This series of self-study lessons on Central Service topics was developed by the International Association of Healthcare Central Service Materiel Management (IAHCSMM). The lessons are administered by Purdue University’s Continuing Education Division.
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New surgical devices that help physicians perform modern miracles are constantly being introduced by medical technology. These new devices also create new challenges for the Central Service (CS) technicians who must process them for reuse. Because of their effectiveness and cost efficiency, steam sterilization units have long been the preferred method for reprocessing surgical devices. The materials used to construct many of the newest surgical instruments, however become damaged when they are processed in a heat or moisture environment and so, these devices require a low-temperature sterilization process.
Ethylene Oxide (EO) has become the most popular low-temperature alternative because of the wide range of materials with which it can be used and because of its effectiveness in destroying microorganisms. Other popular alternatives include Hydrogen Peroxide gas plasma, liquid peracetic acid, and glutaraldehyde systems.1
An emerging technology for low-temperature sterilization involves the use of ozone. The application of this system within a specific facility may be carefully analyzed using AAMI’s Chemical Sterilant Selection Criteria to evaluate and compare this chemical sterilant to the other chemicals sterilants available.
Most people are familiar with ozone. They may know about its benefits in the earth’s upper atmosphere, where it protects us from the sun’s harmful ultraviolet (UV) rays and at ground level where it is a very powerful oxidizing agent. Ozone has also been used as a germicide to sterilize foods, air, and drinking water that contain organic matter such as fungi, viruses, and bacterial sports. The ozone sterilizer was developed for surgical instruments because it is a strong oxidizer with a long history of effectiveness. Ozone has a high microbial efficacy and ability to readily diffuse and permeate at low temperatures and it rapidly reverts back to O2. In CS applications, only electricity, water, and medical grade oxygen are needed to produce ozone in a sterilization system. Because these components are readily available in hospitals, devices to be sterilized at an extremely cost-effective rate.2
In addition to low cost, ozone sterilization offers another significant advantage in employee safety. Because the ozone sterilizer produces its own sterilizing agent, the sterilant does not require any transportation or physical contact by technicians. It also releases only oxygen and water vapor into the environment. An ozone leak from the ozone sterilizer is unlikely because the process is run under vacuum and the door is not allowed to open until the ozone has been converted back to oxygen. In the event of an ozone leak in the sterilizer, the distinct smell of the sterilant would be apparent before a dangerous exposure level for humans is reached.
Ozone is a pale-blue gas with a characteristic pungent odor. It has been used for medicinal applications since the late 1800s, when it was used to therapeutically purify blood. By the early 1900s, ozonated water was being used to treat numerous diseases including anemia, diabetes, influenza, and even canker sores. During World War I, ozone was used to treat wounds, gangrene, and the after-effects of poisonous gas.
The ozone sterilization system marketed today evolved from a concept submitted at a 1991 meeting about the use of ozone for water treatment. By 1999, clinical trials had begun, and the ozone sterilizer was cleared to market by Canada in 2002 and by the U.S. Food and Drug Administration in 2003.3 Improved lumen claims for ozone sterilization was cleared by the FDA in 2006, allowing instrumentation with a diameter of 0.9mm or larger and a length of 460mm to be processed.
Ozone’s ability to destroy pathogens at low cost in a worker-safe environment was noted briefly above. By contrast, EO is a mutagen (a substance or agent that causes an increase in the rate that genes change), a carcinogen (a cancer-causing substance), and a reproductive hazard. It is also explosive and dangerous to handle, and the Occupational Safety and Health Administration (OSHA) has indicated a desire to ban its use. In addition to all these drawbacks, instruments sterilized with the EO process must be aerated for 12 hours or longer, which requires a relatively large inventory of medical devices. The residual level of EO released into the environment must also be monitored carefully to assure that no environmental problems are created.
The cost of sterilizing with ozone is much less than with other low-temperature sterilization processes. For example, the ozone required for one sterilization cycle costs less than one dollar: the same sterilization cycle with EO has a sterilant cost of up to several hundred dollars per cycle; gas plasma cost between eleven and thirty dollars. Low-temperature sterilization methods allow facilities to carry a smaller inventory of instrumentation than needed utilizing EO sterilization process resulting in another economic advantage.
In January 2008 the manufacturer of the ozone sterilizer announced they had obtained promising preliminary results on the capacity of the ozone sterilizer to deactivate prions. Prions are infectious proteins which are responsible for transmissible spongiform encephalopathy (TSE) agents such as Bovine Spongiform Encephalopathy (BSE) [also called mad cow disease] or Creutzfeldt - Jakob disease (CJD) in humans. These results come from the research currently in progress at the Health Protection Agency’s Centre for Emergency Preparedness and Response (HPA-CEPR) in England, which consists of comparing the capacities of ozone sterilization process with those of a steam sterilization process at high temperatures and elevated pressure suggested by the World Health Organization (WHO). The final results of the study should be available in approximately a year.
Ozone is generated in the ozone sterilizer with the use of frequency electricity. The electricity converts medical grade oxygen (o2) into ozone (O3). Sterilization happens when the oxidation reaction created by ozone ruptures a pathogen’s cell membrane. Instruments to be sterilized with ozone must be prepared for sterilization according to the guidelines issued by regulatory or professional organizations and from the applicable instrument manufacturers. All infection control practices and procedures used by the CS department for processing instruments by any other method should also be used for ozone sterilization.
