Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
  • A61L2/26—Accessories or devices or components used for biocidal treatment
  • A61L2/28—Devices for testing the effectiveness or completeness of sterilisation, e.g. indicators which change colour

Definitions

• the invention relates to sterilizers and, in particular, to a method and apparatus for improving the assurance of effective operation of sterilizers, especially those of the prevacuum type.
• a uniform color change (supported by a record showing a satis- factory time-temperature relationship in the chamber drain) indicated a satisfactory result and could be interpreted as showing rapid steam penetration, adequate air removal, and freedom from significant air leaks.
• Bowie and Dick type tests are typically run once a day and, if run and interpreted correctly, can determine only the condition of air leakage and can determine it only at that time.
• the sterilizer operations which are actually responsible for assuring the safety of patients are conduct ⁇ ed under load conditions and cannot be monitored with accu ⁇ racy with current technology.
• Joslyn disclosed a method and apparatus for detecting entrapped air in a steam steril- izer.
• the device is shown outside the steam chamber to enable quantitative measurement of the amount of air or other noncondensible gas at the chamber drain.
• the device is intended for use with a sterilizer of the type that employs steam to displace air.
• the device does not, howev ⁇ er, eliminate the need for a Bowie and Dick test.
• Chamberlain and Cook monitor the temperature of the exhausted steam at the drain and the pressure within the chamber, and compare these to the steam table values to determine if all the air has been evacuated.
• the positioning of sensors within the chamber, especially by retrofitting, can, however, create further problem areas for future concern.
• Joslyn describes a small device for indicating air inside a sterilization chamber of the type used with steam or ethylene oxide.
• the device includes an upright tube holding an indicator strip and a heat sink. Air is said to pass into the tube where it interferes with the steam contacting the indicator strip.
• the present invention provides methods and apparatus for determin- ing the effectiveness of air removal from a steam sterilizer and for monitoring the sterilization conditions therein.
• the apparatus provides a test device, a controller and a system which utilizes one or both.
• the methods achieve the objects of the invention in its broad as well as specific aspects.
• the test device compris ⁇ es: a wall member defining an elongated test cavity having an opening at one end to permit entrance of ambient gases; a temperature sensor capable of generating a signal (T r ) indicative, of the temperature at its location at an end of the test cavity opposite from said opening; and a heat sink located in said test cavity between said opening and said temperature sensor.
• the test device will comprise: means for sensing the tempera ⁇ ture at a location within a sterilization chamber and generating a signal (T ) indicative thereof; and radio transmission means for transmitting signal T ⁇ to a location outside of the sterilization chamber.
• storage means are provided for storing signal ⁇ within said chamber.
• the controller in one of its preferred forms comprises: means for receiving a signal (T r ) indicative of the tempera ⁇ ture at a predetermined location within the chamber of a steam sterilizer; means for generating a signal (T r ) indica ⁇ tive of a reference temperature, which can be either a preselected reference temperature such as the desired ster- ilization temperature or a calculated temperature such as the average of selected temperatures reported in the latest of a predetermined number of cycles of operation in either two modes (namely, (1) Bowie and Dick test or (2) operation under load) ; means for comparing signal T j _ to signal T_; and means for generating a signal indicative of either a pass or fail condition based on the results of the comparison.
• the means for receiving the signal ⁇ can comprise a radio receiver or connector means to electrically couple the controller to the test device.
• the system in one of its embodiments comprises: a test device capable of sensing the temperature at its location and generating a signal (T x ) indicative thereof; means for generating a signal (T_) indicative of a reference tempera ⁇ ture, as above; means for comparing signal T L to signal T r ; and means for generating a signal indicative of either a pass or fail condition based on the results of the compari ⁇ son.
