Author: Sam Harrison, Clinical Analyst

Most SPD personnel are familiar with ultrasonic cleaning, which was first used in the 1950s but did not become widespread until the 1980s. Ultrasonic cleaning provides substantial benefits over other conventional cleaning options and is a required piece of equipment in all Sterile Processing Departments, due to:

  • Effectiveness with fine cleaning
  • Material compatibility
  • Being listed on the manufacturer’s instructions for use cleaning
  • Improved time efficiency and quality
  • Reduced human component to the cleaning
  • Being environmentally friendly

 

How Ultrasonic Cleaners Work

Ultrasound is high-frequency sound waves, above those detectable by human hearing. Humans can detect sound waves between 20 Hz and 20,000 Hz. For comparison, dogs hear frequencies between 40 Hz to 60,000 Hz and bats hear frequencies between 9,000 Hz to 200,000 Hz. The ultrasonic process uses the ultrasound range above 20,000 Hz to create cavitation bubbles that can agitate a fluid and remove contaminants from solid surfaces. The cavitation works by forming bubbles or voids within a liquid that implode or collapse, releasing energy, which causes the cleaning. The high-frequency sound waves are very effective at cleaning joints crevices, lumens and other areas.

 

The History of Ultrasound

Long before its use in the medical field, ultrasound and the study of sound has a long history, dating back to the sixth century BCE, when Pythagoras studied the mathematical properties of stringed instruments. The first commonly agreed-upon understanding of the existence of ultrasound was in 1790 when Lazzaro Spallanzani discovered bats moved using hearing rather than vision. Spallanzani saw that owls could not fly in a room with no source of light, but bats were able to not only fly but also avoid wires hanging around the room. He tested his theory by eliminating the bats’ ability to use their eyesight, which did not affect their flight accuracy; and by interfering with their ears, which did disrupt their ability to maneuver the room.

 The next major advancement was the discovery of the piezoelectric effect in 1877, defined as the ability of certain materials to generate an electric charge in response to applied mechanical stress. This discovery led to the invention of sonar devices at the beginning of WWI. Sonar (SOund Navigation And Ranging) initially used a two-earphone (air tube) device worn by an operator, who listened to sounds in the water through a stethoscope and determined locations by mechanically rotating a receiver. Applying the piezoelectric effect allowed sonar to advance to generating sound waves and “listening” for a returning echo.

The first noted use of ultrasound in medicine involved European soccer teams that used a form of ultrasound in the 1920s, 30s, and 40s for arthritis and eczema. Karl Dussik is credited with the first diagnostic use of ultrasound in 1942 when he attempted to use ultrasound to detect brain tumors. Ultrasounds for the OB/GYN field were first incorporated in 1958, and the first 3-D image of a fetus was taken in 1986.

 

 The Birth of Ultrasonic Cleaning

Prior to the introduction of ultrasonic cleaning, items were cleaned by hand-washing and immersing them in water or another solution, then rinsing with water. This then advanced to immersion in a hot chlorinated solvent. A later development involved placing the object to be cleaned above a tank of chlorinated solvent and vaporizing the solvent. This improved the ability to clean inside small locations and complex shapes. While this process was more effective for cleaning than previous strategies, it had substantial drawbacks environmentally and degraded the instruments due to the solvents used. Chlorinated solvents for cleaning were banned in the 1980s.

Ultrasonic cleaning was first introduced in the 1950s and has not undergone significant modifications since its introduction other than adding flushing capabilities for cannulated devices. Using a transducer generates invisible sound waves through a liquid in a basin with an intensity that creates cavitation. An item is added to the liquid and the “bubbles” implode, pulling matter and energy inward. These implosions break up solid particles that are stuck on the item being cleaned, thus cleaning the surface, cracks, crevices, and areas that are difficult to access. The basin is filled with a cleaning solution specific to the items being cleaned. Outside of the basin, typically a generator produces power, which it sends to the transducer. Items to be cleaned are placed in the solution, usually in another container with mesh or holes making the item accessible and preventing the items from sitting on the basin floor, and reducing the surface areas to be cleaned.

 

Why Use Ultrasonic Cleaning?

 There are several major advantages with ultrasonic cleaning:

  • Reduction in human processing for cleaning
  • Consistency of performance
  • Effectiveness at cleaning difficult to clean areas such as crevices, lumens and joints

Using ultrasonic cleaning allows for greater confidence within the medical field for reusable instrumentation if not contradicted by the device manufacturers' written IFU. The versatility of available solutions offers a wider variety of options, compared to previous cleaning methods for improved effectiveness and attention to environmental concerns. Delicate and complex instruments can be cleaned with improved quality and ease, including robotic instruments. Many ultrasonic machines now have the ability to flush cannulated instruments while also providing cavitation which increases cleaning efficacy even more due to the flushing mechanism.

 

Disadvantages of Ultrasonic Cleaning

Although the advantages of ultrasonic cleaning have allowed it to become widespread in most medical facilities with a sterile processing department, there are drawbacks to the technology as well.

  • Ultrasonic cleaners are not safe for all materials, including cork, wood, rubber, and most needles; as well as fiberoptic instruments and devices that cannot be immersed
  • It does not disinfect or sterilize instrumentation, steps that are still critical in the processing of reusable medical instrumentation
  • Spores and viruses may remain after using the ultrasonic
  • Used only after gross soil and other detergents have been removed

 

Other Uses for Ultrasound

Numerous fields use ultrasonic cleaners, including automotive, 3-D printing, machining, manufacturing, and PPE gear.

Ultrasonics in general have a wide variety of uses in addition to cleaning.

Dentistry: Dentistry has also benefitted from ultrasonic technologies, using ultrasound to eliminate stains, dental plaque, and calculi quicker with less hand and wrist fatigue and repetitive strain concerns.

Medical Imaging: Another commonly used application for ultrasonic technologies is with ultrasounds to see a fetus in utero. Technologies have improved to allow 3-D ultrasounds clear enough for non-medical parents to see and understand the images displayed of the baby. Medical staff also use ultrasounds for diagnostic testing for examining internal organs as well as guiding certain medical procedures.

Ultrasound can be a bane or a blessing, depending on its application. One thing is sure: it has changed how we work and our understanding of the world around us.

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