Critical sterilizing cycles

Industrial sterilization cycles tend to vary considerably, not only from manufacturer to manufacturer, but often from product type to product type, depending on the bioburden present on a given load. Chemical indicators have historically been used only to differentiate between sterilized and nonsterilized packages. More recent developments have resulted in the availability of chemical dosimeters of sufficient accuracy to permit their appHcation either as total monitors or as critical detectors of specific parameters. 

Electronic records include data-storing memory cards used in embedded control systems such as steam sterilizers. These cards are used to transfer data (critical parameters, cycle times, etc.) from the control system to a main database application which is usually networked. A memory card is about the size of a credit card. Manual installation, removal, and transfer of the memory cards must be conducted in accordance with defined procedures. Reuse of cards must be carefully considered data must not be deleted until confirmation is received that it has been successfully downloaded to the database. The local operating enviromnent and the possibility of EMl/ESD damage to data integrity of the memory card must also be evaluated. 

The WFI distribution system (storage tanks, circulation pumps, pipework) is steam sterilized. The sterilization cycle is controlled and monitored by temperature indicators located at critical points. 

Critical processes other than the actual product manufacturing process — such as sterilization, component washing, and equipment cleaning — require prevalidation cycle development work. This may include establishment of appropriate sterilization cycle types, cleaning agents, etc. This test work is performed during or after Operational Qualification. 

It is critical to ensure that the length of time between the removal of a load from the preconditioning chamber and the beginning of its sterilization cycle is rigorously controlled It is all too easy, particularly in dry climates with very low humidities, for equilibrium to be rapidly lost. 

Five variables are critical to the EtO process. They are EtO concentration, relative humidity, temperature, time, and pressure/vacuum. Temperature is the easiest variable to measure and monitor, therefore temperature is used as the indicator of the worst-case location within the loaded EtO sterilizer. Once the worst-case location is identified the validation studies are conducted with the goal of inactivating a known concentration of indicator micro-organisms in the worst-case location using a specific loading pattern with a specific EtO cycle with all variables defined and controlled. 

The critical parameters of ethylene oxide sterilization are temperature, time, gas concentration, and relative humidity. The critical role of humidity has been demonstrated by a number of studies (11,18,19). Temperature, time, and gas concentration requirements are dependent not only on the bioburden, but also on the type of hardware and gas mixture used. If cycle development is not possible, as in the case of hospital sterilization the manufacturer s recommendations should be followed. 

Experimental support for the multiple wavelet hypothesis developed out of work done by Allessie et al. in 1985. They were able to map the spread of excitation in the atria of a dog heart during rapid pacing-induced AF in the presence of acetylcholine, and provided the first demonstration in vivo of multiple propagating wavelets giving rise to turbulent atrial activity (44). They estimated that maintenance of AF would require a critical number of four to six wavelets. In a canine sterile pericarditis model of paroxysmal AF, unstable reentrant circuits of very short cycle length have been shown to be critical for maintenance of AF (45). In addition, pharmacological experiments have further shown that termination of AF by class IC antiarrhythmic drugs is preceded by a decrease in the mean number of wavelets (46,47). 

Recipes verification that each automated cycle was programmed within its Kmits in the form of a recipe (lyophilization, sterilization, etc.) and complies with the specification. This test is an additional system-specific test for critical parameters (see 7 above). 

In practice, such ozone celts are extensively automated to control the process cycle (Fig. 5< 14(b)) and may incorporate ultraviolet facilities. Current applications include those sectors of the pharmaceutical and fineultra-pure water for critical synthetic steps or to meet stringent purity limits. In such applications, the electrolytic route to ultra-pure water, via ozone generationf is competing against the more traditional methods of sterile filtration (e.g. ultra-filtration), ultraviolet irradiation and the use of conventional air-phase corona-discharge ozonizers. 

Electron beam irradiation can be used to precisely tailor properties of silicone rubber and it is a valuable tool to define the response of these materials in medical applications where irradiation sterilization is used. E-beam is an effective technology for crosslinking to predict property changes to materials used in critical applications. E-BEAM Services has performed other studies to predict life cycle estimates. Two examples are wire and cable materials used in nuclear facilities and polymeric materials designed for use in space applications. 

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