• the method of the invention in one of its forms com- prises: placing a test device capable of sensing a tem ⁇ perature within the chamber of a sterilizer and generating a signal (T ⁇ ) indicative of the sensed temperature; generating a signal T ⁇ ; generating a signal T_ indicative of a refer ⁇ ence temperature; comparing signal T 1 to signal T_; and generating a signal indicative of either a pass or fail condition based on the results of the comparison.
• Figure 1 is a perspective view of a preferred system of the invention including a test unit inside the chamber of a steam sterilizer, positioned for recording test data and transmitting by radio to an external controller unit;
• Figure 2 is a perspective view of a preferred form of test unit of the invention.
• Figure 3 is a perspective view of a preferred form of controller unit of the invention.
• Figure 4 is a side elevation view of the controller unit shown in Figure 3, partially cut away to illustrate major components
• Figure 5 is a side elevation view of the test unit shown in Figure 2, partially cut away to illustrate major compo ⁇ nents;
• Figure 6 is a cross-sectional view taken along line 6-6 in Figure 5; .
• Figure 7 is a block diagram of the circuitry for a test unit such as shown in Figure 2;
• Figure 8 is a block diagram of the circuitry for a controller unit such as shown in Figure 3;
• Figure 8A is a block diagram illustrating a simplified circuitry for a controller unit
• Figure 9 is a flow-chart depicting the operation of a preferred test unit according to the invention.
• Figure 10 is a flow chart depicting the operation of a preferred controller unit according to the invention.
• Figure 1 illustrates a preferred system of the invention which includes a test unit 100 inside the chamber 202 of a sterilizer 200.
• the test unit is shown positioned near drain 204, for obtaining data and transmitting via radio frequency to controller 300 which is shown outside of the chamber 202.
• the system can operate by obtaining tempera ⁇ ture data alone or in combination with pressure and/or dispersed liquid moisture data.
• the data can be transmitted from the chamber by radio to provide real time monitoring, or it can be stored within the test unit 100 for later later transmission to controller 300 such as through electrical connection, infra red data transmission, or other suitable means.
• a permanent archiveable record 302 can be generated by display means such as a thermal printer or a chart recorder. This enables accurate records to be kept, whether the system is operated in a mode to perform a Bowie and Dick type test (Bowie and Dick mode) or in a mode to monitor the operation of the sterilizer under load conditions (load mode).
• FIG. 2 shows a preferred form of test device of the invention in greater detail, as do the partially cut away view of Figure 5 and the sectional view of Figure 6.
• the test unit 100 is seen to be comprised of two principal components, illustrated as a replaceable test module 110 and a data collection and transmission unit 120.
• data is transmitted via radio circuitry from transmission unit 120 via antenna 108 as will be described in greater detail below.
• means are also provid ⁇ ed to store the data within the unit 100 for later process ⁇ ing. It is also possible to provide a test unit such as 100 which is not equipped with radio transmission means.
• Figure 7 corresponds to Figure 5 by showing the major components in block diagram form.
• Temperature sensor 122 is preferably a solid state tempera ⁇ ture transducer, such as an Analog Devices (Maynard, MA) model AD 590 with a resolution of 0.5°F and a measurement range of 257 ⁇ -286°F.
• the pressure sensor 124 is preferably a pressure transducer as shown in Figures 5 and 6.
• the temperature sensor 122 and port 123 to the pressure sensor 124 are shown as component parts of replaceable test module 110.
• the moisture sensor 126 is desirably embedded within heat sink material 112 in the test module 110.
• the tempera ⁇ ture sensor 128 will be embedded within or closely associat- ed with the temperature-sensitive electronic components, such as multiplexer 130 within the transmission unit 120.
• the temperature sensor 128, can be similar to sensor 122 and is capable of generating a signal indicative of the tem ⁇ perature within the transmission unit 120 to warn of over- heating.
• the temperature sensor 122 senses the temperature within test cavity 115 located at a position in the steril ⁇ izer, usually near the drain 204, where it would be most sensitive to the presence of air. All of the test devices of the present invention have the capability of obtaining temperature data by sensing the temperature within a chamber 202 and generating a signal indicative of that temperature.
