STERIS has a leading global position in sterilization solutions, but there are many technology considerations when choosing a safe, reliable and clinically efficacious low temperature sterilizer for healthcare applications.
Brisia López Ortega, senior marketing manager, STERIS, discusses the options for choosing the right low temperature sterilization solution
Over the last decade medical device technology has evolved significantly. Today’s instruments being reprocessed in a hospital central sterilization service department (CSSD) are more complex than ever before. Steam sterilization is still the most predominant sterilization method used in healthcare facilities for instrument reprocessing, however many of the surgical instruments developed for today’s advanced surgical applications cannot be processed in high temperature environments or within high humidity levels.
These newer devices may have electronic components or heat-sensitive materials such as plastics, silicone etc. and moving away from traditional ‘all-metal’ construction. Hence, new low temperature sterilizer solutions have become almost unavoidable in healthcare facilities.
Low temperature sterilization brings many advantages (dependent on which sterilization modality): the possibility to sterilize devices that cannot be sterilized in steam, such as flexible endoscopes, better material compatibilities compared to steam sterilization, where extreme temperatures could be detrimental, significantly shorter sterilization cycle times (sometimes as fast as 16 minutes) and elimination of cool-down times associated with steam sterilization.
The ultimate benefit is allowing healthcare facilities to have a better control and use of their limited medical device inventory, reprocessing turnaround time, management of demanding surgical schedules for instrument demand and thus capital investment and operational savings.
There are a few low temperature sterilization technologies that can be used in healthcare facilities, each of these differing in methodology and capability. The choice of the preferred method is firstly (and most importantly) dependent on manufacturer instructions for use (IFUs).
After confirming device manufacturer guidelines for reprocessing, there is a number of variables to be considered, based on the options available; namely cycle times, availability, compatibility, safety, cost and, if considering a new acquisition, installation requirements. Table 1 compares low temperature sterilization options based on these variables.
Ethylene oxide and low temperature steam-formaldehyde are methods that have been abandoned in healthcare in many parts of the world because of the risk they represent to operators and because of the constraints related to long cycles times, aeration and utility requirements.
On the other hand, liquid peracetic acid (PAA) sterilization is a more widely adopted technology, particularly in endoscope reprocessing, but very few PAA systems offer true sterilization (in accordance with EN ISO 14937 all elements of the scope should be exposed to sterilizing agent – e.g. STERIS SYSTEM 1™ ensures a controlled flow of sterilizing agent over the entire surface of the device port where all parts of the scope including connectors are exposed to the sterilizing agent). In most cases PAA is implemented as high level disinfection (HLD) rather than true sterilization.
The low temperature sterilization method that has gained the most popularity recently is vaporized hydrogen peroxide (VH2O2) sterilization. Its advantages are multiple: fast cycles, wide device compatibility, safe for the user, patient and environment (no toxic byproducts – water vapour and oxygen), and finally no special utility requirements – plug and play. Today, there are around 40 000 VH2O2 sterilizers operating around the world and around 100 in the United Kingdom.
VH2O2 sterilizer cycle description – How does it work?
VH2O2 low temperature sterilizers have been specifically designed to process goods using vaporized hydrogen peroxide under vacuum conditions. The sterilization cycles are fully automated and pre-programmed with different cycles available to accommodate varying loads and medical devices.
Typically, there will be three types of cycles: 1) medical devices without lumens (e.g. forceps, scissors, batteries…) 2) flexible scopes with lumens (e.g. bronchoscopes) and 3) rigid lumen devices (e.g. arthroscopes, cystoscopes). Recently a fourth type of cycle has been added, the rapid cycle, that will accommodate the same devices as described before, but in lower quantities and a shorter cycle time.
There are basically three types of VH2O2 sterilizers in the market: 1) pure VH2O2 2) VH2O2 with plasma and 3) VH2O2 with ozone. It is important to acknowledge that the only active sterilization agent is vaporized hydrogen peroxide, as the plasma and ozone used by some processes are used to help eliminate the hydrogen peroxide (H2O2) residuals.
Publications1 have pointed out that the use of plasma is not directly associated with sterilization, so the term “plasma sterilization” may be misleading. Indeed, the International Standards Organisation (ISO) only recognises ‘VH2O2’ as an accepted terminology for this sterilization process.
With some variations and different parameters, VH2O2 sterilization cycles proceed through three phases: conditioning, sterilization and aeration.
