GB2547012A

GB2547012A - Pump assembly suitable for use in aspirators

Info

Publication number: GB2547012A
Application number: GB1602018.2A
Authority: GB
Inventors: Gallagher George
Original assignee: Aspirate N Go Ltd
Current assignee: Aspirate N Go Ltd
Priority date: 2016-02-04
Filing date: 2016-02-04
Publication date: 2017-08-09
Anticipated expiration: 2036-02-04
Also published as: GB201602018D0; GB2547012B; WO2017134462A1

Abstract

A pump assembly 12 for use as part of a pumped aspirator 10, the pump assembly 12 comprising a vacuum pump 38 and a chamber 30, the chamber 30 comprising an inlet 26 connectable to an aspirator tube 14 and an outlet 34 connectable to the pump 38. The chamber 30 further comprises a hollow interior volume containing a porous or perforated element 32 separating the inlet 26 from the outlet 34; the porous or perforated element 32, when dry, permitting the passage of gas from the inlet 26 to the outlet 34, but when wetted by a liquid, inhibiting the passage of fluids from the inlet 26 to the outlet 34. The pump 38 is further preferably driven by a motor 40 connected to a power supply 44 via a switch gear of a control circuit 42, and wherein the switch gear is adapted to switch off the motor 38 when the air pressure downstream of the outlet 34 drops below a threshold value; indicative of the porous or perforated element 32 inhibiting the passage of fluids from the inlet 25 to the outlet 34.

Description

Title: Pump assembly suitable for use in aspirators Description:

This invention relates to pump assemblies, and in in particular to pump assemblies suitable for use in aspirators. Specifically, pumped aspirators of the type described herein may be suitable for aspirating (drawing) fluids from within a body cavity of a human or animal patient.

Aspirators are used in a range of medical procedures where fluids need to be drawn from within a body cavity, e.g. for diagnostic, sampling and/or therapeutic purposes.

Where only relatively small amounts of fluids need to be aspirated, it is commonplace for a practitioner to use a syringe-based aspirator. In such a situation, the syringe is emptied (i.e. its plunger depressed) before being connected to the end of an aspirator tube. Prior to this, of course, the aspirator tube will have been inserted into the patient, such that its tip is submerged in the liquid to be aspirated. It should then be a relatively straightforward task to connect the syringe to the free end of the aspirator tube to aspirate the liquid by drawing on they syringe's plunger, to create a vacuum within the aspirator tube, thereby aspirating the liquid/fluid.

The use of syringes to aspirate fluid from a patient is generally indicated because syringes are relatively inexpensive. However, using syringes, in practice, can sometimes be problematic for a number of reasons. Specifically, when attempting to aspirate relatively viscous or sticky fluids; or when aspirating through a long aspirator tube, an oversized syringe is often needed to achieve the necessary vacuum (i.e. to overcome hydrodynamic drag and friction/adhesion ("stiction"); and to remove the air in the tube). Larger syringes tend to be in shorter supply in medical settings than smaller syringes, and they are, in any event, usually more expensive than smaller syringes to buy. An alternative solution is to use a smaller bore aspirator tube, but narrower tubes tend to be more susceptible to clogging and pinching-off, as well as increasing the hydrodynamic drag coefficient of a viscous aspirated liquid.

It is known to use, instead of a syringe, a vacuum pump in conjunction with an aspirator tube to overcome one or more of the above problems. The advantage of using a pump, as opposed to a syringe, is that pumps can sometimes generate a higher vacuum, and also a continuous vacuum, as well as not burdening the user with the somewhat laborious task of manually "pumping" a syringe.

