Office size instrument sterilization system.

The present invention pertains to the decontamination art. It finds particular application in conjunction with sterilizing medical equipment and will be described with particular reference thereto. It will be appreciated, however, that the invention is also applicable to disinfecting systems as well as to microbially decontaminating a wide range of items, including medical and dental instruments, laboratory equipment, industrial equipment, and the like.

Disinfection connotes the absence of pathenogenic life forms. Sterilization connotes the absence of all life forms, pathogenic or not. Often, sterilization is measured against the elimination of bacterial endospores which are the living organisms most resistant to conventional sterilants. "Microbial decontamination"is used herein as the term generic to both sterilization and disinfection.

Many hospitals and larger facilities have a central sterilizing area. Medical equipment to be sterilized is forwarded to the sterilizing area where it is processed by trained technicians and returned to the individual medical units. One problem with a central sterilizing area is that the turnaround time on sterilization is relatively long, often of the order of days. This long turnaround time increases the need for duplicate sets of medical equipment, sufficient numbers of sets that a sterilized set is available for each patient during the turnaround time. Another drawback of the central sterilization area resides in the complexity of transporting and sorting equipment, the storage areas required, and the space required for a central sterilization facility. Like medical instruments tend to be interchanged such that physicians who send well cared for equipment for sterilization often receive mistreated equipment in return. A result and perhaps greater problem is that equipment is not always sent to a central sterilization facility before it is reused.

Commonly, medical equipment is sterilized in a steam autoclave. Autoclaves kill life forms with a combination of high temperature and pressure. Steam autoclaves have several drawbacks. The high temperature pressure vessel tends to be relatively bulky and heavy. The high temperature and pressure tends to dry or curtail the useful life of endoscopes, rubber and plastic devices, lenses and other portions of devices made of polymeric materials, and the like. Further, the sterilizing cycle is relatively long from the start of the cycle until the instruments are cool enough to use.

More sensitive medical equipment is often sterilized with an ethylene oxide gas system which is thermally less severe than steam. However, the ethylene oxide has several drawbacks. First, the instruments must be exposed to the ethylene oxide for a relatively long time, of the order of 3-1/2 hours. Thereafter, an 8-12 hour degassing period is normally required for removing absorbed ethylene oxide from plastic and other ethylene oxide absorptive materials. The pressure and depressurization cycles of ethylene oxide sterilization may damage lens and other delicate instruments. Second, the ethylene oxide is relatively expensive. Third, ethylene oxide is sufficiently toxic and volatile that extensive precautions and training are commonly taken to ensure operator safety. Usually, a trained operator and a dedicated facility are required.

Liquid sterilization systems are often used for heat-sensitive and other delicate instruments. Commonly, a technician mixes a liquid sterilant composition and manually immerses the items until he deems them sterilized. The high degree of manual labor introduces numerous uncontrolled and unreported variables into the sterilization process. Manual timing of the immersion raises assurance problems that the item was immersed for a sufficient duration. Further, sterilants tend to weaken, i.e. have a limited shelf life. Variations in the duration between when the technician mixed the sterilant and actually used it also raises problems with sterilization assurance and reproduceability of the microbial decontamination.

Another problem with the prior art liquid system resides in the corrosive nature of the strong oxidants that are commonly used as liquid sterilants. Normally, the sterilized items are rinsed to remove chemical residues. This rinsing also adds a variable that reduces the assurance the item has been disinfected or sterilized. Once rinsed, the item is susceptible to reinfection by airborne microbes.

In accordance with the present invention, a new and improved sterilization apparatus and method are provided which overcome the above-referenced problems.

<b>Summary of the Invention</b>

In accordance with one aspect of the present invention, a distributant sterilization system is provided. A relatively small, compact sterilization unit is provided for one or a small number of medical service provider areas, such a examination rooms.

