Guide to Ultrasonic Cleaning of Medical Devices: How Ultrasonics Work and More

What Is Ultrasonic Cleaning?

Ultrasonic cleaners in hospitals provide an automated cleaning process for surgical instruments and support compliance with the manufacturer's instructions for use (IFUs) of those instruments. Many complex instruments have crevices or narrow lumens, which can be difficult for other washing methods, such as a washer/disinfector, to clean. Correctly performing ultrasonic cleaning requires knowledge of the equipment, cleaning chemistries, and techniques to maximize cavitation and remove soils.

Ultrasonics can be particularly useful for washing hard-to-reach areas on a medical device, including fine serrations and box lock joints. Ultrasonic cleaning is also useful on small surgical instruments, including select microsurgical and ophthalmology devices.

How does an Ultrasonic Cleaner work?

Ultrasonic cleaning is only one part of the complete cleaning (or decontamination) process. The cleaning process starts in the procedure room, where pre-treatment products are applied to keep surgical instruments moist. Once the instruments arrive in the sterile processing department (SPD) for decontamination, they are rinsed, and lumens are flushed. They are often soaked for an amount of time specified in the IFU. Manual cleaning uses specialized instrument cleaning brushes and cleaning chemistries to remove soils from instrument surfaces. If the device IFUs require ultrasonic cleaning, this is the next step in the decontamination process.

How an Ultrasonic Cleaner Works

Ultrasonic cleaning provides the power needed to remove residual soils from intricate instruments. In sterile processing, these ultrasonic cleaners use powerful sound waves to create cavitation capable of removing residual soils from complex instruments.

Ultrasonic cleaners work based on a successful combination of three key parameters:

• Detergents
• Cavitation
• Flow/Sonic Irrigation

First, instruments are fully submerged in a cleaning solution with detergents such as Prolystica™ HP Instrument Cleaning Chemistries in a specialized basket or holder. The ultrasonic cleaner then creates high-frequency sound waves that agitate the solution.

Generation of Ultrasonic Waves

Ultrasonic systems consist of generators and transducers. The generators produce high-frequency electrical signals, which transducers convert into vibrations to agitate the solution. Some systems mount the transducers to the bottom of the tank. Since the ultrasonic waves are coming up from the bottom of the tank, cavitation may only reach instruments in the bottom tray.

Large-capacity ultrasonic cleaners, such as the InnoWave™ Pro Sonic Irrigator, mount transducers to the sides of the tank to evenly clean multiple layers of trays.

Cavitation

As the ultrasonic waves pass through the solution, they create alternating high and low-pressure cycles. During the low-pressure cycle, small bubbles are formed. When the high-pressure cycle occurs, these bubbles rapidly collapse or implode in what is known as cavitation.

The bubbles imploding across the instrument's surfaces act like scrubbers and remove contaminants from the devices' surfaces.

Flow and Sonic Irrigation

The solution the instruments are submerged in allows for efficient cleaning, while the use of pressurized flow can provide additional mechanical cleaning to the internal channels of lumened or cannulated medical devices.

Innowave Ultrasonic Irrigators have sonic irrigation capabilities, delivering ultrasonic energy and cavitation to reach the devices' exterior and interior. Lumen flushing facilitates the cleaning of the challenging soils within lumens, and power flushing provides a high-pressure irrigation force through lumens. This combination provides cleaning inside these hard-to-reach lumens.

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How To Use An Ultrasonic Cleaner For Surgical Instruments

Typical steps for using an ultrasonic cleaner for surgical instruments include:

• Visually inspect instruments for debris and manually clean them at the sink
• Instruments should be separated in batches by metal type because mixing metals within a solution causes metal ions to transfer between instruments, which can result in pitting and etching of the instrument surfaces
• Prepare an appropriate cleaning solution following the manufacturer's instructions:
  • Most modern ultrasonic cleaners in hospitals use an automated fill and dosing system
  • It is good practice to empty, clean, rinse, and dry the unit at least daily, or preferably after each use, as defined by facility procedures
• Load the ultrasonic cleaner, ensuring instruments are submerged but not overcrowded
  • Place instrumentation within a validated basket or on the ultrasonic cleaner's shelf. Instruments should not be placed directly on the bottom of the tank, as they might damage the transducers and scratch the tank surface. Follow the ultrasonic cleaner's instructions for instrument placement, including the maximum weight allowed.
• Connect any lumened instruments to flow ports, ensuring the tubing is not kinked, then follow the instructions of your ultrasonic cleaner to begin the cycle.
• Set parameters or select the cycle to be run

After the ultrasonic process, instruments must be thoroughly rinsed with critical water. Though the instruments have been cleaned and rinsed, they may still be contaminated with microorganisms. Appropriate precautions must be taken to ensure technicians are not exposed to potential pathogens left on devices. Processing in an automated washer after an ultrasonic can offer thermal disinfection to make the devices safe to handle. Always refer to the device IFU before running a device through a washer/disinfector.

Ultrasonic Cleaning Of Ophthalmic Instrumentation

Incorrect cleaning and sterilization of ophthalmic instrumentation have been linked to the formation of Toxic Anterior Segment Syndrome (TASS). TASS is an acute inflammation of the anterior chamber of the eye occurring postoperatively and has caused blindness in some patients. It occurs when foreign matter such as enzymatic cleaners, residual debris, steam chemical carryover, powder from surgical gloves, or other material is transferred to the eye during surgery.

Due to the low threshold of contaminant needed to cause TASS, ophthalmic instrumentation must undergo special processing. For example, some manufacturers require the use of treated water only instead of cleaning chemistries.