Pumped aspirators generally comprise a vacuum pump connected to a tube that can be inserted, or fed, into a body cavity, such that when the pump is switched on, the vacuum from the pump draws fluid from the body cavity through the tube, provided, of course, that the free end/tip of the tube is located within the fluid to be aspirated. In a pumped aspirator, a liquid trap is usually interposed between the tube and vacuum pump itself to prevent aspirated liquids from being drawn into the pump. When using a vacuum pumped aspirator, care needs to be taken to ensure that the vacuum is not too high and that the quantity and rate of aspiration is monitored. Monitoring and control circuitry can often be used to facilitate this, as well as the manual interventions of an experienced operator. A drawback of known pumped aspirators (i.e. incorporating monitoring and control circuitry) is complexity: the monitoring and control circuitry often needing to comprise moisture sensors for detecting the presence of otherwise of aspirated liquid at different locations, differential pressure sensors and motor speed controllers to monitor and adjust the settings of the pump, and switch gear to switch off the pump once a detected quantity of fluid has been aspirated. A further drawback of known pumped aspirators is the liquid trap, which often becomes contaminated in use, and the possibility of accidentally drawing aspirated liquid into the pump, which can lead to contamination and/or cross-infection issues. A need therefore exists for an improved and/or alternative type of pumped aspirator.

Various aspects of the invention are set forth in the appended claims.

According to a first aspect of the invention there is provided a pump assembly, suitable for use as part of a pumped aspirator, the pump assembly comprising: a chamber comprising an inlet connectable, in use, to an aspirator tube and an outlet connectable, in use, to a vacuum pump, the chamber comprising a hollow interior volume containing a porous or perforated element separating the inlet from the outlet, the porous or perforated element, when dry, permitting the passage of gas from the inlet to the outlet, but when wetted by a liquid, inhibiting or preventing the passage of fluids from the inlet to the outlet.

The chamber comprises an inlet that is connectable, in use, to an aspirator tube and an outlet that is connectable, in use, to the vacuum pump. This permits the chamber to be a single-use, replaceable and/or a consumable item, which is necessary, of course, where the porous or perforated element becomes wetted, in use, by the aspirated liquid.

Suitably, the inlet and outlet comprise connectors for releasably connecting items thereto, such as "Luer-lock" connectors, bayonet-type fittings, screw threads, push fit connectors, being either male or female. Preferably, the inlet comprises a connector for connecting the inlet to the connector of the enteral or NG tube, such as a female Luer-lock connector. Suitably, the outlet comprises a connector suitable for connecting the outlet to the pump, such as a male Luer-lock connector.

The porous or perforated element separates the inlet from the outlet. Suitably, the chamber is made in two parts that are fitted together. The first part may comprise the inlet, and the second part may comprise the outlet. The first and second parts are suitably clipped, glued, welded or otherwise fixed together and there is suitably a formation, such as a flange or peripheral edge portion that clamps a periphery of the porous or perforated element between the two parts. This configuration suitably forms a seal between a periphery of the porous or perforated element and either or both of the two parts of the chamber, thereby effectively separating the inlet from the outlet by the porous or perforated element. This configuration suitably means that fluids can only pass from the inlet to the outlet through the porous or perforated element.

The porous or perforated element, when dry, permits the passage of gas (e.g. air) from the inlet to the outlet. However, when the porous or perforated element is wetted by an aspirated liquid, its pores or perforations suitably become blocked or clogged by the aspirated liquid, thereby inhibiting or preventing the passage of fluids from the inlet to the outlet. When this happens (i.e. when the pores or perforations become blocked or clogged by the aspirated liquid thus inhibiting or preventing the passage of fluids from the inlet to the outlet), the chamber and porous or perforated element effectively work as a closed valve upstream of the pump. Thus, the pump will no longer be able to aspirate further fluids once the pores or perforations become blocked or clogged by the aspirated liquid.

The porous or perforated element permits air to pass through it, but not fluids. The porous or perforated element suitably comprises a material, such as paper, which when dry, comprises pores or perforations that allow air or gases to pass through the material, but when wetted, for example by an aspirated fluid, the fluid closes or blocks the pores or perforations thereby preventing fluids (air and/or gas and/or liquid) to pass through it. Such a configuration conveniently provides a self-closing valve that permits air or gasses to pass through it, but when wetted, self-seals to prevent fluids from passing through it.

