Updated: Jul 3
Author: Daniel Zhou
Editors: Angela Pan and Yanxi Chen
Artist: Jade Li
When performing on a patient, medical tools must be sterilized — completely removed from all forms of bacteria, viruses, fungi, and spores.
There are many ways to sterilize tools, such as using steam, dry heat, ethylene oxide gas, or liquid chemo sterilizers. It’s uncertain that a tool is microorganisms-free, but the sterility assurance level (SAL) can be used. The SAL, expressed as the log10, measures the survival of microorganisms after sterilization. A SAL of 6 has the lowest probability of contamination: one in a million. A SAL of 6 is acceptable for critical items such as surgical instruments, cardiac and urinary catheters, implants, and ultrasound probes used in sterile body cavities.
There are 3 main methods for sterilization: steam sterilization, dry heat sterilization, and ethylene oxide sterilization. Steam sterilization is effective, fast, safe, and affordable. It involves an autoclave and a large steel chamber circling steam that destroys microorganisms and bacterial spores via high temperatures and pressure. This steam must be maintained at a temperature of approximately 120°C for a minimum of thirty minutes. There are many benefits of this form of sterilization. For example, it is non-toxic and safe for humans. Additionally, it can penetrate the packaging to sterilize the liquids inside. This form of sterilization is economical and environmentally friendly. Steam sterilization is easy to control and monitor, however, it cannot sterilize heat/moisture-sensitive material as it requires multiple utilities and can cause burns.
The second method of sterilization is dry-heat sterilization: the removal of moisture from coatings and other materials. This method should only be used on materials or tools that can be damaged or impenetrable by moist heat; examples include powders, petroleum products, and sharp instruments. Similarly to steam sterilization, it is non-toxic, requires electricity to run, is water-conservation friendly, and has relatively low operating costs. However, it poses a fire risk, cannot sterilize liquids, and is time-consuming as it involves the heating of air with little moisture content, requiring a minimum of 180°C.
Finally, ethylene oxide sterilization uses gas to sterilize equipment. The gas reacts in such a way that disrupts cell growth and division, killing microorganisms. It is one of the only methods used by medical device manufacturers to sterilize equipment. This form of sterilization can be used in heat/moisture-sensitive environments. It can also be used on various materials without distortion and functionality disruption. Similar to dry heat sterilization, this method only requires electricity. It also has the ability to penetrate packaging, but this method is dangerous as it’s toxic to humans. Products need to be aerated before human use. This can be very time-consuming because of ethylene oxide sterilization’s lengthy cycle times. Ethylene oxide is also a carcinogen and is highly flammable, so it needs to be degraded before emission.
Although there are plenty of other methods out there, steam sterilization, dry heat sterilization, and ethylene oxide sterilization are the three main types of sterilization most commonly used by the scientific community.
“Types of Sterilization (Steam, Dry Heat, And Ethylene Oxide).” Betastar.com,
“Rational Approach.” Centers for Disease Control and Prevention, Centers for Disease Control and
Prevention, 18 Sept. 2016, https://www.cdc.gov/infectioncontrol/guidelines/disinfection/rational-approach.html#:~:text=Top%20of%20Page-,Critical%20Items,microbial%20contamination%20could%20transmit%20disease.
Center for Devices and Radiological Health. “Sterilization for Medical Devices.” U.S. Food and Drug
Administration, FDA, https://www.fda.gov/medical-devices/general-hospital-devices-and-supplies/sterilization-medical-devices#:~:text=Medical%20devices%20are%20sterilized%20in,acid%2C%20and%20nitrogen%20dioxide).
Equipment Sterilization Disinfection - Louisiana Department of Health,