BACKGROUND OF THE INVENTION

There are three distinct types of dry heat sterilizers: (1) Static hot air sterilizers in which air convection is generated solely by gravity as hot air rises and cooler air descends; (2) Mechanical convection sterilizers in which air is moved by blowers to uniformly distribute heated air and equally transfer heat throughout a load; and (3) High velocity hot air sterilizers in which air is moved at a high rate, as much as 2500 feet per minute, with flowing air serving as a heat transfer medium. Both static air and mechanical convection sterilizers require minimally one hour (at 340° F.) or two hours (at 320° F.) to achieve sterilization whereas high velocity hot air sterilizer can sterilize in six to twelve minutes (at 375° F.), depending on instrument type or packaging.

A high velocity hot air sterilization device has been disclosed by Cox et al. in U.S. Pat. Nos. 4,824,644; 4,894,207; 4,923,681; and 4,975,245. The single-door high velocity hot air sterilization device of Cox was designed and marketed for use in the dental and orthodontic markets to rapidly sterilize small instruments, typically made of metal or temperature-resistant materials, without instrument corrosion. The device accommodates wrapped or unwrapped instruments which are placed into a wire mesh, open basket and held for a specified time at 375° F. as prescribed under the U.S. FDA 510(k) notification. The basket containing the instruments is placed into the sterilizer through a door located at the front of the sterilizer. Upon completion of the sterilization cycle the basket is removed from the sterilizer though that front door. The air handling system to supply air to and to exhaust air from the sterilization chamber was designed specifically for this small, single-door sterilizer to provide adequate air and temperature distribution within the sterilization chamber for sterilizing small instruments and small instrument loads.

The Cox device supplies high velocity hot air to a sterilization chamber vertically through a plenum located underneath the sterilization chamber. This air supply is pushed through a perforated jet plate to create high velocity streams of air that traverse a short distance to a deflector plate located on a ceiling of the sterilization chamber. The deflector plate redirects the air, causing turbulence required to mix air to a more uniform temperature within the sterilization chamber. As air is supplied to the sterilization chamber there is an equal exhaustion of the chamber air at a rear wall of the sterilization chamber perpendicular to the direction of air entry from under the sterilization chamber. The air exhausts the sterilization chamber by way of a fan wheel, subsequently re-heated, and returned to the air supply plenum underneath the sterilization chamber for the continuous recharging of the sterilization chamber's hot, high velocity air supply. For this system to provide the aerodynamics of rapid airflow required to heat instruments to a temperature that will allow rapid instrument sterilization while providing a narrow range of temperature to avoid material incompatibility of instruments and their packaging, internal dimensions of the sterilization chamber are limited. The sterilization chamber of Cox comprises a width of 10 inches, a depth of 8 inches, and a height of 4 inches. Attempts to increase the sterilization chamber size under the embodiments of Cox resulted in increasing already large temperature ranges generated in the existing sterilization chamber and resulted in inconsistent and inadequate microbial kill efficacies across all three dimensions of the sterilization chamber.

While effective for instrument sizes and load capacities found in dental and orthodontic practices, the air handling system of the Cox device is limited in application and capability to serve the expanded requirements and needs of a healthcare facility such as a hospital or clinic. To service instrument processing needs in a healthcare environment a sterilizer must have a capacity for larger instruments as well as a higher number of instruments. To maintain sterility of items post-sterilization, hospital Sterile Processing departments are required to designate areas as “contaminated” or as “sterile.” Sterilized items, wrapped or unwrapped, must be removed directly from a sterilizer after being sterilized and into a designated sterile area to prevent instrument or packaging exposure to environmental microbial contaminants. This is achieved in hospital settings and some larger clinics by utilizing large, floor-standing, double-door steam sterilizers having an entry door on the contaminated side of the Sterile Processing Department and an exit door on the sterile side of the Sterile Processing Department.

Healthcare has evolved into more specialized services and availability through local neighborhood clinics and settings. These smaller facilities have neither space to accommodate nor an instrument processing volume to justify use of a large steam sterilizer normally used in hospital Sterile Processing departments. However, with healthcare-acquired disease transmission increasing in both incidence and severity, smaller healthcare facilities require similar attention in mitigating disease transmission by ensuring sterilized items are directly placed into a sterile area after sterilization processes.

The Cox sterilizer has inherent design limitations that limit its ability to accommodate a double door configuration and to expand sterilization chamber dimensions required for increased instrument capacity and instrument size. The existing vertical orientation of airflow into the chamber precludes the use of the Cox sterilizer as a double door, pass-through sterilization device as the device requires the back of the sterilization chamber for the plenum which houses the fan wheel and the heater element. These components would require relocation to one side of the unit to accommodate a rear door opposite the front door for direct pass-through of post-sterilized instruments to a sterile area, which would further impact the efficacy of the device.