In another embodiment, the porous or perforated element comprises two components, namely a liquid-absorbent layer, such as paper, and a porous or perforated hydrophobic layer. The two layers are suitably conjoined to form a laminated structure. In this embodiment, the hydrophobic layer comprises pores or perforations that enable, when dry, air to pass through them (i.e. through the hydrophobic layer). However, when wetted by liquid, e.g. absorbed by the liquid-absorbent layer, the liquid is repelled from the surface of the hydrophobic layer and forced to overlie the less hydrophobic regions, that is to say, the openings of the pores or perforations. Provided the pores or perforations of the hydrophobic layer are small enough (i.e. significantly smaller than the size of a water droplet), the water that overlies the pores or perforations effectively blocks the pores or perforations, thus inhibiting or preventing the passage of air or liquid through them.

The porous or perforated element, and/or a liquid-absorbent part thereof, may be impregnated with a reagent that changes colour upon contact with a target substance. In such a situation, the porous or perforated element is ideally visible from outside the chamber, for example, through a viewing window or transparent portion of the receptacle.

The porous or perforated element, in certain embodiments of the invention, may be manufactured from litmus paper, which changes colour on contact with acids or bases. Using litmus paper in the self-closing valve conveniently enables it to be used to test for the presence of stomach acid, for example, when the invention is used as an enteral aspirator or as part of an NG tube.

Suitably, the testing chemical can test for the presence of other target substances, such as any one or more of the non-exhaustive list comprising: an acid; a base (alkali); carbohydrate; glucose; sugar; blood; iron; protein; ketone; bilirubin; urobilingen, nitrates; leukocytes; etc.

Suitably, the chamber is manufactured from a transparent or translucent material such that the porous or perforated element can be seen viewed from the outside of the chamber. Suitably, the chamber is manufactured from a transparent plastics material, of glass. Additionally or alternatively, the chamber may comprise a viewing window to permit the contents of the receptacle to be visually inspected from the outside of it.

The pump is suitably an electrical positive displacement pump and may have a typical base pressure of between 1 to 50 kPa.

In one embodiment of the invention, the pump assembly comprises a pressure sensor located downstream of the outlet of the chamber, i.e. interposed between the outlet and the pump. The pressure sensor is suitably operatively connected to switch gear controlling a motor of the pump such that when a sensed threshold vacuum pressure is detected, the motor is switched off. Such a configuration greatly simplifies the invention, compared with known pumped aspirators insofar as there is no need for complex control circuitry: the pump is switched on and stays on until liquid has been aspirated into the chamber. When this happens, the porous or perforated element becomes wetted, thereby inhibiting or preventing the passage of fluids through the porous or perforated element. This effectively blocks the outlet of the chamber and thus the sensed air pressure downstream of the outlet will drop until a threshold value has been reached, whereupon the switch gear will switch off the vacuum pump's motor. This automatically ends the aspiration procedure, and a user can inspect the contents of the chamber.

In another embodiment of the invention, a control circuit comprises a current sensor in the motor circuit, which is operatively connected to the switch gear controlling the motor of the pump. In this situation, when the pump is switched on, the motor will drive the pump and will draw a first current. However, when liquid has been aspirated, and the inlet becomes blocked, the current in the motor circuit will rise, due to the increased effort required by the motor to drive the pump. This rise in current can be detected by the control circuit using the current sensor, and can be used as a signal to switch off the pump, thus completing the aspiration procedure. Again, such a configuration greatly simplifies the invention, compared with known pumped aspirators insofar as there is no need for complex control circuitry: the pump is switched on and can stay on until liquid has been aspirated into the chamber. When this happens, the porous or perforated element becomes wetted, thereby inhibiting or preventing the passage of fluids through the porous or perforated element. This effectively blocks the outlet of the chamber causing the pump to need to work harder. This increase in power requirement is manifest as a rise in the current in the motor circuit, and this current increase can be detected the switch gear, which then switches off the vacuum pump's motor. This automatically ends the aspiration procedure, and a user can inspect the contents of the chamber.

Suitably, the vacuum pump comprises an "on/off" switch, which when depressed once, starts the vacuum pump's motor. The control circuitry, including the pressure sensor and the switch gear, suitably keeps the vacuum pump running until the aspiration procedure is complete (as explained above), or until a user presses the on/off switch again, to switch-off the vacuum pump.

