Ultrasonic Solutions

Cavitation: The fundamental process that empowers ultrasonic cleaners to be so effective is called cavitation. Cavitation refers to the formation, growth, and implosive collapse of microscopic bubbles in a solution.  Cavitation happens when ultrasonic waves pass through the cleaning solution and create high-pressure and low-pressure cycles.  During the low-pressure phase, microscopic bubbles or “cavities” form, and as the high-pressure wave follows, these bubbles implode.

The reason this is significant for healthcare is because these imploding bubbles produce extreme temperatures and pressures locally, essentially creating “micro-jets” of cleaning solution that impact the surface of the instrument being cleaned.  This method is very effective at dislodging contaminants at a microscopic level, which makes it particularly useful for cleaning complex medical devices with difficult-to-reach areas, often inaccessible by manual cleaning methods. 

The Generator: How does an ultrasonic cleaner create the ultrasonic energy for cavitation? The generator, also referred to as the power supply, plays a vital role in an ultrasonic cleaner by producing the high-frequency electrical energy required to power the transducers. This transformation of facility current into high-frequency electrical energy is what enables the transducers to generate mechanical vibrations. These vibrations create cavitation bubbles, which are central to the cleaning process. The generator operates at varying frequencies, typically ranging from 20kHz to 400kHz.

The varied frequencies supplied by the generator to the ultrasonic transducers has a direct effect on the cleaning performance of the cleaner.  Higher frequencies produce smaller bubbles with decreased cavitation energy in the solution.  The smaller bubbles can affect cleaning in smaller areas but take considerably longer to clean.  Lower frequencies produce larger bubbles with greater cavitation energy in the solution.  The more turbulent cleaning process caused by lower frequencies emitted can clean faster, but over time can shorten the life and quality of the instrument.  The Ultrasonic generator and transducers should be balanced and optimized to produce a safe and effective cleaning process for surgical instruments.

Transducers: Transducers serve as the heart of ultrasonic cleaners, performing a critical role in converting electrical energy into high-frequency mechanical vibrations that generate cavitation within the solution. These vibrations are central to the ultrasonic cleaner's ability to thoroughly clean surgical instruments and other medical tools. Depending on the size of the ultrasonic cleaner, there will be multiple transducers placed around the tank to emit ultrasonic energy into the tank.

One of the challenges ultrasonic transducers face is “cold spots” in the cleaning solution—areas which receive reduced cavitation due to the positioning of the transducers.  Bonded transducers, which are affixed to the base of the cleaning tank and emit energy upward in conical fields, can experience cold spots in between the transducers.  Titanium Rod Transducers (TRT) produces high cavitation energy output with a titanium rod that sits inside the basin rather than being fixed below it, providing uniform energy distribution and eliminating cold spots.  This technology can lead to increased cleaning power in a shorter wash-cycle time than bonded transducers.

Heating Element: The heating element within an ultrasonic cleaner serves the vital purpose of heating the cleaning solution to enhance its cleaning effectiveness, especially against stubborn soils found on surgical instruments. Exact temperature requirements may vary based upon the specific cleaning solution used, the type of material being cleaned, and institutional policies. However, best practice suggests that for enzymatic detergents, a temperature range of 90°F to 120°F Is optimal for enzymatic activity and cleaning performance.  As always, check the manufacturer recommendations for your detergent for temperature requirements.

Understanding the temperature requirements for cleaning is significant, because when your ultrasonic cleaner fills, it may require time to come up to temperature before being ready for that first cycle.  If your ultrasonic cleaner does not have a heating element, the temperature of the cleaning solution should be monitored.  If the cleaning solution cools below the required temperature for your detergent, the cleaning solution should be discarded and replaced.

Utilities: While the operation of ultrasonic cleaners in Sterile Processing is pretty straightforward, the installation of one requires some careful thought. Like other mechanical washers, ultrasonic cleaners are far from being “plug and play.” Every piece of equipment is going to have different requirements for utilities; here are some that your equipment may need:

• Electrical – First and foremost is the electrical supply, which must be consistent and reliable, and match the specifications of the equipment spec sheet.
• Water – Equipment will vary on which kinds of water must be supplied to the unit. Some of the smallest units require no water supply, and the user must manually fill the tank.  Other cleaners may require a cold water supply, hot water, or both.  Advanced machines that perform final rinses may also require critical rinse water, which has been further treated to remove contaminants and ions.
• Drainage – Ultrasonic Cleaners must be regularly drained and refilled. Proper functioning drains are important to prevent overflows and back-up. It can be tempting to have the ultrasonic share existing sink or washer drains, but be certain that the drain is adequately sized to handle the ultrasonic washer draining at the same time as the sink or washer it is sharing with.

Control Panel: The control panel and display of an ultrasonic cleaner serve as the central command interface, enabling the user to manipulate various operational parameters such as time, temperature, frequency, and special cleaning cycles. This interface may be digital or analog, depending on the model. Through the control panel, users can adjust cleaning settings to match the specific requirements of the instruments being cleaned, enhancing both efficiency and effectiveness. Alert messages are displayed when errors occur, providing immediate feedback and guidance for troubleshooting. Some control panels may also offer lock-out options to prevent unauthorized tampering, ensuring consistent cleaning results and compliance with standardized protocols. Familiarity with the control panel's functions, features, and programming options is essential for the sterile processing technician. Mastery of this interface leads to optimized cleaning processes and a higher level of confidence in the reprocessing of surgical instruments. In essence, the control panel and display act as the user's direct connection to the ultrasonic cleaner's capabilities, facilitating a tailored and responsive approach to instrument cleaning.

