Post on 03-Apr-2018
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Introduction
Many chemical substancestoxic to m/organisms. Very limited numbers used as sterilizing agents. Example of gaseous sterilants: --Ethylene oxide (mostly used) Formaldehyde (LTSF) Hydrogen peroxide Gas Plasma Peracetic acid Gluteraldehyde Ozone Chlorine dioxide Propylene oxide Ethylene oxide and formaldehyde;1. Broad spectrum biocidal activity2. Applications in sterilization of ;
Re-usable surgical instruments. Medical, diagnostic & electrical equipments Surface of powders. Disposable medical devices (alternative to
radiation).
3. Do not offer the same degree of sterility assurance as heat
sterilization.4. Reserved for heat-sensitive items Mechanism of antimicrobial action:1. Alkylation of sulphydryl, amino, hydroxyl & carboxyl
groups on protein & imino groups of nucleic acids.2. At concentration employed in sterilization, type A survivor
curve produced.3. Lethality increasing in non-uniform manner with
increasing concentration, exposure temp & humidity.
4. Concentration & temp ranges (wt of gas per unit chamber):Ethylene oxidex800-1200mg/L (45-63oC)
Formaldehydex15-100mg/L (70-75oC)
Sterilization process lengthy even at higher temp:Not suitable for re-sterilization of highturnover articles.Need to remove toxic residues of gaseous.Extended quarantine period (sterility tests).
Alkylating agents:mutagenic
carcinogenic
may cause:
i. Acute toxicity-via inhalation-symptoms- irritation of skin, nasal mucosa,conjunctiva).
ii. Chronic toxicity-due to chronic expousure-symptoms-neurological,ocular,haematological
#therefore, its important to
control [ATM]
develops safe working protocols
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Ethylene oxide Formaldehyde (LTSF) Hydrogen peroxide gas plasma Highly explosive in mixture of>3.6% v/v in air.
Thus, supplied for sterilization as:
10% mix with CO2
8.6% mixture with HFC 124
Pure ethylene oxide gas used below ATM pressure
in sterilizer chamber (all air must be removed).
Normally used to sterilize:Dressings
Catheters
Infusion & giving setsSyringes
Prostheses
Some plastic containers & closuresSome thermolabile powders (if humidity is not a
problem)
Formaldehyde gas: heating formalin (37%
w/v aqueous solution of formaldehyde) temp of 70 -75
oC to(or 60-80oC) with steam
. Formaldehyde + steam= LTSF (low temp
steam & formaldehyde)
Toxicity = ethylene oxide
Absorption to materials lower but = desorption routinerecommended.
Widely used to disinfect clean rooms.
Also has been used for sterilization of rangeofmedical devices.
Major disadvantagexxpenetrating
powerx limit packaging materials that canbe employed:
Paper
Cotton fabric
Alternatives to ethylene oxide and
formaldehyde sterilization.
Advantages:
Non-toxic (by-productx water, oxygen).
Desorption unnecessary.
Shorter cycle time.
Sterilized items can be safely used/storedimmediately.
Gas plasma: 4th state of matter.
Gas plasma produced underfollowingconditions to excite gas molecules &
produce charged particles:
Enclosed chamberDeep vacuum
Radio frequency / microwaves energy
function Used to sterilize surfaces. Cannot penetrate through many walls of many
containers to the products inside.
x sterilize sealed vials or ampoules of liquid
products.
x penetrate certainplastic films & bags.
Mode of antimicrobial activity:
Free radicalsproduced (hydroxyl &
hydroperoxyl) interact with essential cell
components (i.e. enzymes, nucleic acids)x
disrupt metabolisms
broad antimicrobial activity includingresistant bacterial spore
Factors affecting efficacy of ethylene oxide as
sterilant:Concentration of the gas
Temperature (50-60Gas pressure
Humidity (some moisture must be present, activity
declined when in excess)x30-70%.
