Which should you use for your surgical instruments?

Which does a better job of cleaning surgical instruments, ultrasonic cleaning or manual cleaning? Several studies have shown that ultrasonic cleaning is more thorough than manual cleaning,1, 2 especially for complex and lumen instruments. But most studies conclude that instruments need to be manually cleaned before being placed in an ultrasonic cleaner.1, 3

A 2022 study that compared manual, automated, and ultrasonic cleaning of surgical instruments found that “ultrasonic cleaning resulted in significantly the lowest residual blood levels on the instruments (p<0.05).” It also cited a 2007 study that showed “tissue debris persisted less on the ultrasonically cleaned instruments than the automatically cleaned instruments.” The 2022 study concluded that “ultrasonic cleaning was by far the most effective in removing blood and protein residues from the surgical instruments.”2

Manual cleaning

Most instrument and ultrasonics manufacturers’ instructions for use (IFU) recommend manual cleaning to remove larger soils, as does ANSI/AAMI ST79 and the US Centers for Disease Control. Manual cleaning includes soaking the instrument in an enzymatic detergent solution to break down and loosen surgical soils, and then using a brush to remove gross debris.

While the detergent solution can reach inside joints, hinges, box locks, and other small crevices, brushes aren’t always able to. And, while there are brushes for cleaning inside lumens, whether they reach every surface often depends on brushing technique. Lumens also must be flushed during manual cleaning to remove loosened debris.

Brushes used in manual cleaning must be chosen carefully to keep the instruments from being damaged in the process. At the same time, brushing techniques vary from technician to technician, so instruments may not get consistently cleaned. The strength of the ultrasonic waves in an ultrasonic cleaner is set to provide thorough cleaning while not damaging delicate instruments.

Increased ultrasonic effectiveness

Ultrasonic cleaners use sound waves to create microscopic bubbles in a detergent solution, a process called cavitation. The bubbles grow until they implode, creating both heat and a vacuum that loosens and pulls soils off instruments. Larger soils, like pieces of tissue, can interfere with the ultrasonics, reducing their effectiveness.

The soil loosening provided by manual cleaning only increases the effectiveness of an ultrasonic cleaner. The microscopic bubbles created by ultrasonic waves can get into the small cracks and crevices of complex instruments, scrubbing microscopic soils and breaking up biofilm to uncover hidden bacteria. Biofilm must be removed so that sterilization can kill the bacteria hidden underneath it.

Detergent solution is flushed through lumens and robotic instruments, where sonic waves can create more microscopic bubbles to scrub away soils. The detergent contains sufactants that suspend soils in solution so they cannot adhere to the instruments again but are washed away when the instruments are rinsed.

Manual cleaning is effective in removing gross debris and visible soils. Ultrasonic cleaning, however, has proven more effective at removing microscopic soils and biofilm. Manual cleaning is still important because the larger debris that can be easily scrubbed off with a brush can interfere with ultrasonic waves if still present when the instrument is placed in an ultrasonic cleaner. Getting that debris out of the way allows the ultrasonic cleaner to remove smaller soils and clear the way for effective sterilization.


  1. Pennsylvania Patient Safety Authority (2006). Patient safety advisory: Bioburden on surgical instruments. National Library of Medicine website. https://digirepo.nlm.nih.gov/master/borndig/101727488/200603_20.pdf
  2. Hashemi Beni H, Shafiei Z, Ghadami A. A Comparative Study of the Manual, Automated, and Ultrasonic Surgical Instrument Cleaning Methods. J Iran Med Counc. 2022;5(3):486–93.
  3. Griffin, Ava and Concu, Patti (2017). Basics of ultrasonic cleaning. HSPA CRST Self-Study Lesson Plan. Retrieved May 30, 2021 from CRCST153.pdf (purdue.edu).