Low Temperature Sterilization

Low temperature sterilization is a sterilization process best used for heat-sensitive devices that may be damaged by the conditions of a steam sterilization cycle. It IS AN EFFECTIVE MEANS TO process heat and moisture sensitive surgical instrumentation, implants, and general equipment. Low temperature sterilization (LTS) has invaded the Sterilization Service Departments (SSD) because many components of advanced minimally invasive surgical (MIS) instruments, including robotic surgery equipment, have zero tolerance for high temperature steam sterilizers.

Modern low-temperature sterilization processes include ethylene oxide (ETO), hydrogen peroxide plasma, low-temperature steam and formaldehyde (LTSF), gamma radiation, electron beam technology and liquid chemical sterilizing (LCS), with the latest addition being ozone (O3 ).

Basic Sterilization Requirements Basic Sterilization Requirements

Effectiveness

Safety

Monitoring

Quality Assurance

Penetration

Material Compatibility

Adaptability

Approval

The purpose of low-temperature Sterilization: The most cost effective method of processing surgical instrumentation and equipment is steam sterilization; however, heat- and moisture-sensitive items cannot be processed with steam sterilization. Low-temperature sterilization is typically used to sterilize unique devices with complex designs and/or those made of heat and moisture sensitive materials including fiber optics, polymers on cameras, flexible scopes, and certain plastics that cannot withstand the heat and moisture associated with steam sterilization. Devices may be constructed with electrical or other delicate components, which also are affected by heat and moisture. Low-temperature sterilization methods differ in their mode of action, and the method chosen is based on the process for which the device has been validated by the original equipment manufacturer. Low-temperature sterilants are capable of harming humans. Reactions to exposure can vary depending on the type of exposure. If exposure occurs, employees need to know what to do immediately. An emergency response plan helps to ensure that employees and patients are protected from exposure to chemical sterilants.

Certain sterilization processes do not change regardless of whether the device is processed by steam or low temperature. For example, all devices must be thoroughly cleaned, rinsed and dried. They must be disassembled to ensure the sterilant’s contact on all surfaces. The correct chemical and biological monitors must be selected and placed in the correct. location within the pack, and the correct packaging materials must be used. The sterilizer must be properly loaded to ensure sterilant contact. At the completion of the sterilization cycle all quality monitors, including physical monitors, must be reviewed to assure that sterilization parameters were met before releasing the load. The device.

The low temperature sterilization techniques are constantly being improved and updated with introduction of new technology to cater for MIS instruments, video laryngoscopes and the green OT concept. Ethylene Oxide (EtO) was the standard low-temperature sterilization method until the early- to mid-1990s when gas plasma was introduced. While EtO still has its place in healthcare sterilization processing, it is not the first option considered in hospital settings today. Reasons include the length of total cycle time and aeration and the potential carcinogenic effects on staff.

Ethylene oxide sterilization

EtO Sterilization is a low-temperature process (typically between 37 and 63°C) that uses Ethylene Oxide gas to reduce the level of infectious agents. EtO is used in gas form and is usually mixed with other substances, such as CO2 or steam. ETO sterilizer has excellent penetration capabilities. This kills microorganisms by alkylation. Alkylation is the process of destroying microorganisms by making the cell unable to metabolize and/or reproduce. Advantages of ETO gas sterilisation include no damage to instruments from excessive heat, moisture or radiation. However it requires prolonged aeration times besides being mutagenic, carcinogenic, irritant to the eye, skin and airway, and can cause neurological, liver and kidney damage.

There are two main ways to divide the cycle; a three phase cycle and a five phase cycle. The difference being that a three phase cycle does factor in the pre and post exposure phases. Two types of ETO sterilizers are available, mixed gas and 100% ET . Advantages of ETO gas sterilisation include no damage to instruments from excessive heat, moisture or radiation. However it requires prolonged aeration times besides being mutagenic, carcinogenic, irritant to the eye, skin and airway, and can cause neurological, liver and kidney damage. The ethylene oxide sterilizers combined ETO with a chlorofluourocarbon (CFC) stabilizing agent, most comm ratio of 12% ETO mixed with 88% CFC. Ethylene oxide is the oldest low temperature sterilization method and has been used since the 1950's to reprocess heat-sensitive medical-hospital materials. Different factors have influenced professionals and health institutions to look for new sterilization technologies. The reasons for this search among health professionals such as complying with environmental legislation that establishes the elimination of CFC (chlorofluorocarbons) gas use, which is a better thinner than ethylene oxide, which affects the ozone layer, and regulating acceptable exposure levels to ethylene oxide, established by the public occupational health body. Low temperature sterilization techniques are constantly being improved and updated with introduction of new technology to cater for MIS instruments, videolaryngoscopes and the green OT concept.

