05/209867

01/29/1974

12/20/1971

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73/19.120

436/1, 340/632

G01N27/16; G01N27/14; G01H7/00; G08B21/00

23/232E,254E,255E 73/19,23 340/237

2083521	Analysis of fluid mixtures	June 1937	Miller
3640688	CARBON MONOXIDE MEASURING METHOD AND DEVICE	February 1972	Walther
3537296	SAMPLE HANDLING SYSTEM FOR AUTO EXHAUST ANALYZER	November 1970	Gamache
3471261	METHOD AND MEANS OF OVERCOMING UNDESIRABLE ELECTRICAL FORCES IN A CHROMATOGRAPHIC PROCESS	October 1969	Patterson

Goldstein, Herbert

Driscoll, David M.

What is claimed is

1. Apparatus for lowering the concentration of ethylene oxide residue remaining in a previously sterilized item and for determining when a safe low level of ethylene oxide is present, said apparatus comprising;

2. The apparatus of claim 1 wherein said electrical means includes meter means for indicating concentrations of ethylene oxide.

3. The apparatus of claim 2 wherein said electrical means includes visual means for indicating a safe low level of concentration of ethylene oxide.

4. The apparatus of claim 2 including means for venting the eluted ethylene oxide from the apparatus so that said meter means has a gradually decreasing concentration indication.

5. The apparatus of claim 1 including a first screen means for supporting said one or more items above said funnel-shaped bottom member, and a second screen disposed near the top of the chamber and defining in part the intake plenum chamber.

6. The apparatus of claim 5 wherein both said screen means include perforated metal plates and said first screen means has a larger perforated area than the second screen means.

7. The apparatus of claim 1 comprising means for changing the predetermined level to a different level in the concentration range of 0 to 1,000 parts per millon.

8. The apparatus of claim 7 wherein said predetermined level is on the order of 500 parts per million.

9. The apparatus of claim 1 wherein said means for indicating includes a bistable device assuming a first state indicating a safe level at concentrations below the predetermined level and a second state indicating an unsafe level at concentrations above the predetermined level.

10. The apparatus of claim 1 wherein said chamber is relatively large in comparison to said input and output ports so as to provide relatively rapid aeration of the item.

11. A method of lowering the concentration of ethylene oxide residue remaining in an item which has been sterilized with ethylene oxide and for determining when a safe low level of ethylene oxide is present, said method comprising,

FIELD OF THE INVENTION

The present invention relates in general to a method and associated apparatus for detecting the residual concentration of a sterilizing gas being eluted from an item previously sterilized. More particularly, the present invention is concerned with a method and associated apparatus for detecting a safe low residual concentration of a sterilizing gas such as ethylene oxide, and automatically indicating when the safe low residual level of concentration has been attained.

BACKGROUND OF THE INVENTION

Sterilizing gases and particularly ethylene oxide have been used heretofore for sterilizing surgical instruments and other medical items. Because ethylene oxide may at some concentrations be harmful to the skin and soft tissue, the sterilized item is aerated to remove the gas residue from the article. The aeration of the item to elute the gas therefrom may be accomplished by simply storing the item for an extended period of time, or the aeration may be accelerated by forcing heated air over the item or by applying a vacuum at elevated temperatures of 50°C to 60°C.

The various types of instruments and items being sterilized tend to exhibit different affinities for ethylene oxide, and thus their rate of elution differs depending at least in part upon the permeability/porosity of the particular instrument. Therefore, the total elapsed time for aerating the item to a safe condition for use can vary widely depending also on the particular method of elution that is employed. Manufacturers of sterilizers and aerators have thus published somewhat arbitrary tables indicating nominal aeration times for common instruments or items. Many hospitals, more acutely aware of the inflammatory and toxic effects of ethylene oxide on human tissue, have added a safety factor and thus replaced the manufacturer's listings with their own longer aeration schedules. Thus, in some instances the items are aerated for unnecessarily long times, thereby requiring an unnecessary large inventory of items.

Another problem associated with the use of timetables relates to the identification of the particular item being sterilized. It is difficult sometimes to correctly idenfity the item which has been sterilized, relate the item to the relevant timetable, and accurately determine the length of time the item should be aerated. Thus, there is a definite need for an apparatus that will sample the eluted sterilizing gas and register continuously or periodically the concentration thereof.

