A sterilization company has cut manufacture-to-market time for medical products from two weeks to two days by taking extra care in monitoring operations. For example, just making sure every sterilization cycle is the same lets the company meet stringent FDA requirements without the usual week-long germ-kill verification tests.

Instead, the company runs the product through several test cycles and includes a glassine envelope filled with a species of bacilli spores highly resistant to ethylene glycol (EtO), the sterilization gas. Then the spores are incubated for a week. If the spores' kill rate meets FDA requirements, the sterilization cycle is validated. This means the company can release the product as long as sterilization replicates the time, temperature, humidity, pressure, and /EtO levels recorded during testing. Eliminating quarantine periods shortens delivery time by a full week or more.

Until recently, maintaining EtO levels inside sterilization chambers was a major challenge. Time, temperature, humidity, and pressure could be closely controlled, but EtO levels could not.

In fact, EtO levels vary wildly during sterilization. One contributing factor is the product itself. Cloth, for example, absorbs EtO more readily than plastic or paper. Another factor is that during the initial rush of EtO into the chamber, the product soaks it up, dropping EtO levels. Product packaging is another factor. Plastic wrap, for example, keeps out EtO. So adding steam forms a molecular conduit that lets EtO penetrate the wrap and get to the product. And too much moisture can condense on the product, plastic wrap, and chamber walls.

A crude way to measure EtO levels or density is to check for pressure changes. As the EtO/H₂O mixture goes into the chamber, pressure rises, giving a coarse indication of EtO levels.

But such estimates are rough at best because pressure variations can also be caused by product absorption, leaking chamber seals, worn gaskets, and evaporation of water. This method also doesn't indicate where the EtO is in the chamber. With an EtO resistant product, much of the sterilizing gas might be in the dead space while other components end up in the product, despite consistent pressures.

Unfortunately, conventional EtO sensors can cost $40,000 to $70,000, plus they're cumbersome, inaccurate, and require a sample be drawn from the chamber. The tubing and fittings needed to draw samples increases the likelihood of leaks, which can lead to explosions.

To compensate for inaccuracies, operators boosted EtO levels and sterilization times, thus boosting costs as well. Even so, all the sterilization variables could not be replicated, meaning every batch had to include a spore packet and endure week-long incubation periods before the batch could be certified.

One solution for these problems is the Signature DIR, a dual-gas analyzer developed by Minneapolis-based Sensor Electronics. The device simultaneously measures and monitors EtO and H₂O over the entire sterilization cycle, including the initial EtO inrush. The analyzer, which measures 4.5 × 4 × 3 in. and weighs a little over 3.5 lbs., can meet FDA requirements, thus eliminating the week-long manufacture-to-market delay.

The analyzer has twin IR sensors continually measuring EtO and H₂O levels through the entire sterilization cycle, ignoring fluctuations in chamber temperature, pressure, humidity, air movement, and product absorption rate.

Those IR sensors focus on any changes in the molecular “signatures” of EtO and H₂O, comparing the two twice every second against standard reference signals for each gas. The machine gives constant and continuous readouts of real-time values of both gases inside the chamber, regardless of variations in the other operating parameters. This analyzer effectively maintains EtO levels to meet rigorous FDA verification requirements.

The analyzer operates despite harsh working conditions, including elevated temperatures, dust, corrosion, oil mist, pressures/vacuums, and toxic and explosive atmospheres. It plugs directly into the chamber recirculation airways, giving direct EtO/H₂O measurements. And its accuracy is maintained for hundreds of cycles without recalibration or fine-tuning. The analyzer even monitors itself: If anything goes wrong, it flashes an alarm, then pinpoints the problem.