The Principles of Medical Device Decontamination

Another interesting aspect of alkaline detergents is that they have shown to be capable of the inactivation of prion proteins.

Neutral detergents are detergents that form a solution in water that is near neutral pH, typically between 6.5 to 8 (with pH 7 of course being neutral). These detergents are normally used as a two-part cleaning regime – firstly an enzymatic detergent is used, followed by a neutral detergent. These are typically used as an alternative to alkaline detergents where material compatibility could be an issue; as well as being less aggressive than alkaline detergents, there is usually an increased cycle time and a need for a higher temperature for equivalent cleaning efficacy.

Cleaning parameters

It is accepted that there are four variables that will affect cleaning efficacy – time, temperature, mechanical action (sometimes called impingement within automated washer-disinfectors) and chemical action by way of the detergent. It stands to reason that a longer time will produce a more thorough cleaning effect. Almost every sterile service department would want a faster process; unfortunately, the actual detergent cleaning mechanisms are much more complicated than maybe first realised; for example, many of the individual mechanisms such as emulsifying, dissolving and suspending soil are time dependent. Cleaning time can be decreased by increasing the other variables, such as mechanical action, temperature, and concentration of detergent, however care is needed with protein-based soils, as the higher temperature may lead to protein denaturing and fixing. Higher detergent concentrations increase cleaning efficacy, but at the trade-off with material and device compatibility, rinsing issues, safety in handling and cost. A higher cleaning temperature is generally better (noting the exceptions with protein-based soils) and may be critical for lipids – these waxy and fatty soils can be difficult to remove in lower-temperature processes.

Water quality

One of the bigger variables with cleaning in practice can be water quality; pure water is a much better solvent but can in itself be corrosive. But perhaps the biggest issue is the consequence of dissolved substances within the water.

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