One known technique for determining the concentration of ethylene oxide residue remaining in an item is with the use of a gas chromatography device. The problem with this technique is that the equipment that is used is quite costly and requires manipulation by a highly skilled operator in a laboratory environment. In another technique laboratory scales can be used to measure the weight of the item prior to sterilization and also after elution of the sterilizing gas. This technique is also primarily for laboratory use and is not readily usable by an unskilled operator. Also, neither of these devices can be embodied in an aerator but would have to be used separately. Moreover, these devices are time consuming to operate and are impractical for extensive use in the medical field.

OBJECTS OF THE INVENTION

Accordingly, one important object of the present invention is to provide a method and associated apparatus for detecting a safe low residual concentration of a sterilizing gas such as ethylene oxide being eluted from an item previously sterilized by the gas. The amount being eluted per unit of time is directly proportional to the residue retained by the item being aerated.

Another object of the present invention is to provide an apparatus in accordance with the preceding object that is portable, easily operable by a relatively unskilled person, and can be integrally formed as part of the aerator in a single unit.

A further object of the present invention is to provide an apparatus in accordance with the preceding objects including means for continuously or periodically registering the concentration of the eluted gas, and indicating either a safe or unsafe condition.

Still another object of the present invention is to provide an apparatus for detecting a safe low residual concentration of a sterilizing gas such as ethylene oxide including a set point control which is adjustable to change the desired safe/unsafe concentration level.

Another object of the present invention is to provide an apparatus for detecting a low concentration level of a sterilizing gas such as ethylene oxide wherein the apparatus is portable and may readily be designed to interface with presently existing aerators.

Still a further object of the present invention is to provide an apparatus for detecting a safe low concentration level of ethylene oxide in a closed environment.

SUMMARY OF THE INVENTION

To accomplish the foregoing and other objects of the invention the apparatus continuously or periodically monitors the concentration level of the eluted sterilizing gas. The apparatus generally includes a chamber for containing the items or instruments, means coupled to the chamber for eluting the sterilizing gas from the items or instruments, means for sampling the eluted sterilizing gas, and means coupled to the means for sampling for registering the concentration of the gas. The latter means may include a bridge circuit and means for indicating a safe level of concentration when it decreases to or below a predetermined concentration level. The means for indicating may comprise indicator lights or possibly a chart recorder observed by the operator of the apparatus.

In accordance with one feature of the present invention there is also included a means for changing the predetermined level of concentration. For example, it is generally agreed in the medical profession that a concentration of 500 ppm of ethylene oxide is a safe predetermined level. However, for those that disagree with this determination other levels can be used as safe levels such as 300 ppm.

BRIEF DESCRIPTION OF THE DRAWINGS

Numerous other objects, features and advantages of the invention will now become apparent upon a reading of the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of one embodiment of the apparatus of the present invention employing a vacuum technique for eluting the sterilizing gas from an item previously sterilized;

FIG. 2 is a block diagram of another embodiment of the apparatus of the present invention employing a forced air technique;

FIG. 3 shows a control console associated with the apparatus of the present invention;

FIG. 4 is a timing diagram associated with the block diagram of FIG. 1;

FIG. 5 is a primarily circuit diagram showing, inter alia, the alarm control electronics of FIGS. 1 and 2;

FIG. 6 is a cross sectional view of an aerator constructed in accordance with the principles of the invention and associated with the block diagram of FIG. 1; and

FIG. 7 is a cross sectional view of another aerator constructed in accordance with the principles of the present invention and associated with the block diagram of FIG. 2.

DETAILED DESCRIPTION

In this description like reference numerals are used to designate like parts of the apparatus or system.

Referring now to the drawings and in particular to FIG. 1 there is shown a block diagram of one embodiment of the apparatus of the present invention employing a vacuum technique for eluting the sterilizing gas from the item or instrument. This apparatus generally comprises a power supply 10, a regulator 12, alarm control electronics 16, a concentration sensor 20, meter 24, and timer 26. The cross sectional view of the aerator shown in FIG. 6 is discussed hereinafter in conjunction with the block diagram of FIG. 1.

