GB2287407A

GB2287407A - Electrically destroying medical implements

Info

Publication number: GB2287407A
Application number: GB9404387A
Authority: GB
Inventors: Camille Lefefvre
Original assignee: CLAREMONT MEDICAL EQUIPMENT LI
Current assignee: CLAREMONT MEDICAL EQUIPMENT LI
Priority date: 1994-03-07
Filing date: 1994-03-07
Publication date: 1995-09-20
Also published as: GB9404387D0

Abstract

A device for electrically destroying a medical implement, comprises electrodes (12, 15) for passing a current through the implement so as to heat and destroy it. The current through the implement is controlled by first switching means (16). The first switching means (16) is controlled by timing means (20) which is triggered by momentary operation of second switching means (13). The device allows one-handed operation thus reducing the risk of needle-stick injuries. In an embodiment, the destroying current is supplied by a lead acid battery (6). In order to avoid the battery (6) becoming excessively discharged, comparator (19) compares the battery voltage with a reference when the second switching means (13) is operated. Only if the battery voltage is above a threshold is the timing means (20) triggered. <IMAGE>

Description

A DEVICE AND METHOD FOR ELECTRICALLY DESTROYING MEDICAL IMPLEMENTS DESCRIPTION The present invention relates to a device for electrically destroying a medical implement capable of one-handed operation. The present invention also relates to a circuit for monitoring and protecting lead-acid batteries.

Many devices exist which destroy medical implements, such as syringe needles, by passing an electric current through them between two contact electrodes. The electric current causes the implement to melt and the high temperatures generated sterilise any un-melted portions. Devices have been proposed which make use of mains ac electricity and dc electricity from a battery, conventionally a lead-acid battery.

The prior art devices may be categorised into two classes according to their switching arrangements. In the first class are those that employ a latching on/off switch to place the electrodes in circuit with the power source. In the other class are those that employ a push-to-make switch.

The first class suffer from the disadvantage that they may be inadvertently left on. The electrodes would then remain live providing a potential hazzard. Although the second class does not suffer from this disadvantage, they require a user to use one hand to hold the implement to be destroyed and the other to hold closed the switch. Needles and scalpels are by their nature very sharp and consequently there is always the risk of accidental injury. Such injuries may lead to fatal infections such as AIDS.

Therefore, good practice requires that the risk of accidental injury be minimized. One way of minimizing risk is to keep the hand, not holding the implement, far away from it. This cannot be done if the free hand is needed to depress continuously a push button switch.

According to a first aspect of the present invention, there is provided a device for electrically destroying a medical implement capable of one-handed operation, comprising means for passing a destroying current through a medical implement, first switching means for controlling the destroying current, second switching means and timing means, wherein the timing means is responsive to momentary operation of the second switching means to close the first switching means for a predetermined period. The requirement for momentary operation of the second switching means means that the hand holding the implement to be destroyed may be used to energize the device. The timing means ensures that the device cannot normally be left unattended with its electrodes live.

Typically, the means for passing a destroying current through a medical implement is arranged to pass a destroying current through a syringe needle or a scalpel.

Preferably, the means for passing a destroying current through a medical implement includes a rechargeable battery for supplying a destroying current. This means that the device may be portable. Conveniently, the device would include charging means for the battery. Additionally, the device may include comparator means for comparing the battery voltage with a reference. The timing means may then be inhibited by the comparator means when the battery voltage is below the reference. The reference may be set by a zener diode and the comparator means compare a predetermined proportion of the battery voltage with the voltage across the zener diode.

Preferably, the device includes charge storage means, for example an electrolytic capacitor, arranged to be charged during said momentary operation of the second switch means, wherein the timing means is energized by charge stored in the charge storage means.

Preferably, the timing means comprises monostable means. If the monostable means is non-retriggerable, the first switching means will open after the predetermined period even if the second switch means remains closed. Thus, should the second switch means remain closed due to a fault or the accidental placement of an object thereon, the electrodes will no remain live after the end of the predetermined period.

Conveniently, the device includes a housing having an aperture for axially inserting a medical implement for destruction, wherein the aperture is located on an inclined face of the housing. Such an arrangement has been found to be particularly and surprisingly advantageous in that the result in apparatus is easier to use than prior art designs where the aperture is locate in a vertical of horizontal face. The advantages of this feature are independent of the electrical configuration of the device.

Preferably, friction means are provided for frictionally engaging a surface on which the device is supported.

Suitable friction means are elastomeric feet.

According to a second aspect of the present invention, there is provided a method of destroying a syringe needle having a plastics material stub, comprising the steps of passing a destroying current through the needle and pressing the resultant stub against anvil means while it is still hot from passage of the destroying current so as to drive any exposed needle remnant into the hub.

Preferably, the distal end of the hub is sealed with a layer of relocated hub material by the step of pressing the stub against the anvil means.

