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monitored and verified indirectly via pressure. System controls ensure the appropriate sterilant is used for each sterilisation cycle. The process used ensures an appropriate hydrogen peroxide concentration is delivered to the steriliser and maintained during the sterilisation process. The presence of sufficient sterilising agent is verified indirectly by the pressure within the chamber upon sterilant injection, which is monitored and independently verified during the process. Following each hydrogen peroxide injection into the chamber, the pressure rise inside the chamber is measured and monitored. The chamber pressure must be controlled between the values established for each type of cycle. During validation, a correlation is made between 6-log microbiological inactivation in a half-cycle and pressure change upon injection of sterilant; this half- cycle result is extrapolated to a full-cycle result to guarantee a 12-log reduction for the entire cycle.
In addition to pressure, other means exist to monitor VH2O2 concentration. Until now, probably the most known has been the use of a spectrometer inside the steriliser chamber. Spectrometers use an indirect measurement of infrared or ultraviolet spectrum light absorbance by the sterilising agent by a sensor in a part of the chamber. The spectrometer used in VH2O2 sterilisers only brings information on the light absorbance, that information can be correlated to VH2O2 concentration in that specific area of the chamber (typically near the door) and does not directly provide information about the sterilising agent
concentration throughout the whole load. It is also important to note VH2O2 sensors in the chamber have several disadvantages: the sensor measurements can be affected by the movement of inflating packaging, due to pressure variations during the cycle. The result is aborted cycles for no reason; this is an additional indirect cost for the user (equipment price and maintenance price) and does not dispense with the requirement to monitor the load with a chemical indicator.
Good practice sterilisation monitoring consists of three separate steps: steriliser monitoring, cycle monitoring and pack monitoring. For VH2O2 sterilisation, the monitoring tools consist of a user-assembled PCD for routine monitoring consisting of a biological indicator (conforming to ISO 11138-1) and a chemical indicator (conforming with ISO 11140-1), to confirm the steriliser functionality; a BI adjacent to the load in the chamber, for cycle monitoring: and chemical indicators (Type 1 and Type 4) in each pack, for load monitoring.
Improving VH2O2 cycle monitoring tools
Users are always looking to improve monitoring (steriliser, cycle, pack) and confirm sterility. Unlike steam sterilisation (a physical sterilisation process utilising steam at high temperature as the sterilising agent), VH2O2 sterilisation is a chemical sterilisation process (utilising vaporised hydrogen peroxide as the sterilising agent), thus the sterility assurance products are also different, particularly when it comes to measuring VH2O2 concentration. Current ways to confirm the required VH2O2 concentration and penetration seem unclear to users as there is no tool providing a direct measurement of VH2O2 concentration. There is also the question of VH2O2 penetration into lumens. VH2O2 sterilisers have the capability of sterilising channelled devices such as flexible surgical endoscopes and rigid endoscopes. Confirming VH2O2 penetration into these channels is as crucial as VH2O2 concentration for sterility assurance. The means to confirm VH2O2 penetration need to be appropriate, i.e. the design of process monitoring devices needs to be as close as possible to the actual medical devices intended to be processed and in conformance with steriliser cycle sterilisation ability claims. Today, we see there are in use ‘helix’ devices taken from steam steriliser monitoring applications but using a VH2O2 chemical indicator (CI) to assess VH2O2 penetration. These ‘helix’ devices usually consist of a 1.5 metre length of PTFE tubing with a terminal capsule containing the CI. These have not been specifically
JANUARY 2023
designed for VH2O2 processes, and do not consider the specificity of the technology. For example, the device material, design and geometry are not related to the medical devices being sterilised. PCDs (Process Challenge Devices) are frequently used to monitor VH2O2 sterilisers during use. A PCD, per ISO 11139-1:2018, is an “item providing a defined resistance to a cleaning, disinfection, or sterilisation process and used to assess performance of the process”. For routine use, PCDs should be processed with loads in accordance with local guidance and hospital practices. Recently, STERIS developed the V-PRO
Low Temperature Steriliser Lumen Process Challenge Device (PCD) for the V-PRO Low Temperature Steriliser, which will provide users with means of confirming vaporised hydrogen peroxide penetration into lumened devices that closely replicate typical medical devices and match the open-ended lumen device sterilisation claims. These have been tested in actual sterilisation cycles with worst case validated loads, to confirm the PCDs provide a sterilising agent challenge equivalent or more difficult to the lumened medical devices routinely/likely to be processed in these cycles.
Narrow bore stainless steel and PTFE tubing provide a penetration challenge to the sterilant; at the centre of the tortuous path is a capsule into which the chemical indicator is placed.
These PCDs will be supported by a chemical indicator that will allow monitoring of verification of hydrogen peroxide penetration at the correct concentration for the non-lumen PCD in the STERIS V-PRO maX, maX 2, 60 and s2 Low Temperature Steriliser Lumen and Flexible cycles. The chemical indicator result can be used to support parametric load release and conforms to ISO 11140-1 Type 4 specification for VH2O2 chemical indicators. In addition to the different PCD packs that allow the verification of VH2O2 concentration and penetration into the steriliser chamber and load, an extra independent monitoring system (IMS) can be installed in the most recent VH2O2 Steriliser models, e.g., the V-PRO maX 2 Low Temperature Steriliser. The IMS is an accessory to facilitate independent monitoring the key cycle parameters of the VH2O2 Steriliser. The IMS is an optional feature, for newly manufactured and existing VH2O2 units, that may be purchased and installed on the steriliser. It is an independent data collection system. All of the monitoring sensors are independent from the system sensors and the data collected from the IMS is identified separately from the sterilisation system’s data. Thus, the IMS facilitates compliance with the monitoring requirements of ISO 22441. Additionally, users will be able to require operator ID inputs whenever a cycle is
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