The power supply 10 may be a conventional design including a conventional rectifier circuit and has an input coupled from a typical 110 volt AC line. The output of power supply 10 which may be a 12 volt DC level couples to regulator 12 which may also be of conventional design. The output of regulator 12 couples to alarm control electronics 16 and provides a regulated voltage for the bridge circuit of control electronics 16. The control electronics 16 have outputs that couple to lamps on the control console (see FIG. 3). Meter 24 and chart recorder 28 both of which may be of conventional design, are controlled from electronics 16. Meter 24 may be a precision microammeter.

The concentration sensor 20 shown in FIG. 1 includes a sample input line and a sample output line (see also FIGS. 6 and 7). The sensor 20 also has an electrical connection to alarm control electronics 16 for registering an indication therein of the concentration sensed by sensor 20. This concentration is indicated on either meter 24 or a continuous recording of it may be registered on chart recorder 28.

The power supply, regulator, control electronics and concentration sensor of FIG. 2 may be identical to the same items shown in FIG. 1. The primarily circuit diagram of FIG. 5 is discussed in more detail hereinafter with reference to FIGS. 1 and 2.

In FIG. 1 the timer 26 may be a commercially available timer that is operated from the AC input line. The timer 26 has a start input 27 and a reset input 29 which may physically be two switches forming part of the timer. In the embodiment of FIG. 1 one output of timer 26 couples via line 30A to vacuum pump 30 and by way of line 30B to solenoid 32, heater 34 and AND circuit 36. AND circuit 36 also includes a connection from sail switch 40. The operation of the timing portion of the apparatus of FIG. 1 is discussed hereinafter in more detail with reference to FIGS. 4 and 6.

In FIG. 2 the timer 26 similarly has an input coupled from the AC power line, and has a start input 27 also associated therewith. The output of timer 26 couples to fan 42, heater 44 and AND circuit 46. A sail switch 48 also couples to a second input of AND circuit 46. The operation of the timing portion of FIG. 2 is discussed in more detail hereinafter with reference to the cross sectional view of FIG. 7.

Referring now to FIG. 3 there is shown a view of one embodiment of a control console. The console includes the meter 24 which may be of conventional design and in the embodiment shown has a scale of 0 - 1,000 ppm (parts per million). The SAFE/UNSAFE level is shown at 500 ppm but may be varied as discussed in more detail hereinafter. The console includes a SAFE indicator 50 and an UNSAFE indicator 52. Indicator 50 is illuminated when the meter is in the range between 0 and 500 ppm. Alternatively, the indicator 52 is illuminated in the range from 500 to 1,000 ppm.

The console of FIG. 3 also shows a chart recorder 28 which is of conventional design and a time display 26A associated with timer 26. This display indicates the time remaining in a predetermined aeration cycle. The console also includes a start button 27 and a reset button 29 coupled to timer 26 along with a power button 11 which may be coupled to the input of power supply 10 as indicated in FIG. 5. For the vacuum technique the console will include a vacuum gage 54. For both the vacuum and forced air techniques the console will include a temperature gage 56. In the central bottom portion of the console there are located three indicator lamps, vacuum lamp 57, filter lamp 58, and heater lamp 59. The vacuum lamp couples to the vacuum switch 83A (see FIG. 6) and is illuminated during the period that the vacuum is above a predetermined value as determined by switch 83A. If one desires to open the chamber containing the items being aerated, the operator notes that the vacuum pump is operative and presses the reset button 29 to stop the pump and thereby allow the chamber to be safely opened but only after the vacuum gage indicates no remaining vacuum pressure. The filter lamp 58 is preferably illuminated when the filter is clogged and is otherwise extinguished. The operation of lamp 58 is discussed in more detail hereafter with reference to the operation of the apparatus of the present invention. The heater lamp 59 couples to either heater 34 or 44 depending upon the aeration technique used and is preferably illuminated during the period that the heater is on.

There are two adjusting screws shown in FIG. 3 as alarm adjust 61 and null adjust 63. The alarm adjust is used to change the SAFE/UNSAFE level from, for example, 500 ppm to 300 ppm. Its exact operation is discussed with reference to FIG. 5. The null adjust zeroes the meter 24 initially when no ethylene oxide is being detected.

