacturer. The cleaning and rinsing conditions should be validated and specified by the detergent and ultrasonic system manufacturer. It is the responsibility of the operator to ensure that all instruments are submerged, all lumens are connected to the flush tubing (if applicable), instruments are disassembled per manufacturer's instructions, and all instruments are positioned for surface contact during cleaning/rinsing.
Flow of the detergent and rinse water allows for more efficient cleaning of the internal channels of lumened or cannulated devices. This may be provided in some ultrasonic designs with the use of connecting tubing that will flush the device/instrument, but may not be available in others. Lumened devices that are not adequately flowed cannot be expected to be cleaned in ultrasonic cleaning systems.
Overall, a combination of all these variables in ultrasonic cleaning systems can provide an optimal cleaning process for devices.
It is important to note that ultrasonic cleaning systems can vary significantly in their design, intended use, operation, and maintenance. The system labeling including instructions for use should be read carefully.
Ultrasonic Cleaning Recommendations
The following recommendations are given for the safe and effective use of ultrasonic cleaning systems:
- Ultrasonic cleaning systems should be installed, used and maintained in accordance with manufacturer's instructions. This will include the use of specific detergents for cleaning which should be compatible with the equipment and cleaning process and adherence to recommended preventative and routine maintenance.
- The cleaning solution should be designed for use in ultrasonic systems to assist in the removal of soil and prevent soil reattachment to surfaces.
- Degassing of freshly prepared cleaning solution is generally recommended before processing devices, following manufacturer's instructions.
- Some devices/materials of construction (such as certain types of rubber) are not recommended for sonication due to the risk of damage to device components. The device instructions for use should be consulted to ensure compatibility.
- Devices that contain metals such as brass, copper, aluminum, or chrome-plate may not be compatible if mixed with other device materials such as stainless steel.
- Gross soil should be removed (pre-cleaned) from the device prior to cleaning in the ultrasonic system and lumens brushed/flushed.
- The ultrasonic cleaning system should be fitted with a lid and the lid should be closed during ultrasonic cleaning to prevent aerosolization.
- Unless validated in the system design, rinsing is required following ultrasonic cleaning.
- Cleaning solutions should be frequently changed, preferably with each use and always before processing ophthalmology instruments.
- Periodic verification testing of the sonic unit is recommended to confirm that the cleaning process is functioning properly. This will include daily maintenance and periodic service maintenance.