Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Sample mechanical transport means in or for automated...
Reexamination Certificate
1999-11-19
2003-12-02
Warden, Jill (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Sample mechanical transport means in or for automated...
C422S051000, C436S001000
Reexamination Certificate
active
06656429
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to devices for testing the adequacy of air removal in a sterilization apparatus, and in particular, a prevacuum sterilization apparatus utilized for sterilizing medical equipment. Even more particularly, the present invention relates to a test pack having a steam reactive chemical indicator to determine the efficacy of air removal in a sterilization apparatus. The present invention is particularly useful, although not exclusively useful, for the testing of air removal in prevacuum sterilization equipment used for the steam sterilization of hospital medical equipment.
The sterilization of medical equipment by exposure to sterilization gas such as steam is typically accomplished by using an autoclave. Normally the equipment to be sterilized is placed into the autoclave and a vacuum may or may not be drawn depending on the particular procedure being followed. The sterilization medium, steam, is then introduced into the autoclave to permeate the equipment and sterilize it.
In the gravity displacement steam sterilizer, a sterilizer chamber, with objects to be sterilized within, is subjected to steam for a predetermined period of time. The steam inlet to the camber is typically located in the middle of the rear wall of the chamber. Because steam is lighter than air, it will accordingly rise towards the top of the chamber, displacing the air towards the bottom of the chamber and out the chamber drain. A temperature sensor and a thermostat are provided in the exhaust line to detect when the temperature rises sufficiently, indicating that steam is exiting the chamber, and that, accordingly, air has been completely displaced by the steam.
The above described sterilization apparatus is called a gravity displacement steam sterilizer because gravity and steam under pressure are relied on to cause the lighter steam to displace the heavier air towards the drain in the bottom of the chamber. Because the chamber is constantly under positive pressure, it is impossible for air to enter. The entry of steam under pressure and the operation of the thermostat in the drain ensure total air removal.
In another form of sterilizer, called a prevacuum sterilizer, shown schematically in
FIG. 10
, the vacuum pump
100
is usually first operated before steam is supplied into the sterilizing chamber
102
to evacuate the air in the chamber. Once air has been partially evacuated, after operation of the pump for a sufficient time, steam is introduced into the chamber via steam inlet
104
until a specified pressure is reached. A series of vacuum pulses followed by introductions of steam are used depending on the model of sterilizer. These steam/vacuum pulses are designed to remove virtually all the air from the chamber and the packs within. After the final vacuum, steam is introduced into the chamber until the correct sterilization temperature/pressure is attained. During the vacuum phase, air reentry is possible because the chamber is under a negative pressure. Air can be drawn into the chamber via leaks in the door gasket or other areas. In these instances, the residual air in the chamber and packs can act as a deterrent to steam penetration into the packs to be sterilized.
According to recommended procedures, steam sterilization equipment in hospitals and other health care facilities needs to be periodically tested to ensure the sterilization procedure is efficacious. In one test, resistant bacterial spores are subjected to the sterilization cycle and subsequently observations are made as to whether they have remained viable. To ensure the sterilization process is adequate, the spores are placed into a specified challenge pack. This pack is designed to challenge penetration by steam as much as or better than the challenge provided by standard hospital packs and packaging. The test is carried out in a normally loaded sterilizer under normal conditions. It is a true test of the sterilizer's ability to sterilize. This test is known as a biological test.
Several procedures have been proposed to test the sterilization efficacy of steam sterilization equipment. Typical of these and perhaps the best known and most widely accepted, is the procedure recommended by the Association for the Advancement of Medical Instrumentation (AAMI) as ANSI/AAMI ST46-1993 (“Good Hospital Practice: Steam Sterilization ad Sterility Assurance”). According to the AAMI recommended practice, 16 freshly laundered all cotton towels are folded by hospital personnel and stacked to construct a challenge test pack approximately 6 inches high. The biological indicator is embedded into the center of this challenge pack. This pack is then subjected to the sterilization cycle as part of a routine sterilization load.
Although apparently efficacious for its intended purpose, the construction of a biological challenge pack according to the AAMI procedure is labor intensive and the resulting pack is relatively bulky.
Applicant's prior U.S. Pat. No. 5,345,971 provides a biological challenge type test pack which obviates the problems inherent in the AAMI procedure by providing a disposable biological challenge pack which has the same performance characteristics as the referenced AAMI towel challenge pack. It is suitable for use as a sterilization test pack for hospital sterilizers.
A different type of test, which employs a different test pack is also recommended for the routine testing of hospital sterilizers. This test is limited to prevacuum sterilizers only. The aim in a prevacuum sterilizer is to remove virtually all air prior to the final introduction of steam for sterilization into the chamber. A test pack known as a Bowie-Dick test pack has been used in such prevacuum tests in the past. In particular, the test pack
112
of
FIG. 10
is used to determine the adequacy of the air removal from inside the test pack and replacement of the air by steam. Unlike the biological test, this is not a test of sterilization. It is solely a test of air removal. It is carried out under conditions where the test pack is the only pack in the sterilizer, whereas the biological challenge pack is used in a full load.
In these Bowie-Dick types of test packs, the pack includes a sheet of paper printed with a steam-reactive ink which will change color in the presence of steam under pressure, but will not change color in the presence of air heated to the same degree as steam. The pack is placed into a prevacuum sterilizer, and a cycle is run. The test sheet is removed from the pack and examined to determine if air was removed and replaced by steam. If the air removal has been adequate, the indicator ink will have uniformly changed color throughout the test sheet due to the even presence of steam in the pack and no residual air entrapped in the pack. If the air removal process was in some way defective, air would be trapped in the center of the pack, and its presence would prevent steam from evenly contacting the test sheet and steam reactive ink. In this case, the reactive ink throughout the test sheet would exhibit an uneven color development. Since it is the only pack in the sterilizer, the Bowie-Dick pack provides a sensitive detector of the presence of residual air. If air is not detected by this pack, it can be assumed that air will be adequately removed from packs and will not reenter them during a sterilization run in a fully loaded sterilizer.
In order to assist personnel in determining if color development was correct, and thus air removal was complete, a sample of a correctly exposed test sheet or simulation as well as sheets showing marginal as well as major air entrapment are usually provided for comparison purposes.
An example of a prior art Bowie-Dick test pack is shown in FIG.
9
. The figure shows a number of stacked towels about 10-11 inches in height, about twelve inches in length and about 9 inches in width with a Bowie-Dick test sheet or crossed tape disposed at approximately the center of the height dimension. The test sheet has deposited ink or a tape thereon which change
Cross LaToya
Ostrolenk Faber Gerb & Soffen, LLP
Propper Manufacturing Co. Inc.
Warden Jill
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