The alarm control electronics 16 depicted in FIGS. 1 and 2 is shown in more detail in a preferred embodiment in FIG. 5. FIG. 5 shows the power supply 10, regulator 12, meter 24 and concentration sensor 20. The input to power supply 10 couples by way of ON-OFF power switch 11 from a typical 110 volt AC line. There is a low voltage AC signal taken from power supply 10, of preferably 12 volts AC, and this voltage is coupled to the SAFE, UNSAFE and POWER lamps of FIG. 5. The power supply 10 also provides a DC output designated as B+ and B- which couple to regulator 12. The regulator 12 may be of conventional design and is adapted to maintain its output voltage at a relatively constant value regardless of temperature fluctations, variations in line voltage and/or change of input loads.

The output of regulator 12 couples to bridge circuit 60 and also to meter 24 and its associated circuitry. The bridge circuit 60 is of a Wheatstone bridge configuration and includes two branches; one contains resistors R1 and R2 and potentiometer P1, and the other contains sensor 20 which includes sensor elements 20A and 20B. The potentiometer P1 adjusts the null position or zero position of the bridge (see null adjust 63 of FIG. 3) when the sensors 20 are subjected to essentially no concentration of ethylene oxide. The movable contact of potentiometer P1 and the junction between elements 20A and 20B couple to two separate inputs of differential amplifier 62 which may be of conventional design. Initially, when potentiometer P1 is adjusted the voltages on both inputs to amplifier 62 are identical and there is essentially no output voltage signal at the output to the amplifier.

The concentration sensor 20 may be of the type disclosed in U.S. Pat. No. 3,237,181 and includes an active sensor element 20A and a compensating or reference sensor 20B. This prior art patent teaches that each of the sensor elements may be constructed of a metal wire such as platinum enclosed in a porous tube through which the gas seeps. Only one of the elements, namely element 20A in FIG. 5, is coated with finely divided platinum particles so that in the presence of ethylene oxide combustion of the gas takes place, the wire heats, and the resistivity of the element 20A changes. Because element 20B is not treated its resistance should not change relative to change in the concentration of the ethylene oxide. The placement of the concentration sensor 20 is discussed in more detail hereinafter with reference to FIGS. 6 and 7.

When the sensor 20 is subjected to a concentration of ethylene oxide the amplifier 62 registers an output voltage which is proportional to the concentration. The output of amplifier 62 couples to meter 24 which also registers a visible concentration indication, such as the one shown in FIG. 3. The output of differential amplifier 62 also couples to difference circuit 66 which includes transistors Q1 and Q2 that connect in a common current switching pair configuration. When a very low or essentially no concentration of ethylene oxide is being detected the output of amplifier 62 is at its low level and transistor Q1 is biased into conduction. The majority of the current flowing in resistor R3, therefore, flows through transistor Q1 instead of through transistor Q2. The capacitors C1 and C2 which couple to the bases of transistors Q1 and Q2, respectively, along with associated resistors provide low pass filtering. When the output of amplifier 62 goes sufficiently positive, transistor Q1 tends to stop conducting and the majority of the current flowing in resistor R3 is then diverted to transistor Q2. When this occurs the voltage across the collector resistor R4 associated with transistor Q2 increases and this signal is fed to output amplifier circuitry 70.

The circuitry of FIG. 5 also includes threshold adjusting means 68 which comprises resistor R5 and potentiometer P2. The setting of potentiometer P2 determines the concentration at which an alarm condition will be generated. This setting is made by the alarm adjust screw 63 of FIG. 3. By varying the value of potentiometer P2 the bias normally at the base of transistor Q2 is changed so that the changeover of conduction from transistor Q1 to transistor Q2 occurs at a different voltage output of amplifier 62. The output of potentiometer P2 also couples to output amplifier circuitry 70 for controlling its amplification or gain.

The output amplifier circuitry generally includes transistors Q3, Q4 and Q5 and relay K1. As previously indicated when the output of amplifier 62 reaches a certain positive level transistor Q1 turns off, transistor Q2 turns on and the voltage across resistor R1 increases positively. This action causes transistor Q3 to conduct which in turn supplies a base current to transistor Q4 causing it also to go into conduction. The output of transistor Q4 taken at its collector electrode couples by way of resistor R6 to the base of transistor Q5. When transistor Q4 goes into conduction the base of transistor Q5 goes negative with respect to its emitter and transistor Q5 is also driven into conduction. Relay coil K1 is then energized.