Time of exposureGas distribution & penetration
Rubber, plastic, fabric & paper Drawback: level ofethylene oxide in sterilizer lower
due toabsorption during the process & treated articles
must undergo desorption stage to remove toxic
residues.
tosterilize the loads.thus, necessary to include biological
indicators in each load
#cycles used have included:250 mg/L -1500 mg/L (gas concentration)
30% - 90% (relative humidity)
30oC - 65oC (temperature)1hr30hr (exposure time)
#sterilization cycle !
Applications of H2O2 gas plasma
sterilization include:Medical & surgical devices
PlasticsElectrical devices
Corrosion susceptible metal alloys
Most commonly used plasma sterilizerknown as
STERRADOperating tempx40-50oC.
Operating cyclex45-70 mins (or even lesser!)Uses combination of H2O2 vapor + low temp gas
plasma.
Operated under low moisture environment.
Sterilization process occurs in the following order:
1. Item placed in the chamber, chamber closed,vacuum drawn.
2. Aqueous solution of H2O2 injected into chamber
& vaporized, surrounding items to be sterilized.
3. After a period of H2O2 diffusion, chamber
pressure low, thus low temp.
4. Radio frequency (RF) applied to create electric
field and form low temp gas plasma.
5. In the plasma state H2O2 break apart to produce
reactive species including free radicals.6. Combination of H2O2 vapor + plasma kill the
organisms and sterilized the items.
7. Following reaction, highly reactive species losetheir energy and recombine to form non-toxic by
products.7. When process completed, RF energy turnedoff.
8. Vacuum released, ATM pressure restored byadmission of filtered air into the chamber.
9. Items sterilized and ready for use.
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Ethylene oxide Formaldehyde (LTSF) Hydrogen peroxide gas plasma
Sterilizer design -proof stainless
-300 L. Surrounded by hot-water jacketx provide
uniform chamber temp.
Successful operation involved:Product loading according to predefined
configuration.Removal of airfrom chamber by evacuation.Humidification & conditioning of loadby passage
of sub-ATM pressure steam.
Followed by furtherevacuationperiod &
admission of pre-heated vaporized ethyleneoxide from external pressurized canisters/single
charged cartridges.
Forced gas circulationx minimize variations in
conditions throughout chamber.
Internal fan
External re-circulation loop
Packaging materials:
Air, steam, gas permeable to permit suitableconditions for
sterilization. Absorption of ethylene oxide by load compensated
for by introduction ofexcess gas aspressuredrops
during sterilization process.At the beginning.
Once the pressure drop during the process.
moisture absorption
Addition of water to maintain appropriate relative
humidity.
After treatment, gases are evacuated:
Directly to outside ATM or,
Via special exhaust system.
Then, filtered, sterile air admitted for:Repeat of vacuum/air cycle.Air purging until chamber is opened.
Safe removal of ethylene oxide achieved, reducing
toxic,hazard to the operator.
Sterilized articles removed directly from
chamber & arranged fordesorption:
Naturally on open shelves:takes days to complete
Assisted by special forced aeration cabinet whereflowing, heated air encourages gas removal (2-24 hr ).
Operation of ethylene oxide sterilizerx
automatically controlled & monitored.
LTSF sterilizer: designed to operate with
sub-ATM pressure steam.
Air removal (evacuation), and Steam admission to chamber:
Allow heating of load.
Assist in air removal. Sterilization period starts with release of
formaldehydeby vaporization from formalin(in vaporizer in steam jacket). Continued with either:
Simple holding stage.
Series of pulsed evacuation & steam and
formaldehyde admission cycles. Chamber temp maintained through:
Thermostatically controlled water-jacket.
Steam & condensate removal via drain
channel & evacuated condenser.
At the end of treatment period:
Formaldehyde vapor expelled by steam flushing.
Load dried by alternating stages of evacuation &
admission of sterile, filtered air.
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