According to a third aspect of the present invention, there is provided a circuit for monitoring and protecting a leadacid battery comprising first switching means for controlling the supply of power from a battery to a main circuit, comparator means for comparing the voltage of the battery with a reference, second switching means and latch means responsive to the comparator means output to close the first switching means if the battery voltage is above a threshold, wherein momentary operation of the second switching means operates the comparator means.

Preferably, the latch means closes the first switching means for a predetermined period.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of a device embodying the present invention; Figure 2 is a diagrammatic sectional side view of the device of Figure 1; Figure 3 is a top view of the device of Figure 1; Figure 4 is a schematic diagram of the circuitry of the device of Figure 1; and Figure 5 shows a needle hub being sealed according to the present invention.

Referring to Figures 1 to 3, a needle destroyer 1 comprises a generally rectilinear box 2. The box 2 has one edge replaced by an inclined face 3. A rectangular aperture 4 is located centrally in the inclined face 3. A drawer 5 is located below the rectangular aperture 4. A lead-acid battery 6 and a circuit board 7 are located within the box 2. A board 8 is also mounted in the box 2 and located below the aperture 4 parallel to the inclined face 3. A plate 9 is located behind the aperture 4 within the box 2. At rest the plate 9 is held up to the aperture 4 by springs 10, located between the plate 9 and the board 8. The plate 9 may be made to move towards the board 8 by applying pressure on it through the aperture 4. A hole 11 is located centrally in the plate 9 and gives access to an anode 12, mounted to the plate 8. The anode 12 is formed from copper sheet and has a V-shaped notch aligned with the hole 11. A start switch 13 and indicating LEDs 14a, 14b are mounted through the top of the box 2 and electrically coupled to the circuit board 7. A cathode (see Figure 5) is mounted to the board 8. The box 2 is provided with four anti-slip feet 2a, formed from elastomeric material.

Referring to Figure 4, the operating circuitry of the device 1 includes the battery 6, the anode 12 and a cathode 15.

The anode 12 is connected to the positive terminal of the battery. The cathode 15 is coupled to the collectors of a plurality of parallel-connected npn transistors 16 (only one shown for clarity). The emitter of the transistor 16 is connected to the negative terminal of the battery 6.

A voltage and current regulator 17 is connected to receive external power and supply it to the battery 6 for charging thereof.

A push-to-make switch is connected between the positive terminal of the battery 6 and a comparator circuit 19. The output of the comparator circuit 19 is coupled to the trigger input of a non-retriggerable monostable circuit 20.

The Q output of the monostable circuit is applied to the base of the transistor 16.

A red LED 14a is coupled between a subsidiary output of the comparator circuit 19 and the output side of the switch 13.

The positive terminal of a large value, e.g. 4400;iF, electrolytic capacitor 22 is coupled to the output side of the switch 13 via a diode 23. The negative terminal of the capacitor 22 is connected to the negative terminal of the battery 6.

A green LED 14b, in series with a current limiting resistor (not shown), is connected between the positive terminal of the capacitor 22 and the NOT Q output of the monostable 20.

The operation of the device shown in the Figures will now be described.

Assuming that the battery 6 is in an acceptably charged state, the user operated the switch 13 to start the device.

When the switch 13 closes, the capacitor 22 charges quickly through the diode 23 to the voltage of the battery 6, this causes the green LED 24 to be illuminated, indicating that the device is operational. The comparator circuit 19 compares a predetermined proportion of the voltage of the battery 6 with an internally generated reference during the period when the switch 13 is closed. The reference may be generated using a zener diode and the predetermined proportion of the battery voltage may be obtained by means of a potential divider. In the present case, the predetermined proportion of the battery voltage is greater than the reference voltage and the comparator circuit 19 outputs a triggering signal to the monostable 20. Having been triggered, the monostable 20 outputs a signal turning on the transistor 16 for a period set by the monostable's time constant. As a result the cathode 16 is connected to the negative terminal of the battery 6.

A user then inserts the needle of a syringe through the hole 11 so that the distal end of the needle contacts the cathode on the board 8 and a proximal region of the needle contacts the apex of the notch on the anode 12. The needle thus connects the anode 12 to the cathode 15 and current begins to flow. The flow of current through the needle is sufficient to cause it to melt. Melting occurs preferentially at the distal end of the needle. Therefore, in order to maintain a current path between the anode 12 and the cathode 15, the user must apply an axial force to the syringe. This force acts to compress the springs 10, and the plate 9 and the board 8 move together as the needle becomes shorter thereby enabling substantially all of the needle to be melted.

At the end of the period set by the monostable 20, typically 10 seconds, the transistor 16 is switched off, isolating the cathode 15. As the NOT Q output of the monostable changes state, the green LED 24 is extinguished.