In an alternative embodiment, the switch is a normally open push switch, such that the motor only runs whilst the switch is depressed. A user can thus operate the aspirator by pressing and holding the switch and/or terminate the aspiration procedure by releasing the switch; and/or may operate the aspirator by pressing and holding the switch, but the control circuit may override the switch to turn off the pump upon completion of the aspiration procedure.

The control circuit may additionally comprise an indicator, such as an LED and/or a beeper, to indicate the progress of the aspiration procedure. In one embodiment of the invention, the LED comprises a colour-changing LED, which can, for example, illuminate green when the pump assembly is ready for use, illuminate amber when the pump assembly is in use (e.g. pumping) and red when the aspiration procedure is complete. A similar configuration with a beeper could be used, such as with a short beep; repeated beeping and a long beep, respectively.

Suitably, the pump comprises a rechargeable battery, such that the pump may be recharged at a designated docking station, conveniently between usages. Preferably, however, the pump comprises a single-use battery that is sealed into a housing of the pump assembly. Replacement or recharging of the battery is this inhibited or prevented. This is useful from a servicing and/or maintenance perspective because it means that the pump assembly can be disposed of and/or factory reset when its battery becomes discharged. Additionally or alternatively, the pump may comprise a timer or a counter, which prevents its use after a certain amount of time, or after a certain number of operations. Additionally or alternatively, the pump may comprise a battery charge monitor, which prevents its use once its battery charge level has fallen below a particular value.

The aforementioned features of the invention potentially avoids problems of wear and/or poor calibration and/or detonation of efficacy, which may occur if the device's service interval were extended and/or if the pump's battery could be replaced or recharged, thus extending its service life.

Another aspect of the invention provides an aspirator comprising an aspirator tube and a pump assembly as described herein. The aspirator tube is suitably a flexible tube, such as a plastics or rubber tube. The tube is suitably sterilisable or a disposable, single-use item. The tube is suitably an enteral aspirator tube or a nasogastric (NG) tube. A preferred embodiment of the invention shall now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of an aspirator including a pump assembly in accordance with the invention;

Figure 2 is an exploded view of a chamber for a pump assembly in accordance with the invention;

Figure 3 is a perspective view of the chamber of figure 2, assembled;

Figure 4 is an exploded view of an embodiment of an aspirator in accordance with the invention; and

Figure 5 is an assembled view of the aspirator of Figure 4.

Referring to Figure 1 of the drawings, an aspirator 10 comprising a pump assembly 12 and an aspirator tube 14 is shown. The aspirator tube 14 is inserted into the body of a patient 16, specifically in the case of an enteral aspirator, into the stomach 18 of the patient 16.

The tip 20 of the aspirator tube 14 is located within a liquid 22 inside the patient's stomach 18 and the other end of the aspirator tube 14 is connected, via a Luer lock 24 to an inlet 26 of the pump assembly 12.

The inlet 26 is in fluid communication with a chamber 28, which has a hollow interior volume 30, in which a porous or perforated element 32 is located. The porous or perforated element 32 divides the chamber 28 such that the inlet 26 is separated from an outlet 34 by the porous or perforated element 32.

The outlet 34 is connected to an inlet 36 of a pump 38. The pump 38 is driven by a motor 40 which is controlled by switchgear (not shown) forming part of a control circuit 42. The control circuit 42, and hence the motor 40, powered by a rechargeable battery 44.

The motor 40 can be switched on by a user (not shown) by pressing on a push switch 46 forming part of the control circuit 42. Upon pressing the push switch 46, the control circuit 42 connects the battery 44 to the motor 40, thereby driving the pump 38.

The pump 38 is a positive displacement pump and creates a vacuum at its inlet 36. Because the inlet 56 of the pump 38 is connected to the aspirator tube 14, via the chamber 28, liquid 22 from within the patient's stomach 18 is drawn up the aspirator tube 14 and into the hollow interior volume 30 of the chamber 28 when the pump 38 is operated.

