Medical Device & Diagnostic Industry Magazine
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Originally Published February 2001

It's toxic, explosive, and generally quite nasty—yet ethylene oxide (EtO) remains a remarkably effective method for eliminating microorganisms from medical products. Until an equally effective sterilant is proven, however, the challenges and hazards of working with EtO will remain.

This month, potential advantages of an advanced sensing technology are discussed in "Continuous Monitoring of EtO Concentrations During Sterilization," which begins on page 80. According to Patrick G. Smith, vice president of engineering and director of research and development at Sensor Electronics Corp. (Minneapolis), "Sterilization procedures for medical products are tightly controlled, well researched, and closely documented under the watchful eye of the FDA. Every tool available is used and every measurable parameter is monitored to make sure products come out of the chamber absolutely sterile—except one." He explains that because no reliable, affordable EtO monitor has been available, determining in-chamber EtO concentrations has required calculations to be based on other chamber parameters and assumptions.

"The availability of an affordable continuous EtO monitor has many implications," Smith explains. Absorption profiles, which "watch" chamber concentrations, show load absorptive properties and absorption rate. "This could be very useful for load validation by showing when the EtO has reached the product," he states. Verification by actual measurement that all EtO has been evacuated from the chamber adds an additional safeguard to protect the operator when opening the door after a cycle.

Smith adds that parametric release is a way to verify product sterilization by monitoring sterilization cycle parameters. "This allows product shipment after sterilization, eliminating the time and expense required for biological indicator development. Continuous EtO monitoring could be part of the equation for parametric release."

In addition to sterilization processes involved in medical device manufacturing, hospitals are major users of EtO sterilization. Smith says, "Hospitals regularly sterilize reusable medical equipment, such as surgical instruments." He adds that being able to continuously monitor EtO concentrations offers hospitals comparable advantages in verification and for protecting the health of personnel.

Says Smith, "Why should sterilization verification be any less rigorous for the surgeon's scalpel than for the device she/he is about to implant? This is an opportunity for everyone doing EtO sterilization to step up to continuous EtO monitoring without spending a fortune or rebuilding their chambers."

"The new EtO sensor is based on technology that was originally developed for gas monitoring in very difficult and demanding environments such as offshore platforms, coal mines, and chemical plants," Smith notes. The EtO monitor was developed using a similar approach and comparable algorithms. "The sterilizer application turned out to be one of the most difficult we have seen, but the technology is up to it. Our core sensing technology is patent pending."

Development and testing of the new sensing approach required two years' work, and the specific development of the EtO monitor took an additional year.

Smith adds that one of the most difficult problems was combating dew points. He explains sterilizers "create their own 'weather'—rain, fog, dew—which adversely affects an optical sensor." The answer to such problems was use of a two-stage filtering system and heat to ensure accuracy throughout sterilization. The sensor's principal achievement, Smith suggests, has been the ability to continuously measure EtO levels—regardless of the weather.

Gregg Nighswonger is executive editor of MD&DI.

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