REUSABLE MEDICAL DEVICES
Choosing a high performancedetergent
RichardBancroft,BSc (Hons), science and technicaldirector at STERIS Corporation, discusses the importance of highperformance detergents for cleaning reusablemedical devices.
Water, detergent and time, together with mechanical action, are generally accepted as the key variables for successful cleaning of reusable medical devices. Herbert Sinner described the inter-relationship for cleaning between mechanical action, chemical (detergent) action, time and temperature in a water-based system, as long ago as 1959, and his work gained widespread knowledge as Sinner’s Circle. The key aspect of Dr Sinner’s approach is that the Circle can be described as a summation of all factors needed in order to clean optimally (see figure 1). But perhaps one of the most useful applications of the Sinner Circle concept is that all of these variables are inter-related; a reduction in one of the variables will necessitate an increase in one or more of the other variables. The opposite is also of course true; increasing one of the variables can reduce the others. As well as consideration of external factors like energy and water consumption, the commodity that we would always like more of in our daily lives is time, hence it is possible to optimise the Sinner Circle variables to allow a reduction in process time, but necessitating an increase in the other variables (see figure 2).
Cycle variables - temperature
Increasing the temperature variable of the Sinner Circle can potentially improve the cleaning outcome; however, caution must be exercised when dealing with loads that have protein soiling; it is generally acknowledged that water that is too hot will coagulate or denature proteins. When the temperature of the process reaches these levels (typically at
or above 45˚C to 50˚C), there will be a marked reduction in protein cleaning efficacy; so, while a temperature increase may help to optimise the process, increasing this temperature too much may have the opposite effect to that desired.
Cycle variables – mechanical action
In a typical washer-disinfector, the mechanical action is delivered by the force of water in the mechanical spray arms. It is of course desirable to increase the mechanical action as much as possible; this may be achieved by increasing the pump pressure, which in turn gives greater water force from each spray arm jet, giving greater impingement on the load to be cleaned. However, in practice, this can present problems as the increased water pump demands can cause cavitation within
The cycle variable of time is perhaps the easiest to comprehend; greater time will result in greater cleaning efficacy, however as noted above, we are generally always looking to save time by shortening processes.
AUGUST 2019
the pump. This cavitation is caused when there are extreme pressure changes within a liquid, usually caused by the pump impeller. These pressure changes cause the creation of lower-pressure vapour cavities (hence the term cavitation) in the water; as these pockets collapse, they generate significant shock waves, noise, and a significant reduction in pump pressure. The addition of a detergent to a system, and an increase in temperature of the water, resulting in a higher vapour pressure, can either create or exacerbate this cavitation phenomenon. In addition to the efficiency reduction and noise, cavitation can cause significant equipment damage too.
Cycle variables – time
The cycle variable of time is perhaps the easiest to comprehend; greater time will result in greater cleaning efficacy, however as noted above, we are generally always looking to save time by shortening processes. There are, in addition, often unintended consequences that affect time. For example, increasing the process temperature will have an associated increase in time, as the time taken to reach a higher operating temperature will of course be longer. Reducing processing time is often a desired outcome in process optimisation, and if
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