An MD&DI February 1997 Feature
The difficulty of measuring EtO and water vapor during processing has been a major obstacle to adoption of parametric release by EtO sterilizers, but the latest gas analysis techniques are making in-process monitoring and control possible.
According to industry experts, ethylene oxide (EtO) is used for more than half of all medical devices sterilized. Despite its popularity, EtO sterilization, as it is performed by most companies today, has one major disadvantage when compared with steam or radiation methods. Unlike these methods, EtO typically involves more than just in-process monitoring to determine that products are adequately sterilized.
Most EtO sterilizers still rely on incubating biological indicators (BIs) to confirm sterility after processing, but retrieving the BI samples and waiting for them to incubate can add several days to product distribution. This final testing also requires additional handling of the sterilized products and introduces the potential for human error.
In theory, by simply making sure that the critical parameters of the process are correct, a technique called parametric release, EtO sterilization providers can be sure that their procedures are successful without using BIs. If the time, temperature, mass of water vapor per unit volume, and concentration of sterilant gas are within the process specifications, then it should be unnecessary to test the products or BIs after the procedure.
There are three basic steps necessary for implementing parametric release:
- Conducting a complete performance qualification through physical and microbiological studies.1
- Extracting from the resulting data a set of physical process parameters including load configuration, which, when maintained, will consistently yield the desired sterility assurance level (SAL).
- Maintaining, monitoring, and recording these critical parameters through direct analysis during routine processing.
Physical and administrative controls must be sufficient to ensure that the load configuration will never deviate from validated parameters, that all procedures will be followed, and that the sterilization equipment will consistently perform within the specifications listed in its original commissioning. If the controls meet these qualifications, then real-time direct monitoring of all process parameters can replace the use of BIs for routine product release.
Even though FDA accepts parametric release and the technique obviously saves time and money, only a few EtO sterilizers have yet ventured to use it. One reason for this is a lack of regulatory guidance on parametric release implementation.
Before 1994, the principal EtO sterilization guidance document was the American National Standards Institute's Guideline for Industrial EtO Sterilization of Medical Devices (ANSI/AAMI ST-27). Although this document said that parametric release was an acceptable practice, it provided no guidance on two of the most important issues facing those who would adopt it. These issues are, how does one validate and control a parametric release process, and what are the gas analysis technologies available to monitor in-chamber process gases?
With no official answers to these two crucial questions, only a very few companies have attempted parametric release. Those that have done so have typically submitted the validation protocols with their products' 510(k)s to get FDA to approve this revolutionary release method. These firms have been able to afford the time and expense, but pursuing regulatory acceptance in this way has generally remained out of reach for smaller manufacturers and contract sterilizers.
Recently, however, regulatory agencies have begun to take steps to provide more guidance. Since 1994, both the United States and Europe have adopted International Organization for Standardization (ISO)-compliant EtO sterilization standards that contain details on validating parametric release.2,3 In addition, in 1995 the Association for the Advancement of Medical Instrumentation (AAMI) formed an EtO task group to write a technical information report that will include a section on parametric release.4
Another reason that many have hesitated to use parametric release is that the technique requires sophisticated gas analysis equipment to monitor cycle parameters. Currently, however, microprocessors can ensure that each EtO phase is accurately timed, beginning only when certain variables come within required specifications. And although EtO vessels, whether operating at positive or negative pressure, require a seal as close to perfect as possible, direct temperature monitoring of both product and headspace can be easily achieved using temperature sensor leads that are passed directly through penetration points in the walls of the vessel.
Efficient and accurate monitoring of the headspace gases--water vapor and EtO--is more difficult and has been a major obstacle to widespread adoption of parametric release. However, technological innovations in this area are making even this aspect of process control practical.
- Headspace Gases
- Load Configuration
- Sampling the Gases
- Gas Analysis: Chromatography
- Gas Analysis: IR Spectroscopy
- IR Spectroscopy for Gas Diffusion
- Gas Analysis: MW Spectroscopy
Copyright © 1997 Medical Device & Diagnostic Industry