Low Temperature Steam Formaldehyde (LTSF) sterilization

Formaldehyde (FORM) sterilization processes are so-called low-temperature-steam-formladehyde (LTSF) sterilization processes and are standardized steam sterilization processes using temperatures between 50 and 80°C. Under these conditions instruments cannot be disinfected or sterilized. Therefore, formaldehyde is added to the sterilization process. Compared to ethylene oxide sterilization processes formaldehyde has the advantage that it does not penetrate into plastic materials. At the end of the sterilization process formaldehyde is eroded by the steam. Since formaldehyde can be observed even in extremely low concentrations that are not toxic, you can very easily tell by the smell if the formaldehyde is completely removed from the load.

Low-temperature steam with formaldehyde is used as a low-temperature sterilization method in many countries, particularly in Scandinavia, Germany, and the United Kingdom. The process involves the use of formalin, which is vaporized into a formaldehyde gas that is admitted into the sterilization chamber. A formaldehyde concentration of 8-16 mg/l is generated at an operating temperature of 70-75°C. The sterilization cycle consists of a series of stages that include an initial vacuum to remove air from the chamber and load, followed by steam admission to the chamber with the vacuum pump running to purge the chamber of air and to heat the load, followed by a series of pulses of formaldehyde gas, followed by steam. Formaldehyde is removed from the sterilizer and load by repeated alternate evacuations and flushing with steam and air. This system has some advantages, e.g., the cycle time for formaldehyde gas is faster than that for ETO and the cost per cycle is relatively low. However, ETO is more penetrating and operates at lower temperatures than do steam/formaldehyde sterilizers. Low-temperature steam formaldehyde sterilization has been found effective against vegetative bacteria, mycobacteria, B. atrophaeus and G. stearothermophilus spores and Candida albicans

Formaldehyde vapor cabinets also may be used in healthcare facilities to sterilize heat-sensitive medical equipment950. Commonly, there is no circulation of formaldehyde and no temperature and humidity controls. The release of gas from paraformaldehyde tablets (placed on the lower tray) is slow and produces a low partial pressure of gas. The microbicidal quality of this procedure is unknown951.

Reliable sterilization using formaldehyde is achieved when performed with a high concentration of gas, at a temperature between 60o and 80°C and with a relative humidity of 75 to 100%.

Studies indicate that formaldehyde is a mutagen and a potential human carcinogen, and OSHA regulates formaldehyde. The permissible exposure limit for formaldehyde in work areas is 0.75 ppm measured as a 8-hour TWA. The OSHA standard includes a 2 ppm STEL (i.e., maximum exposure allowed during a 15-minute period). As with the ETO standard, the formaldehyde standard requires that the employer conduct initial monitoring to identify employees who are exposed to formaldehyde at or above the action level or STEL. If this exposure level is maintained, employers may discontinue exposure monitoring until there is a change that could affect exposure levels or an employee reports formaldehyde-related signs and symptoms269, 578. The formaldehyde steam sterilization system has not been FDA cleared for use in healthcare facilities.

Hydrogen Peroxide (Gas Plasma) Sterilization

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.

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.

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! 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.

Hydrogen peroxide is one of the most widely used biocides for various antiseptic, disinfectant and sterilization application.1 When in the gas phase, hydrogen peroxide (also known as VHP for Vaporized Hydrogen Peroxide) demonstrates significantly greater antimicrobial efficacy and compatibility than in the liquid form. This may be due to the more reactive nature of the gas but recent evidence would also suggest that the mechanism of action of the gas is different to the liquid. Gaseous peroxide is not a new technology, being used for over 15 years for low temperature disinfection and sterilization applications, in particular in high risk pharmaceutical and medical device manufacturing. The technology is new to clinical applications, already being used for environmental disinfection (under atmospheric pressure) and now as a rapid, low temperature vacuum sterilization process. Gaseous hydrogen peroxide has been confirmed to have broad spectrum antimicrobial activity with confirmed virucidal, bactericidal, fungicidal, mycobactericidal, fungicidal, cysticidal and sporicidal activity. Antimicrobial activity has been confirmed in the presence of interfering soils, with activity dependant on the gas concentration and exposure time.3 In addition, recent reports have confirmed that peroxide gas is also effective against various strains of prions, the agents responsible for Transmissible Spongiform Encephalopathies such as Creutzfeldt-Jakob disease.4 Mode of action studies indicate that hydrogen peroxide gas has different mechanisms of action in comparison to liquid peroxide; the gas, as an oxidizing agent, has been particularly shown to attack and breakdown the various macromolecules that make up cellular and viral structure such as proteins, lipids and nucleic acids.1,2 From these studies, the mode of action of liquid peroxide (including when present under saturated gas conditions) appears to be distinctly different.