When this happens, the porous or perforated element 32 becomes wetted by the aspirated liquid 22 and its pores or perforations become blocked or clogged, or in certain embodiments (for example where the porous or perforated element 32 is manufactured from paper), the pores of the porous or perforated element swell and close-off. This clogging/closing of the pores of the porous or perforated element 32 separates the chamber's inlet 26 from its outlet 34 thereby causing the pressure at the inlet 36 of the vacuum pump 38 to drop.

As can be seen from Figure 1 of the drawings, a pressure sensor 48 is interposed between the outlet of the chamber 34 and the inlet 36 of the pump 38. The pressure sensor 48 is configured to sense the pressure downstream of the outlet 34 of the chamber 28. When the sensed pressure falls below a threshold value (indicating that the porous or perforated element 32 has become blocked, thereby preventing further aspiration of liquid 22 into the chamber 28) a signal 50 is sent to the control circuit 42 to indicate this. Upon receipt of the control signal 50 from the pressure sensor 48, the control circuit 42 disconnects the motor 40 from the battery 44 using switchgear (not shown). This ends the aspiration procedure automatically and a user (not shown) is able to inspect the contents of the chamber, that is to say liquid 22 drawn up into the hollow interior volume 30 of the chamber 28.

In a simple embodiment of the invention, the control circuit 42 is provided with a beeper 52 and a colour-changing LED 54 whose operation shall be described below.

When the pump assembly 12 is first switched on (for example when the battery 44 is connected and optionally determined to be sufficiently charged), the indicator LED 54 will illuminate green signifying that the pump assembly 12 is in a "standby" sate and ready for use. A user (not shown) can then depress the push switch 46 to start the aspiration procedure, at which point, the control circuit will cause the LED 54 to illuminate amber, signifying that the aspiration procedure is in progress. When the pressure sensor 48 detects the threshold drop in pressure and emits its control signal 50, the control circuit 42 causes the LED indicator 54 to illuminate red, thereby signifying to a user (not shown) that the aspiration procedure has been completed.

Further, the beeper 52 can be configured to emit audible signals indicating similar states of operation, for example a short, double-beep to indicate that the pump assembly 12 is ready for use, a series of short beeps to indicate when the aspirating procedure is underway, and a long, continuous beep to indicate to the user (not shown) that the aspiration procedure has been completed.

It will be appreciated from the foregoing description that the pump assembly 12 of the invention is significantly simpler in construction and operation than other known pumped aspirators of this general type. For example, it does not include a differential pressure sensor, nor does it require a liquid trap - as this function is performed by the chamber 28 and porous or perforated element 32 therewithin.

In an alternative embodiment of the invention (not shown), the pressure sensor 48 can be omitted altogether. In this embodiment of the invention, the control circuit 42 comprises a current sensor 56 in the motor circuit 57 adapted to monitor the current in the motor circuit 57. It will be appreciated that during the normal aspiration procedure, the current in the motor circuit 57 will be of a particular value. However, when the porous or perforated element 32 becomes clogged, blocked or closed-off by the aspirated liquid 22, the current, as sensed by the current sensor 56, will increase as the motor 14 needs to work harder due to the drop in pressure at its inlet 36. The control circuit 42, by monitoring the current in the motor circuit 57 is able to determine when the aspiration procedure is complete simply by monitoring the current in the motor circuit 57 using the current sensor 56. It will be appreciated further, this additional simplification of the pump assembly 12 further distinguishes the invention over known pumped aspirators, which are generally altogether more complicated devices.

The operation and principle of the invention having been described above, we now turn to certain specific details of the construction of the pump assembly.

In particular, referring to Figure 2 of the drawings, the chamber 28 is formed in two parts 60, 62 which are generally dish-shaped. Each part 60, 62 comprises an integrally-formed spigot 64, which forms either the inlet 26 or the outlet 34 of the chamber 28, respectively. The two parts 60, 62 can be connected to one another by any suitable means, for example by a snap-fit connection, by gluing, ultrasonic welding, etc. to form a unitary component. The porous or perforated element 32 is formed, in this embodiment, as a circular disc of litmus paper, whose peripheral edge 66 is clamped between peripheral lip portions (not shown) of the first and second parts 60, 62. Thus, when the chamber 28 is snapped together as shown in Figure 3, the porous or perforated element 32 is clamped between the two parts 60, 62 thereby separating the inlet 26 from the outlet 34 as previously described.

