Method of delivering liquid sterilant to a sterilizer

Background of the Invention

0001This application relates to the delivery of sterilant from a cassette to an instrument sterilizer, and more particularly to the extraction of sterilant from the cassette.

0002One popular method for sterilizing instruments, such as medical devices, is to contact the devices with a vapor phase chemical sterilant, such as hydrogen peroxide. In many such sterilizers, it is preferred to deliver the sterilant in liquid form and vaporize it in the sterilizer. One particularly convenient and accurate method for delivering the liquid sterilant is to put a predetermined quantity of sterilant into a cassette and deliver the cassette to the sterilizer. The sterilizer then automatically extracts the sterilant from the cassette and uses it for sterilization procedure. Typically, such a cassette would entail multiple cells containing equal amounts of liquid sterilant with a sterilization procedure employing the sterilant from one or more cells. Such a system is currently available in the STERRAD® sterilization system available from Advanced Sterilization Products in Irvine, California.

0003U.S. Patent Nos. 4,817,800; 4,869,286; 4,899,519; 4,909,287; 4,913,196; 4,938,262; 4,941,518; 5,882,611; 5,887,716; and 6,412,340 disclose such cassettes and a method for draining liquid sterilant from a cell within a cassette. In essence, the cassette travels horizontally with a horizontally oriented cell and one or more needles pierces the cell from below while compressed air is applied to an upper surface of the cassette cell. The cell is made from a flexible material so that the air compresses the cell and forces the sterilant out through the needles. Such a system limits the cassette design to an outer shell providing rigidity enclosing an inner cell of a flexible material. Further, the cell needs to be designed carefully to allow a complete collapse without trapping any of the liquid sterilant within a wrinkle in the cell during its collapse.

0004The present invention overcomes these and other limitations of the prior art.

Summary of the Invention

0005A method, according to the present invention, of delivering a liquid sterilant to a sterilizer comprises the steps of: a) piercing a cell of a cassette with a first needle having a first lumen, b) flowing a gas into the cell to pressurize the cell relative to a pressure within the first lumen and drive the liquid sterilant out of the cell through the first lumen, and c) flowing the liquid sterilant from the lumen to a vaporizer in the sterilizer.

0006In one aspect of the invention, a second lumen through the first needle opens into the gas is injected into the cell through the second lumen. In another aspect of the invention, the method includes the steps of piercing the cell with a second needle having a second lumen opening so that the lumen opens into the cell and injecting the gas into the cell through the second lumen.

0007In one aspect of the invention, the gas is at atmospheric pressure and the first lumen is at a pressure below atmospheric pressure. In another aspect of the invention, the gas is at a pressure greater than atmospheric pressure.

0008The method is suitable for use with cassettes having multiple cells and steps a), b) and c) can be repeated therewith.

0009Preferably, the liquid sterilant comprises hydrogen peroxide.

0010In one aspect of the invention, in step a) the needle enters the cell laterally. In another aspect of the invention, in step a) the needle enters the cell at an upper portion thereof and travels downwardly therein. The needle can be positioned such that the first lumen opens into the cell at or near its lowest point to maximize extraction of liquid sterilant from the cell, or at a predetermined vertical position to extract the liquid sterilant above the predetermined position, such that less than a total amount of liquid sterilant in the cell is thus extracted.

