Sterilization

There is no degree of sterility. An item is either
sterile or non-sterile. It can never be
relatively sterile.

STERILIZATION – is the process by which all
living micro-organisms both pathogenic and
non-pathogenic including spores are killed.

 The prevention of surgical site infection in
health care areas is largely dependent on the
rigorous adherence to the principles of aseptic
techniques by all personnel who performs any
invasive procedures on patients, the sterility of
all items directly used in such procedures and
the disinfections of all surfaces and other items
in the immediate environment.

 Surgical instruments, linen and heat
sensitive items are sterilized by the method
recommended by the manufacturer. No
disposable items designed for sterile single
use should be processed.

It is essential for a sterilizing agent to
be in contact with every surface of
each item or device to be sterilized
for the specified period of time at the
specified temperature.

Heat – is the earliest, the safest and surest
method of sterilization. It may be dry (hot air
ovens infra red conveyor ovens) or moist
(steam).

 Dry heat, at normal atmospheric pressure.
› Hot air ovens – these are electrically heated and
usually with an internal fan to provide and even
distribution of heat. Sterilizing time is one hour at
160ºC. This is suitable for ophthalmic instruments,
glassware and sealed jars.
› Infra red conveyor oven – items are passed on a
conveyor through a tunnel heated by infra red
elements. The infra red radiation is lethal so it is not
commonly used now days.

 Moist heat, at a raised atmospheric pressure
› Steam autoclave (steam under pressure) Steam
sterilization is the most inexpensive and effective
method of sterilization. Steam under pressure
permits permeation of moist heat to porous
substances by condensation and results in
destruction of all microbial life. This is the usual
method of sterilizing surgical instruments, dressing,
drapes, swabs, laps sponges and culture media.

 An autoclave is a closed chamber in which
items or objects are subjected to steam at high
pressures and temperatures above 100ºC.
Steam is a more efficient method of sterilization
than air at the same temperature. If air is
present in the sterilizing chamber, a satisfactory
temperature will not be achieved and pockets of
air may prevent penetration of the load of
articles by the steam. The air must therefore be
removed.

 DOWNWARD DISPLACEMENT
AUTOCLAVES – Air is removed in two stages
and sterilization is effected by an atmosphere
of pure steam.
 The minimum exposure time is required for
sterilizing instruments is 50 minutes at 131ºC
or 60 minutes at 136ºC. Bulky dressings,
surgical swabs and surgical drapes require
exposures two or three times as long.


 HIGH VACCUM / HIGH
PRESSURE AUTOCLAVE –
Air is removed by powerful
pump. Steam penetrate the
load instantaneously and
very rapid sterilization of
dressings, instruments,
raytec swabs, lap sponges
and packs is possible in 15
to 30 minutes at 134ºC.

Faults in the autoclave and the way it is
operated
It maybe:
› Poor quality steam
› Failure to remove air and condensate
› Faulty gauges and timings
› Leaking door seals

Errors in loading
Examples:
› Large packs
› Excessive layers of wrapping materials
› Over packing

Recontamination after sterilization due to:
› An inadequate air filter and leakage into the
chamber
› Wet or torn packs
› Incorrect storage

PHASE I
The loading phase - in which the objects or items
are packaged and loaded in the sterilizer.
PHASE II
The heating phase – in which the steam is
brought to the proper temperature and allowed
to penetrate around and through the objects in
the chamber.

PHASE III
The destroying phase – or the time-temperature cycle, in
which all microbial life is exposed to the killing effect of
the steam.
PHASE IV
The drying and cooling phase – in which the objects are
dried and cooled, filtered air is introduced into the
chamber, the door is opened and the objects are
removed and stored.

PHASE V
Testing phase - in which the efficiency of the
sterilization process is checked. All mechanical
parts of sterilizers, including gauges, steam
lines and drains, should be periodically checked
by a competent engineer.

Packages/Instrument Sets should have the
following external indications, showing that
they have been processed:
 Autoclave tapes that show a package has been through
a sterilization cycle should be visible on the outside of
every package sterilized. The autoclave tape is designed
black when a certain temperature inside the autoclave is
reached. This is usually at 120ºC to 135ºC depending
upon the length of the selected time cycle.
 Every package must be labeled as to its contents and
expiry date.
 Every package, tray or item is to be labeled with the
processing date, autoclave used and load number. This
will assist locating processed items in case of recall.

1. Decontamination
2. Disassembly
3. Washing
4. Drying
5. Packing
6. Loading in sterilizer

 Sterile packages/items should be left
untouched and allowed to be cooled before
storage to avoid condensation inside the
packs.
 Sterile packages must be handled as little
as possible to reduce the risk of
contamination.

 Sterile packages should be stored on open
shelves.
› The lowest shelf should be 8 inches from the
floor
› The highest shelf should be 18 inches from the
ceiling
› All shelves should be at least 2 inches from the
walls

 Sterile packages must be stored and issued in
correct order.
 Sterile items are good for either 30 days or 6
months depending solely on how the
packages are wrapped and what type of
wrappers are used. This is called the shelf life
which refers to the length of time a package
maybe considered sterile.

 The storage room must be subjected to
adequate pest control to prevent
contamination from rodents, ants and
cockroaches.
 Traffic is restricted to CSSD personnel and
trainees only.