As can be seen from Figures 2 and 3 of the drawings, the inlet 26 comprises a female Luer lock connector which connects to a corresponding connector of the aspirator tube 14.

As shown in Figure 2 of the drawings, an additional (optional) in-line check valve 68, is interposed between the inlet 26 of the chamber 28 and the end of the aspirator tube 14. The provision of a check valve 68 may be advantageous to prevent aspirated liquid from flowing back down the aspirator tube 14 either during, or after, the aspiration procedure.

An embodiment of the invention 10 is illustrated schematically in Figures 4 and 5 of the drawings in which the pump assembly 12 comprises a main body 70 housing the pump 38, the motor 40, the control circuit 42 and the battery 44. The main body 70 has, on its exterior surface, a single push button switch 46 which operates as previously described; and in this particular embodiment of the invention, a display screen 72 instead of the LED 54 previously described. The main body 72 has an inlet spigot 74 that is, effectively the pump inlet 36 previously described. The inlet spigot 74 connects, via a Luer lock connection 76, to the outlet 34 of the chamber 28. The chamber 28 has an inlet 26, which either connects directly to aspirator tube 14, or via a Luer lock connector 24 as previously described.

In this embodiment of the invention, the user operates the pump assembly 12 in the same way as previously described, but rather than having a simple LED/beeper indicator, the progress of the aspiration procedure is indicated by the display screen in a graphical form.

Finally, in Figure 5 of the drawings, the aspirator 10 shown in Figure 4 is shown assembled but with the additional inclusion of a check valve 68 interposed between the aspirator tube 14 and the chamber 28.

Claims

Claims:

1. A pump assembly, suitable for use as part of a pumped aspirator, the pump assembly comprising: a chamber comprising an inlet connectable, in use, to an aspirator tube and an outlet connectable, in use, to a vacuum pump, the chamber comprising a hollow interior volume containing a porous or perforated element separating the inlet from the outlet, the porous or perforated element, when dry, permitting the passage of gas from the inlet to the outlet, but when wetted by a liquid, inhibiting or preventing the passage of fluids from the inlet to the outlet.

2. The pump assembly of claim 1, wherein the inlet and outlet comprise connectors being any one or more of the group consisting of: a Luer-Lock connectors; a bayonet-type fitting; a screw thread; a push-fit connector; and the inlet comprising a female Luer-lock connector and the outlet comprising male Luer-lock connector.

3. The pump assembly of claim 1 or claim 2, wherein the chamber comprises first and second parts fitted together, the first part comprising the inlet and the second part comprising the outlet, and wherein either or both of the first and second parts comprise a formation adapted to clamp a peripheral edge of the porous or perforated element between the said two parts.

4. The pump assembly of claim 3, wherein clamping a peripheral edge of the porous or perforated element between the said two parts forms a seal between a periphery of the porous or perforated element and either or both of the two parts of the chamber.

5. The pump assembly of any preceding claim, wherein when the porous or perforated element is wetted by an aspirated liquid, its pores or perforations become blocked or clogged by the aspirated liquid, thereby inhibiting or preventing the passage of fluids from the inlet to the outlet.

6. The pump assembly of any preceding claim, wherein the porous or perforated element is manufactured of a material, which when dry, comprises pores or perforations that allow air or gases to pass through it, but whose pores or perforations, when wetted, close and/or become blocked or clogged.

7. The pump assembly of any preceding claim, wherein the porous or perforated element comprises a liquid-absorbent layer and a porous or perforated hydrophobic layer.

8. The pump assembly of claim 7, wherein the liquid-absorbent layer comprises a paper layer.

9. The pump assembly of claim 7 or claim 8, wherein the porous or perforated hydrophobic layer comprises pores or perforations that enable, when dry, air to pass through them, but when wetted by liquid, the hydrophobicity of the hydrophobic layer repels the liquid from its surface towards the openings of the pores or perforations.