In accordance with a more specific aspect of the present invention, a microbial decontamination system is provided. A body portion has a face panel which defines an access opening to a microbial decontamination chamber, an access opening to an anti-microbial concentrate receiving chamber, and a rinse fluid outlet opening in direct fluid communication with a filter means for removing at least pathogenic organisms from incoming rinse fluid. A door closes over and seals to at least a portion of the face panel surrounding the microbial decontamination chamber access opening, the anti-microbial concentrate chamber access opening and the rinse fluid outlet opening. A means defines fluid flow paths between the face panel and an interior surface of the door. The flow paths provide fluid communication among the microbial decontamination chamber access opening, the anti-microbial concentrate chamber access opening and the rinse fluid outlet opening. A fluid circulating means selectively circulates fluid through the anti-microbial concentrate chamber to form an anti-microbial solution. The antimicrobial solution flows through the fluid flow paths to the microbial decontamination chamber and through the microbial decontamination chamber. The circulating means selectively supplies the fluid through the filter means to create a microbially decontaminated rinse fluid that flows out of the rinse fluid outlet opening, through the flow paths to the microbial decontamination chamber to rinse the anti-microbial solution from items in the microbial decontamination chamber.

In accordance with another aspect of the present invention, two gaskets are provided between the face panel and the interior surface of the door. The two gaskets surround the microbial decontamination chamber access opening, the anti-microbial concentrate chamber access opening, and the rinse fluid outlet opening, and interconnecting flow paths. The two gaskets define a generally annular region therebetween. A vacuum means selectively draws a vacuum in the annular region to force the door and face panel into a tight fluid sealing relationship.

In accordance with another more limited aspect of the present invention, a cassette for receiving items to be microbially decontaminated is received in the microbial decontamination chamber. The cassette includes upper and lower portions which mate in a fluid tight sealed relationship. The upper and lower portions are openable to provide access to the interior for inserting items to microbially decontaminated or for withdrawing microbially decontaminated items for use. Fluid inlet apertures are defined in an uppermost portion of the cassette when inserted in the microbial decontamination chamber for enabling the cassette to receive and be filled with anti-microbial solution and the rinse fluids. At least one fluid outlet aperture is defined in a lowermost portion of the cassette when inserted in the microbial decontamination chamber to enable the interior of the cassette to be drained of the anti-microbial solution and the rinse fluids. A means is provided for preventing airborne microbial contaminants from passing through the fluid inlet and outlet apertures. A means is provided for controlling the orientation with which the cassette is received in the microbial decontamination chamber such that the fluid inlet apertures are at the uppermost portion of the cassette and the fluid outlet apertures are at the lowermost portion of the cassette.

One advantage of the present invention is that it assures sterilization or disinfection of medical and other items with liquid sterilants.

Another advantage of the present invention is that it is relatively compact and easy to use. Medical personnel, such as doctors, dentists, and nurses, can sterilize their own instruments on site without a specialized technician.

Another advantage of the present invention is that it makes sterilized equipment readily available. Not only is equipment sterilized quickly on site, it is held in an organized microbial contamination-free inventory ready for use.

Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.

The present invention may take form in various parts and arrangements of parts, or in various steps and arrangement of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention.

There is now described, by way of example and with reference to the accompanying drawings, apparatus (referred to below also as "system") according to a preferred embodiment of the invention. In the drawings: <ul id="ul0001" list-style="none"><li>FIGURE 1 is a perspective view of a microbial decontamination system in accordance with the present invention;</li><li>FIGURE 2 is a front view of the system of FIGURE 1 with the front door shown in phantom lines and with a cartridge (referred to herein also as "cassette") of items to be sterilized;</li><li>FIGURE 3 is a sectional view through section 3-3 of FIGURE 2;</li><li>FIGURE 4 is a sectional view through section 4-4 of FIGURE 2;</li><li>FIGURE 5 is a diagrammatic illustration of the plumbing system of the system of FIGURE 1;</li><li>FIGURE 6 is a sectional view illustrating details of an O-ring sealing arrangement between the door and gaskets of the system of FIGURE 1;</li><li>FIGURE 7 is a view in partial section illustrating details of an O-ring sealing arrangement between the check valves and face panel of the system of FIGURE 1;</li><li>FIGURE 8 is a top view of the cassette of FIGURE 2;</li><li>FIGURE 9 is a front view of a top portion of the cassette of FIGURE 8;</li><li>FIGURE 10 is a side view of the top portion of the cassette of FIGURE 8;</li><li>FIGURE 11 is a bottom view of the cassette of FIGURE 2;</li><li>FIGURE 12 is a front view of the cassette of FIGURE 11; and,</li><li>FIGURE 13 is a side view of the cassette of FIGURE 11.</li></ul>

