Gas Sterilization

7/28/2019 Gas Sterilization

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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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Gas Sterilization