|
Value-Add
Why 'Class-B' Autoclave?
All medical professionals must possess basic knowledge
about the process of sterilisation
There has been a growing understanding of the microbial threats that exist
in laboratory and medical practice as of today. Simultaneously, these threatening
trends have been accompanied by a tremendous advance in the science and technology
of in-clinic sterilisation. All medical professionals must possess a good basic
knowledge about the process of sterilisation. So what exactly is sterilisation?
Sterilisation is the destruction or removal of all viable microorganisms, including
many of the resistant bacterial spores. Since this process covers the broad
range of pathogens that may be found in dental, ophthalmic and any surgical
procedure, it is the only clinically acceptable means for dealing with reusable
instruments between patients. In order to understand 'Why Class B autoclave?,'
let us first understand how a steam pressure steriliser - commonly known as
an autoclave - steriliser.
Autoclaves commonly sterilise by exposing its charge (items to be sterilised)
to elevated temperatures of 121 to 134ºC under pressure of 15 to 30 psi,
for a holding time of anywhere between three to 30 minutes. Please note that
the three to thirty minutes time is the holding time at the set elevated temperature
and not the total process or cycle time. Total cycle time would be far greater.
The combination of the three lethal parameters of time, temperature and steam,
deliver a powerful kill rate which even the hardest of bacteria find hard to
survive. This effective and yet clean method of lethality is unmatched by any
of the other methods of sterilisation.
Saturated steam at this temperature is an excellent carrier of heat. The operative
word is saturated steam. The steam condenses onto its charge and as it does
so, it not only expands its huge latent heat but also draws in additional steam
to replace the condensed steam. Thus, the heat transfer is very efficient and
the penetration levels extremely high.
However, if there is residual air in the chamber and load, it will interfere
with steam-instrument contact and may compromise sterilisation. This residual
air can prevent penetration of steam to the depths of the load, leaving your
sterilisation incomplete. When you load the autoclave with instruments and close
the lid, there is already a lot of stale air trapped inside. For sterilisation
to take place, this air needs to be effectively purged and replaced with saturated
steam. To resolve this problem of purging entrapped air, normal autoclaves will
have a manual, mechanical or electrically operated valve open till about 100ºC.
Once it is closed, the pressure and temperature begins to rise. It is presumed
that by this time, the entire entrapped inner air has been purged. However,
tests have shown that this is not an effective method for vials, wrapped items,
implants, garments and certain types of hollow ware. You can never be assured
of efficient penetration of steam right inside, if you are using a regular autoclave.
Even a small volume of entrapped air can compromise your sterility assurance
level simply because ordinary entrapped air is a very bad conductor of heat
and moisture. These pockets of air cannot conduct heat to the load with the
same vigour as steam and therefore cold spots remain within the load.
The type N-cycle is suitable for sterilising only unwrapped and solid instruments.
N-cycle sterilisers are the most popular bench top autoclaves (top or front
loading) and are classified as passive systems (also known as gravity or non-vacuum).
Typically, as steam is generated or admitted into the sterilisation chamber,
it forces unsaturated and saturated air out through a vent. The major concern
with the N-cycle sterilisers is the non-removal of trapped air (especially air
pockets in lumens and difficult-to-access areas of the load) during displacement.
Errors in packaging or overloading the steriliser chamber can result in cool
air pockets where items are not sterilised.
The type B sterilisation cycle is used to process loads that can retain air.
It can sterilise solid, hollow, and porous instruments, be they wrapped or unwrapped.
Pressurised steam is an effective sterilising agent provided that the internal
air has first been removed from the chamber as well as the air retentive load.
Residual air prevents direct contact between steam and the load to be sterilised.
Hence this B-cycle involves the use of active (forced) air removal, usually
by using an inbuilt vacuum pump. These pre vacuum or Class-B sterilisers create
a vacuum, thus removing air from the load prior to the chamber being pressurised
with steam. This can be done from one to three times, depending on the cycle
selected. This technique allows faster and more effective steam penetration
throughout the entire instrument load than the gravity displacement technique
typically employed in sterilisers with N-cycles.
Contact: Hemant Shah (CE)
Medica Instrument Manufacturing Company
hs@medicainstrument.com
|