Brief Description of the Drawings

0011<ul id="ul0001" list-style="none" compact="compact"><li>FIG. 1 is a block diagram of a sterilizer employing a cassette handling system according to the present invention;</li><li>FIG. 2 is a rear perspective view of a cassette handling system according to the present invention;</li><li>FIG. 3 is a front perspective view of the cassette handling system of FIG. 2;</li><li>FIG. 4 is a front perspective view of the cassette handling system of FIG. 2 showing a spent cassette collection box;</li><li>FIG. 5 is a rear perspective view of the cassette handling system of FIG. 2 showing its carriage in the insert position;</li><li>FIG. 6 is a rear perspective view of the cassette handling system of FIG. 2 showing its carriage as it moves toward the home position;</li><li>FIG. 7 is a rear perspective view of the cassette handling system of FIG. 2 showing its carriage in position to read a bar code on the cassette;</li><li>FIG. 8 is a rear perspective view of the cassette handling system of FIG. 2 showing its carriage in the home position;</li><li>FIG. 9 is a front perspective view of the cassette handling system of FIG. 2 showing its carriage in position to tap the cassette's first cell;</li><li>FIG. 10 is a cross sectional view of the cassette showing a cell therein;</li><li>FIG. 11 is a front perspective view of the cassette handling system of FIG. 2 showing upper and lower needles on an extractor subsystem penetrating the first cell of the cassette;</li><li>FIG. 12 is a front perspective view of the cassette handling system of FIG. 2 showing upper and lower needles on the extractor subsystem in position to penetrate the last cell of the cassette;</li><li>FIG. 13 is a front perspective view of the cassette handling system of FIG. 2 showing the cassette being ejected therefrom;</li><li>FIG. 14 is a flow chart of the cassette handling process;</li><li>FIG. 15 is a rear perspective view of an alternative embodiment of a cassette handling system of the present invention employing RFID technology;</li><li>FIG. 16 is a memory map of an RFID tag of the cassette shown in FIG. 15;</li><li>FIG. 17 is a top plan view of an unfolded blank for forming the spent cassette collection box of FIG. 4; and</li><li>FIG. 18 is a perspective view of the blank of FIG. 17 folded to form the spent cassette collection box.</li></ul>

Detailed Description

0012FIG. 1 shows in block diagram form a vapor phase sterilizer 10 employing a cassette handling system 12 according to the present invention. The sterilizer 10 comprises a vacuum chamber 14 and a vacuum pump 16 for exhausting atmosphere therefrom. A vaporizer 18 receives liquid sterilant from the cassette handling system 12 and supplies it in vapor form to the vacuum chamber 14. A screen grid electrode 20 is provided within the vacuum chamber 14 for exciting the contents into the plasma phase during a portion of the sterilization cycle. A micro filtered vent 22 and valve 24 allow sterile air to enter the vacuum chamber 14 and break the vacuum therein. A control system 28 ties in to all of the major components, sensors and the like within the sterilizer 10 to control the sterilization cycle.

0013A typical sterilization cycle might include drawing a vacuum upon the vacuum chamber 14 and turning on power to the electrode 20 to evaporate and extract water from the vacuum chamber 14. The electrode 20 is then powered off and a low vacuum of less than 1 torr drawn on the vacuum chamber 14. Sterilant, such as hydrogen peroxide solution, is vaporized by the vaporizer 18 and introduced into the vacuum chamber 14 where it diffuses into contact with the items to be sterilized and kills microorganisms thereon. Near the end of the cycle, power is again applied to the electrode 20 and the sterilant is driven into the plasma phase. The electrodes 20 are powered down and filtered air is drawn in through the valve 24. This process can be repeated.

0014Turning also to FIGS. 2 to 4, the cassette handling system 12 according to the present invention is shown. It comprises in gross, a carriage 32 for holding a cassette 34, a lead screw 36 and motor 38, an extractor subsystem 40 and a scanner 42.

0015The carriage 32 comprises a bottom panel 44, a side panel 46 and top panel 48 along with small vertical flanges 50 and 52 on the top and bottom and top panels 48 and 44, respectively, to capture the cassette 34. The bottom, side and top panels 44, 46 and 48 flare outwardly at an entrance 54 of the carriage to aid in insertion of the cassette 34. Two spring catches 56 on the flanges 50 and 52 engage irregular surfaces of the cassette 34 to firmly position the cassette 34 within the carriage 32.

0016The carriage 32 travels along the lead screw 36 and is supported on an upper rail 58. A lead screw nut 60 attached to the bottom panel 44 and having a threaded opening 62 and an unthreaded opening 63 receives the lead screw 36 and effects horizontal movement of the carriage 32 in response to rotations of the lead screw 36. Flanges 64 extend outwardly from the top panel 48 and flanges 66 extend outwardly from the side panel 46 each having openings 69 for receiving the upper rail 58. The motor 38 is preferable a stepping motor and connects to the lead screw 36 to precisely control the horizontal position of the cassette 34 relative to a frame 68.

0017The extraction assembly 40 comprises an upper needle 70 and a lower needle 72, each being of a lumened configuration. The upper needle connects to an air pump 74 which can force air out through the upper needle 70. The lower needle 72 connects to a valve 76 and from there is plumbed to the vaporizer 18.

