Wilder’s First Law of Sterile Processing: Each step of the processing should almost make the next steps unnecessary.

Wilder’s Second Law of Sterile Processing: Cleaning’s goal is to get to zero residual soil.

Washers (washer-disinfectors, ultrasonics) are only as good as they are measured to be. AAMI ST79:2017 sections and Annex D recommend that you should verify cleaning performance weekly, but to be sure, you should test each washer daily. Why? It saves a recall back to the last successful cleaning verification.

What are we testing? Per AAMI ST79 section D.3, the following should be tested:[1]

For cavitation, either the old-school aluminum foil test will work (does your ultrasonic perforate aluminum foil?), or you can use color-changing indicators that are now available from at least two manufacturers.

Frequently, the same indicator can be used with a different process challenge device (PCD) to test washers and ultrasonics. This makes for a reasonable comparison of cleaning results.

Lumen connections should be tested with lumened holders of cleaning indicators. For washers with lumen racks, these should be tested, too, in the same way.

But what’s a good result?

Honestly, there should be no residual soil after the wash phase for any normal cleaning verification indicator. If there is, you aren’t cleaning well enough. The acceptance threshold value for residual protein is <6.4 µg/cm2. That’s not a lot. In the UK, the limit is 5 µg per side of an instrument. That’s less.

Cycle optimization
If cavitation tests aren’t working, you need to call service. This could be a failed transducer, a transducer that’s making poor contact with the ultrasonic tank, or something else that cannot be fixed unless someone programmed the unit to not turn on the ultrasound.

If you aren’t getting to zero visible soil, and service has given the machine a clean bill of health, you need to improve the cycle. What are your available tools?

  • Detergent dose
  • Ultrasonic duration
  • Prewash duration
  • Temperature
  • Enzyme phase duration
  • Neutral phase duration

All of these are programmable, or should be. Some manufacturers do not allow the factory programs to be modified, but will permit new programs to be created based upon these programs. So, where do you start?

Detergent dose
Detergent dose should depend upon the water quality you are using. If you have high total dissolved solids (TDS)/hard water, the dose has to be higher. If you have low TDS or soft water, the dose can be lower. The detergent manufacturer should be able to tell you how to deal with your utility water supply’s water quality. If you’re among the few using critical water for all cycle phases, the dose should be at the manufacturer’s minimum recommended level.

Ultrasonic duration
An ultrasonic washer can only pump so much ultrasonic energy into the tank, and if it is a deep tank, the bottom levels will get more than the top ones. Testing can’t just be limited to one location. Some ultrasonic washers do a more-uniform job than others, depending on the way ultrasound is delivered to the tank. All else being equal, more is more here. A longer ultrasound phase will remove more soil. And you may have to lengthen the ultrasound phase to get to zero visible soil.

Prewash duration
Everyone wants their cleaning procedure to take 14 seconds or less. It isn’t going to happen. Cleaning takes time. The prewash, which softens soil and allows it to be removed more easily in subsequent steps of the washer cycle, should run with cold utility water for at least two, preferably three, minutes. If it isn’t, you need to extend this.

Biological processes, like enzymatic detergent digestion of patient soil, double in rate for each 10°C increase in temperature. Unfortunately, biological materials like patient soil and enzyme detergent can denature, turning your detergent to sludge and your soil to something really hard to remove. So, you can’t set the enzyme temperature at 176°F/80°C unless you really don’t want the instruments to get clean. Enzyme detergent phases should be run at the maximum temperature recommended by the detergent manufacturer, typically 122°F/50°C. If your setpoint is lower, you aren’t cleaning as well as you could or should be. For neutral detergents, this is about 158°F/70°C.

Enzyme and neutral detergent duration
Both of these detergents take time to do their job. A two-minute enzyme phase followed by a one-minute neutral phase will probably not do a good job. Optimally, these should be four to five minutes, and at least three minutes, respectively.

Okay, those are all recommendations. How do you tailor your unique situation to work best?

If you want to focus on a particular phase, zero out the other phases to see how the indicators respond to that phase. Get it to the best it can be and leave it there. Work through the other phases until you get to zero visible soil on the indicators.

But what if you get to zero without optimizing all of the phases? Once an indicator is clean, no changes in the cycle will be visible. There are two approaches to this.

One is to set durations for the optimized phases to one-half of what they are in their optimized state.

The other is to raise the bar on the challenge by using a more-difficult challenge. There are cleaning indicators on the market that are generally too hard to clean completely in a normal or even optimized cycle. Their PCD is also designed to test cleaning in three directions and against an analog to a box lock. These may never get completely clean, but if you document the results of your best cycle optimization against them photographically, you will be able to see improvements. Why raise the bar? Because there are instruments that are hard to clean or have not been properly precleaned at point of use which provide a real-world analog to these indicators. Also, they have calibrated doses of protein on them, so quantitative protein reduction can be measured. Contact me for more information.

Thanks for reading, and I wish you the best results possible, because we are all going to be patients one day.


  1. ANSI/AAMI ST79:2017 Comprehensive guide to steam sterilization and sterility assurance in health care facilities. Arlington, VA: Association for the Advancement of Medical Instrumentation; 2017. Annex D.3, pp. 127–128.