Reconfiguration of airflow from vertical orientation to horizontal orientation into the sterilization chamber would require airflow supply to traverse a distance at least double that of the Cox device. It has further been demonstrated that expansion of the vertical airflow distance beyond four inches significantly alters airflow velocity, which dramatically reduces air mixing and leads to reduced microbial kill efficacy. Such limitations would preclude a sterilization chamber with horizontal airflow from having a chamber width greater than four inches.

The design embodied by Cox et al. did not produce an airflow with temperature uniformity prior to reaching the sterilization chamber. To compensate for the wide temperature ranges created as a result of heater element orientation and short air pathway to the sterilization chamber, the Cox device relies on a waffled jet plate, an air deflector plate, and a plenum diversion insert to achieve an adequate temperature uniformity for instrument sterilization. The use of these mechanisms increased air turbulence in the sterilization chamber to narrow a temperature range of the heated air supply entering the sterilization chamber from a temperature ranging from 400 to 600 degrees Fahrenheit to a tolerable temperature ranging from 380 to 410 degrees Fahrenheit within the sterilization chamber.

To meet the airflow dynamics required in obtaining uniform heat distribution and airflow velocity that allow for parameters necessary in high velocity hot air sterilization requires an air handling design that ensures the delivery of an air supply having a minimized temperature variation range before entering the sterilization chamber, alleviating the need for a jet plate and an air deflector or other devices to generate air turbulence for mixing air to temperature uniformity. Such an air supply system would allow varying sterilizer chamber dimensions, relying solely on the air supply to be delivered both uniformly across the air supply wall and into the sterilization chamber to assure conditions for high velocity hot air sterilization whether having a vertical or horizontal airflow.

Two critical factors influence temperature uniformity in supply air before entering the sterilization chamber: design and length of an air pathway and configuration, placement, and control of the heating element at the beginning of the air pathway. Although the length and design of the air pathway is important in allowing time, distance and airflow interference to homogenize air temperature, this factor alone will not assure temperature uniformity at air entry point to the sterilization chamber. Increased pathway length, plenum diversions, and ninety-degree turns will assist in air mixing, but large variations in air temperatures generated by heater element exposure cannot be offset by these design components.

In a computational fluid-air dynamics analysis of the Cox sterilizer conducted by the Rochester Institute of Technology using airflow simulation, a two hundred-degree Fahrenheit temperature variation was observed in airflow immediately after heater element exposure. Airflow mixing by the air supply jet plate and top wall diverter plate allowed adequate mixing to occur as shown in this simulation, but pockets of air remained within the sterilization chamber having temperature range variations of twenty to thirty degrees Fahrenheit or more caused by resultant eddy currents. The simulation analysis, when compared to actual thermocouple measurements demonstrated accurately the observations of temperature variation within the sterilization chamber.

Minimizing temperature variations within the supply air pathway can be achieved with the proper design, placement, and control of a heater element. The importance of the heater element as a critical factor for air temperature variation control has not been implemented in the art; with most devices relying on pathway modifications to compensate for temperature extremes created by heating a recirculated air supply. Orientation of a heater element to the airflow is critically important, as well as maximizing the amount of air exposed to the heating element in order to minimize air temperature extremes produced as a result of heated and unheated or minimally heated air. Employing a heater element of low thermal mass enables more rapid response from a thermocouple sensor and its controller by minimizing temperature overshoot and undershoot, generating heated air with less temperature extremes. Thermocouple placement is critical in obtaining downstream air temperature data necessary in modulating the heating element for constant temperature maintenance and further minimizes temperature extremes. Placement of thermocouples downstream within the air supply plenum in contrast to the sterilization chamber allows for better representation of air temperature homogenization and enables faster responses to a temperature controller. The controller receives the thermocouple input and compares the actual temperature with the required control temperature and relays the data to activate or deactivate the heater element. The use of a proportional-integral-derivative controller would further optimize sterilization chamber warm-up, more precisely maintain plenum temperatures, minimize temperature overshoot and undershoot, and speed heater element response.

A third temperature sensor located within the sterilization chamber at the air exhaust port would further serve to monitor sterilization chamber temperatures during the sterilization warm-up, instrument heating, and sterilization cycle. Air pre-heated to 375° F. travels horizontally through the sterilization chamber and across the metal or temperature-resistant material of the instruments before entering the exhaust portal for re-heating and recirculation. Heated air passing across the instruments is cooled as the heat from the air is transmitted to the instruments. As the sterilization process proceeds during instrument heating, the temperature measured at the exhaust portal increases as the temperature differential between the instruments and heated flowing air decreases. Initiation of microbial inactivation begins once the sterilization threshold temperature is reached on the instruments. The time required to reach the sterilization temperature threshold varies according to the mass of the instrument load. The temperature sensor located at the exhaust portal would provide a quantitative measure indicating when the instruments in the sterilization chamber have achieved this minimum sterilization threshold temperature. Once the critical exhaust portal temperature has been achieved that data is relayed to activate the sterilization cycle. Since instrument mass may vary from load to load, this quantitative measure is critical to assuring that required instrument temperature thresholds are achieved and maintained for a pre-requisite time to assure the level of microbial inactivation required.