0018The scanner 42 is oriented so as to be able to read a barcode 80 on the cassette 34 as well as a barcode 82 on a spent cassette collection box 84. Upon insertion of the cassette 34 into the carriage 32 the scanner 42 reads the cassette barcode 80. The barcode 80 is preferably encoded with information regarding the contents of the cassette 34, including lot numbers and expiration dates. This information can be used to determine whether the cassette 34 is fresh and of the correct type and whether the cassette 34 has been used in the system before and thus is at least partially empty. The code is communicated to the control system 28 which makes these determinations.

0019The scanner 42 can also see the spent cassette collection box barcode 82 when the carriage 32 moves inwardly and away from the scanner 42. Each spent cassette collection box 84 preferably has two barcodes 82, one in each opposing corner so that the scanner 42 can see one of them regardless of which end of the spent cassette collection box 84 is inserted first. With the spent cassette collection box 84 filled, the spent cassettes 34 block the barcode 82 which alerts the control system 28 that there is no capacity for receiving additional spent cassettes 34. Preferably this message will be output to a user, such as on a display screen (not shown). If the cassette 34 is empty it will not be ejected and no new cycles will be run until a spent cassette collection box 84 having capacity to receive a spent cassette 34 is placed into the sterilizer 10.

0020A forward flag 86 and rearward flag 88 project outwardly and downwardly from the carriage side panel 46. They slide through a slot 90 in a slot sensor 92 which detects their presence within the slot 90, such as by blocking a beam of light. Travel of the front flag 86 and rear flag 88 through the slot sensor 92 provides a reference location of the carriage 32 to the control system 28.

0021The top panel 48 of the carriage 32 can rotate about the upper rail 58. A spring 94 between the top panel 48 and side panel 46 biases the top panel 48 downwardly to hold the cassette 34 within the carriage 32. A disposing cam 96 sits behind the side panel 46 and aligns with an ejecting tab 98 which extends outwardly and downwardly from the top panel 48 and which can project through an opening 100 in the side panel 46 when the top panel 48 rotates upwardly. Such rotation of the top panel 48 releases its hold upon the cassette 34 and due to the ejecting tab 98 projecting through the opening 100 pushes the cassette 34 out of the carriage 32 and into the spent cassette collection box.

0022The disposing cam 96 controls rotation of the top panel 48. It comprises a generally triangular shape, having an outwardly facing side 102, forwardly facing side 104 and rearwardly facing side 106. Turning also now to FIG. 5, it mounts for rotation upon an upwardly extending spindle 108. A spring 110 biases the disposing cam 96 counterclockwise, urging the outwardly facing side 102 into contact with an abutment 112. Inward movements of the carriage 32 allow the ejecting tab 98 to cam over the rearwardly facing side 106 of the disposing cam 96, thus allowing the disposing cam 96 to rotate clockwise and allow the ejecting tab 98 to pass thereby without effecting rotation of the top panel 48. However, outward movement of the carriage 32 causes the ejecting tab 98 to cam over the forwardly facing side 104 of the disposing cam 96. During such motion contact between the outwardly facings side 102 of the disposing cam 96 and the abutment 112 prevents rotation of the disposing cam 96. The camming of the ejecting tab 98 thus causes it to move laterally toward the side panel 46 thereby rotating the top panel 48 upwardly and releasing the cassette 34 from the carriage 32.

0023Prior to inserting the cassette 34 the carriage 32 is fully retracted to its outward position (to the left as shown in FIG. 5). In this position also, a forward end 114 on the lead screw nut 60 engages a stop 116 thus positively locating the position of the carriage 32. Turning also now to FIG. 6, manual insertion of the cassette 34 causes the carriage 32 to move inwardly (to the right as shown in FIG. 6) and moves the front flag 86 into the slot sensor 92. This movement is preferably caused by the physical force from inserting the cassette 34, however, a torque or other sensor could be applied to allow the stepping motor 38 to take over this movement upon feeling the force of the cassette 34 being inserted into the carriage 32. Allowing this movement to come from the force of the insertion of the cassette 34 ensures that the cassette 34 is fully seated within the carriage 32 before the movement begins.

