AUTOCLAVE VALIDATION – WHAT IS REALLY REQUIRED? Guy Snelling PO Box 10907 Vorna Valley 1686 [email protected] Abstract Steam autoclaves have been with us for many years and are used in many different industries. Their primary task is to sterilize items so that these same items can be used in situations where the introduction of micro-organisms would pose a health-risk. But how can we be sure that the autoclave is doing its job? Biological indicators form part of this validation, but there are many tests that should be performed regularly. This paper describes these tests, and how often they should be performed in order for the user to be confident that their autoclave is functioning properly and within the requirements of the regulatory bodies. Introduction There are four general types of sterilizers namely, Gamma Irradiation, Gas Sterilization, Dry Heat and Moist Heat. Whilst validation of all types of sterilizers follows the same basic principles, by far the most prevalent type in South Africa are steam or moist heat autoclaves and this paper therefore deals specifically with this type. Method of Operation Steam autoclaves generally follow the principles shown in Figure 1. Water is heated and the steam pressure is built up in the jacket. Once sufficient pressure is obtained, the steam is allowed to enter the chamber, thereby driving the air out of the drain port. Once all the air has been replaced by steam, the drain valve closes and steam pressure builds up in the chamber. The resultant pressure causes the temperature in the chamber to rise to the required point, usually 121 or 135 °C. Some type of autoclaves have a vacuum function that pumps out the air before the steam is allow to enter. This method is much faster and more efficient. Figure 1 Diagram of a horizontal steam autoclave An alternative method is used in vertical autoclaves. See figure 2. Water is placed in the bottom of the chamber and heated by an electrical element. The resulting steam drives the air out of an evacuation port near the top of the chamber. Again the evacuation port is closed once all the air has been removed and the steam pressure is allowed to build. Evacuation valve Steam Element Figure 2 Diagram of vertical autoclave Cycles Stages Generally an autoclave cycle consists of 3 stages viz. heating, sterilizing, de-pressure. Vertical autoclaves may have a “water fill” stage before the heating stage. Autoclaves fitted with vacuum facility may have vacuum stages before the heating stage and also as part of the depressurizing stage. Load Types Autoclaves are used different types of loads: to sterilize several Solid – metal, glass, plastic Porous – linen, gowns, paper, gauze, complex instruments, hollow tubes Liquid – water, saline, media Laboratory waste – Petri dishes, sample bottles, syringes [1] Heating Sterilizing Depressure Complete There are various methods of validation, depending on the usage of the autoclave. Instrumentation Figure 3 Typical autoclave cycle Why Validate? The instrumentation fitted to an autoclave will vary depending on the complexity and price of the autoclave. A vertical autoclave may only be fitted with a pressure gauge (also marked in °C) and a pressure regulator. A more complex, fully automated large autoclave may have a computer controlled display showing various temperature and pressures throughout the workings of the autoclave. Typically though, jacket pressure and chamber pressure would be indicated, along with chamber temperature. Validation requires that these instruments be checked for accuracy. System supplies Most autoclaves are electrically powered and all steam autoclaves require some form of a water supply to produce steam. The electrical supply must be able to handle the maximum peak power of the autoclave. The quality of the water supply will affect the quality of the steam Figure 4 Temperature and Physical Control of Microorganisms As can be seen from Figure 4, if the temperature in an autoclave does not reach 121 °C, not all spores will be destroyed in the typical cycle time of 20 minutes. Validation is therefore required to ensure that the autoclave is operating correctly and that complete sterilization is being achieved. The drainage system must be able to handle the maximum flow of water and condensate and should be able to tolerate 100 °C. [1] Validation Validation is described as a documented procedure for obtaining, recording and interpreting data required to show that a process will consistently comply with predetermined specifications. [3] In the case of autoclaves the validation process may be broken down into the following tests: Commissioning Installation Checks Installation Tests Commissioning Tests Performance Qualification Thermometric Tests Microbiological Tests [1] According to EN554:1994 “Sterilization of medical devices – Validation and routine control of sterilization by moist heat” [3], the Commissioning tests need only be performed at initial installation and after certain repairs while the Performance Qualification tests should be performed regularly and routinely. Commissioning “Commissioning: Obtaining and documenting evidence that equipment has been provided and installed in accordance with its specification and that it functions within predetermined limits when operated in accordance with operational