There are no existing countertop sterilizers in the art that feature a double door configuration that can provide entry of contaminated instruments into a sterilizer from a contaminated area and subsequently, post-sterilization, have direct pass-through access into a sterile area through a second, exit door from that same sterilizer. A need exists for a small, countertop, high velocity hot air sterilization device capable of accommodating higher throughput capacities and larger instruments, having a double door design that allows direct pass-through of post-sterilized instruments to a sterile environment, all while still maintaining thermal uniformity and microbial kill efficacies within the sterilizer chamber.

The present invention attempts to remedy the shortcomings of prior art sterilizers by providing a small, countertop, high velocity hot air sterilization apparatus capable of accommodating higher capacities and larger instruments through a double door design that allows direct pass-through of post-sterilized instruments to a sterile environment while still maintaining thermal uniformity and microbial kill efficacies within the sterilizer chamber.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide an apparatus and process for sterilization of metal and temperature-resistant items, most notably surgical instruments, used in medical, dental, veterinary, or other patient-care markets. The invention relates, more particularly to an improved counter-top high velocity dry heat sterilization device that can be utilized to allow transport of post-sterilized items through a sterilizer directly into a sterile area by way of a second door opposite the entry door of the sterilizer.

The present invention comprises a countertop, high velocity, hot air sterilization device for sterilizing medical, dental, or veterinary instruments or other metal or temperature-resistant objects used in critical-care environments. The sterilization device improves upon devices known in the art by: (1) incorporating a double door configuration to allow pass-through access of post-sterilized instruments directly into a sterile instrument processing area; (2) providing an air supply heating system configured to minimize high and low temperature extremes from a heating unit that typically cause uneven and uncontrollable temperature variations in an airflow pathway; (3) providing a dual airflow pathway by which recirculated and reheated air is supplied to a sterilization chamber with uniform heat distribution and horizontal airflow velocity to meet parameter requirements of high velocity hot air sterilization within the sterilization chamber; and (4) providing a temperature sensing monitor disposed within the sterilization chamber that accounts for instrument load mass variances and controls initiation of a sterilization cycle to assure required microbial inactivation thresholds are met.

In an embodiment of the invention, the sterilization device comprises: (1) a minimized overall size allowing for countertop operation; (2) a double door configured to allow efficient pass-through of sterilized instruments, objects, and instrument cassettes directly through a sterilization chamber to a sterile instrument processing area, thereby avoiding environmental conditions which may re-contaminate sterilized articles; (3) at least one modulation control configured to regulate opening and closing of a non-sterile entry door and of a sterile exit door to prevent an open pathway between contaminated areas and sterile areas of an instrument processing facility through both doors being open at a given time; (4) a sterilization chamber configured to accommodate increased size and volume of instruments and containers required for patient care through uniform heat distribution within the chamber; (5) an air supply heating system configured to generate and deliver high velocity hot air to instruments, objects, or instrument cassettes within the sterilizer chamber; (6) an air supply system further configured deliver only high velocity and thermally uniform hot air to a sterilization chamber allowing identical sterilization parameters of time and temperature prescribed by instrument sterilization regulations; (7) at least one temperature sensor disposed within the sterilization chamber configured to monitor sterilization chamber temperature, account for instrument load weight and mass variables, and initiate pre-set sterilization cycles; and (8) a closed system wherein all sterilizer doors, air handling plenums, vents, and other potential air infiltration areas are sealed to prevent the flow of external air into the air handling system or sterilization chamber during the sterilization cycle, thereby maintaining a sterile environment within the sterilization chamber.

The present invention comprises a countertop sterilizer device having an entry door at a front end of a sterilization chamber and an exit door at a back end of a sterilization chamber. The sterilizer is further configured to allow non-sterile, contaminated instruments and instrument containers to be inserted into the sterilizer from a contaminated area of an instrument processing facility and, once sterilized, allows removal from the sterilizer chamber into a sterile area of the instrument processing facility. The countertop sterilization device may be further configured such that only an entry door or exit door may be open at any one time, to prevent an open pathway between the contaminated area and the sterile area. In some embodiments, both an entry side and an exit side of the sterilizer device have separate control panels with touch screen controls to monitor and control door operation, internal temperature status, and sterilization cycle status. The device may also be configured to repeat sterilization cycles until sterilization of a given instrument load is successful. The sterilizer may also be configured to allow removal only through the entry door and into the non-sterile area where an unsterilized load requires removal from the sterilizer. In some embodiments, the sterilizer may be installed through a common wall between a contaminated area and a sterile area with only a single electrical connection required for operation.