Conditioning
This cycle phase includes a vacuum pulled to a setpoint to remove air and water, followed by a moisture check. Some models of VH2O2 sterilizers, such as the V-PRO™ Low Temperature Sterilizer System from STERIS, will automatically perform a moisture check and abort the cycle if any moisture is detected before any sterilant is injected into the chamber (included in the overall cycle time).
Other sterilizers will equally abort the cycle if there is excess moisture in the load, but this will generally happen when the sterilant has already been introduced into the chamber, thus resulting in wasted sterilant, higher costs and compromising user safety.
Some manufacturers have added a conditioning phase similar to the one available in V-PRO sterilizers, however this feature needs to be selected before running each cycle and will prolong the cycle time by 5 to 10 minutes. It is important to consider this when comparing cycle times.
Sterilization
This cycle phase starts when the vaporized sterilant is introduced in the chamber. The concentration of the sterilizing agent and exposure time are cycle and manufacturer dependent. Generally, this phase is composed of 2 or 4 pulses (or injections) depending on the cycle and sterilizer model. Each pulse phase consists of vacuum, H2O2 vapour drawn into chamber, hold for programmed set time, evacuation of H2O2 vapour.
Aeration
This cycle phase pulls a vacuum to a setpoint and evacuates for a programmed time to reduce chamber H2O2 vapour concentration. It is during this vacuum that some VH2O2 sterilizers use “plasma” or “ozone” after the sterilant contact phase to help break down the H2O2 residuals. However, the catalytic converter is here in all models to deliver this process. Once the aeration phase is complete, chamber pressure returns to atmospheric and the chamber door is unlocked.
At the completion of the sterilization cycle, the load can be immediately used or stored for later use.
Cost of ownership
Unlike steam sterilizers, VH2O2 sterilizers have minimal costs related to installation (e.g. customised plumbing, exhaust systems, steam or water quality equipment) and utility requirements (only electricity required). They are cost effective and easy to maintain with main recurrent costs associated to sterilant, sterility assurance products and specific sterile barrier system (packaging).
Most users identify the costs of running a cycle (sterilant cost) as a key question when deciding which VH2O2 low temperature sterilizer to acquire. This is a complex question as different criteria need to be considered dependent on the facility and throughput requirements and sterilizer model cycle times and capacities.
However, it is worth keeping in mind that direct comparison on cost per cycle may be misleading. It is more relevant to consider the cost of reprocessing the load as each VH2O2 sterilizer model has different claims, cycle times and load capacities. As an example, table 2 below shows V-PRO maX and maX 2 Sterilizers compared to other VH2O2 sterilizers.
Table 2 shows that VH2O2 sterilization cycles cannot be compared just on cycle cost. For example, in STERIS V-PRO non lumen cycles it is possible to process up to 23 kg of load in the same cycle, whereas in an equivalent cycle in other sterilizers, a maximum of 5 kg of load can be processed, almost five times less compared to V-PRO Sterilizers.
Material Compatibility
While all VH2O2 sterilizers share many process similarities, there are three process differences between vaporized hydrogen peroxide sterilization (STERIS V-PRO Sterilizers) and vaporized hydrogen peroxide sterilization with plasma that can contribute to negative material effects on medical devices: sterilant concentration, process temperature and the presence of a gas plasma.
For comparable sterilization cycles, VH2O2 sterilizers with a gas plasma phase dispense a higher total dose of sterilant and the process results in higher device temperatures at the end of the cycle, compared to STERIS V-PRO Sterilizers (without plasma).
Both factors increase the potential to degrade device materials more rapidly. The inclusion of gas plasma can cause additional degradation to certain device surfaces.2 With a lower temperature process, lower total sterilant dose and a plasma-free process, STERIS V-PRO Sterilizers offer cycles that are gentler on devices.
Most VH2O2 sterilizers use sterilant as ~59% hydrogen peroxide in its liquid form. However, what is most relevant is the theoretical total dose, calculated by H2O2 injection volume (mg) * chamber volume (L). STERIS scientific data shows that a minimum 6 mg/l of H2O2 is required to deliver a 6-log reduction in a half cycle on the worst-case biological model with a population of 106 Geobacillus stearothermophilus endospores. Figure 1, however, highlights the variability of the different concentration levels seen in hydrogen peroxide sterilizers. Higher concentration levels of H2O2 can have a detrimental impact on device longevity and function.
In addition, the chamber temperature of STERIS V-PRO Sterilizer and other VH2O2 sterilizers is similar (~50 °C), but device temperature at cycle completion is very different. While devices post-processing in a V-PRO Sterilizer will be at ~ 30-40 °C, competitors cite a temperature of <55 °C. The difference in device temperature is most likely due to the use of plasma that will heat devices to 55 °C.
