Author: Vincent Sanchez, CRCST
Sterilization of medical devices was a revolution in medicine. For the ﬁrst time, doctors could operate on their patients without fear of causing infections and death in the patients they were striving to save. Steam sterilization came about in the late 1800s, and during the 1900s, methods of sterilization continued to diversify and improve. Now, as sterilization via ethylene oxide is being phased out, new technologies are emerging to both replace it and provide alternatives to hydrogen peroxide gas plasma. In this article, we will discuss three emerging technologies being developed or deployed to provide low-temperature sterilization of complex devices that could not be sterilized at all or were not sterilized as eﬀectively with current technologies.
VP4: Vaporized Hydrogen Peroxide + Ozone
VP4 is a chemical sterilant mixture and cycle derived from normal the H2O2 cycle. H2O2 and ozone are used together to increase the lethality of the process and ensure eﬀective sterilization of multi-channel ﬂexible endoscopes. This is the only (other than plain ozone) emergent technology discussed that has been approved by the FDA for use in the United States.
Mechanism of Action
The VP4 process occurs in two phases, much like the standard H2O2 process. First, vapor-phase H2O2 is injected into the chamber and allowed to penetrate the load. Following H2O2 injection, ozone is injected into the chamber. This reacts with the remaining H2O2, producing hydroxyl radicals. The hydroxyl radical is extremely reactive, and cause oxidative damage to microbes, which enhances the lethality of the standard H2O2 process, allowing processing of items that could not be reprocessed with standard H2O2 cycles previously.
+ Allows rapid sterilization of previously un-sterilizable items, due to length and number of channels.
+ Uses variable amounts of sterilant depending on load contents and weight.
+ Low to no toxic risk to staﬀ
Ozone Gas (O3)
Ozone is a naturally occurring peroxide molecule that consists of three oxygen atoms bound to one another, as opposed to the usual two. Ozone occurs in nature due to interactions between normal diatomic oxygen (O2) and UV rays from the sun striking the atmosphere.
Mechanism of Action
Ozone consists of a normal diatomic oxygen molecule (O2) that is loosely bound to a third oxygen atom, forming O3, or ozone. Because this extra oxygen atom is only loosely bound to the other two, ozone is an unstable molecule that will readily release the extra oxygen atom as a free radical. When this free oxygen interacts with microbes present on the items to be sterilized, it causes oxidation of cell structures that leads to microbial death. Ozone has been FDA cleared and has demonstrated a sterility assurance level of 10−6 against a variety of microorganisms, including Geobacillus stearothermophilus.
Ozone is generated onsite using medical grade oxygen and electricity. It does not require a separate chemical sterilant and is widely eﬀective against microorganisms, including the G. sterothermophilus, the most sterilization resistant organism. Further, at the end of the sterilization cycle, remaining ozone is processed via catalyst back into normal diatomic oxygen and water vapor, both of which are non-toxic. Ozone itself is compatible with a wide range of materials and can sterilize a range of lumens up to 60mm in length.
Ozone is highly ﬂammable, highly reactive, and can cause respiratory issues if it is inhaled directly.
Nitrogen Dioxide (NO2) Gas
Mechanism of Action
Nitrogen dioxide is another oxidative molecule that attacks and destroys microorganisms by reacting with their DNA, damaging it and causing cell death. While it has not been FDA cleared for sterilization of surgical instruments, it has demonstrated a sterility assurance level of 10−6 against G. sterothermophilus.
NO2 is an eﬀective sterilant at room temperature and does not require a deep vacuum. Compared to ethylene oxide, it is more eﬀective for sterilization of delivery devices (such as syringes) containing drugs and other biologics, because the elevated temperatures required in ETO sterilization can damage the drug or biologic contained in the device to be sterilized. Additionally, the entire sterilization process for NO2 takes place in two to three hours, versus the 12+ hours required for ETO.
Direct exposure to Nitrogen Dioxide is toxic and the gas is mutagenic when inhaled. Skin and eye exposure result in irritation and possible eye damage. OSHA has set a workplace exposure limit of 5ppm, not to be exceeded at any time.
As more complex and exotic medical devices continue to be developed, sterilization technology continues to grow and adapt to the changes. Although bureaucracy can be slow to approve and accept these changes to our sterilization systems, companies and developers around the world continue to demonstrate that they are developing sterilization methods for tomorrow’s challenges today. The three methods discussed above are just a few of the sterilization methods being developed and tested to ensure that as surgical instruments evolve, patients can rest assured that the instrumentation they’re exposed to during routine surgery is safe and completely free of pathogens.
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 See https://www.tso3.com/wp-content/uploads/2019/04/MK-0066_01_New-Standard-of-Care-for-Duo-Reprocess-Terminal-Sterilization....pdfCenters for Disease Control and Prevention. https://www.cdc.gov/infectioncontrol/
 See guidelines/disinfection/sterilization/other-methods.html#anchor_1554397475
American Lung Association. https://www.lung.org/our-initiatives/healthy-air/outdoor/air-pollution/ozone.html#atrisk
Evan Goulet, PhD, April 2015, Medical Device and Diagnostic Industry. See https://www.mddionline.com/why-manufacturers-should-consider-nitrogen-dioxide-sterilization
PLoS One. 2015 Jun 22. See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4476675/
New Jersey Department of Health. See https://nj.gov/health/eoh/rtkweb/documents/fs/1376.pdf