An MD&DI February 1997 Feature
STERILIZATION
Speeding EtO-Sterilized Products to Market with Parametric Release (continued)
Conclusion
There are still many challenges to face in EtO sterilization. For example, it is difficult to determine the amount of sterilant to use, and so companies must estimate based on worst-case predictions. Because of variations in load configuration, as well as condensation of water vapor in low-temperature areas within the vessel, it is impossible to decide in advance exactly how much sterilant and water vapor will be needed in a given cycle. Therefore, EtO cycles typically employ more sterilant and water vapor than is actually necessary. In this way, fluctuations in the load's capacity to absorb gas are compensated for and the SAL is consistent with validated levels.
However, the use of excessive quantities of sterilant and water vapor will also yield higher than necessary residual levels of EtO and by-products, such as ethylene glycol and ethylene chlorohydrin (ECH). Patients and health-care workers are later exposed to these residuals, which can cause health problems. Also, water vapor condensing on the product and packaging traps EtO, which, during storage of the product, can once again become airborne, representing a danger to facility workers.
But many of the difficulties of EtO sterilization are already solvable using existing technology. Installation of a direct gas analysis system on an EtO sterilizer allows the user to map the kinetics of water vapor and EtO throughout the entire cycle, constantly access the leak rate of the chamber, quantify the gas- absorption characteristics of each load to reveal the relationship that exists between individual product types and the process, and achieve parametric release. The time-consuming step of BI incubation can be avoided. Releasing products parametrically will help most EtO sterilizers accelerate market response times.
The benefits of parametric release are sometimes limited by extended product aeration times to remove residuals. But once parametric release becomes common practice, reducing this necessary aeration phase will surely be the focus of industry attention and resources.
MW radiation has already been applied to accelerate desorption of EtO from medical supplies.16,17,19 With respect to traditional desorption in a heated aeration area, a 400% increase in desorption efficiency for polyvinyl chloride when using MW radiation to energize the EtO molecules has been documented. The effect of injecting steam during postevacuation phases to reduce residuals of both EtO and ECH has also been studied. These two methods are commonly referred to as MW and steam distillation.20
Today, EtO holds approximately 52% of the medical device sterilization market.21 EtO compatibility with nearly every device or component material, recent progress in the field of parametric release, and future developments in more efficient product conditioning and aeration techniques will soon make EtO sterilization even more widespread.
