Factors associated with steam sterilisation failure
Abstract
The continued prevalence of antibiotic resistant bacterial infections has raised awareness and standards of hygiene within veterinary practices. As the range and complexity of surgical procedures carried out within veterinary practice increases, so does the awareness and expectations of clients.
Infection control measures, such as the appointment of a designated infection control officer, and protocols, such as the World Health Organisation (WHO) 6-step hand hygiene method, have done much to raise standards, and are now routine practice throughout many veterinary surgeries. But has the same level of consideration been given to surgical supplies? Can we be sure that as long as the chemical indicator has initiated the expected colour change, the contents of a pack is sterile? Human errors are frequently associated with sterilisation failure. This article aims to discuss some such errors and the ways in which they may be prevented.
Any object that enters sterile tissue or the vascular system is defined as a ‘critical item’. Critical items are so called due to the high risk of infection if such an item is contaminated with any microorganism, including bacterial spores (Rutala and Weber, 1999).
Sterilisation renders items safe for contact with tissue and blood without transmission of infection as long as sterility is maintained (Phillips, 2004). Sterility is considered an absolute term — to put it simply, an item is either sterile or it is not. Vegetative organisms are relatively easy to destroy, however spores are resistant, and as such referenced as a benchmark for achieving sterility (Gasson, 2009).
Disinfection of surgical instruments and equipment by boiling was introduced in the 1880s, replacing Joseph Lister's method of soaking items in carbolic acid (a phenol compound), and by 1876, heat-resistant bacteria were demonstrated. Around 1886, Ernst von Bergmann and his associates introduced the steam steriliser, but surgeons soon discovered that steam in itself was inadequate for sterilisation; steam must be under pressure in order to raise the temperature sufficiently to kill heat resistant microorganisms (Phillips, 2004). This basic concept of heating water in a closed vessel to produce steam above atmospheric pressure, thus at a higher temperature, has changed remarkably little since (Gasson, 2009). The science of sterilisation however, has moved on considerably. Modern day sterilisation processes must be able to demonstrate a minimum sterility assurance level (SAL) of 106. A SAL of 106 represents a one in a million chance of an organism surviving on an item and is universally considered as an acceptable level of risk (Gasson, 2009; Veerabadran and Parkinson, 2010).
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