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DECONTAMINATION


resistance to hydrogen peroxide and is therefore used in biological indicators for this process. On the theoretical side, when recording the death rate of spores subjected to a sterilisation cycle, the log reduction of bacteria, when plotted on a semi log graph, shows that the death curve or ‘kill rate’ is surprisingly linear. So by extending the graph to the full sterilising period the SAL increases from 10-6


to 10-12 . Once the machine is in service periodic


operational validation in line with the manufacturers instruction will be completed to ensure the machine is still operating and sterilising correctly. These would include safety checks, calibration checks and sterilisation efficacy on a quarterly and annual basis. On a more mundane level, the machine


needs to be monitored and challenged by the user to ensure each load is sterile. The load can be released on parametric


evidence, providing the cycle parameters are coincidental with the validation data and there is historical evidence (i.e. negative biological challenges) to show it is a satisfactory cycle. The use of small self contained biological indicators are ideal for checking the cycle performance on a cycle to cycle basis as the vial contains both the spore challenge and cultivating medium giving a result after 24 hours incubation. Chemical integrators can also be packed with the load to show the item has been exposed to the gas.


Limitations The use of hydrogen peroxide as a sterilant has a number of limitations: • Hydrogen peroxide has very low penetrative properties due to the size of the molecules as opposed to ethylene oxide. For this reason care in selecting the medical device to be sterilised must be exercised and consideration given to any lumens holes and channels.


and use of the cartridges which need to be embraced.


• As with all chemical processes it is difficult to ascertain parametric release, and needs some level of biological control.


Advantages? • It is a low temperature process so the primary use is for heat labile equipment such as endoscopes, robotic equipment, defibrillation paddles etc.


Self contained biological indicators – from left to right – unexposed, growth (fail), no growth (pass). Note the indicator in the cap changing from pink to blue on exposure.


• The load needs to be dry to allow a satisfactory cycle. Not only will it cause the machine to fail, but it also affects the concentration of the H2


trick is to place a small container of water in the chamber, when the machine fails the water has turned to ice.


O2 • Cellulose absorbs H2


concentration of chemical in the chamber. Because of this paper cannot be utilised, the packaging and labelling needs to be made of polyethylene and is commonly referred to as Tyvek.


O2


• The proven Sterility Assurance Level (SAL) is low 10-6 in common with other gas processes.


• Not all materials are compatible with H2


finishes of material are compatible and others are not. As with other sterilisation processes some devices have a limit on the number of times they can be subjected to the process.


O2


• There are Health & Safety and COSHH (UK) regulations on the transport, storage


. Additionally, some grades and/or , affecting the . One party


• It is a relatively quick cycle, depending on the cycle selected and make of steriliser, of between 45 and 120 minutes. No degassing is required therefore no separate ventilated area is needed to aerate the load.


• The H2


hydrogen, therefore there are no residues on the products.


O2


• Items can be ready for instant use, providing all appropriate risk assessments and controls are in place.


• The chemical risks associated with ethylene oxide and formaldehyde are not present meaning the installation of these units in hospital sterilising departments is simplified. Some of these units can in fact be termed as transportable.


References 1 EH40/2005 Workplace Exposure Limits. – EH40 (Second edition, published 2011).


Further reading • ISO 14937 Sterilization of healthcare products – General requirements for characterisation of a sterilising agent and the development, validation and routine control of a sterilisation process for medical devices.


• STERRAO NXTM Sterilization System User’s Guide.


• Plasma (physics) Wikipedia, the free encyclopedia.


• Sterilisation (microbiology) Wikipedia, the free encyclopedia.


breaks down to water and





IFHE DIGEST 2014


35


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