With reference to FIGURES 1, 2, 3, and 4, a sterilizing apparatus <b>A</b> is configured to sit on a countertop or other convenient work surface. Preferably, the sterilizing apparatus is dimensioned such that it fits on a standard 60 cm (24 inch) deep countertop without interfering with overhead cupboards. A front door <b>B</b> is manually openable to provide access for inserting a cartridge <b>C</b> and a sterilant, preferably in the form of a cup or ampule <b>D</b>, into the system.

With continuing reference to FIGURES 2 and 3, and further reference to FIGURE 5, items to be sterilized are loaded in the cartridge <b>C</b> which is slidably received in a cartridge receiving chamber <b>10</b>. The chamber <b>10</b> is open at the front to receive a free flow of sterilant through the front. A drain or outlet port <b>12</b> at the end enables sterilant to circulate continuously over and through the cartridge.

With reference to FIGURES 2, 4, and 5, an anti-microbial composition is loaded into an anti-microbial mixing chamber <b>20</b>. A premeasured dose of the anti-microbial agent, in the illustrated embodiment, is held in a cup <b>22</b> which is pierced by a cutter <b>24</b> as it is inserted into the mixing chamber <b>20</b>. The anti-microbial cup is again open at the front to allow free fluid flow therefrom. An inlet port <b>26</b> receives water or other fluids with which the anti-microbial agent is diluted or dissolved. An anti-microbial mixing chamber drain port <b>28</b> provides an outlet for the water sterilant mixture to assist in recirculation.

Various anti-microbial agents may utilized. In the preferred embodiment, the anti-microbial agent is a mixture of powders which reacts when wet to form a sterilant, such as a strong oxidant, corrosion inhibitors, and a wetting agent. More specifically to the preferred embodiment, the dry ingredients include a water-soluble acid precursor and a water-soluble persalt which, when dissolved in water, form a peracetic acid solution with an anti-microbially effective concentration of peracetic acid. The dry ingredients further include a buffer, e.g. a borate, for bringing the pH to a neutral level to inhibit steel corrosion. The dry ingredients include other corrosion inhibitors, such as a molybdate for inhibiting aluminum and steel corrosion, a triazole for inhibiting copper and brass corrosion, and the like. Powdered wetting and sequestering agents may also be included. In the preferred embodiment, the acid precursor is acetylsalicylic acid and the persalt is sodium perborate. The total volume of dry ingredients is such that the resultant water solution has a concentration of peracetic acid of at least 0.2% W/V - a biocidally effective concentration.

Other oxidizing or anti-microbial agents can also be generated <u>in situ</u>, such a chlorine dioxide, chlorine, hydrogen peroxide, and mixtures thereof. For example, the powdered ingredients may include a mixture of potassium chromates, sodium chloride, and phosphates. As another example, hydrogen peroxide can be generated from a mixture of sodium borate and phosphates. Chlorine dioxide can be generated from a mixture of sodium chlorate and lithium chlorite. Sodium chloride can be added to peracetic acid to produce hyperchlorous acid.

Other copper and brass corrosion inhibitors are also contemplated, such as benzotriazoles, tolytriazoles, mercaptobenzathiozol, azoles, benzoates, and other five-membered ring compounds. Other anti-corrosives include chromates, dichromates, tungstates, vanidates, borates, and combinations thereof. A suitable sequestering agent for sequestering any precipitated calcium and magnesium salts is sodium hexametaphosphate.