Hydrogen peroxide gas also offers further advantages. In addition to its rapid antimicrobial activity, it provides a balance of material compatibility and safety in comparison to other gaseous oxidizing agents. In gas form, hydrogen peroxide has been shown to have compatibility with the most commonly used metals.

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

Ozone Low Temperature Sterilizers

Ozone has been used for years as a drinking water disinfectant. Ozone is produced when O2 is energized and split into two monatomic (O1) molecules. The monatomic oxygen molecules then collide with O2 molecules to form ozone, which is O3. Thus, ozone consists of O2 with a loosely bonded third oxygen atom that is readily available to attach to, and oxidize, other molecules. This additional oxygen atom makes ozone a powerful oxidant that destroys microorganisms but is highly unstable (i.e., half-life of 22 minutes at room temperature).

A new sterilization process, which uses ozone as the sterilant, was cleared by FDA in August 2003 for processing reusable medical devices. The sterilizer creates its own sterilant internally from USP grade oxygen, steam-quality water and electricity; the sterilant is converted back to oxygen and water vapor at the end of the cycle by a passing through a catalyst before being exhausted into the room. The duration of the sterilization cycle is about 4 h and 15 m, and it occurs at 30-35°C. Microbial efficacy has been demonstrated by achieving a SAL of 10-6 with a variety of microorganisms to include the most resistant microorganism, 

The ozone process is compatible with a wide range of commonly used materials including stainless steel, titanium, anodized aluminum, ceramic, glass, silica, PVC, Teflon, silicone, polypropylene, polyethylene and acrylic. In addition, rigid lumen devices of the following diameter and length can be processed: internal diameter (ID): > 2 mm, length ≤ 25 cm; ID > 3 mm, length ≤ 47 cm; and ID > 4 mm, length ≤ 60 cm.

The process should be safe for use by the operator because there is no handling of the sterilant, no toxic emissions, no residue to aerate, and low operating temperature means there is no danger of an accidental burn. The cycle is monitored using a self-contained biological indicator and a chemical indicator. The sterilization chamber is small.

Advantages:

Needs only medical grade oxygen, which is not a dangerous gas to handle or transport

Medical-grade oxygen is readily available in hospitals all over the world, removing the additional overhead of stocking expensive sterilant

Does not leave toxic fumes or residue that must be aerated; rather converts back to oxygen that can be safely released into the air

If there were to ever be a leak, even very tiny amounts of ozone could be detected from its pungent smell

               Cycle time is shorter than EtO sterilization

Cost per cycle is cheaper than EtO since oxygen is cheaper to acquire than EtO

Disadvantages

               Ozone itself is a toxic and flammable gas

               Cycle time is longer than hydrogen peroxide plasma sterilization

Ozone has exciting potential as a sterilizing agent in the world of low-temperature sterilization. After all, it has been used for many years to disinfect drinking water, food, and air. Now that the infection control industry has gured out how to maximize its germicidal properties inside a sterilizer, we expect to see more ozone sterilizers in hospital CSSD/SPD rooms. It’s relatively safe and its cost effectivity will ultimately prove to be a selling point over the more dangerous alternatives, such as formaldehyde. And in some ozone sterilizers it is already being paired with hydrogen peroxide plasma in order to perform a double-fronted assault on microorganisms. One thing is for sure: we will be hearing more in the coming years about ozone as a viable alternative for low-temperature sterilization.

Conclusion

Low temperature sterilization techniques are constantly being improved and updated with introduction of new technology to cater for MIS instruments, video laryngoscopes and the green OT concept. Rise in hospital-associated infections, higher global awareness regarding cleaning and sterilization, and rise in the number of surgeries are propelling the use of low-temperature sterilization. The key factors driving the growth of low temperature sterilization market are improving economic growth, growth in ageing population, increasing healthcare expenditure, increasing life expectancy rate, increasing surgical procedures, increase in healthcare associated infections, and occurrence of superbugs. 

Please Contact for Further information/ Queries

Stalin Selvamoni

Consultant-Biomedical Engineering Projects,

7, Customs Colony,

Thuraipakkam,

Chennai-600097,

India

Tel: +91 9789845776

Email: [email protected]