Sunday, September 26, 2010

Chemical Sterilization

By - Pauline W. Fallis,

Chemical sterilization includes both liquid and gas chemicals. Most electrologists are familiar with liquid chemical sterilization, but there are gas forms as well.
The most frequently used liquid sterilants used in office settings are 2% alkaline glutaraldhyde, peroxyacetic acid, and sodium hypochlorite (household bleach). All liquid sterilants are disinfectants that have the capability of sterilizing when the exposure time is considerably lengthened. As with any other form of sterilization, all items must be clean before sterilizing. In order for sterilization to take place, each item must be completely immersed in the sterilant solution, so that all surfaces are in contact with the liquid for the specified time indicated by the manufacturer. As only unwrapped instruments are sterilized in liquid sterilants, they do not stay sterile, after they are removed from the solution. The chances of contamination of sterile items is very high, because there is nothing to protect them. Alkaline glutaraldehyde 2% is the most common of the liquid sterilants used today. For this solution to be effective the item must be completely immersed in the liquid for about 10 hours. There are no monitoring devices to ensure the effectiveness of the process. However, there are testing kits available from the suppliers, to test the strength of the solution so that it is within the parameters to be an effective sterilant. As long as the results of the test show it has not been contaminated by organic material (protein or blood) or diluted by too much rinse water, it may be used for the shelf life of the chemical (14 to 30 days, depending on the formulation). Being a toxic substance, 2% alkaline glutaraldehyde is regulated by the Occupational Safety and Health Administration (O.S.H.A.), in the U.S.A., and is included in the Workplace Hazardous Materials Information System (W.H.M.I.S.) in Canada. Be careful when using this solution. Use it only in well ventilated rooms, in covered containers (plastic) and when wearing household rubber gloves. Immediately after removing articles from the solution, make sure they are rinsed thoroughly with sterile distilled water. Peroxyacetic acid is a liquid sterilant that is only used safely within the confines of a special sterilizer. It is used in a formulation of .2%, with a buffer and anticorrosive dry powder added. The sterilizer automatically controls and monitors the time, temperature and concentration of the solution. The cycle is completed when the items are rinsed with sterile distilled water. The cycle is usually 12 minutes exposure time, followed by 4 thorough rinses. When the cycle is completed the solution and rinse water are discharged down the drain into the sanitary sewer system. Peroxyacetic acid can not be reused. One thing about peroxyacetic acid is that the process may be monitored by either bacillus subtilis or bacillus stearothermophilus biological indicators. Due to the ability of this process to be monitored and due to the short length of the sterilizing cycle, this method of sterilization for immersible but heat sensitive items is becoming more popular in hospitals. But due to the high cost of the sterilizing device and the chemical, it is not a viable alternative for electrologists. Sodium hypochlorite, or household chlorine bleach, is the last liquid chemical sterilant. This sterilant is not often used. Although it is powerful, it is an unstable sterilant. As with all other methods of sterilization, items must be cleaned before being sterilized in sodium hypochlorite. The items must be completely immersed in the solution for at least 20 minutes at 20 degrees C. or 68 degrees F., then rinsed thoroughly with sterile distilled water. This process can not be monitored. Because sodium hypochlorite gives off a strong odour which will irritate eyes and skin, it should only be used in a well ventilated room. Chemical vapour, is another chemical sterilizer. Chemical vapour sterilization is used for items made from metals like carbon steel that will corrode in the presence of steam or moisture. The sterilizer uses a combination of 1% formaldehyde and alcohol in a gaseous form as the sterilant. It sterilizes at 132 degrees C. or 270 degrees F., and therefore is not suitable for the sterilization of items that are heat sensitive, like plastic or rubber. As liquids absorb gas, they cannot be sterilized by this method either. The sterilization cycle takes approximately 30 to 35 minutes. When the gas is exhausted from the chamber it is normally captured by a chemical filter canister. When fabric items are sterilized, each load must contain a biological indicator because the fabric tends to absorb the gas, and thus it may not be as effective. The biological indicator of choice is bacillus stearothermophilus. Of all the chemical sterilization processes, the gas chemical vapour method of sterilization is the only one that can be done for wrapped items, therefore sterility can be maintained. The problem with this method of chemical sterilization, is that the sterilizer is quite expensive. These are the main liquid and gas chemicals used for sterilization in an office setting. They are by no means the only ones sold, but they are the only ones that have been thoroughly studied and are proven to be effective. Sterile items must be carefully handled after they are removed from the liquid sterilants, and must be used immediately. There is no method of monitoring the effectiveness of 2% alkaline glutaraldhyde or sodium hypochlorite. For the purpose of sterilizing instruments that must be used sterile, liquid sterilants are not recommended for electrologists. Steam under pressure is still the preferred method of sterilization, followed closely by dry heat. Remember, that the time that a sterilized item must be sterile, is at the moment that it is used. References - AAMI - Chemical sterilants and Sterilization Methods: A guide to Selection and Use. AAMI Technical Information Report, The Association for the Advancement of Medical Instrumentation, Arlington, Virginia, U.S.A., 1990. Jdorette, W.H.L, ed. - The Central Service Technical Manual, International Association of Hospital Central Standards Association, Chicago Illinois, U. S. A., 1981. Fallis, P. W. - Handbook of Infection Control in Office-Based Health Care and Allied Services - Canadian Standards Association, Plus112, Toronto, Ontario, Canada, 1994. Rutala, W. A., The 1994, 1995 and 1996, APIC Guidelines Committee, APIC Guideline for the Selection and Use of Disinfectants - American Journal of Infection Control, August, 1996, Volume 24, Number 4, Page 333. Whipple, L., Helgeson, J., Infection Control Practices and Sterilization Standards, The Society of Clinical and Medical Electrologists Inc., Massachusetts, U. S. A., 1993

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