Of course, liquid sterilants, such as liquid hydrogen peroxide, peracetic acid, and the like may also be utilized. If liquids are utilized, it is preferred that the liquid be held in a cup or vial from which the liquid may be aspirated by water flowing through the sterilant cup. The cup or vial may also be punctured or fractured on insertion to permit a free-flowing communication between the water and the liquid sterilant.

With particular reference to FIGURE 5 and continuing reference to FIGURES 1-4, a water inlet <b>30</b> is connected by flexible hose with a sink or other source of water. A pressure regulator <b>32</b> regulates the pressure to a preselected pressure. An inlet valve <b>34</b> is selectively actuated to channel fill water to a heater tank <b>36</b>. The heater tank maintains the water therein, preferably about 5 liters, at a preselected elevated temperature. As cold water enters the heater tank, it forces hot water in front of it through a check valve <b>38</b>. The check valve <b>38</b> separates a sterile side of the system and a non-sterile portion of the system adjacent the heater tank.

A circulation pump <b>40</b> circulates the hot water through a control valve <b>42</b> to the anti-microbial mixing chamber <b>20</b>. The water mixes and interacts with the sterilant composition to form a liquid sterilant that flows out the open front end of the mixing chamber <b>20</b>.

With particular reference to FIGURE 3 , water flowing out of the front of the mixing chamber flows through channels <b>44</b> defined between a face plate <b>46</b> and the door <b>B</b>. The face plate <b>46</b> is a molded structure which defines the mixing chamber <b>20</b>, the cassette chamber <b>10</b>, the flow paths <b>44</b>, and other elements of the system. A channel <b>48</b> extends between the mixing chamber and a water sterilizing filter <b>50</b>. The face plate also defines a passage <b>52</b> extending from the sterilizing filter 50 to the cassette receiving reservoir <b>10</b>. Gaskets <b>54</b> on the door assist in defining and sealing the flow paths <b>48</b> and <b>52</b> and permit fluid feedback to increase mixing turbulence around the mixing chamber <b>20</b>. A peripheral gasket <b>56</b> between the door and the face plate defines the periphery of fluid flow paths defined between the face and the door.

The circulation pump <b>40</b> pumps hot water through the mixing chamber <b>20</b> displacing all air from the sterilization chamber <b>10</b> and substantially all area between the face plate <b>46</b> and the door <b>B</b> and replacing the air with the sterilant or anti-microbial solution. At the highest point, an overflow valve <b>58</b> permits excess sterilant solution to be discharged to a drain <b>60</b>. The cassette receiving chamber outlet port <b>12</b> is also connected through a supplemental heater <b>62</b> with the circulation pump <b>40</b> such that the sterilant solution is actively drawn through the sterilization chamber <b>10</b>, heated, and recirculated.

The circulation pump continues to recirculate the sterilant solution through the chamber <b>10</b> and the various plumbing paths until the inside of the cassette and all items are sterilized, the outside of the cassette is sterilized, the exterior surface of the face panel inside the gaskets, the interior surface of the door inside the gaskets, all accessible surfaces of the sterile water filter <b>50</b>, the interior surfaces of all tubing, fittings, and valve surfaces through which fluid is circulated, and the circulation pump are sterilized or disinfected. Once all these surfaces are microbially decontaminated, the anti-microbial solution is drained through the drain outlet <b>60</b> into the drain of a sink or other liquid waste disposal system. Because strong oxidants, such as peracetic acid,break down relatively quickly to water, salt, and oxygen, there is no pollution or polluting contaminants that require special disposal. The drain outlet is connected by check valves <b>64</b> and controlled valves <b>66</b> and <b>68</b> with various drain points of the system. To ensure substantially complete drainage, the control valve <b>66</b> is opened and control valve <b>42</b> is closed such that the circulation pump withdraws the antimicrobial solution from the system and pumps it through controlled drain valve <b>66</b> to the drain outlet <b>60</b>. The plumbing is preferably physically positioned for complete drainage through outlet valve <b>66</b> by gravity.