10. The pump assembly of any of claims 7 to 9, wherein the liquid-absorbent layer and a porous or perforated hydrophobic layer are conjoined to form a laminated structure.

11. The pump assembly of any preceding claim, wherein the, or a part of, the porous or perforated element is coated or impregnated with a reagent that changes colour upon contact with a target substance.

12. The pump assembly of claim 11, wherein the reagent comprises a colorimetric reagent that changes colour when in contact with a target substance, the target substance being any one or more of the group consisting of: an acid; a base (alkali); carbohydrate; glucose; sugar; blood; iron; protein; ketone; bilirubin; urobilingen, nitrates; and leukocytes.

13. The pump assembly of claim 11 or claim 12, wherein the porous or perforated element is manufactured from, or comprises, litmus paper.

14. The pump assembly of any preceding claim, wherein the chamber is manufactured from a transparent or translucent material.

15. The pump assembly of any preceding claim, wherein the chamber comprises a viewing window.

16. The pump assembly of any preceding claim, wherein the pump is driven by an electric motor connected to a power supply via switch gear of a control circuit.

17. The pump assembly of claim 16, wherein the control circuit comprises a current sensor connected in-series with the motor and the power supply, and wherein the control circuit is adapted to actuate the switch gear to switch off the motor upon detection of a rise in the current indicative of the porous or perforated element inhibiting or preventing the passage of fluids from the inlet to the outlet.

18. The pump assembly of any preceding claim, further comprising a pressure sensor interposed between the outlet and the pump.

19. The pump assembly of claim 18, wherein the pressure sensor is operatively connected to switch gear adapted to control a motor of the pump.

20. The pump assembly of claim 19, wherein the switch gear comprises a control circuit adapted to monitor an output of the pressure sensor and to cause the switch gear to switch off the motor of the pump when the sensed air pressure falls below a threshold value indicative of the porous or perforated element inhibiting or preventing the passage of fluids from the inlet to the outlet.

21. The pump assembly of any of claims 16 to 20, wherein the control circuit comprises an on/off switch, which when depressed once, starts the vacuum pump's motor, and wherein the control circuit is adapted to switch off the motor when a signal indicative of the porous or perforated element inhibiting or preventing the passage of fluids from the inlet to the outlet has been received.

22. The pump assembly of any of claims 16 to 20, wherein the control circuit comprises a push switch, which when held down, starts the vacuum pump's motor, and wherein the control circuit is adapted to switch off the motor when a signal indicative of the porous or perforated element inhibiting or preventing the passage of fluids from the inlet to the outlet has been received.

23. The pump assembly of any of claims 16 to 22, wherein the control circuit further comprises an indicator adapted to indicate the progress of an aspiration procedure.

24. The pump assembly of claim 23, wherein the indicator comprises a colour-changing LED, which illuminates a first colour when the pump assembly is ready for use, which illuminate a second colour when the pump assembly is in use, and which illuminates a third colour when the aspiration procedure is complete.

25. The pump assembly of claim 23 or claim 24, wherein the indicator comprises a beeper, which beeps in a first sequence when the pump assembly is ready for use, which beeps in a second sequence when the pump assembly is in use, and which beeps in a third sequence when the aspiration procedure is complete.

26. The pump assembly of any preceding claim, wherein the pump comprises an electrical positive displacement pump.

27. The pump assembly of claim 26, wherein the pump has a base pressure of between 1 to 50 kPa.

28. The pump assembly of any preceding claim, further comprising a rechargeable battery.

29. The pump assembly of any of claims 1 to 27, further comprising a single-use battery sealed into a housing of the pump assembly.

30. The pump assembly of any preceding claim, further comprising a timer or a counter, which prevents its use after a certain amount of time, or after a certain number of operations.

31. The pump assembly of any preceding claim, further comprising a battery charge monitor, which prevents its use once its battery charge level has fallen below a particular value.

32. An aspirator comprising an aspirator tube and a pump assembly according to any preceding claim.

33. A pump assembly or aspirator substantially as hereinbefore described, with reference to, and as illustrated in, the accompanying drawings.