The relay coil K1 has a contact 72 associated therewith which includes a movable pole 72A and two fixed poles 72B and 72C. When relay K1 is de-energized, as depicted in FIG. 5, the AC power provided to movable pole 72A is coupled to pole 72B and in turn to the SAFE lamp 50 for illuminating it. When an unsafe level of concentration is reached, as previously indicated, transistor Q5 goes into conduction causing relay K1 to latch. This then causes the AC power at pole 72A to be coupled to pole 72C and in turn to the UNSAFE lamp 52 causing it to illuminate. The SAFE and UNSAFE lamps are also shown in FIG. 3 on the console. A power lamp 11A is coupled across the 12 volt AC line and is illuminated when power button 11 is closed to apply AC power to supply 10.

Referring now to FIGS. 6 and 7 there are shown two different embodiments for the aerator of the present invention. The cross-sectional diagram of FIG. 6 is for use with a vacuum aeration technique whereas the diagram of FIG. 7 employs heated forced air technique. In both FIGS. 6 and 7 the aerator generally comprises sidewalls 75 and 76, the bottom ends of which are used as legs for the aerator. A backwall and front door (not shown) would also obviously be provided. The aerator also includes a top wall 77 and an internal vertical wall 78 which partially defines the chamber 80. Chamber 80 contains the instruments or items I previously sterilized by ethylene oxide and now ready for the elution of the ethylene oxide.

One of the features of the present invention is the incorporation of a top plenum chamber 81 defined in part by walls 75, 76 and 77 and also by wire screen 82 which is suspended by suitable means from the top wall 77. It is noted that the screen 82 only extends intermediate walls 75 and 78 and that a plate portion 82A extends from wall 78 out to external wall 76. This top intake plenum ensures that articles loaded into the chamber, to be aerated, will not impede the main flow of air.

The bottom of chamber 80 is defined by a funnel-shaped bottom member 83 having an exit opening 84 at the bottom thereof. A second wire screen 85 is disposed horizontally at the top of the funnel-shaped member 83 and is used to retain the instruments or items being aerated. This downwardly extending funnel-shaped portion of the chamber tends to ensure that all of the eluted gas which is generally heavier than air is readily displaced through the sensor, and will prevent pockets of ethylene oxide from forming thus providing a more accurate measurement of the ethylene oxide residue.

Screen 82 is preferably designed with relatively small apertures so that the flow into chamber 80 is relatively uniform. Alternatively, screen 85 has larger apertures so that the flow of the eluted gas is not impeded. Screen 82 may be a perforated plate while screen 85 may be a thin wired mesh durable enough to hold instruments.

Referring now to the vacuum technique of the present invention and in particular to FIGS. 1, 4 and 6, the exit opening 84 couples by way of a conduit section 85 to vacuum pump 30. The output of vacuum pump 30 couples via conduit section 86 to an output vent which may in turn connect to an absorption unit. The conduit section 86 has a pair of lines 87A and 87B, referred to as the sample input and sample output lines, that connect to concentration sensor 20 which is also depicted in FIGS. 1 and 5. The output of sensor 20 shown in FIG. 6 couples to the alarm control electronics 16 for registering an indication of the concentration of ethylene oxide being eluted by way of vacuum pump 30. The structure of FIG. 6 also shows a bacteriological intake filter 88 which couples by way of conduit section 89 and solenoid 32 to intake plenum 81. The conduit section 89 also has a sail switch 90 disposed therein which is responsive to air passing through section 89. In the embodiment of FIG. 6 there is also included a heater 34 (see FIG. 1) for heating the chamber 80 during the vacuum oepration.