• the pressure sensor 124 is optional, but preferred, and provides the ability to sense the pressure at the location of the sensed temperature and to generate a signal which corresponds to it.
• the pressure sensor 124 is preferably located within the transmission unit 120, but is open to the test module 110 through port 123 which can simply be a tube which fits into the transducer.
• the moisture sensor 126 is also preferred, but option ⁇ al, and adds the ability to sense the presence of liquid water dispersed in the steam. Most modern sterilizers include moisture traps near the steam inlet, e.g.
• the replaceable test module 110 is designed to concen ⁇ trate air to the specific location of the temperature sensor 122. It is shown to simply comprise a wall member 114 which defines an elongated test cavity 115 having an opening 116 to one end to permit entrance of ambient gases, a tempera ⁇ ture sensor 122 as described, and a heat sink 112 in the cavity between the temperature sensor 122 and the opening 116.
• the heat sink can be of any suitable material which is capable of condensing steam and retaining the condensed steam therein.
• the heat sink material should be of a densi ⁇ ty, porosity and thermal conductivity to condense a suffi ⁇ cient amount of steam to cause air, if present, to collect at the end of the test chamber where the temperature sensor 122 is located. It is preferably absorbent enough to hold condensed water and, yet, dry rapidly. Gauzes or felts of cotton with or without metalic fibers should be effective as will standard central supply wrap or open-celled polymer foam.
• test unit Under conditions of use the test unit is placed within sterilizer 200 and is subjected to a vacuum before steam is applied. Steam, when introduced, will enter opening 116 and will progress into cavity 115 wherein it will begin to condense in heat sink 112. If any air is present in the steam due to a defective chamber seal, such as rubber seal 208 (or defective vacuum pump or piping) , the air will remain uncondensed as the steam around it condenses. As this process continues, air, to the extent present, will concentrate at the rear of test cavity 115 and insulate the temperature sensor 122 from the heat of the steam.
• a defective chamber seal such as rubber seal 208 (or defective vacuum pump or piping)
• the replaceable test module 110 is desirably in car ⁇ tridge form which can simply be snapped into and out of position (see Figure 5) . It is recommended that these modules be replaced periodically, e. g. weekly or monthly, and whenever subjected to excessively wet steam. Good hospital practice would dictate eliminating the variability which, could arise by using a wet test module or one which has been used for a period of time which would permit corro- sion of the sensors or degradation of the heat sink material 112 by steam.
• the cartridges When employed in the load mode to monitor the conditions during sterilization, the cartridges may be changed after each cycle to assure that a dry cartridge at room temperature is present at the start of each run. These cartriges may be reused several times. In one embodiment, it is desireable to provide means for preventingoperation of the unit in the load mode unless the cartridge has been replaced.
• the transmission unit 120 is shown to -have a casing 129 with an internal layer of insulation 127 (shown here as foamed plastic) and an exter ⁇ nal handle 125 for ease of handling. Potting in a high— mass, low-thermal-conductivity material is also effective.
• the casing and insulation together should provide tempera ⁇ ture protection for the sensitive internal components up to at least about 290°F, a vacuum of less than one-half inch of mercury and a pressure differential of at least 5 atmo- spheres.
• the transmitting antenna 108 is a length of 1/4— wave wire located perpendicular to the base of casing 129 which acts as a ground plane.
• Unit 150 Transmission of the data is effected by unit 150 shown in Figure 5 which includes UART 152 (universal asynchronous receiver-transmitter) , modem 156 and radio transmitter 158.
• UART 152 universal asynchronous receiver-transmitter
• modem 156 modem 156
• radio transmitter 158 radio transmitter 158.
• the UART can be an Intersil 6402 unit and the modem and transmitter can be combined as in an FM unit such as a Motorola RNet 9600 series.
• Power is preferably provid ⁇ ed by a battery pack, preferably rechargeable.