0024Once the front flag 86 is read by the slot sensor 92 the stepper motor 38 takes over and starts to move the carriage 32 inwardly. Turning also now to FIG. 7, during this stage, the scanner 42 scans the barcode 80 on the cassette 34. The control system 28 interprets the information coming from the barcode 80 and determines whether the cassette 34 has been used in the sterilizer 10 before, whether the cassette contains fresh sterilant, and other data as appropriate. Preferably, the information on the barcode 80 is encrypted to prevent unauthorized parties from creating cassettes which may not meet the quality standards necessary for proper sterilization.

0025If the control system 28 rejects the cassette 34 a carriage 32 is moved sufficiently inwardly so as to pass the ejecting tab 98 past the disposing cam 96 and is then moved back to the insertion position shown in FIG. 5 to eject the rejected cassette 34. If the cassette 34 is accepted, the carriage 32 continues inward movement to the home position as shown in FIG. 8 in which the rear flag 88 has just passed out of the slot sensor 92.

0026Turning also now to FIGS. 9 and 10, the cassette 34 comprises a plurality of cells 118 containing liquid sterilant 120. Various structures of a cassette may be employed. The cassette 34 shown comprises a hard outer shell 122, preferably formed of an injection molded polymer, such as high impact polystyrene, high density polyethylene or high density polypropylene, which encloses the individual cells 118, the cells 118 being formed of a blow molded polymer such as low density polyethylene. However, a more rigid material can be used to form the cassette cells 118 in which case the outer shell 122 could be omitted. In the cassette 34 shown, an upper aperture 124 and lower aperture 126 through the shell 122 allows the upper and lower needles 70 and 72 to penetrate the shell. The cell 118 is formed of a material easily penetrated by the needles. If the cell 118 is formed of a more substantial material, a thinning of the material could be provided at the locations to be penetrated by the needles 70 and 72.

0027The control system 28 uses the home position of FIG. 8 as a reference position for positioning the various cells 118 in front of the extractor subsystem 40. By moving the carriage 32 a predetermined amount from the home position a given cell 118 can be brought to face the extractor system 40. In FIG. 9, cell one has been placed in front of the extractor system 40. Turning also now to FIG. 11, an actuator 128 drives the extractor subsystem 40 toward the cassette 34 causing the upper and lower needles 70 and 72 to penetrate the upper and lower apertures 124 and 126 and enter the cell 118. After the needles have fully extended, the air pump 74 drives air into the cell 118 through the upper needle 70. The system waits a couple of seconds before starting the air pump 74 and opening the valve 76 to ensure proper placement and settling of the needles within the cell 118. The sterilant 120 flows out through the lower needle 72 and is piped off to the vaporizer 18. After a sufficient time to extract the sterilant 120, the air pump 74 switches off and the actuator retracts the extractor subsystem 40 from the cassette 34.

0028The vaporizer 18 connects to the vacuum chamber 14 which allows the lower needle 72 to easily be placed at a pressure below atmospheric. Thus, the pump 74 can optionally be replaced by a valve (not shown) open to atmosphere, in which case the incoming atmospheric pressure air will provide the driving force to empty the cell 118.

0029Rather than employ upper and lower needles 70 and 72, one needle having two lumens therethrough would suffice. One of the lumens would provide pressurizing gas and one would extract liquid sterilant. A further alternative arrangement would be to pierce the cell 118 vertically, or substantially so, from an upper part of the cell 118, preferably with such a double lumen needle. This would minimize leakage around the hole created by the needle entering the cell 118. Such entry would also allow the tip of the needle to come closer to the lowest point of the cell 118 for maximum extraction efficiency. If one desired to extract less than all of the contents of the cell 118, one method would be to position the needle extracting the sterilant, such as the lower needle 72 or the just mentioned double lumen needle, at the level in the cell 118 down to which extraction is desired. Liquid sterilant above the position would be extracted and sterilant below would remain. This would be particularly convenient with the just mentioned vertically traveling needle.

0030Turning also to FIG. 12, each time the control system 28 determines that a new dose of sterilant 120 is required, the stepper motor 38 moves the cassette to position the next cell 118 in front of the extractor subsystem 40 and a new extraction takes place. Multiple extractions may be employed for a given sterilization cycle. When the cassette 34 has been depleted, the carriage 32 moves towards the insert position thus causing the ejecting tab 98 to cam over the disposing cam 96 to rotate the top panel 48 upwardly and project the ejecting tab 98 through the opening 100 to drive the cassette 34 out of the carriage 32 as described above and as shown in FIG. 13. The cassette 34 falls into the spent cassette collection box 84 and the carriage 32 returns to the insertion position as shown in FIG. 5.

