Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using disinfecting or sterilizing substance
Reexamination Certificate
1998-12-30
2001-12-04
McKane, Elizabeth (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using disinfecting or sterilizing substance
C422S023000, C422S027000, C422S028000
Reexamination Certificate
active
06325972
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for sterilization of medical instruments using a liquid sterilant. More particularly, the invention relates to a process in which sterilization is achieved by concentrating a liquid sterilant such as hydrogen peroxide solution inside of a sterilization chamber and sterilizing articles therewith.
BACKGROUND OF THE INVENTION
Medical instruments have traditionally been sterilized using either heat, such as is provided by steam, or a chemical, such as formaldehyde or ethylene oxide in the gas or vapor state. Each of these methods has its drawbacks. Many medical devices such as fiberoptic devices, endoscopes, power tools, etc., are sensitive to heat, moisture or both. Formaldehyde and ethylene oxide are both toxic gases that pose a potential hazard to healthcare workers. Problems with ethylene oxide are particularly severe, because its use requires long aeration times to remove the gas from articles that have been sterilized. This lengthens the sterilization cycle time undesirably.
Sterilization using liquid hydrogen peroxide solution has been found to require high concentrations of sterilant, extended exposure time and/or elevated temperatures. However, sterilization using hydrogen peroxide vapor has been shown to have some advantages over other chemical sterilization processes (see, e.g., U.S. Pat. Nos. 4,169,123 and 4,169,124 which are incorporated herein by reference). The combination of hydrogen peroxide with a plasma provides certain additional advantages, as disclosed in U.S. Pat. No. 4,643,876 which is incorporated herein by reference. Commercially available sterilization devices, such as the STERRAD® sterilization systems sold by Advanced Sterilization Systems division of Ethicon, Inc. automate the process of injecting a solution of hydrogen peroxide into a sterilization chamber, vaporizing the solution to provide a hydrogen peroxide vapor, contacting articles to be sterilized with the vapor, and exciting the vapor into the plasma stage. The hydrogen peroxide for each sterilization cycle is shipped to the location of the sterilization system, generally by air or ground transportation. Preferably, as in the case with the STERRAD® brand systems, premeasured amounts of a hydrogen peroxide and water solution are provided in sealed enclosure, such as a capsule inside of a cassette housing which can be automatically opened by the system to reduce contact between the system user and the hydrogen peroxide solution. Such cassettes are described more fully in U.S. Pat. Nos. 4,817,800 and 4,899,519 incorporated herein by reference.
The sterilization of articles containing diffusion-restricted areas, such as long narrow lumens, presents a special challenge. Methods that use hydrogen peroxide vapor that has been generated from an aqueous solution of hydrogen peroxide have certain disadvantages. One disadvantage is that because water has a higher vapor pressure than hydrogen peroxide, it will vaporize faster. Another disadvantage is that because of its lower molecular weight, water will diffuse faster than hydrogen peroxide in the vapor state. Because of these physical properties, when an aqueous solution of hydrogen peroxide is vaporized in the area surrounding the items to be sterilized, the water reaches the items first and in higher concentration. The water vapor inhibits penetration of hydrogen peroxide vapor into diffusion-restricted areas, such as small crevices and long narrow lumens. Simply employing a more concentrated solution of hydrogen peroxide fails to adequately address the problem due to the difficulty in handling highly concentrated hydrogen peroxide solutions. Transportation of such solutions can be particularly difficult. In general, such solutions are limited to concentrations of less than 60% hydrogen peroxide, however, regulations and the like regarding such concentrations may of course be modified in the future. In any event, shipping and handling of highly concentrated solutions remains impractical.
U.S. Pat. No. 4,952,370 discloses a sterilization process in which aqueous hydrogen peroxide vapor is first condensed on the article to be sterilized, followed by application of a vacuum to the sterilization chamber to remove the water and hydrogen peroxide from the article. This method is suitable for surface sterilization, but not for sterilization of diffusion-restricted areas such as long narrow lumens because it depends on the diffusion of hydrogen peroxide vapor into the lumen to effect sterilization.
U.S. Pat. No. 4,943,414 discloses a process in which a vessel containing a small amount of a vaporizable liquid sterilant solution is attached to a lumen, and the sterilant vaporizes and flows directly into the lumen of the article as the pressure is reduced during the sterilization cycle. This system has the advantage that the water and hydrogen peroxide vapor are pulled through the lumen by the existing pressure differential, increasing the sterilization rate for lumens, but has the disadvantage that the vessel needs to be attached to each lumen to be sterilized. In addition, water is vaporized faster and precedes the hydrogen peroxide vapor into the lumen.
In U.S. Pat. No. 5,492,672, there is disclosed a process for sterilizing narrow lumens. This process uses a multicomponent sterilant vapor and requires successive alternating periods of flow of sterilant vapor and discontinuance of such flow. A complex apparatus is used to accomplish the method. Because flow through of vapor is used, closed end lumens are not readily sterilized in the process.
U.S. Pat. No. 4,744,951 to Cummings attempts to address this problem by providing a separate prechamber connected to the sterilization chamber. Hydrogen peroxide is first admitted to the prechamber where it is concentrated in a distillation procedure employing the differing vapor pressures of hydrogen peroxide and water. Water's higher vapor pressure allows one to select a vaporization pressure which selectively vaporizes water from a hydrogen peroxide solution, thus concentrating the solution. Cummings pumps air out of the prechamber and lowers its pressure to a level at which the water preferentially vaporizes from the hydrogen peroxide solution. The pump which is evacuating the prechamber draws out the water vapor thus released from solution to concentrate the remaining solution. To prevent the water vapor from traveling into the narrow spaces such as endoscope lumens, Cummings carries out the concentration process in the prechamber. This adds complexity be requiring additional chambers, pumps and valves.
Those of skill in the art, both in Cummings day, and now, would not think to employ such a concentration process in the same chamber as the sterilization occurs due to the problem of water vapor rushing to occlude the narrow lumens. In fact, the theory predicts that such a process would sterilize lumens less well than by simply vaporizing all of the hydrogen peroxide solution at once, because the slow vaporization would more efficiently block the lumen with water vapor. However, the present inventors have suprisingly found that concentrating the hydrogen peroxide vapor within the sterilization chamber greatly increases the ability to sterilize long narrow lumens over the convential process of essentially vaporizing all of the hydrogen peroxide at once.
SUMMARY OF THE INVENTION
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patent: 4643876 (1987-02-01), Jacobs et al.
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patent: 5851485 (1998-12-01), Lin et al.
patent: 5980825 (1999-11-01), Addy et al.
patent: 6030579 (2000-02-01), Addy et al.
patent: 916937 (1999-05-01), None
PCT International Search Report International Applicatio
Jacobs Paul
Lin Suz-Min
Wang Jenn-Hann
Ethicon Inc.
Farmer Andrew C.
McKane Elizabeth
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