The instruments or items to be aerated are disposed in chamber 80 and initially the solenoid 32 is in a closed position (see FIG. 4). During that time period the vacuum pump 30 is on evacuating the air from the chamber 80 to approximately 15 to 20 inches of mercury. Upon reaching the desired level of vacuum the vacuum pump 30 which is controlled from line 30A (see FIGS. 1 and 4) is turned off. As depicted in FIG. 4, the solenoid is opened only after the vacuum has been turned off so that a vacuum is not being attempted to be maintained after the solenoid is opened. As soon as the pump turns off the chamber will remain as a sealed unit and maintain the evacuated atmosphere. When the solenoid is opened fresh air is drawn in through the bacteriological filter 88 and the ethylene oxide is evacuated. As the ethylene oxide is exhausted the restriction 92 in coupling section 86 causes a predetermined amount of the residue (such as 1 or 2 litres per minute) to be coupled by line 87A to sensor 20 which registers an indication of the concentration level being eluted from the instruments in chamber 80.

The diagram of FIG. 4 shows a time sequence for operation of the solenoid 32 and the vacuum pump 30. The heaters 34 and AND circuit 36 may also be operated from line 30B. In FIG. 4 it is noted that the opening of the solenoid and the turning off of the vacuum pump can occur at a cyclical rate which is determined by the particular instruments being aerated. After a predetermined number of such cycles sensor 20 should indicate a concentration that is successively decreasing and when the safe concentration level is reached the meter 24 indicates such or, an audible alarm may be sounded indicating that the instruments are sufficiently aerated and now ready for use.

With the arrangement shown in FIG. 1 the heater 34 is operated during the time that the solenoid is closed. In an alternate embodiment the heater may be operated in conjunction with power switch 11 so that the heaters are cycled on and off by means of a conventional thermostat arrangement. The AND circuit 36 is enabled only during the time the solenoid is opened. Thus, if the filter 88 is properly filtering the sail switch should be in its appropriate position during the opening of the solenoid 32 and the output of AND circuit 36 will indicate that there is no need to change the filter. However, when the sail switch 40 does not respond during the time that the solenoid 32 is open the output of the AND circuit 36 couples to filter lamp 58 (see FIG. 3) indicating that the filter 88 should be changed as it is clogged or possibly the solenoid 32 is not operating.

The apparatus of FIG. 6 also schematically illustrates the vacuum gage 54 and heater gage 56 both of which functionally couple to chamber 80. A vacuum switch 83A may also be provided in member 83 of the aerator, and couples to lamp 57 for indicating when the vacuum exceeds a set value. The apparatus may also have a thermostat 83B disposed in wall 83 and coupled to lamp 59.

Referring now to the heated forced air technique of the present invention and in particular to the aerator shown in FIG. 7, this aerator has a structure similar to the one in FIG. 6 but includes a fan 42 suitably mounted in plenum chamber 81 instead of vacuum pump 30. The fan 42 is positioned to draw in fresh air via filter 88, which air passes by sail switch 48, over heaters 44 and through panel 82 to chamber 80 which contains the instruments or items I to be aerated.

The exit opening 84 couples via conduit section 85 and restriction 92 to an output vent. On either side of the restriction there are a pair of lines referred to as the sample input line 87A and sample outlet line 87B. As with the embodiment of FIG. 6, the restriction of FIG. 7 is dimensioned so that about 1 to 2 litres per minute of the ethylene oxide residue pass to sensor 20.

In the embodiment of FIG. 7 and associated diagram of FIG. 2 the fan 42 is continuously aerated when power is turned on for a predetermined period as determined by timer 26. In an alternate embodiment the fan 42 may be continuously operated as long as power is on. In either case the air stream passing via switch 48, is heated by thermostatically controlled heaters 44 and passes to chamber 80. The wire panels 82 and 85 of FIG. 7 may be identical to those shown in FIG. 6 and are provided for the same purpose as previously discussed. The air passes over the instruments and the air contaminated with the ethylene oxide passes via conduit sections 85 and 87A to sensor 20, which continuously registers a concentration level of the ethylene oxide.

The sail switch 48 connects to AND circuit 46 which may or may not be needed depending upon the exact operation of timer 26. In the embodiment shown, the AND circuit is enabled when the timer is operating and, if the sail switch does not operate because the filter is clogged, the AND circuit causes the filter lamp 58 to illuminate.

The apparatus of the present invention is also adapted for use with sterilizing gases of the type containing a percentage of ethylene oxide, such as ethylene oxide 88/12 which contains 88 percent freon and 12 percent ethylene oxide. Also, the apparatus of the present invention is readily adaptable to existing aerators and would include an input valve for selectively or continuously sampling the eluted gas.