0031The foregoing discussion described the operation of the cassette handling system in some detail. FIG. 14 shows, in block diagram form, the basic operation of the cassette handling system 12.

0032The system of reading barcodes on the cassette 34 and spent cassette box 84 can be replaced with radio frequency identification tags, commonly known as RFID tags. An RFID system 130 is shown in FIG. 15. It comprises a controller 132 connected via an SPDT reed relay 134 to a cassette insertion antenna 136 located on the carriage 32 and a cassette disposal antenna 138 located beneath the spend cassette box 84. Each cassette 34 carries a cassette RFID tag 140. Similarly, each spent cassette collection box 84 carries a collection box RFID tag 142. Preferably, the controller 132 comprises a Texas Instruments multifunction reader module S4100 and the RFID tags 140 and 42 comprise Texas Instruments RFID tag RI-101-112A each of which are available from Texas Instruments, Dallas, Texas.

0033The control system 28 (FIG. 1) selects one of the antennas, as for instance the cassette insertion antenna 136 and sends a signal to the relay 134 to engage this antenna with the RFID controller 132. The antenna reads the information stored on the cassette insertion RFID tag 140 which identifies the cassette 34 and its contents. The information read is similar to the information read using the barcode, however preferably, the RFID tag 140 has the ability to update the information stored thereon. Accordingly, additional data such as the filling status of individual cells 118 within the cassette 34 can be stored on the RFID tag. Thus, if the cassette 34 is removed and then reinserted into the sterilizer 10, or even into different sterilizer 10, the control system 28 can be apprised of the status of each of the individual cells 118 within the cassette 34. This allows the reuse of a partially used cassette 34. Also, since the RFID tag 140 can hold more data than the barcode 80, more data about the cassette 34, its contents and manufacturing can be included thereon.

0034The spent collection box antenna 138 reads the spent collection box RFID tag 142 to determine the presence or absence of the spent cassette collection box 84. Other data such as a unique identifier for the box 84, the capacity of the box 84, how many cassettes 34 are currently in the box 84 and how many of the cells 118 therein are not empty can be included on the RFID tag 142. The control system 28 can track how many cassettes 34 have been ejected into the box to determine whether it has room for more spent cassettes 34. The antenna 138 can also read the cassette RFID tags 140 and count the number of cassettes 34 within the box 84. When the box 84 is full the control system 28 alerts the operator, as by a message on a screen. This message can also include information regarding the cassettes 34 within the box 84. For instance if not all of the cassettes 34 have been completely drained the operator can be informed of this to decide if more careful disposal may be indicated.

0035RFID technology is disclosed in the following U.S. Patents: U.S. Patent Nos. 6,600,420; 6,600,418; 5,378,880; 5,565,846; 5,347,280; 5,541,604; 4,442,507; 4,796,074; 5,095,362; 5,296,722; 5,407,851; 5,528,222; 5,550,547; 5,521,601; 5,682,143 and 5,625,341.

0036RFID tags typically comprise an antenna and an integrated circuit produced in a thin form factor so they can be inconspicuously placed upon an object such as the cassette 34. Radio frequency energy sent by the antennas 136 and 138 induce sufficient current within the antenna inside the RFID tags 140 and 142 to power the integrated circuit therein. Some types of RFID tags carry their own power source and have longer detection ranges, but that adds additional expense and is probably not justified for the present use.

0037FIG. 16 shows the memory map for the memory within the RFID tags 140 and 142. A 64-bit unique ID (UID) is set at the factory and cannot be changed. Each RFID tag has its own unique number here. Sixty-four 32-bit blocks can be programmed by the user. These can be populated with information such as the manufacture date, expiration date, product ID, serial number, lot numbers, manufacturing location, filling status of the cells, strength and type of sterilant, time spent within the sterilizer 10 and the like.