A microbially decontaminated, preferably sterile, air filter <b>70</b> is connected between exterior air and a check valve <b>72</b>. The filter is a porous membrane whose apertures are sufficiently small that microbes are not permitted to pass. In this manner, sterile air is allowed to fill the volume left as the anti-microbial solution is drained. A float type air vent <b>74</b> permits air to be vented to the drain <b>60</b> but seals if its chamber fills with liquid to prevent liquid to flow therethrough.

After the sterilant is drained, the drain control valve <b>66</b> is returned to its closed state and the recirculation control valve <b>42</b> is returned to its open state. Water inlet valve <b>12</b> channels incoming water to an inlet port <b>76</b> of the now sterilized, microbe removing water filter <b>50</b>. The water filter <b>50</b> is again a porous membrane whose apertures are sufficiently small that water is passed but microbes, particularly all pathogenic microbes, are restrained. The surfaces of the membrane toward the open end have all been sterilized by the liquid sterilant as have most underlying portions. As the incoming water passes through the membrane, sterile rinse water passes through the front outlet end of the sterile water filter and flows through channel <b>52</b> toward the front opening of the cassette chamber <b>10</b>. When rinse water is introduced such that sterile rinse water fills the entire volume between the face and the door insert, the circulation pump circulates the fluid to assure that sterilant residue is removed from all interior surfaces. Once at least the items in the cassette <b>C</b> have been fully rinsed, the controlled valves <b>42</b> and <b>66</b> change states such that the rinse solution is pumped out of the system and replaced with sterile air. It will be noted that all surfaces with which the sterile rinse comes in contact including the plumbing and valve surfaces engaged during circulation were previously sterilized or microbially decontaminated during the sterilization or microbial decontamination portion of the cycle.

With particular reference to FIGURE 6 and continuing reference to FIGURES 2, 3, and 4, a fluid tight seal between the lid and the body portion is maintained by a pneumatic pressure system <b>80</b>. A pair of 90° V-shaped grooves or seats <b>82</b>, <b>84</b> are defined in one or both of the face portion <b>46</b> and the lid <b>B</b>. O-ring seals <b>56</b>, <b>86</b> are mounted partially in the V-shaped grooves and partially extending outward therefrom. The V-shaped grooves and O-rings define two closed loop paths around the fluid circulation portion and define a path 88 therebetween. A vacuum pump <b>90</b> is connected by appropriate tubing with vacuum ports <b>92</b> in the area between the two seals. The vacuum pump maintains a preselected negative pressure which causes the lid and body portions to squeeze the O-ring into the seats with a fluid tight seal. A vacuum release valve <b>94</b> is selectively actuated to release the vacuum to allow the lid to be opened. Optionally, a water sensor <b>96</b> is mounted along the vacuum tubing to sense a failure of the sealing arrangement which results in anti-microbial or rinse fluid being sucked past the inner gasket <b>56</b> into the vacuum path <b>88</b>. An electronics module <b>98</b> includes a microprocessor which is programmed to operate the valves, pumps, and other elements in the sequence described above. Preferably, the electronics include a clock and date module, temperature sensors, a key pad, and a printer for printing a record of the time, date, operator, and system operating parameters.

As illustrated in FIGURE 7, a similar arrangement is used to seal check valves <b>58</b> and <b>72</b> to the face <b>46</b>. The face <b>46</b> defines a V-shaped groove <b>100</b> with a 90° angle surrounding the check valve. The check valve has a flange <b>102</b> over and closely adjacent to the face overhanging the groove <b>100</b>. An O-ring <b>104</b> is received in the V-shaped groove abutting the underside of the flange <b>102</b>. A threaded nut or flange member <b>106</b> engages threads on the exterior of the check valve to urge the check valve flange to press the O-ring into the groove in a fluid tight seal.