In another embodiment of the invention, the sterilizer may be configured to allow sterilization of medical, dental, veterinary instruments, or other objects requiring total sterility of such instruments or objects. The sterilizer may comprise a closed and sealed, recirculating air handling system and sterilization chamber which disallows influx, intrusion, or infiltration of outside contaminated air into the sterilizer or in contact with said instruments or objects.

In another embodiment of the invention, the sterilizer may have an air handling system comprising a fan wheel, an electric heater unit, dual hot air supply plenums, an air supply wall, a sterilization chamber, and an air return exhaust having a connection with the sterilization chamber and the fan wheel for air recirculation through the system. The air handling system may comprise a completely sealed and closed system, configured to eliminate the infiltration of outside air once a sterilization cycle is initiated, including sealing a motor shaft connected to the fan wheel.

In another embodiment, the air handling system brings air to a necessary velocity by means of a fan wheel. Air is then discharged to an air pathway, directed by generated air pressure and velocity into both an upper air supply plenum and a lower air supply plenum. Prior to entering the upper air supply plenum and the lower air supply plenum, the air supply is directed into contact with at least one electric heating unit located proximal and downstream of the fan wheel. The at least one electric heating element may be so positioned in order to maximize airflow contact and bring the air supply to a target temperature with minimal temperature variation. The air supply is then directed by the upper air supply plenum and the lower air supply plenum into the air supply plenum, which is configured to direct the air supply into the sterilization chamber through a perforated wall on a side opposite a wall attached to an air exhaust and the fan wheel. During air transit through the plenums and prior to entry into the sterilization chamber, the high velocity air is mixed to achieve temperature uniformity. The high velocity air enters the sterilization chamber, moving horizontally lateral across the sterilization chamber, toward and through an air exhaust portal and back into the fan wheel for recirculation.

In some embodiments of the invention, the sterilizer may comprise a mechanism for heating recirculated air to a required temperature with minimum temperature variation through a combination of a modulated heating unit system, heating unit position in an air pathway, and feedback sensor control.

In some embodiments of the invention, the sterilizer may be configured to deliver an air supply of uniform temperature and high velocity to a sterilization chamber having multiple dimensions with lateral or vertical airflow. The sterilizer may be further configured to continuously recirculate air to maintain a required air velocity and temperature for a duration of a given sterilization process.

In some embodiments of the invention, the air handling system of the sterilizer may be configured as sealed, closed, and configured to retain positive pressure relative to an outside environment in order to prevent infiltration of external, non-sterile air into the sterilizer air handling system during a sterilization cycle.

In another embodiment of the invention, the sterilizer may comprise at least one temperature sensor and at least one timer integrated with a controller configured to monitor, maintain, control, and record desired temperatures and sterilization cycle times to ensure proper sterilization conditions. The monitoring devices may further be integrated with a controller. In some embodiments, the heater unit and at least one temperature sensor may be integrated with a proportional-integral-derivative controller and configured to receive, monitor, and compare temperature input data with a preset required temperature. In another embodiment, the controller may comprise a microcontroller-based system having high-resolution analog-to-digital converters (ADC) configured to read a monitoring device input data such as temperature and further provide control of an output device such as a blower, heater, alarm, door locking mechanism, or sterilization chamber access restrictions. The controller may further be integrated with an input system, such as a suitable interface, configured to allow a user to review, monitor, and change system settings and status, and to otherwise control the sterilizer.

In another embodiment of the invention, the sterilizer further comprises an insulation cavity surrounding the sterilization chamber configured to provide temperature insulation and to retain heat in the sterilization chamber and within the air supply plenums.

In another embodiment, the sterilizer comprises a locking mechanism disposed within at least one door and configured to maintain an airtight seal during a sterilization process and to prevent access to the sterilizer chamber prior to completion of a sterilization cycle.

In another embodiment, the sterilizer may be configured to accept multiple layers of instruments, instruments that are uncovered, instruments on perforated trays, or instruments in baskets. It may also be configured to accept instruments and cassettes that are wrapped or pouched.

The methods, systems, and apparatuses are set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the methods, apparatuses, or can be learned by practice of the methods, apparatuses, and systems. The advantages of the methods, apparatuses, and systems will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the methods, apparatuses, and systems, as claimed. More details concerning these embodiments, and others, are further described in the following figures and detailed description set forth herein below.