• Figure 7 shows, in addition to the multiplexer 130 which receives the signals from the sensors and distributes them as called for, a signal processing unit 140 and a transmit ⁇ ter and modem unit 150.
• a suitable transmittter is an RNet 9600 unit manufactured by Motorola Inc. Radius Division, Schaumberg, IL, which transmits at 464 MHz FM with a fre ⁇ quency deviation of 7.5 KHz.
• the signal processing unit 140 can include an analog to digital converter (ADC) which digitizes the analog signals from the multiplexer, a timing and control unit 144 which instructs the multiplexer on the distribution of signals from the sensors to the ADC 142.
• ADC analog to digital converter
• the sensors are in one embodiment sequentially sampled at a 2 Hz rate and digitized to 6 bits, and two address bits are appended to identify from which of the four sensors the data word is generated.
• the 8-bit words are applied sequentially to UART 152 which converts them to a standard 9600 baud even parity 2-stop bit message.
• a microprocessor 146 can be employed to enable storage and manipulation of digitized signals from the sensors.
• a microprocessor or other controller can receive signals representative of the temperature within the steril ⁇ izer, compare this to a signal representative of a designat ⁇ ed temperature (T 0 ) for powering up the transmitter, and subject to the results of the comparison, either waiting or powering up the transmitter to send data to the external controller 300.
• the same sequence can be fol ⁇ lowed to shut down the unit when the temperature drops below T 0 .
• the unit can be shut down and a warning given when the temperature exceeds a preselected upper value.
• the microprocessor can also be provided with means to store the sensor data for transmission to the controller or other signal processor only after removal from the chamber.
• a-hard data link such as by female receptacle 128 on the test device 100 and a male plug 310 on the control unit can be provided to elec ⁇ trically couple the two units.
• other data transmission means including those based on infrared trans ⁇ mission, can be employed.
• FIGS 3 and 4 show the principal components of a preferred controller 300 according to the invention.
• Figure 8 shows the arrangement of the components in a block diagram.
• the controller can display the test results in printed form 302 in any desired format and can provide real time indication of conditions on displays (e. ⁇ r. , liquid crystal) for temperature 304 and pressure 306. Data on the conditions inside the steam sterilizer chamber is received preferably by radio, employing antenna 308. Alternatively, as discussed above, the data can be transmitted after the transmitter unit is removed from the sterilizer through a wired data link employing male plug 310.
• the face of the controller is also shown to include indicators (e.g., light emitting diodes) which provide visual warning of a wet condition 312 in the sterilizer and confirmation of effec ⁇ tive reception 314 of transmission from the transmission unit. Power can be provided from standard current through line 311 or from a designated source, as desired.
• the system will be capable of operation in at least of two modes: (1) a Bowie and Dick test mode, typically run once a day (e. g. , each morning) on an empty sterilizer, and (2) a test under load.
• the partic ⁇ ular reference temperatures, and if employed, reference pressures and moistures which are referred to to determine the effectiveness of operation of the sterilizer, will differ depending on whether or not a load is present. Accordingly, the controller must be set for the particular mode for each cycle of operation and be programmed with the reference conditions for that mode.
• the load mode reference conditions will typically be unique to an individual steril ⁇ izer.
• the microprocessor is preferably programmed to re ⁇ ceive reference temperature, pressure and moisture data by a trained operator, periodically, via data link such as 310.
• Reference to Figure 8 shows a user program data block 311 which can be a keyboard, disk drive or other suitable data entry device.
• a mode switch 318 includes a light source which will flash until a mode (as displayed on panel 316) is selected by actuating the switch.
• the controller preferably includes means which prevent the test cycle from beginning and any report to be printed until the mode switch is activated.
• the controller components are illustrated in block form for a preferred device in Figure 8 and for a simplified version in Figure 8A. This latter Figure shows a radio receiver 320 which receives the data transmission from the transmitter in test unit 100 inside the steam sterilizer 200 and sends the data to UART 330.
