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Medical Device Sterilisation : Key Essentials, Options And Challenges

Factors such as non compatibility of polymers like PTFE & poly propylene with Gamma and the low-cost advantage that EtO sterilisation has to offer have so far ensured the continuity of this method. Eg: Disposable Syringes are exclusively treated with EtO due to their non compatibility with Gamma. However, in today’s dynamic world, it would be foolish to assume this continuity to carry on perpetually without staying up to date with current trends that have raised the bar for carrying out this activity. The purpose of this article is to highlight these key areas, which have gained importance over the past few years and are now an absolute mandate.

Validation, which marks the first step of any process, is the most critical aspect, more so for sterilisation, because sterility of every individual unit cannot be verified. The ISO 11135-1:2007 standard prescribes the methodology for EtO validation, of which the Halfcycle approach specified in Annex B is the most adaptable and widely accepted. This method involves the use of biological indicators, having a population of 106 spores. Traditional use of spore strips has now been replaced by SCBI (Self Contained Biological Indicators), which are easy to handle, test & retrieve from the product. Additionally, the use of SCBI eliminates the possibility of errors due to testing/re-contamination as the spore strips are never exposed to the environment.The use of SCBI during routine sterilisation is also encouraged to ensure a sterility assurance level of 10-6.

One important component of parametric release is the direct measurement of humidity (the most critical sterilisation parameter) during conditioning phase. Most readily available humidity sensors are likely to get poisoned by repeated exposure to Ethylene oxide gas. However, advancements in this field have also made EtOcompatible humidity sensors readily available in our country. The other component of parametric release is the direct analysis of ethylene oxide concentration inside the steriliser, for which a cost effective solution is yet to be found.

Another important component of validation is the mapping of temperature and humidity throughout the product load during the “Performance Qualification – Physical” stage. This step traditionally involved the use of multiple temperature and humidity sensors, often connected to a central data logging device through long, rigid cables. Such systems were cumbersome to install and placement of sensors at locations where sterilisation conditions are most difficult to achieve is a challenging task. Such installations being time consuming would also result in significant process downtime. Wireless/Infrared temperature and humidity probes are now available in abundance which has built-in storage to store process data. This data can then be easily transferred to a PC and analysed.

EtO Sterilisation & Packaging has been a much debated issue over the years. Being a terminal mode of sterilisation, the packaging has to be permeable to Ethylene oxide & moisture, yet impermeable to bacteria. It should also not be deformed or damaged due to variations in pressure and vacuum. Thankfully, dependence on plastic films for primary packaging has reduced. The use of Medical grade paper on one side has become the norm due to its better breathability. Not only does it provide better permeability to gas and moisture, but also helps in faster aeration of the EtO gas. Such packaging material is available commercially and has aided the medical device sterilisation industry in a big way.

Due to the toxic nature of this gas, EtO Sterilisation process has come under the scanner of various regulatory bodies and adherence to safety is of prime importance. It is therefore mandatory to have an exhaustive ‘Risk Analysis” in place for every sterilisation facility, to assess the hazards and mitigate risks that occur in all potential risk areas including Operations, Handling, Storage, Residues, Disposal & Environment. Gone are the days when it was acceptable to release EtO into the atmosphere. EtO gas abatement /scrubbing solutions are available that convert EtO into a non hazardous form, which can then be easily disposed through appropriate channels. Periodic monitoring of EtO levels in work areas using portable monitors is also critical to ensure that the sterilisation system is working correctly and that worker safety isn’t compromised. The generally followed limit in India is 1 ppm in air over an 8 hour TWA. Alternatively a short term exposure limit of 5 ppm over a 15 minute interval is permissible.

Considering the sensitive nature of this application, the sterilisation cycle should have minimal manual intervention. This implies that all functions such as opening/closing of the valves, control of utilities, gas injection etc should be PLC controlled. For redundancy, it is also mandatory to have an independent monitoring system to record the actual cycle data. Control over such electronic records is important, which can be achieved by simple practices such as maintaining an audit trail, having multilevel passwords and software validation. These factors have to be considered before finalising the software to be used.

Like any other field, technology and opportunity haven’t spared this small industry of EtO sterilisation either. But harnessing these and being commercially competitive has been a challenge. Sterilisation companies have to constantly keep up with changing technology trends as well as meet market demands. With invention of newer medical devices, significant resources need to be dedicated towards R&D as well.

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