1. BOWIE DICK TEST PACK – It is a large
pack with a chemical indicator both on
outside and the inside to verify that steam
has penetrated the pack.
2. MECHANICAL- Chart and gauges usually
carried out by Biomed Engineer.

3. CHEMICAL- by the use of autoclave tapes,
strips and card. A daily test in an empty
chamber using a heat sensitive tape. This is
for high vacuum/high pressure autoclaves.
Ex. Routine use of Browne's TST strips or
tube.

4. BIOLOGICAL- indicators of live organism. It is
the microbiological monitoring of sterilizers and
is recommended at least once a week with
commercial preparation of spores of
Geobacillus stearothermophilus formerly
Bacillus Stearothermophillus. This
microorganism is having spores that are
particularly resistant to moist heat thus assuring
a wide margin of safety.

 First- They run it empty for one cycle.
 Second- They put inside in the middle of the
chamber of the SA the Bowie Dick Test Pack
and run it again and finish the whole cycle.
Oh high pressure- to test leaks and presence
of air.
 Third They load it with items and trays for
sterilization ( little bit lower pressure). It is
done once daily.
 Fourth- Live Organism- done once in every
Saturday morning.

 This high speed steam sterilizer is adjusted to operate
at 132ºC (270ºF) and 27 PSI for 3 minutes. It is most
frequently used in the OR for the urgently needed
unwrapped instruments. It should be used only when
time does not permit sterilization of unwrapped sets.
 Implantable devices are not recommended to be flash
sterilized because the reliability of sterilization is
reduced by the speed of the cycle. Spore tests cannot
be used reliably and the margin of safety is lower.

 Gaseous Sterilization
 a. Ethylene Oxide (EO) – This is
a well established technique for
sterilizing heat labile articles. It is
colorless at ordinary
temperatures, has an odor
similar to that of ether and has
an inhalation toxicity similar to
that of ammonia dioxide or
fluorinated hydrocarbons
(FREON).

 It can be used for sterilizing vascular and bone grafts,
delicate instruments, plastic articles such as disposable
syringes, surgical instruments such as cystoscopes,
catheters, bacteriological media and vaccines.
 Before EO sterilization, objects also need to be cleaned
thoroughly and wrapped in a material that allows the
gas to penetrate.
 Chemical indicators for EO should be used with each
package to show that it has been exposed to gas
sterilization process.

 Gas sterilizers are recommended to be checked at least
once a week with commercial preparation spores,
usually Bacillus Atropheus formerly BACILLUS
SUBTILIS VAR. NIGER.
 All objects processed by gas sterilization also need
special aeration according to manufacturer’s
recommendation before use to remove toxic residues of
EO.
 In general, an exposure period of 3 to 7 hours is
necessary for complete sterilization. Temperature for
sterilizing is 21º C to 60º C 70º F to 140º F).

 Materials aerated in a mechanical aerator
that provides a minimum of four air changes
per hour and elevates the temperatures
within the cabinet to 50º C to 60º C (122º F
to 140º F) require 6-8 hours of aeration
based on the composition of the sterilized
items and the aerator manufacturer’s
instructions.

 EO sterilization should be used only if materials
are heat sensitive and unable to withstand
sterilization by saturated steam under pressure.
 EO is easily available and is effective against all
types of microorganisms.
 EO easily penetrates through masses of dry
materials; does not require high temperatures,
humidity or pressures.
 EO is non- corrosive and non- damaging to
items.

 It is lengthy process in the long exposure and aeration
periods.
 EO sterilization is expensive and more complex
process.
 Liquid EO may produce serious burns on exposed skin
if not immediately removed.
 Insufficiently aerated materials can cause irritation,
burns of body tissues, hemolysis of blood and diluents
used with EO cause damage to some plastics.
 It is toxic and can cause Cancer. Precautions should be
taken to protect personnel.

 b. Gamma Radiation
This involves the use of gamma radiation from a Cobalt
60 source and is used commercially.
 c. Ultraviolet light
This is a form of surface radiation and its penetrating
capacity is poor, so it is used for sterilizing surfaces,
bone chips, grafts and blades.

 d. Plasma (Sterrad)-
Autoclave - Low
Temperature Hydrogen
Gas Sterilizers. It is used
to sterilize delicate
instruments. Spore testing
should be performed at the
same interval as testing of
other sterilizers.

 When used properly liquid chemo sterilizers
can destroy all forms of microbial life
including bacterial and fungal spores,
tubercle bacilli and viruses.
 Liquid chemicals can be used for sterilization
when steam, gas or dry heat is not indicated
or available.

 Aqueous Formaldehyde- is one of the oldest chemo
sterilizers known to destroy spores; it is rarely used because
its pungent odor is objectionable.
 Aqueous Glutaraldehyde- is more rapid and less
irritating than formaldehyde solutions. Instruments must be
free of bioburden and completely immersed in activated
aqueous glutareldehyde solution for 10 hours to achieve
sterilization. During immersion all surfaces of the
instruments must be rinsed thoroughly with sterile distilled
water before being used. Any period of immersion less than
10 hours will not kill spores that may be present and must
be considered as only a disinfection process.

Sterilization

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