Sterilization Methods

Sterilization is a process that kills all micro-organisms such as fungi, bacteria, viruses and spores that are present on a surface.

The aim of sterilization is to destroy all forms of microbial life

Methods of Sterilization

• Heat sterilization– Moist heat– Dry heat

• Chemical sterilization– Liquid– Gas

Moist Heat

• The quickest most effective method of sterilization is the Steam Autoclave

• Autoclaving will inactivate all fungi, bacteria, viruses and also bacterial spores and most prions (Prions cause “mad cow” disease)

Moist Heat

• Autoclaves use steam heated to 121–134 °C (250–273 °F) with a holding time of at least 15 minutes at 121 °C (250 °F)

• Additional sterilizing time is required for liquids and instruments packed in layers of cloth, as they may take longer to reach the required temperature

What is a Steam Autoclave?

• An autoclave has a heavy metal steel chamber surrounded by a jacket with a space between

• Autoclaves have indicators that record or display information (temperature & pressure)

• A vacuum in the chamber removes air which could become trapped and cause cold areas which could lower the temperature of the steam and prevent steam penetration

What is a Steam Autoclave?

• An autoclave works by steam under pressure which creates a high temperature

• Pressure forces the steam through everything which needs to be sterilized

• A vacuum after sterilization dries the contents

• Filtered air is reintroduced to equalize pressure before opening the door

Steam Autoclaves

• Indicator tape is placed on packages prior to autoclaving. A chemical in the tape will change color when the appropriate conditions have been met. Some types of packaging have built-in indicators on them.

• Biological indicators and Bowie Dick tests can also be used to independently confirm autoclave performance.

Steam Autoclaves

• Indicators should be placed in the most difficult places for the steam to reach to ensure that steam actually penetrates

• For effective sterilization, steam needs to penetrate the autoclave load uniformly, so an autoclave must not be overcrowded, and the lids of bottles and containers must be left ajar

• All instruments must be double wrapped in linen or special paper or placed in a special metal box equipped with a filter before sterilization

Steam Autoclave

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Steam Autoclave on FEH

Flash Autoclave

• Flash sterilization was designed for OR for the immediate use of a forgotten or unanticipated instrument or for one that was accidentally dropped on the floor

• Flash Autoclaves use steam heated to 134 °C (273 °F) for 3 minutes

• Instruments are autoclaved unwrapped for a shorter period of time.

Flash Autoclave on FEH

Dry Heat Sterilization

• Was used in Ancient Rome to sterilize instruments by means of a flame. During the Middle ages, it mostly disappeared resulting in disabilities and death following surgical procedures

• More effective method is the Hot Air Oven

Hot Air Oven

• Electrical device which uses dry heat to sterilize articles

• Operated from 50 to 300 °C (122 to 572 °F)

• Fitted with adjustable wire mesh or aluminium trays

Hot Air Oven

• Thermostat digitally controls the temperature

• Double walled insulation keeps the heat in and conserves energy

• An air circulating fan helps in uniform distribution of the heat

Hot Air Oven

• Indicators and controls for temperature and holding time

• These are widely used to sterilize articles that can withstand high temperatures

Advantages of Hot Air Oven

• Does not require water

• Not much pressure build up, making them safer to work with

• Much smaller than an autoclave but can still be as effective

• Faster than an autoclave

• Rapidly reaches higher temperatures

Disadvantages of Hot Air Ovens

• As they use dry heat instead of moist heat, some organisms like prions may not be killed by them every time

Chemical Sterilization

• Liquid– Glutaraldehyde (Cidex)

• Gas– Ethylene Oxide (ETO)– Formalin

Glutaraldehyde

• The only liquid chemical capable of sterilizing an item is Glutataraldehyde (Cidex)

Glutaraldehyde

• Disadvantages– Extremely caustic to the skin, mucous

membranes and other tissues– Carcinogenic– Short shelf life (<2 weeks)– Expensive– 10 hours sterilization time

Gas

• Most effective is Ethylene Oxide (ETO)– Should only be used for items that will not

withstand sterilization by steam under pressure

• Disadvantages– 3-7 hours sterilization time– Airing out period to allow ETO gas to be

expelled from surface of item according manufactures instructions

One Chamber ETO Sterilizer

Two Chamber ETO Sterilizer

Chemiclave

Formalin Tablets

• Sterilization of catheters, anaesthetic masks and valves, syringes, needles, small instruments, scopes like bronchoscopes, cystoscopes & items that cannot be autoclaved

Formalin Tablets

• Effective against a wide spectrum of organisms and the storage of non-wrapped sterilized instruments

• Used only in air tight containers like instrument cabinets using 10 tablets / dm3

Formalin Tablets

Formalin Tablets

• Used as a fumigant in gaseous form, formaldehyde sterilization is complex and less effective

• It should only be used if steam under pressure will damage the item to be sterilized and ethylene oxide and glutaraldehyde are not available

Formalin Tablets

• No longer used in the United States, Canada, and Australia. The method dates back to 1820, but is still used in Europe and Asia

Disadvantages of Formalin Tablets

• Caustic to the skin, mucous membranes and other tissues

• Carcinogenic

• Exposure time ranges from 15 to 24 hours

Points to Remember

• Never sterilize surgical drains, disposable rubber gloves or disposable rubber catheters

• An article is either sterile or unsterile-there is no in-between. If in doubt-consider it unsterile

• If sterility field has been compromised-replace the contaminated field

Points to Remember

• Do not open sterile articles until they are ready for use

• Don’t leave sterile articles unattended once they are opened and placed on a sterile field

• Do not return sterile articles to a container once they have been removed

• Never reach over a sterile field

Points to Remember

• When pouring sterile solutions into sterile containers or basins, do not touch the sterile container with the solution bottle

• Discard any liquid remaining in the bottle

• Never use an outdated article. Unwrap it and if re-usable, rewrap it in a new wrapper for sterilization

Questions

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