DECONTAMINATION
are processed every year.
The Bowie Dick test was an incredible breakthrough, but it soon became apparent that even more could be done to ensure successful sterilisation and air detectors were introduced. Designed to work on every cycle in a loaded chamber, they detected residual air in the steam steriliser. In 1969, the British Standard BS 3970, Sterilizing and disinfecting equipment for medical products, was amended to include a requirement for an ‘air detector’. Later, BS 3970 would become one of the key inputs into the first publication of EN 285, Sterilization – Steam sterilizers – Large sterilizers, in 1997. However, the presence or nature of the load placed in the steriliser would affect the results, meaning that air detectors were not as good at picking up the presence of air in the process as the Bowie Dick test. More recently, integral or ‘built-in’ Bowie Dick tests have entered the market, though their name is somewhat deceptive as they are not Bowie Dick tests – they are simply air detectors by a different name. They work by a number of different means, usually with temperature or other sensors placed within the drain and a challenge location within the chamber. They offer no independent challenge as the test is integral to the steam steriliser and hence is not independent to the control system.
Another recent development has been the introduction of electronic Bowie Dick tests. Like the traditional Bowie Dick test, it verifies the rapid and even steam penetration into a defined load and is independent of the steam steriliser. They are also used in an otherwise empty steriliser chamber, at the start of each day that the steriliser is used. They use temperature probes to compare against a reference temperature to indicate steam penetration, with the results monitored using proprietary software. Today, these developments mean SSD managers have a multitude of options available to them to ensure their steam sterilisers successfully sterilise, but with choices come decisions, and so which options and factors should we consider? Ultimately, while in an ideal world, every steriliser would be successful every time, in reality, many factors can prevent this, and if the system fails, it is critical that the user knows it has failed. So, while we aim for a Bowie Dick pass result, it is the fail result that is most important – an indicator that never fails has failed as an indicator. Let’s look now at the five ways to get that critical fail, and how they compare.
The Bowie Dick Test
The Bowie Dick steam penetration test remains one of the most widely used methods of verifying rapid and even steam
Browne Bowie Dick pass result
28 l
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penetration. Used at the beginning of each day or shift, it is a simple and cost-effective way to check that the steriliser is functioning as it should. It is used alone in the chamber to be the sole attractor of air for a more accurate result and relies upon a heat- and steam-sensitive chemical indicator placed within the load.
Browne Bowie Dick test before processing
The ink of the indicator changes colour to indicate steam penetration. Not all inks are equal though and the quality of the ink determines the quality of the test pack. SSD managers should look for products manufactured with the latest in ink technology to ensure the pack offers a clear, well-defined, abrupt endpoint colour change. The ink should also be non-toxic and free from lead and other heavy metals. All too often, pass results are shown by a subtle change, for example from one colour to the same, but darker colour, and are therefore, easy to misinterpret. A good indicator will provide a more dramatic change, for example, from a light colour, such as yellow, to a darker more differentiable colour, such as blue. Anything less can lead to a misinterpretation of the result, and potentially allow a user to miss that all-important fail when it occurs. A good Bowie Dick test will also meet the requirements of EN ISO 11140-3:2007 (Sterilization of healthcare products – Chemical indicators – Part 3: Class 2) indicator systems for use in the Bowie and Dick-type steam penetration test and EN ISO 11140-4:2007 (Sterilization of healthcare products – Chemical indicators – Part 4: Class 2) indicators as an alternative to the Bowie and Dick-type test for detection of steam penetration.
Anyone considering test options should check the products’ declaration of conformity to see which standards it meets and pay special attention to the small print, as some declarations of conformity can list important exceptions that indicate they do not completely meet the standard. Some independent accreditation and certification, for example, the BSI kitemark, go above and beyond the requirements set by these standards and can offer true assurance of a best in class, highly sensitive product. It is also advisable to select an indicator that holds the CE mark; while this is not a requirement, currently, it is set to change on 26th May 2021 when the Medical Device Directive 93/42/EEC transitions into the Medical Device Regulation 2017/745. This is a welcome change that will ensure higher standards for Bowie Dick and other chemical indicators in future, increasing patient safety. The physical attributes of the Bowie Dick test pack are important too. A larger pack will require more steam to heat it, thus it has the ability to attract more air. This means that a 7 kg pack is preferable to a smaller
AUGUST 2020
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