As the operation of the switch 13 is momentary, the monostable 20 is isolated from the battery 6 during needle destruction. However, the capacitance of the capacitor 22 is sufficient to store enough charge to operate the monostable 20 for the necessary period.

It will be apparent from the foregoing that when the battery voltage is low, indicating a state of low charge, the comparator circuit 20 does not output a triggering signal in response to operation of the switch 13. Instead, it causes the red LED 14a to light an indicate that the battery 6 requires recharging. This protects the battery 6 from the damage that can occur from its being completely discharged.

The user can recharge the battery by applying a source of dc power to the regulator circuit 17. Suitable source of power are the battery of a vehicle or a mains supply in combination with a step-down transformer and a rectifier.

It has been found that a small length of the needle at its proximal end is not destroyed by the destroying current.

This is undesirable. Referring to Figure 5, the hole 11 and the notch in the anode 12 are made large enough for the needle hub 25, attached to a syringe 27 to pass therethrough. Consequently, immediately after the needle has been substantially destroyed by the current flow through it, the user may press the needle stub 28 and the hub 25 against the cathode 26 which acts on an anvil. Whilst the plastic hub 25 remains hot, the needle stub 28 may be easily driven into the hub 25. The hub 25 is then deformed by the users continued pressure so that the needle passageway is sealed with the material of the hub itself.

Two bars 29 of insulating material, such as PTFE, are affixed across the upper face of cathode 26 so that, when the springs 10 are fully compressed, the anode 12 and cathode 26 do not come into direct contact.

During destruction, the needle reaches a temperature in the region 13000 C and the hub 25 is heated to approximately 3000 C. Thus, it can be seen that both the needle and the hub 25 are reliably sterilized.

It will be apparent that many inconsequential modifications may be made to the described embodiment. For instance, the transistor 16 may be of a pnp type or connected in an emitter follower configuration. Also, the bipolar device may be replaced by a FET of some sort. The capacitor 22 could be replaced by a small rechargeable battery, such as a nickel-cadmium battery.

Claims

1. A device for electrically destroying a medical implement capable of one-handed operation, comprising means for passing a destroying current through a medical implement, first switching means for controlling the destroying current, second switching means and timing means, wherein the timing means is responsive to momentary operation of the second switching means to close the first switching means for a predetermined period.

2. A device according to claim 1, wherein the means for passing a destroying current through a medical implement is arranged to pass a destroying current through a syringe needle.

3. A device according to claim 1, wherein the means for passing a destroying current through a medical implement is arranged to pass a destroying current through a scalpel.

4. A device according to claim 1, 2 or 3, wherein the means for passing a destroying current through a medical implement includes a rechargeable battery for supplying a destroying current.

5. A device according to claim 4, including comparator means for comparing the battery voltage with a reference, wherein the timing means is inhibited by the comparator means when the battery voltage is below the reference.

6. A device according to claim 5, wherein the reference is set by a zener diode and the comparator means compares a predetermined proportion of the battery voltage with the voltage across the zener diode.

7. A device according to any preceding claim, including charge storage means arranged to be charged during said momentary operation of the second switch means, wherein the timing means is energized by charge stored in the charge storage means.

8. A device according to claim 8, wherein the charge storage means comprises an electrolytic capacitor.

9. A device according to any preceding claim wherein the timing means comprises monostable means.

10. A device according to claim 9, wherein the monostable means is non-retriggerable.

11. A device according to any preceding claim, including a housing having an aperture for axially inserting a medical implement for destruction, wherein the aperture is located on an inclined face of the housing.

12. A device according to any preceding claim, including friction means for frictionally engaging a surface on which the device is supported.

13. A method of destroying a syringe needle having a plastics material stub, comprising the steps of passing a destroying current through the needle and pressing the resultant stub against anvil means while it is still hot from passage of the destroying current so as to drive any exposed needle remnant into the hub.

14. A method according to claim 13, wherein the distal end of the hub is sealed with a layer of relocated hub material by the step of pressing the stub against the anvil means.

15. A circuit for monitoring and protecting a lead-acid battery comprising first switching means for controlling the supply of power from a battery to a main circuit, comparator means for comparing the voltage of the battery with a reference, second switching means and latch means responsive to the comparator means output to close the first switching means if the battery voltage is above a threshold, wherein momentary operation of the second switching means operates the comparator means.

16. A circuit according to claim 15, wherein the latch means closes the first switching means for a predetermined period.

17. A device for electrically destroying a medical implement, including a housing having an aperture for axially inserting a medical implement for destruction, wherein the aperture is located on an inclined face of the housing.

18. A device for electrically destroying a medical implement, including a rechargeable battery for supplying a destroying current and a recharging circuit, wherein the recharging circuit is arranged to charge the battery from an external nominal 12V or 24V d.c. source.

19. A device substantially as hereinbefore described with reference to the accompanying drawings.

20. A method substantially as hereinbefore described.