The last method of low temperature sterilization for us to explore is the method of hydrogen peroxide plasma sterilization.

As we explained in our posts on formaldehyde (LTSF) and ethylene oxide (EtO), not all medical and scientific equipment can be successfully sterilized in an autoclave, also known as a steam sterilizer. Let’s review why: the more complicated and technologically advanced the equipment, the more likely it will be damaged by the high temperature and humidity of steam sterilization. Our classic case is the endoscope. An endoscope will be damaged and eventually ruined by standard autoclaving. Therefore, we must find a low temperature sterilization method that is more delicate on the life of the equipment but still effective enough to fully sterilize all germs on said equipment.

Enter hydrogen peroxide, also known as H2O2. At low concentration levels, hydrogen peroxide is a common disinfecting agent sold in pharmacies. At higher concentration levels, it is used as a sterilant in many industries. And it is our sterilant of choice for this method of sterilization. How does it work?

Plasma, the Fourth State of Matter

Before we explain how hydrogen peroxide works in a low temperature sterilizer, we first need to explain the concept of plasma. Plasma is the fourth state of matter (solid, liquid, gas, and plasma) and is created when a gas is heated sufficiently or exposed to a strong electromagnetic field. What happens when a gas becomes a plasma? It becomes an unstable state of matter in which the number of electrons are increased or decreased, thus producing ions, which are positively or negatively charged electrons. In other words, plasma is an ionized gas that has special properties not seen in any other state of matter. Common examples of manmade plasmas include neon signs, fluorescent light bulbs, plasma displays used for televisions and computers, plasma lamps (as in the image above), and nuclear fusion. Naturally occurring plasmas include fire, lightning, the sun, stars, auroras, tails of comets, the Northern Lights, and even 99% of the galaxy!

How does plasma kill germs? Plasma sterilizes by a process called oxidation. The plasma produces a chemical reaction in which all microorganisms are deactivated. The high heat turns the molecules of the hydrogen peroxide into free radicals, which are highly unstable. In their “search” for returning to a stable state, they latch on to the microorganisms in the load -- thus effectively destroying the components of their cells, such as enzymes, nucleic acids, and DNA.

Hydrogen Peroxide Plasma in the Sterilizer

Liquid hydrogen peroxide is inserted into the sterilizer. The liquid is heated up in a vaporizer in order to turn it into gas. Once that has been accomplished, the hydrogen peroxide gas is heated to an even higher temperature, at which point it turns into plasma. And as we just explained, the plasma is dispersed inside the sterilizer chamber in order to oxidize all microorganisms on the load. Goodbye germs!

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Tuttnauer's PlazMax Low Temp Sterilizer

Application

Common applications for hydrogen peroxide plasma sterilizers include sterilizing the following:

  • Non-hollow loads, such as electrocautery instruments, dopplers, laser probes, defibrilator paddles, thermometers, Ophthalmic lenses, and harmonic cables
  • Hollow loads, such as Laryngoscopes and their blades, shaver handpieces, fiber optic light cables, and surgical power drills
  • Endoscopes, such as rigid and flexible endoscopes.

As you may recall from our posts on ethylene oxide and formaldehyde, which are both toxic chemicals, hydrogen peroxide plasma has the serious advantage of safety -- both for the environment (including the sterilizer operator) and the contents of your load. The importance of this safety cannot be overstated. And because hydrogen peroxide does not produce toxic fumes, there are no long aeration/degassing times in the cycle. At the end of the cycle, the plasma is “cracked” into the non-toxic byproducts of water and oxygen, which safely evaporate into the air.

And just one more point about the short cycle: most hydrogen peroxide plasma sterilization cycles run for less than an hour, with the average cycle running 35-45 minutes, depending on the size of the sterilizer, and size and contents of the load. That is a huge advantage over, say, EtO sterilization, which can take upwards of 14 hours for just one cycle!

Advantages of Hydrogen Peroxide Plasma

By using hydrogen peroxide plasma as a method of low temperature sterilization, one benefits from:

  • No chemical residues
  • Safety of handling
  • Safety for the environment
  • Short aeration time.

As you may recall from our posts on ethylene oxide and formaldehyde, which are both toxic chemicals, hydrogen peroxide plasma has the serious advantage of safety -- both for the environment (including the sterilizer operator) and the contents of your load. The importance of this safety cannot be overstated. And because hydrogen peroxide does not produce toxic fumes, there are no long aeration/degassing times in the cycle. At the end of the cycle, the plasma is “cracked” into the non-toxic byproducts of water and oxygen, which safely evaporate into the air.

And just one more point about the short cycle: most hydrogen peroxide plasma sterilization cycles run for less than an hour, with the average cycle running 35-45 minutes, depending on the size of the sterilizer, and size and contents of the load. That is a huge advantage over, say, EtO sterilization, which can take upwards of 14 hours for just one cycle!

Disadvantages of Hydrogen Peroxide Plasma

Every type of sterilization method has its plusses and minuses. Let’s take a look at the minuses:

  • Inability to sterilize: liquids, powders, and strong absorbers
  • Requires specific synthetic packaging of the load
  • Sterilization chamber is relatively smaller than that of an EtO sterilizer.

Let’s Recap

First we discussed how steam sterilization in an autoclave is not appropriate for all medical and scientific equipment. The more technologically advanced a device is, the more sensitive it is to humidity and high temperatures. Then we discussed how hydrogen peroxide plasma is a type of low temperature sterilization that is used widely today to sterilize such devices, such as endoscopes. We reviewed the concept of plasma being the fourth state of matter, how plasma is created, and popular natural and manmade plasmas. Then we investigated how hydrogen peroxide plasma kills microorganisms by a process called oxidation, which essentially deactivates their cellular components. Next we spoke about common applications of this method of sterilization, such as hollows, non-hollows, and endoscopes. And finally we explored the advantages and disadvantages of hydrogen peroxide plasma sterilization, foremost among the former: safety and short cycle time.

Thanks for joining us in our exploration of sterilization methods. All questions and comments are welcomed below.