instructions” [3] Commissioning tests should include checking: that the electrical supply is suitable for the autoclave that the temperature and humidity are sufficiently well controlled that there is no interference to or from other equipment the accuracy of indicators has been certified to national standards the temperature and pressure of the chamber during a sterilization cycle are within specifications the leakage into the chamber during a vacuum cycle does not exceed the specified maximum that there is no leakage of steam, water or effluent at any point during the sterilization cycle that both water quality and steam quality comply with the sterilizer specification the chamber is capable of withstanding its specified maximum pressure. This test may be a legal requirement and should be performed by a suitably certified organisation. Performance Qualification The performance qualification (PQ) tests actually check that the autoclave is not only functioning correctly, but also that sterilization is taking place. Analysis of documented PQ results can also assist with pro-active maintenance schedules. A thermometric test to determine the temperature profile inside the chamber throughout the holding time, using a data logging system and multiple probes placed throughout the chamber volume. Simultaneous monitoring of the chamber pressure is also useful in checking the efficiency of the air removal/replacement system. Once qualification of the empty chamber has been accepted, load testing should be performed. Here, similar probes as used in monitoring the temperature profile, are placed inside typical loads and the heat transfer time is determined during the sterilization cycle. These tests should be repeated for each type of load and/or preprogrammed cycle that for which it is intended to use the autoclave. During the load testing, biological indicators may also be placed in the load to determine if sterilization is in fact taking place. If the autoclave is to be used to sterilize folded cloth, such as garments, a Bowie Dick test should be performed to ensure complete penetration of the steam into the cloth. Maintenance intervals The intervals between Performance Qualification tests should be determined based on documented experience and the need, type and previous performance of the autoclave. EA-4/10 “Accreditation in Microbiological Laboratories” suggests that the load characteristic for each cycle be determined every two years, while the chamber temperature and time must be monitored during each use. [2] Regular maintenance such as gasket inspection, and cleaning of the chamber should be performed at the manufacturers recommended intervals. A full service should be performed at least annually as should the safety check of the pressure vessel. Any repairs or modifications of the unit may require complete, or at least partial, recommissioning of the autoclave, including full Performance Qualification tests. performance qualification tests should be fully recorded, reviewed, accepted and archived by the relevant personnel in the organisation that uses the autoclave. These results may be recorded on suitable worksheets and certificates may be issued by third-party organisations that perform such tests. Routine Checking Conclusion Routine checking may be broken down into daily, weekly, quarterly and annual checks. The commissioning and performance qualification of an autoclave and subsequent validation of the sterilizing protocols is a costly and time consuming process, both in the actual procedures involved and also in the analysis and review of the resulting documentation. Daily checks should be performed by the operator and should include the observation of all indicators for “normal” values. On a weekly basis safety checks should be performed such as inspection for leaks and electrical wiring faults, inspection of door seals, correct of operation of door interlocks and high temperature and low water alarms. In the case of vacuum autoclaves, a vacuum leak test should also be performed. Quarterly checks may include verification of the calibration of the instrumentation, a check of the automatic control functions, a check of the vacuum leak sensor and a thermometric test on a small load. Annually, a full re-commissioning may be warranted. Thermometric testing should be performed. Load testing should be performed as well, but different loads may be scheduled into bi- or tri-annual cycles. [1] Ensuring that sterilization is occurring in the autoclave is however of prime importance (otherwise why bother to autoclave in the first place) thus such costs should be viewed in the light of human safety rather than that of economics. At the same time, however, to ensure that qualification and validation are performed correctly, the tests should only be carried out by suitably qualified and experienced personnel and organisations. References [1] A. Chandler, Introduction to Sterilization [2] European co-operation for Accreditation EA-04/10 Accreditation for Microbiological Laboratories, July 2002 rev02 European Committee for Standardization EN 554:1994 Sterilization of medical devices – Validation and routine control of sterilization by moist heat, June 1994 [3] Documentation The results of all commissioning tests and
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