0038Some sterilants are affected by heat. The RFID tag 140 can optionally include temperature collection instrumentation and update that information on the tag. If design temperature profiles are exceeded, such as a maximum temperature or excessive temperature over a time period, then the cassette 34 can be rejected by the control system 28. Temperature measuring RFID tags are available from KSW-Microtec, Dreseden, Germany and from Identec Solutions, Inc., Kelowna, British Columbia, Canada. The interior of the sterilizer 10 where the cassette 34 sits may be higher than ambient temperature. Thus, it may be beneficial to put a maximum residence time (on board shelf life) on the tag 140 or even to update on the tag 140 this time the cassette has already spent inside of the sterilizer.

0039To test sterilant measuring equipment in the sterilizer 10, it may be beneficial to provide cassettes 34 having water or other fluids within one or more cells 118. Information regarding the special nature of the cassette 34 and its contents could be written onto the RFID tag.

0040During a cycle the sterilizer may only require part of the contents of a cell 118. For instance, a particular cycle may call for the contents of one and a half cells. The half filled nature of the cell 118 can be stored and then for the next cycle that cell 118 can be drained.

0041Preferably, communications between the tag 140 and 142 and the controller 132 are encrypted. For instance, the UID can be XORed with an eight-bit master key to form a diversified key for encrypting the data. Encryption algorithms such as the data encryption standard (DES) triple DES, asymmetrical encryption standard (AES) or RSA security can be used for the encryption. The RFID controller 132 reads the data and the algorithm in the control system 28 decrypts the data to reveal the stored information.

0042Other methods could be used to communicate between the cassette 34 and the sterilizer 10. For instance information could be stored magnetically on the cassette 34, such as with a magnetic encoded strip, and be read by a magnetic reader on the sterilizer. Wireless technology is becoming cheaper every day and it is envisioned that the cassette 34 could include an active transmitter and a power source (i.e. a battery) such as powered RFID tags or Bluetooth, 802.11b or other communication standard.

0043Further, the sterilizer 10 can be set up to communicate back to a central source, such as the manufacturer or distributor thereof, and provide information regarding its performance and the performance of the cassettes 34. Poorly performing cassettes 34 could be identified, as for instance sterilant monitors in the sterilizer not detecting sterilant during a cycle thus indicating some failure such as an empty cassette or bad sterilant therein. An improperly manufactured batch of cassettes 34 could then be quickly identified and recalled. Such communication could occur over telephone, pager or wireless telephone networks or over the Internet.

0044Turning now also to FIGS. 17 and 18, the spent cassette collection box 84 is preferably folded from a single sheet of printed cardboard or other stock. FIG. 17 shows an unfolded blank 150 and FIG. 18 shows the blank 150 folded to form the spent cassette collection box 84.

0045The blank 150 is divided by a series of fold lines (shown dashed) and cut lines into a bottom panel 152, side panels 154, end panels 156 and top flaps 158. Folding tabs 160 extend laterally from the side panels 154. Additional folding tabs 162 extend laterally from the end panels 156. Barcodes 82 are printed on the side panels 154 in a position to be visible in an upper interior corner of the spent cassette collection box 84 when it is folded into the configuration shown in FIG. 18. A pair of top flap locking tabs 164 extend from the top flaps 158 and fit into slots 166 in the opposing top flap 158 when the box 84 is closed and into slots 168 at the intersection of the bottom panel 152 and side panel 154 when the box 84 is opened.

0046To fold the box, the folding tabs 160 on the side panels 154 are folded upwardly and then the side panels 154 are folded upwardly, thereby aligning the folding tabs 160 with the intersection between the bottom panel 152 and the end panels 156. The end panels 156 are then folded upwardly and the end panel folding tabs 162 are folded downwardly over the folding tabs 160. Locking tabs 170 on the end panel folding tabs 162 fit into slots 172 at the intersection between the bottom panel 152 and end panels 156.

0047To place the box 84 into the open position as shown in FIG. 18, the top flaps 158 are folded downwardly to the outside and the locking tabs 164 fitted into the slots 168. Once the box 84 is filled with spent cassettes, the top flaps 158 are folded upwardly over the top and the locking tabs 164 can then be fitted into the slots 166 on the opposing top flaps 158. This unique folding arrangement allows spent cassettes 34 to fall into the open box 84 easily without the top flaps 158 getting in the way and also allows easy closure of the box 84 once it has become filled.

0048While the invention has been particularly described in connection with specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and that the scope of the appended claims should be construed as broadly as the prior art will permit.