P R O D U C T / T E C H N O L O G Y   B A C K G R O U N D E R 

For Information Contact:
Joni Morford, Communicore
714/721-8081
jmorford@communicore.com


LOW-TEMPERATURE HYDROGEN PEROXIDE GAS PLASMA STERILIZATION:  THE STERRAD¨ STERILIZATION SYSTEM


Introduction

Although dry heat and steam have traditionally been used to sterilize medical and surgical 
instruments, many of today's sophisticated electronics and biomaterials are heat- and 
moisture-sensitive, making these sterilization techniques inappropriate for many microsurgical 
and similar instruments.  Liquid chemical sterilization techniques are able to sterilize at much 
lower temperatures, but they can still damage moisture-sensitive items.

Ethylene oxide (EtO) is a commonly used technology that is capable of sterilizing at 
temperatures considerably lower than dry heat or steam.  In addition, while EtO requires 
humidification within the chamber during the sterilization process, only small amounts of 
water are necessary, making it less damaging to delicate instruments than steam.

Although used for decades, EtO is a recognized carcinogen that requires hospitals to install 
expensive monitoring, abatement, and aeration equipment and to provide protective clothing 
and safety training for workers.  Ethylene oxide is explosive even at dilute levels.  Pure EtO is 
sometimes used as a sterilant, but it is more commonly mixed with flame-retardent "carrier" 
gases because of its high flammability.  

Until recently, the most common carrier gas contained ozone-depleting chlorofluorocarbons 
(CFCs).  Effective December 31, 1995, however, CFCs were banned by the United States 
Environmental Protection Agency (EPA).  Some institutions have chosen to retrofit their 
CFC-based EtO systems to use another carrier gas--containing hydrochlorofluorocarbons 
(HCFCs).  Ethylene oxide may also be diluted with carbon dioxide.  Because of its toxicity, 
EtO sterilization requires a lengthy aeration period to allow any remaining residues to 
dissipate.  As a result, a typical EtO sterilization cycle lasts 12-16 hours--far longer than heat 
sterilization technologies.

Advanced Sterilization Products (ASP), a division of Johnson & Johnson Medical, Inc., has 
developed the patented STERRAD¨ Sterilization System to effectively sterilize medical and 
surgical instruments while overcoming the heat and moisture limitations of steam and the 
toxicity of EtO.  The low-temperature hydrogen peroxide gas plasma technology embodied in 
the STERRAD System has proven to be faster, more cost-effective, and safer for workers, 
patients, and the environment than EtO and other low-temperature sterilization technologies.


What Is Plasma and How Is It Formed?

Scientists refer to the plasma state-not to be confused with blood plasma--as the fourth state 
of matter, different from solids, liquids, and gases.  Plasmas can occur naturally in outer space 
as a cloud-like body of ions, electrons, and neutral atomic and molecular species.  One of the 
more prominent plasmas in nature is the aurora borealis or "northern lights."  The low-
temperature plasma used in the STERRAD System is an adaptation of this phenomenon for 
sterilization.  Forming a plasma requires a closed chamber, a deep vacuum, a chemical on 
which to base the plasma, and a source of energy to create an electromagnetic field to initiate 
the plasma.


How Does the Hydrogen Peroxide Gas Plasma System Work?

In the STERRAD Sterilization System, medical and surgical instruments are placed in the 
sterilization chamber (4 cubic feet in capacity), the chamber door is closed, and air is pumped 
out to create a vacuum.  An aqueous solution of 59 percent hydrogen peroxide is injected into 
the sterilization chamber via a self-contained cassette that is inserted by the operator at the 
beginning of every 10 sterilization cycles.  The solution vaporizes and diffuses throughout the 
sterilization chamber, surrounding the items to be sterilized and initiating the inactivation of 
microorganisms encountered in the sterilization chamber.  After a period of hydrogen 
peroxide diffusion, the pressure is reduced in the chamber and the formation of a low-
temperature gas plasma is initiated by applying radio frequency (RF) energy to create an 
electromagnetic field.  

In the plasma state, the hydrogen peroxide molecules break apart into reactive species that 
include free radicals.  The combination of the hydrogen peroxide diffusion pretreatment 
phase and the plasma phase acts to disrupt the life functions of the microorganisms, including 
viruses and bacterial spores, on instruments and other surfaces within the chamber, thereby 
sterilizing the instruments, and to convert the hydrogen peroxide to non-toxic products, 
primarily harmless oxygen and water vapor, so that the items are ready for use.  

When the process is complete, the RF energy is turned off, the vacuum is released, and the 
chamber is returned to atmospheric pressure by the introduction of filtered air.  The items 
within are sterilized and ready for use.  The STERRAD Sterilization cycle lasts approximately 
one hour.


How Effective Is Hydrogen Peroxide Gas Plasma Sterilization?

The STERRAD System sterilization process exhibits broad-spectrum antimicrobial activity as 
demonstrated by well-established and universally accepted sterilization validation methods 
such as those specified by the Association for the Advancement of Medical Instrumentation 
(AAMI).  In general, the AAMI standards require that, after terminal sterilization, the 
probability of having a non-sterile device is less than one chance in one million.  

The sterility assurance studies performed on the STERRAD System prior to marketing were 
conducted against vegetative bacteria (including mycobacteria), bacterial spores, yeasts, fungi, 
and viruses.  In general, these organisms were chosen for their resistance to sterilization by a 
variety of techniques.


Is the Hydrogen Peroxide Gas Plasma Process Safe?  

The microprocessor-controlled STERRAD System uses various automatic safety and 
monitoring systems to operate the sterilizer once the chamber door has been closed and the 
cycle activated.  Because the principle byproducts of hydrogen peroxide plasma are oxygen 
and water vapor, the STERRAD System sterilization process leaves no toxic residues on 
instruments and poses no risk to operators, patients, or the environment.


Does Plasma Sterilization Technology Require Special Plumbing or Siting?

The patented technology does not require any special electrical, plumbing, ventilation, or 
siting construction.  The STERRAD Sterilizer is fully mobile and electrically shielded to 
facilitate set-up virtually anywhere in a hospital including the surgical suite.  An adapted 208-
volt electrical outlet is the only requirement for installation.  


Summary

The STERRAD Sterilization System is a general-purpose medical sterilizer based on a patented 
process that involves the combined use of hydrogen peroxide and low-temperature hydrogen 
peroxide gas plasma.  Results from laboratory tests of the System prior to its commercialization 
in 1993 show that the technology destroys a broad spectrum of microorganisms on medical 
and surgical instruments.  

Since the STERRAD System leaves no toxic residues on surgical instruments and equipment, 
an aeration phase is not required, and sterile instruments may be used immediately following a 
sterilization cycle of approximately one hour.  The System is safe for healthcare workers, 
patients, and the environment--no vents, drains, monitors, or protective garments are 
required.

The STERRAD System is manufactured and marketed by Advanced Sterilization Products 
(ASP), a division of Johnson & Johnson Medical, Inc., based in Irvine, Calif.


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