Dirty Little Secrets

A summary of the presentation given by Dr Brian Kirk at the IHEEM Dirty Little Secrets seminar

At last month’s IHEEM seminar titled ‘Dirty Little Secrets’, Dr Brian Kirk, Senior Technical Service Specialist at 3M, gave an insightful and thought-provoking presentation into cleanliness validation of re-usable surgical instruments in decontamination departments.

The talk was centred on the subject of ‘what do we mean by clean’ and how, without an absolute definition, assessment of how clean an instrument is largely depends on how sensitive the method used to determine cleanliness is. Dr Kirk explored the options available for protein detection and the merits of each method in terms of sensitivity and convenience of use.

It is vital surgical instruments are cleaned during the decontamination cycle as, if an instrument isn’t clean, it cannot be sterilized. This is because microorganisms embedded in tissue debris may be able to survive the sterilization process, and then when used on a patient, result in a Surgical Site Infection (SSI). Dr Kirk went on to describe the “baking on” effect, in that sterilizing instruments with residual tissue debris makes them more difficult to clean in the future as the tissue is baked onto the surface. Dr Kirk likened this to cooking, saying if you don’t remove food from a baking tray before using it again, this food will get baked on to the tray next time it goes into the oven.

Dr Kirk explained further possible consequences of protein transfer being the transmission of diseases such as CJD and vCJD (a neurodegenerative disorder). It is now recognised both these protein-mediated diseases can be transferred from patient to patient, with fatal consequences. How can it be made certain that surgical instruments which could have been used on a CJD-positive patient will not present a risk to future patients? The concern presented by Dr Kirk is that there is no absolute standard of ‘clean’, so we can’t be certain.

EN ISO 15883-1 stipulates cleanliness assessment through use of a residual protein test, using the Ninhydrin, OPA (Ortho phthallic dialdehyde) or the Biuret method. However, the sensitivity of each of these methods is different; hence the level of cleanliness measured differs, with Ninhydrin being the least sensitive and OPA the most (private communication, Mark Sutton, Health Protection Agency).

Dr Kirk finished by discussing ultra sensitive laboratory methods of assessing cleaning efficacy, but concluded these have questionable practical use in a busy Sterile Service Department. He also talked about ATP bioluminescence, and the benefits of using ATP as an indicator of bio-contamination. The advantage of this method is that it is very sensitive, so a low result on a reader will give the user confidence that the decontamination process is efficient. However, this method measures the presence of ATP and not just protein, so will detect all tissue debris.

Dr Kirk concluded his seminar by restating the need for a formal definition of ‘clean’. Where there is a possibility of cross-contamination, the industry must work to ensure any risks are minimised. Until an absolute safe level of cleanliness is agreed, routine testing will confirm that decontamination equipment is functioning correctly.

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