Medical Device Sterilisation : Key Essentials, Options And
Challenges
Mr. Nishad Dhurandhar
Manager, Operations
MICROTROL Sterilisation Services Pvt. Ltd. |
EtO Sterilisation: Technology Trends And Developments
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EtO (Ethylene oxide)
sterilisation continues to remain the most preferred
mode of sterilisation (over Gamma, E-beam etc) for
several decades now.
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However, globally, the
cost advantage that EtO sterilisation has over other
modes of sterilisation is reducing and this effect
is likely to cascade onto the Indian industry as
well. In spite of these reasons, because of
convenience, EtO continues to be the most popular
mode of sterilisation.
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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 Traditional use of spore strips has now been
replaced by SCBI (Self Contained Biological Indicators),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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