• the UART 350, address decode unit 340 manipulates the data and distributes the designated signals to digital to analog converters (DAC) , e. g.
• DAC digital to analog converters
• the temperature display 372 is most preferred.
• the moisture is preferably " handled simply by a warning light, and excessive tempera ⁇ tures within the transmitter itself are noted by visual indicator similar to wet indicator 312, which can be accom ⁇ panied by an audible warning.
• Figure 9 is a preferred flow diagram for the operation of a test unit 100
• Figure 10 is a preferred flow diagram for the operation of a control ⁇ ler 300.
• Figure 8 is a preferred embodiment of a controller in block diagram form showing a receiver 320, a modem 330, a UART 350, and a microprocessor 380 which drives the condi- tion monitors 372, 374, 376 and 378.
• the microprocessor is instructed as to the mode of operation by mode switch 382, and other data can be input by user program data entry device 311 which can be a keyboard, disc drive, or the like.
• Output to printer 390 will generate a printed report.
• a ster ⁇ ilizer having a preliminary vacuum cycle is opened and the test unit 100 is placed therein.
• the sterilizer cycle is then begun, and a vacuum is drawn for the designated period of time.
• This is followed by the introduction of steam at a designated temperature (e.gr., 285°F) for a designated time (e. g. , 3.5 minutes).
• the test unit continuously monitors the temperature. Analog data from this and other transduc- ers is continuously digitized and presented to the micropro ⁇ cessor.
• T 0 When the temperature reaches a designated T 0 value, the test unit is turned on to collect and store test temperature values, T_ and P-. Temperature T 1 and the signal generated are indicative of the temperature at the location of temper ⁇ ature sensor 122 in cavity 115. Pressure Pi and the signal generated, are indicative of the pressure within cavity 115. Stored within memory is reference temperature information, and a signal T r is generated indicative of this reference temperature.
• the reference tempeature can be a predeter ⁇ mined temperature, e. g. 285°F, or a calculated value based on a computed average of selected values from earlier runs, e. g. , the last ten Bowie and Dick mode temperatures.
• test data is then converted from analog to digital and either stored coded and transmitted.
• the controller 300 or functional equivalent preferably receives transmitted test data and processes it in accor- dance with Figure 10.
• the controller receives and stores data indicative of T_, P x and K l t and then compares signal T x to a stored signal T r which is typically the intended ster ⁇ ilization temperature. If this test is met and if pressure data is being treated, signal P x will be compared to signal P r indicative of a reference pressure.
• the reference pres ⁇ sure can be a pressure obtained from stored steam table information to indicate the pressure for saturated steam at that temperature with or without a designated tolerance.
• the signal P r can take into account a permiss- able 5° or 10"F degrees of superheat.
• P r can be slightly higher than the value for saturated steam at ⁇
• the logic is queried to assure that the test time, or short- er time for the comparison, has not expired. Moisture data can then be taken and compared to a reference moisture, and a report printed.

Landscapes

• Health & Medical Sciences (AREA)
• Epidemiology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Apparatus For Disinfection Or Sterilisation (AREA)
• Pretreatment Of Seeds And Plants (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=25372289

Family Applications (1)

Country Status (7)

Cited By (25)

Families Citing this family (45)

Citations (2)

Family Cites Families (8)

• 1993
  • 1993-05-05 CA CA002135198A patent/CA2135198C/en not_active Expired - Lifetime
  • 1993-05-05 ES ES93911067T patent/ES2183813T3/es not_active Expired - Lifetime
  • 1993-05-05 DE DE69332226T patent/DE69332226T2/de not_active Expired - Lifetime
  • 1993-05-05 EP EP93911067A patent/EP0671956B1/en not_active Expired - Lifetime
  • 1993-05-05 AT AT93911067T patent/ATE222506T1/de not_active IP Right Cessation
  • 1993-05-05 WO PCT/US1993/004233 patent/WO1993021964A1/en not_active Ceased
• 1994
  • 1994-06-22 US US08/263,792 patent/US5422276A/en not_active Expired - Lifetime
  • 1994-06-22 US US08/263,801 patent/US5491092A/en not_active Expired - Lifetime

Patent Citations (2)

Also Published As

Similar Documents

Legal Events