Many organizations, such as the Association for the Advancement of Medical Instrumentation (AAMI) and the Association of periOperative Registered Nurses (AORN), provide special recommendations for ophthalmic instrumentation. A common recommendation is that surgical eye instruments be cleaned in a designated area and with an ultrasonic unit dedicated to these instrument sets. A dedicated sonic is often recommended because enzymatic detergents cannot be used on these instruments, and a shared ultrasonic needs to be cleaned before use.

Cleaning Chemistries for Ultrasonic Machines

Beyond cleaning - selecting a suitable detergent for ultrasonic cleaning is an important consideration. The cleaning chemistry's formulation should be:

• Compatible with the cavitation process
• Effective over a range of different water qualities
• Low foaming
• Free rinsing
• Non-toxic and non-abrasive
• Effective for all soil types
• Preferably biodegradable

Prolystica Instrument Cleaning Chemistries go beyond cleaning to meet all these requirements.

Suitable cleaning chemistries designed for use on medical instruments (with or without enzymes) and optimized for use at lower temperatures should be used. Most ultrasonic units heat the solution to temperatures ranging between 27 °C (80 °F) and 49 °C (120 °F). Enzymatic-based chemistries are sensitive to the effects of temperature ranges. The enzymes work less efficiently or not at all at suboptimal temperatures. Ensure the enzymatic cleaning chemistry is compatible with the ultrasonic cleaner's temperature range.

The medical instrument manufacturer's written instructions should provide specific details on solutions and process conditions for cleaning various instruments. In addition, maintaining a proper level of solution in the tank is important. Low levels of solution can cause adverse effects on the cleaning process as well as the unit itself.

Barriers to Ultrasonic Cleaning

As noted above, cavitation is the cleaning power of ultrasonic cleaners. Conditions or materials that prevent the formation of cavitation prevent cleaning. Since sound waves pass through materials differently, the acoustical properties of the materials have a significant impact on the formation of cavitation. Materials that block or absorb sound waves and inhibit the formation of cavitation include plastics, such as polycarbonate and silicone. On the other hand, metals readily conduct sound waves, which is why metal baskets are often used to hold instrumentation.

Some materials are also not appropriate for ultrasonic cleaning, as they can be damaged:

• Chrome-plated instruments: the mechanical vibrations remove the chrome-plating
• Power instruments: the internal parts can be damaged by fluid invasion
• Endoscopic lenses: the vibration can damage adhesive seals and delicate optic light cables of flexible endoscopes, fiber optic light cables, and some rigid endoscopes
• Delicate small instruments: vibrations can damage delicate fiberoptic, microsurgical, and lensed instruments
• Certain materials: cork, glass, rubber, wood, and chrome

Overloading the ultrasonic can also impede sound wave transmission, reducing cavitation and cleaning effectiveness. Weight limitations, as defined in the IFUs, must be followed. In addition to too much weight, too much gross soil within the tank can also impede the transmission of sound waves. Tissue, bone cement, and other residuals can block or absorb sound waves and reduce cavitation. Lastly, improper cleaning agents may inhibit the formation of cavitation. Avoid cleaning chemistries with excessive foaming, and only use cleaning agents specifically designed for ultrasonic cleaners.

Quality Control Tests for Ultrasonic Cleaning

An ultrasonic cleaner must be maintained in proper working order according to the manufacturer's IFU. Staff must perform daily maintenance, including solution changes and degassing. Larger or more complex ultrasonic cleaners may require calibration and preventative maintenance. Quality controls ensure that the process is followed, the equipment functions, and the expected outcome is achieved.

Ultrasonic Indicator – a test that provides a realistic challenge using a synthetic test soil that mimics blood and tissues found on surgical instruments can ensure that your equipment is functioning properly.

The VERIFY Ultrasonic Indicator provides an independent objective test to evaluate the ultrasonic cycle. Problems such as insufficient energy, water level, improper temperature, and degassing may impact the results.

Residual Protein Test - A residual soil analysis looks for the presence of bioburden that may remain on instruments that have completed the cleaning process. Samples collected from instrumentation are chemically evaluated, and the detection of residual protein shows can indicate that the cleaning process was not successful.

VERIFY RESI-TEST Cleaning Indicators detect the absence or presence of protein and protein residues with a sensitivity of ≥ 1μg. Cleaning verification is provided by collecting a sample from the device. Both cleaning indicators are intended for use after manual or automated cleaning and prior to high level disinfection or sterilization. Easy-to-read results are available in just five seconds.

Ultrasonic Cleaning Recommendations

All staff using the ultrasonic cleaner should follow policies and procedures for operating an ultrasonic cleaning unit. The facility should develop policies and procedures based on the manufacturer's owner's manual and IFUs for the equipment.

Best practice in SPDs for ultrasonic cleaning must be stated in written policies and procedures, as recommended by AAMI: "The health care organization should establish policies and procedures for all methods of cleaning and decontamination of reusable items." (ANSI/ AAMI ST79:2017 7.2; Policies and Procedures).

Daily and preventative maintenance procedures should be in place to ensure the ultrasonic cleaning unit is in optimal working order for the expected performance. Daily maintenance procedures can be found in the manufacturer's IFUs. Some examples might include proper cleaning of the ultrasonic unit's exterior surface, internal surfaces of the tank, and the drain screen.

An ultrasonic preventive maintenance program that the facility designs should follow the manufacturer's recommendation as to how often preventive maintenance is to be performed. These regular maintenance programs should include adjustments and replacements of worn parts so that untimely or costly schedule interruptions can be avoided. The maintenance records should be available for the department, surveying bodies, facility operations, biomedical department, and maintenance department, depending on your facility's organization.

As surgical and reusable medical devices evolve in complexity, the need for proper cleaning equipment is essential to the SPD. Ultrasonic cleaners are one piece of equipment that can assist in this process.

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