With reference to FIGURES 2, and 8-13, the cassettes C each include a top portion <b>110</b> which matingly connects with a bottom portion <b>112</b>. The bottom portion may include a tray or rack (not shown) which has appropriate catches, compartments, guides, and the like for holding the instruments or items to be sterilized in a neat and organized pattern. For example, the tray may be configured to hold and organize a set of dental examination instruments in an appropriate arrangement to facilitate dental use. The exact design of the tray, of course, will vary with the requirements of each end user.

The top <b>110</b> of the cassette includes ports <b>114</b> at an uppermost portion to receive anti-microbial and rinse solutions and permit the escape of any air which might be trapped in the cassette. The ports <b>114</b> are disposed to be in alignment with flow paths <b>52</b>. The lid has U-shaped gasket portions <b>116</b> which engage the periphery of the cassette around the lower portion of ports <b>114</b> to direct the liquids from flow paths <b>52</b> into the cassette. The cassette receiving chamber is canted to horizontal such that the ports <b>114</b> are at the highest point of the cassette. Baffles <b>118</b> present a tortuous path between the ports <b>114</b> and the interior of the cassette. By and large, biological contaminants will not follow a tortuous path to gain access into an otherwise sealed enclosure. A tortuous path has been found reliable in preserving sterility of the enclosed items.

The cassette bottom <b>112</b> includes channels <b>120</b> which receive or interact with guide ridges <b>122</b> in the sterilization chamber <b>10</b> to assure right-way-up receipt. Optionally, other means might be provided for assuring that the cassette <b>C</b> is inserted with the cartridge bottom down and the cartridge top up. The cassette bottom also includes apertures <b>124</b> in a lowermost portion of a rear wall. The low placement of the apertures assures complete drainage of sterilant and rinse solutions from the cassette. Baffles <b>126</b> present a tortuous path to prevent biological contamination of items in the cassette after sterilization or disinfecting.

The cassette bottom portion includes projections <b>130</b> from a rear vertical wall which are received in slots <b>132</b> in the top portion rear wall to assure that the top and bottom portions remain interconnected. The lower portion also includes a U-shaped bale <b>134</b> on a forward wall through which a tab <b>136</b> depending from the upper portion forward wall is slidably received. The tab and bale, particularly aperture <b>138</b> in the tab for receiving a sealing element. More specifically, once the sterilization process is completed, a frangible seal is placed through the tab aperture and the bale and sealed such that it must be broken in order to open the container. Preferably, the seal is encoded with an identification number that identifies the sterilization cycle. This number may be utilized to cross-reference a more detailed listing of sterilization parameters, such as the date of sterilization, the operator, a serial number of the sterilant concentrate, water temperature, sterilization time, and other parameters which verify the sterilization. Alternately, the seal may carry a larger portion or all of such sterilization assurance information.

The top portion has a peripheral flange <b>140</b> with a slight outward bevel which tightly and frictionally engages the outer peripheral vertical surface of the bottom portion to provide a tight friction seal therebetween.

Preferably, the top portion <b>110</b> has projections or ribs <b>142</b> that are positioned at the same distances apart and from the edges as the channels <b>120</b> on the bottom portion such that if the cartridge is inverted, the cassette channels and ribs would be reversed. The sterilization chamber <b>10</b> tapers to be wider at the front and narrower at the back. The cassette is of approximately the same height as the sterilization chamber at the rear. The upward ribs <b>142</b> on the top portion terminate before the rear of the cassette or are tapered toward the rear to provide minimal clearance. If the cassette is inverted and inserted upside down, the interaction of the ribs <b>142</b> and guide ridges <b>122</b> lift the cassette sufficiently that the cassette engages the upper wall of the chamber <b>10</b> before it is fully inserted. In this manner, insertion of the cassette in the sterilization chamber <b>10</b> upside down is prevented. Of course, other means may be provided for preventing the cartridge from being inserted upside down.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.