Lumen Connections: Lumens are naturally a hard challenge for Sterile Processing to clean. We can’t get very large brushes down them, you can’t see inside them (without a borescope), and soil tends to get forgotten about inside them.  But the ultrasonic cleaner is one of the best tools we have in Sterile Processing to help us clean lumens. It gives you the ability to get into the lumens in a way you could not before.

Many ultrasonic cleaners, even small table-top units, have accessories that attach to lumens and flush cleaning solution through the lumen during the cycle.  This irrigating action adds another element of friction inside the lumen in addition to the cavitation action happening in the chamber.  The turbulent flow ensures cleaning solution reaches the entire length of the internal channels in these instruments, ensuring a more comprehensive cleaning.  Technicians utilizing the lumen cleaning connectors should ensure each connector is appropriately sized and properly seated for the instrument being cleaned.   While some attachments are designed with luer connections for suction tips or laparoscopic suctions, other attachments are designed specifically for complex instruments such as robotic instruments.

Trays: Odds are you are not dropping your instruments straight into the ultrasonic cleaner. Trays and baskets are essential to keep instruments together as they are loaded and unloaded from the ultrasonic cleaner, and they protect instruments from directly contacting the ultrasonic transducers in the base of the tank.  But did you know that some baskets and trays can inhibit ultrasonic cleaning?  Trays without perforations, or with mesh that is too fine, can inhibit ultrasonic energy from reaching the instruments in the bottom of the basket.  Small mesh holes also tend to bring air bubbles with it down into

Trays should be made of a compatible material and specifically designed to facilitate ultrasonic cleaning.  Silicone mats are also a popular liner for the bottom of instrument baskets to protect surgical instruments, but they too can inhibit the cavitation cleaning process in your ultrasonic cleaner.  Before ultrasonic cleaning, silicone mats should be removed, and instruments should be placed in a mesh basket that allows cavitation bubbles to fully encompass the instruments.

The Lid: It may seem like the lid of your ultrasonic cleaner is an afterthought, but the lid is an essential component for ultrasonic cleaning. The ultrasonic cleaning cycle is a turbulent process, and the cavitation energy tends to aerosolize the cleaning solution, potentially spreading contaminants into the air.  With the lid closed during the cycle, contaminants are contained within the tank and are not given the opportunity to aerosolize.

Many ultrasonic cleaners have automated lids that will close and lock during the cleaning cycle, preventing the user from opening the lid mid-cycle.  However, if your unit does not have an automated lid, requiring the user to manually open or close the lid, technicians should be informed that the lid should stay closed during the entire wash cycle of the ultrasonic cleaner.  This recommendation can be found in various best practice documents published by AORN and AAMI, but you may also find it to be a requirement in your equipment manufacturer’s IFU.  Read through those instructions carefully, and always follow the equipment manufacturer’s requirements for operation.

Common Mistakes: As we continue to explore the anatomy of ultrasonic cleaners, it is important to consider some of the common mistakes that users make with their ultrasonic cleaners that can undercut the cleaning process.

Not Degassing the Cleaning Solution – Inert gasses dissolved in the cleaning solution can dampen the effectiveness of ultrasonic cleaning.  Cavitation energy first attacks the inert gasses, leaving less energy for instrument cleaning.  Every time the ultrasonic cleaner is filled with new cleaning solution, it must be degassed before use to ensure effective cleaning.  If this is not done automatically by your ultrasonic cleaner, it is performed by running a brief cycle without any instruments.

Shortcutting the Cycle Time - Time is a critical parameter in any cleaning (and sterilization) workflow, and it’s tempting to shorten ultrasonic cleaning cycles for the sake of speed. However, doing so is not just a procedural misstep but also a risk to patient safety. Each device comes with manufacturer-specified instructions for use (IFUs) that outline the required cycle time for effective cleaning. Not adhering to these guidelines can result in suboptimal cleaning, leaving behind organic and inorganic residues on the instruments.

Mixing Metals in the Ultrasonic Cleaner – Not all materials are compatible with ultrasonic cleaning.  Some materials like aluminum, brass, copper, and chrome can cause instrument staining and damage to stainless steel instruments when cleaned in the same ultrasonic cleaning cycle.  Check the compatibility of your instrument materials before washing in an ultrasonic cycle and avoid mixing metals varieties in the chamber.

As we come to the end of our series "Beyond the Bubble: An Inside Look at Ultrasonic Cleaners," let's pause to reflect on the broader impact of our work in Sterile Processing. Each cycle we start on an ultrasonic cleaner is a testament to our role as guardians of instrument cleanliness and contributors to the overall surgical outcomes of patients.

This series has sought to demonstrate the complexity of ultrasonic cleaners, balancing intricate variables of cavitation, cleaning agents, water quality, and cycle timings to effectively clean instruments. But standing beside the closed lid of every ultrasonic cleaner in healthcare facilities worldwide is a Sterile Processing professional tasked with the responsibility of delivering clean surgical instruments for sterilization. They need to be aware of the intricacies of ultrasonic cleaning, the process it requires, and any warning signs that may require further scrutiny.

However, the ultimate beneficiary of our collective expertise and diligence is the patient. Though they may not know the science and labor that go into preparing their surgical instruments, their trust is implicitly placed in the hands of healthcare professionals. They rely on us to implement the latest technology and best practices to ensure their safety and well-being.

We hope this educational series has helped equip you and your team to dig deeper into the anatomy and concepts of ultrasonic cleaning and has piqued your curiosity to continue learning.  More than that, we hope that you’ll now have the tools needed to improve the ultrasonic cleaning workflow at your healthcare facility, better understanding the equipment your team works with every day.

Thank you for your active participation and dedication throughout this series. Together, we’re not just elevating a profession; we are contributing to the global mission of safer, surgical care.