COVER STORY
Sterilisation assurance: raising thebar
Sterilisation of reusable medical devices is the culmination of the decontamination process. In principle, this shouldmean that there are no viable microbiological entities present, but also no residues from the process, such as chemicals or endotoxins, that could affect the next patient on which a device is used. How do we know that a device has been
sterilised? This article explores the development of sterilisation validation processes over the years, andlooks at current available options for best practice. Meeting target temperatures, pressures,
andexposure time, andproof of the presence of steam, has, for some time, been taken as an initial indicator that a cycle will have been effective in an empty chamber in a steam steriliser. Measuring temperature andpressure will be irrelevant in a low temperature steriliser where the sterilant is hydrogen peroxide, for example in a plasma steriliser, andthere will be a need to show that there was an effective dose of the sterilising chemical.
Bowie-Dick The next development in sterilisation assurance standards was the introduction of Bowie-Dick tests, where a chemical indicator is placedin the centre of a pack of strips or at the endof a coiledtube device (to mimic placement in the centre of a 7 kg cotton pack). Each day this is placed into a steriliser to confirm that its operating conditions can penetrate the test pack. However, each different device behaves
differently within a load, and each load behaves differently inside a given chamber. A daily Bowie-Dick test in an unloaded machine will provide no assurance for these situations. Another challenge is to see
what is happening at the centre of a load: there are test strips that can be placedin the load, which can be checked when the pack is opened, but if the sterilisation process hadnot been effective, this will only be discoveredat the point of use. Rejecting an instrument pack at this point could jeopardise a surgical intervention. The ideal test would be to have a
biological indicator present in every load MARCH 2012
in every cycle, to show that the conditions have been able to destroy the biological entity. The disadvantage is that it takes time, from several hours onwards, to show that the entity will not grow, and thus be detected. To overcome this, chemists have devised a number of clever chemical indicators which react differentially to temperature, pressure, chemicals, etc to provide evidence that cycle conditions have reached deep into sterilisation loads, and that the chemical changes detected are parallel with biological kill rates for specified microbes.
Medical device simulators The answer to this problem has been the development of medical device simulators (MDS) which are designed and validated to simulate the worst case scenario for a specified medical device, and can be placed in the steriliser next to the pack containing the genuine device. The MDS’s test strip can be checkedat the endof the cycle.
Batch Monitoring Systems and beyond… The next level of progress has been the development of Batch Monitoring Systems (BMS) which are designed and validated to test the worst case situations for different specific load configurations. This means that each cycle can have a meansof validating the likely efficacy of that cycle, with that load, and that configuration. A new standardwas publishedin 2011 for the test methods to prove the equivalence between instruments andtheir MDS andloadconfigurations, andtheir BMS.
German company, GKE, has been at
the forefront in developing Process Challenge Devices andBatch Monitoring Systems, andthese are now available in the UK from BES Decon in Bristol. As the sterilisation assurance
standards bars are raised, the next development will be a sensitive test system using a biologically based indicator, where the effectiveness of the sterilisation process can be assessedand recorded quantitatively. This system will be on the market within the next couple of years. Meanwhile, how high have you set your safety bar?
For more information contact: GKE Cleaning and Sterilisation Monitoring from BES Decon 131 South Liberty Lane Ashton Vale, Bristol BS3 2SZ Tel: 0845 1300 237 Fax: 0845 1300 238 Email:
marketing@bescorporate.net Web:
www.besdecon.net
FAX ENQUIRY NUMBER: H350
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