Ultrasonic Cleaners

Ultrasonics had its beginning after World War I, but the cleaners were temperamental and inefficient. The more reliable ultrasonic cleaners came about in the 1960s when solid-state devices and transistors were developed.

Ultrasonic cleaners use the energy from high-frequency sound waves, created by transducers in the side or bottom of a sink-like chamber filled with water, to remove fine debris from surgical instruments. They produce vigorous microscopic implosions of tiny vapor bubbles on the surface of objects immersed in the cleaning chamber. This agitation (from 20,000 to 100,000 cycles per second) causes a vacuum scrubbing action on all surfaces which clean box-lock joints, fine serrations and other hard-to-get-at surfaces.

There are many factors that affect the ultrasonic cleaning. Some of these aspects are positive, some are negative. Three factors are: ultrasonic power, frequency of the bubble, and the cleaning solution.

Ultrasonic power is a term used to measure work done in a given time. The effect which power has on ultrasonic cleaning is usually in the time it takes for it to affect the cleaning operation. The higher-powered units produce faster cleaning.

The frequency of operation greatly affects the cavitational force, or the power. The higher the frequency, the quieter the machine. The lower frequency is noisier but you are cleaning by sound. Every time you double the frequency you cut the power in that collapsing bubble by a factor of 10. What if you are running at 40,000 cycles and someone comes along and says they have a 80,000 cycle cleaner that cleans better? If they're both a 100 watt unit, then the 80,000 cycle cleaner is not the best cleaner. It has 1/10th the power of the 40,000 cycle cleaner. Bigger is not always better. The type of cleaner you need depends on what you are using your ultrasonic to clean.

The cleaning solution is probably that most important factor to consider. It is also the most ignored factor. You need a fluid that has high surface tension because this means that the bubble has a heavier walled balloon. You can blow it up higher before it pops and when it does pop, it has greater energy. It also needs to be low enough so that the bubble will penetrate the small cavities. The solution must hold the debris. It must either emulsify it like blood or it has to knock it off and hold it in solution. Using a no-sudsing or low-sudsing enzyme cleaner will not interfere with the cavitational action of the ultrasonic cleaner.

Cleaning is the single most important step in making a medical device ready for reuse. Without adequate cleaning, most disinfection and sterilization processes are ineffective. Debris on a device can interfere with its function or lead to a foreign body or pyrogen reaction in a patient if introduced into the body.

The instruments must be rinsed free of gross debris before being placed in the ultrasonic cleaner, or the sound energy will be absorbed by the larger clumps, making the process ineffective. You must place the instruments in a basket or perforated instrument tray. The tank is a vibrating diaphragm much like your stereo speakers at home. If you put your finger on the speaker coil at home it slows it down and stops it from moving. The same thing happens if you put instruments in the bottom of the tank, plus it dulls the tools. Do not stack instruments on top of one another or overload the ultrasonic. This renders the cleaning process ineffective. Normal cleaning time is 5-10 minutes.

Another important step is to frequently change the water. As the water becomes cloudy or dirty, you need to drain and refill the chamber. Each time you change the water you need to let it run without instruments for 5-10 minutes to remove dissolved air that will interfere with the cleaning process. This is called "degassing" the water.

The ultrasonic cleaner is a very important and useful tool for assisting in the implementation of the decontamination and cleaning of surgical instruments.

Robin Shelnutt, RN, is a nurse manager of SPD at Emory University Hosptial in Atlanta, Ga.