June 05

Steam Sterilization Monitoring
Propper Manufacturing-70 years of leadership

For more information on Propper Manufacturing or their products, call 800.832.4300 or visit www.proppermfg.com.

Hot steam under pressure is a proven method of effective sterilization. Steam sterilizers have been in use in hospitals since the 19th century after the invention of the steam autoclave by Charles Chamberland in 1879. Increasing resistance of microorganisms to antibiotics and decontaminating agents as well as the discovery of Prions – proteinaceous infectious agents resistant to traditional sterilization methods set the new rigorous requirements for efficacy of steam sterilization1. Needless to say, that the quality of sterilization is especially critical for medical facilities performing surgery and invasive diagnostic and treatment procedures.

Traditionally, all sterilizers are equipped with instruments for parametric monitoring of the process parameters. Some models have simple thermometers only; others have more sophisticated monitoring gauges that constantly measure temperature and pressure inside the sterilizer chamber during the cycle. However, these instruments cannot give the complete picture of the sterilization process and its efficacy, especially the conditions inside sterilization packs and hollow devices.

In 1963 J.H. Bowie and co-authors2 introduced the new concept for daily monitoring of the performance of pre-vacuum sterilizers. Autoclave tape applied to a sheet of paper in a St. Andrew’s cross design and placed in the center of a stack of 100% cotton towels demonstrated sensitivity to residual air. The test presented a new, user-friendly technology of the sterilizer’s fault detection using color change of reactive ink. However, the new tape test was not reliable enough and inconvenient in the hospital settings. The need for implementation of the Bowie & Dick test idea in a better way attracted scientists of Propper Manufacturing Company, a developer and supplier of medical products. The company started its history in 1935, and the Propper brand gained true worldwide recognition during World War II when the company developed and supplied the US Military with water purification products.

Once-A-Day® test pack
Foreseeing the future need in sterilization indicators, Propper invested substantial resources in the development of new monitoring technologies. As a result, in 1968 Propper introduced to the market their first Once-A-Day® Test Sheet - Bowie & Dick type test with pre-printed chemical indicator (Fig.1). Since that time, Propper developed an extended line of Once-A-Day products, each of which brought the new excellent features that set the Propper sterilization monitors apart from other indicators. The first pre-assembled Bowie and Dick type test on the market - Propper’s Once-A-Day Test Pack (9”x12”) - brought the new level of reliability and convenience of testing. The pre-assembled pack, equivalent to the standard AAMI linen test pack, eliminated uncertainties caused by variation of linen pack construction, wrong towels and incorrect placements of the test sheets (Fig.2). In addition, the pre-assembled pack substantially reduced the cost of testing.

In 1986, in an attempt to further reduce the cost of testing, Propper developed their mini-version (5”x5”) of Once-A-Day Test Pack, which later was transformed into the Once-A-Day test in a pre-printed box (Fig.3). Process indicator on each box, pre-printed fill-in form on the test sheet and pull-tab for easy removal of the test sheets added more security and convenience. High stability reactive ink allowed retention of test sheets as long as necessary.

In 1991 Propper patented Alert-O.A.D.® - a perfect addition to the Once-A-Day family of products (Fig.4). This “container” style Bowie and Dick type test with transparent plastic walls brought convenience of observation of the results without test pack disassembling. A reference color on the test strips facilitated identification of even minor variations of the dark color after processing.

For the European market Propper developed several Bowie & Dick type tests compliant with regulations EN867-1 and EN-867-4. The numerous patents for the sterilization monitoring products granted to Propper in the USA and overseas proved the company’s tradition in innovation.

New Developments

Once-A-Day® Slim Pack is a new version of disposable Bowie & Dick type test with several patented features. The test is designed for daily monitoring of pre-vacuum sterilizers at 270-274‰F. Reliable and “handy,” Slim Pack secures early detection of residual air or presence of non-condensing gases in steam. Proprietary Propper ink formula guarantees clear interpretation of test sheet color change. Rigorously researched porosity and penetrability of materials to steam assures consistent and reliable results. Compared to the previous version of the Once-A-Day test pack, Slim Pack requires 35% less space for storage.

Vapor Line® PCD is a reusable process challenge device for monitoring prevacuum sterilization process at 270-274‰F. It consists of a metal capsule with a removable cap equipped with a holder for Propper Vapor Line Integrator. Vapor Line PCD presents a significant challenge to steam penetration in standard cycles. The result of testing is available immediately after cooling the Vapor Line PCD. The integrator display will indicate whether sterilizing conditions were attained inside the capsule during the cycle. There is no question about the validity of the result because the performance equivalence of the Vapor Line integrator with respect to biological indicators has been well documented3. Regular use of Vapor Line PCD helps to ensure adequate penetration of steam in wrapped or unwrapped solid, porous and hollow instrument loads as well as sufficient time and temperature of the exposure.

PASS-FAIL™ is a disposable challenge pack for both gravity-displacement and prevacuum cycles at 250‰F and 272‰F. The pack is equivalent in performance to a biological indicator in the AAMI approved linen pack with extra level of sterility assurance. Integrating all critical sterilization parameters, the PASS/FAIL test pack provides the easy-to-read results immediately. Stable dark color of the integrator’s bar allows keeping documentation of correct sterilization exposure as long as necessary. Consistent performance of pre-assembled pack and precise calibration of the enclosed integrator guarantee reliable monitoring of sterilization process in large and small table-top sterilizers.

WATS™. In 2005, Propper expanded their program for doctor's offices and dental practices introducing WATS™ - weekly autoclave monitoring system. This is a complete monthly set of indicators and materials needed to test steam sterilizers in professional offices once a week as recommended by CDC, ADA, and AAMI. Unlike traditional biological monitoring, WATS™ allows for more rapid results with an extra level of sterility assurance and covers standard gravity displacement cycles in the range of 250-273‰F. Using WATS™ reduces expenses due to lowering costs of mailing and processing exposed Biological Indicators.

References:
1. ANSI/AAMI ST46:2002. Steam Sterilization and sterility assurance in healthcare facilities. AAMI, Arlington, VA. 2002.
2. Bowie, J.H., Kelsey, J.C., and Thompson, G.R.: The Bowie and Dick Autoclave Tape Test. The Lancet, 586-587, March 16, 1963.
3. Propper Professional Information Report 95-1. Performance of Propper’s Vapor Line Integrators versus Biological Indicators. Dyckman J., April 1995.

For more information on Propper Manufacturing or their products, call 800.832.4300 or visit www.proppermfg.com.