The ozone sterilization process uses two identical half-cycle. After the chamber is loaded with instruments, the door is closed, and the cycle begins. First, a vacuum is created within the chamber, followed by a humidification phase. Ozone is then injected into the chamber and the sterilization process begins. After the half- cycle is reached, the previous steps are repeated. A final ventilation phase is used to remove ozone from the chamber and the packaging within it. The sterilization cycle lasts approximately four and one half hours at temperatuires from 85° - 94⁻ F (30°-35°C).
During the sterilization cycle, a catalytic converter is used to transform the ozone back into oxygen. There are no toxic/hazardous residues or waste products associated with the process, and no toxic gas is vented into the environment. After the sterilization cycle is complete, sterilized items can be removed immediately since the cycle temperature never exceeds human body temperature
Mechanical, biological, and chemical indicators are used to complete the sterilization assurance monitoring process.4 Typical process (mechanical functions are monitored during the cycle and, at the end of each cycle process parameters are printed for review and retention. During the sterilization cycle, if a parameter is not reached the cycle will abort, and the reason for the interruption will be displayed on a screen and printout.
For routine process monitoring, a sterilization test pack is placed directly in the load. This test pack should be used in each sterilization cycle, as recommended by AAMI for all low temperature sterilization methods.
A process challenge device (PCD) is formed using the following approved items:
To create this PCD; remove the plunger from the syringe, place the BI, with its top toward the catheter tip, inside the syringe, be sure the cap is removed from the syringe tip. Carefully replace the plunger back into the syringe barrel, leave some space between the plunger and the BI. Place the syringe and the CI inside the peel pack. Seal the peel pack. The spores used in the BI are geobacillus stearothermophilus.
Excessive exposure to any sterilant can be a health and safety hazard. At low levels, ozone can be a respiratory irritant, and it causes more serious effects at higher levels. OSHA has established a short-term exposure limit of no greater than 0.3 parts per million (ppm) over a fifteen-minute period, and an exposure limit of not greater than 0.1ppm as an eight hour time-weighted average (TWA). The worst case of ozone released from the ozone sterilizer has been documented as 0.02ppm , which is significantly lower than the OSHA TWA of 0.1ppm or STEL level of 0.3ppm
The human nose can detect ozone at levels of approximately 0.01ppm, so a Central Service technician will typically be aware of ozone in the environment long before a hazard exists. In addition, because the sterilizer creates a negative pressure chamber during the processing cycle, any leaks would enter the chamber and the ozone would be diluted before entering the environment.
The manufacturer, like AAMI and AORN, recommends that all sterilizers be placed in a room with at least ten air exchanges per hour.5
All medical devices should always be processed by following the device manufacturer’s recommendations. Instructions provided by the manufacturer of the sterilization equipment that apply specifically to the sterilization process should also be followed carefully.
Because of the wide variety of heat-sensitive devices and changes in instrument model designs, material and device compatibility must be identified on an individual basis. Many devices containing the following materials can be sterilized with ozone:
The process can also be used with stainless steel lumens of specified diameter and length:
The process can also be used for items with diffusion-restricted spaces, including the hinged portion of hemostats, forceps, and serrated surfaces .
Items that should not be used in this process include those containing:
The following packaging materials may be utilized in the ozone sterilization process:
The following packaging materials are not currently recommended for ozone sterilization:
It is very important the CS professionals interested in this technology carefully research approved alternatives. For instance, staff may find that it is inefficient to stock packaging materials that are not compatible with the sterilizers in current use, and increases the possibility of error for end users.
Central Service managers will find that there are many options as they analyze the most effective way to meet their facility’s low-temperature sterilization needs. Numerous factors-including sterilization efficiency; employee, patient, and environmental safety; cost-effectiveness; and the impact on instrument inventories must be assessed when determining sterilization methods most appropriate for the specific facility.
In the fast-paced world of Central Service, existing sterilization equipment and methods are constantly being improved and updated, and new technology is being introduced. Ozone holds promise as an alternative low temperature sterilization process for the ever-increasing number of medical devices requiring low-temperature sterilization. CS personnel must understand the basics of ozone sterilization and evaluate the factors associated with its use to determine its usefulness to their department.
1 IAHCSMM Central Service Technical Manual, Seventh Edition, 2007
2 Jason Simon. Germ Free: 21st-Century Sterilization Options for Healthcare Facilities. Managing Infection Control. May, 2004
3 For more information about the history of ozone use for medical purposes, see Bryant Broder, Ozone Low-Temperature Sterilization: The Sky’s Not the Limit Anymore. Managing Infection Control. January, 2004
4 Information about operation of the ozone sterilizer are found in: Mark Chaunet, et al. The Sterilization Technology for the 21st Century. TSO3, Inc. Sainte-Foy (Quebec). Canada. No Date.
5 Marimargaret Reichert and Janet Schultz. Is New Ozone Sterilizer Right for Your OR?, Vol. 19, No. 11. November, 2003
6 Skytron & TSO3. Recommended Materials. Sainte-Foye (Quebec). Canada. No date.
Anne Cofiell, CRCST, FCS
Scott Davis, CMRP, CRCST, CHMMC
Susan Klacik, ACE, CHL, CRCST, FCS
Patti Koncur, CRCST, CHMMC, ACE
Natalie Lind, CRCST, CHL
David Narance, RN, CRCST
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