The important effect temperature plays in chemical reactions should not be underestimated; the higher the temperature, the faster the reaction. In general, for a firstorder reaction, for every 10 °C increase in temperature, the rate of a chemical reaction doubles.
In essence the combination of higher device temperatures (due to plasma) and a higher sterilizing agent concentration could impact the material compatibility of medical devices. Beyond increasing load temperature, the material impact of a gas plasma has been documented.
Gas plasmas are known to generate secondary reactions that can be detrimental to outer layers of sterilized devices. This effect is most pronounced on surfaces of non-metallic materials, such as soft plastics and the insertion tube of flexible endoscopes.
Device testing
While STERIS V-PRO Sterilizers can always be used safely and effectively within their use-claims, collaborative validation between STERIS and medical device manufacturers provides additional assurance for the healthcare facility and the medical device manufacturer.
STERIS conducts thorough scientific testing to ensure that the reprocessing solutions work properly with a wide range of medical devices.
Types of testing:
- Device conformance: ensures proper fit of the device in a specific container or processor.
- Material compatibility: a device or material sample is repeatedly processed exposing it to the sterilizing agent or high-level disinfectant and the cycle to verify compatibility.
- Microbial efficacy: confirms the medical device can be repeatedly and effectively sterilized, or high level disinfected.
Through testing, in accordance with recognised standards, devices processed in the V-PRO Sterilizers maintain biocompatibility in accordance to ISO 10993, Biological evaluation of medical devices.
In particular, part 1, Evaluation and testing within a risk management process, part 10, Tests for irritation and skin sensitization, part 5, Tests for in vitro cytotoxicity and part 4, Selection of tests for interactions with blood. STERIS Device Testing is performed in the STERIS Corporate research and development laboratories, certified to ISO 9001 and ISO 13485, by a dedicated group of graduate scientists with many years of experience.
The service has been made available since the late 1980s and since its inception, STERIS Device Testing has performed studies on thousands of medical devices (see table 3). The STERIS Corporate research and development laboratories are certified to ISO 9001 and ISO 13485.
Testing is conducted in accordance with Good Laboratory Practices (GLPs) as outlined by U.S. regulatory agencies and employs a method adopted as a standard test method by the American Society for Testing and Materials.
Load release and record keeping
The final security step in VH2O2 sterilizers is parametric load release and documentation. STERIS V-PRO Sterilizers have been designed to meet parametric release criteria in accordance to the requirements of EN ISO 14937.
The performance of the STERIS V-PRO Sterilizer is ensured through rigorous control and independent monitoring of the various critical parameters during the cycle. The use of biological indicators for routine monitoring is country and facility dependent based on relevant regional standards and guidelines.
Biological indicators (BIs) such as the STERIS Celerity™ 20 HP Biological Indicator offer fast 20-minute read times. Historically these took up to 24 hours, limiting load release where BIs are required, but now less critical in limiting turnaround times. The Celerity Incubator is designed to detect the presence of a fluorescent signal upon as it heats the activated BIs to temperatures which promote the germination, metabolism, and subsequent detection of viable test organisms under evaluation.
Fluorescence is due to an enzymatic breakdown of a fluorogenic substrate present in the recovery media. Cycle data management tools, such as the new STERIS ConnectAssure™ Technology platform make load release and record keeping easier and providing true cycle data management of process graphs, parametric data and imported BI results making documentation simple and compliant.
In a single platform all STERIS equipment (washer-disinfectors, endoscope processors, BI incubators and sterilizers) can be managed in one healthcare facility cycle data tracking system.
The use of STERIS ConnectAssure increases productivity by transforming manual procedures into automated electronic tasks.
The information flow is enhanced by having real-time access to multiple departments and location data and dashboards to track scheduled or assigned tasks. Management is supported with reports such as department performance, machine, cycle, BI and incubator usage.
STERIS Solutions Ltd
Chancery House
Rayns Way
Leicester
LE7 1PF
UK
0116 276 8636
Email: contact_hc@steris.com
Web: www.steris.com
References 1 Gas-plasma sterilization: relative efficacy of the hydrogen peroxide phase compared with that of the plasma phase M.C. Krebs et al. 1998 2 Document # M9185EN.2017-09, Rev. A V-PRO Low Temperature Sterilization Systems: Proven Safety Performance
