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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
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
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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