What's on your device?

Howlin, R.P., Harrison, J., McDonnell, G. and Keevil, C.W. (2008) What's on your device? Medical Device Decontamination, 12, 16-21.

Abstract

Decontamination is a combination of processes (including cleaning, disinfection and/or sterilization) used to render a reusable item safe for return to the operating theatre. Critical to this process are the prevention of drying and the implementation of an effective washer-disinfector process commonly utilizing enzymatic or alkaline detergents within an automated cycle. At this stage the choice of the main wash chemistry is crucial. A balance must be obtained between the vigorous removal of often dense contamination and the maintenance of surface integrity and instrument function. However, ineffective cleaning of surgical instruments may be a vector for the transmission of hospital acquired infections and assessment of cleaning efficacy is dependent on the minimal level of detection of the analytical method.

Currently, following disinfection, instruments are subjected to visual evaluation often using magnifying/illuminated lenses to detect any evidence of residual soiling of damage whereby instruments are reprocessed or discarded. Although this method is clearly both rapid and simple to perform it undoubtedly suffers from serious issues of variability and sensitivity, in addition to being non-quantitative. Whilst this method readily detects the haem pigment in haemoglobin to levels as low as 10 ?g/cm2, bodily fluids without pigments are more difficult to visualise (REF?). Cerebral spinal fluid (CSF) is both colourless and odourless and has been shown to be a carrier of prion disease infection. Due to the realisation of these facts, European guidelines ISO EN15883 and the British Health Technical Memorandum (HTM) 2030 outline two techniques for the further assessment of instrument cleanliness: the Biuret and Ninhydrin test kits. Both require prior swabbing of an instrument surface to obtain a result and are based on colorimetric chemical changes although the methodologies behind these reactions differ. The Biuret technique utilises the reaction of copper ions with peptide bonds under alkaline conditions to form a complex which is then added to bicinchoninic acid (BCA) causing a purple colour change that can be readily visualised. The Ninhydrin test kit uses a reaction of amino acids, peptides and proteins with 1, 2, 3-indantrione monohydrate followed by a 30 min incubation at 110 ºC, although a Ninhydrin gel kit can also be used requiring incubation at only 57 ºC for 60 min. However, a recent study has shown that both the Biuret and Ninhydrin tests suffer from poor sensitivity, demonstrating a minimum level of detection by 75 % of volunteers of 6.7 ?g and 9.25 ?g of protein, respectively, on surgical grade stainless steel tokens1. The authors suggests that, as a result, large amounts of protein (up to 6.5 ?g) may remain undetected, therefore seriously underestimating levels of residual contamination. In practice, sensitivity is likely to be reduced further due to the difficulty in swabbing areas of surgical instruments such as teeth and box joints where contamination is likely to be harder to remove for analysis.

This record has no associated files available for download.

Contributors

Author: C.W. Keevil

Download statistics