STERILIZATION:
Medical devices classified as critical devices should be sterile when used because any microbial contamination could result in disease transmission. These items include surgical instrument, biopsy forceps and implanted medical devices. If these items are heat resistant, the recommended process of sterilization is with steam.
Steam sterilization
This method has the largest margin of safety due to its reliability, consistency and lethality. Steam sterilization is non toxic, inexpensive, rapidly microbicidal, sporicidal and rapidly heats and penetrates fabrics. Moist heat in the form of saturated steam under the pressures is most dependable.
Principle: exposure of the item to direct steam at the required temperature and pressures for the specified time.
Important steps for steam sterilization
- Items to be sterilized must be prepared to permit air removal and ensure contact of stem with all
surfaces of the devices.
- Provide protection for sharp and delicate instrument. It is myth that sharps blunt in steam sterilizers.Blunting is the result of poor quality of autoclaves.
- The items should be thoroughly cleaned to reduce the bioburden and tested to verify functionally
- The items should be appropriately packaged.
Packaging : is required to allow sterilization of the contents and the material used should be compatible with process and it should maintain sterility until the pack is opened. There are several types of packaging material available. Linen packs are likely to get contaminated easily since linen allows microorganisms to pass particularly if the pack is moist and extensively handled. Paper pack, non-woven material and medical grade are the alternatives.
The shelf life of the packaged sterile items depends on the quality of the wrapper the storage conditions, transportation conditions and handling. Sterile items should be stored in a clean room.
Autoclaves
The choice of autoclaves is important. The sterilization system is the heart of the surgical services. Investment in a good quality autoclaves is therefore essential. The shelf life of an autoclave is at least 20 years.
There are two basic types of autoclaves :
Gravity displacement which evacuates air by heating and gravity.
Prevacuum is mechanized evacuation of air.
Lack of air removal hampers with the process of sterilization.
Autoclaves need to be properly maintained. The manufacture is responsible for the calibration and validation checks.
There are four important parameters
- Dry saturated steam
- Pressure which serves as a means to quickly obtain the required temperature
- Temperature 121 degrees Celsius or 134 degrees Celsius
- Time 30 minutes at 121 degrees and 4 minutes at 134 degrees
These physical parameters need to be monitored with every cycle. Record keeping of loads, parameters and validation are important to safeguard the practioners interest.
Most of the sterilizers in use are gravity displacement and the only record available is the pressure, what is actually required is the temperature record.
Thus a quality sterilizer indicates the temperature.
Validation systems for sterilization
Steam Indicator tapes:
These are used as external chemical indicators to immediately indentify processed items and also serve as a closure tape to seal sterilization packs. The chemical indicator lines turn dark brown when exposed to a steam sterilization process.
Steam Chemical Integrators
These are internal chemical integrators used for pack control, which validates that the steam has penetrated to the point of placement in the pack and confirms that sufficient exposure conditions have been met. This is a chemical indicator consisting of a paper wick and steam and temperature sensitive chemical pellet contained in a paper/film/
Foil laminate envelope of laminate material. Steam enters the permeable topside of the device-the chemical pellet melts and migrates as a dark color along the paper wick; the distance or extant of migration depends on exposure to steam, time and temperature, The migration is visible through a window marked Accept of Reject. The dark color has not entered the Accept window, a reject result is indicated.
Biological Indicators
The effectiveness of steam sterilization is monitored with a biological indicator containing spores o Geobacillus stearothermophillus. Positive spore test result are an indicators of inadequate steam delivery or equipment malfunction.
The validation process should consist of a biological indictor at least once a week.
Every pack should carry a temperature sensitive tape which indicates that the item has passed through a cycle. This tape does not validate the cycle.
Ethylene Oxide
This is a low temperature method of sterilization which is recommended for heat and moisture sensitive items. The packaging system consists of sealed cellophane or plastic bags. ETO gas is carcinogenic and the sterilization items required proper aeration on another chamber. This increases the turn around time to nearly 16 hours. Plastic items that are to be sterilised must be dried adequately because EO gas reacts to form a highly toxic compound. Many of the single use devices that are being reused are gas sterilized.
NEWER TRENDS IN STERILIZATION
Hydrogen Peroxide Gas Plasma Sterilization
This method is also useful for temperature and moisture sensitive items, the temperature being 50 degrees Celsius. It is safe for the environment and the healthcare worker, it leaves no toxic residue. It has a short cycle time 45-75 minutes and needs no aeration. It is simple and easy to operate and is compatible with most medical devices. Currently the high cost of the equipment is a major limitation and it requires synthetic packaging of polypropylene and a special container tray. Linen and liquids cannot be processed.
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