Wound therapy system with fill indication

Abstract

A pump unit for delivering negative pressure therapy to a tissue site, which includes an indicator to indicate the presence of liquid in the fluids exiting a negative pressure pump of the pump unit. The indicator changes visual appearance in response to exposure to liquid and provides an indication when an absorbent component of the system is reaching capacity.

Description

PA200103W002WOUND THERAPY SYSTEM WITH FILL INDICATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 777,294, filed on March 25, 2025, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The following disclosure relates to negative pressure treatment apparatus with a fill indicator.BACKGROUND

[0003] Negative pressure wound therapy is a well-known method of treating patients by reducing the pressure over a tissue site to below atmospheric pressure. Negative pressure systems generally supply negative pressure to the tissue site from a pump unit having a negative pressure source. Exudate from the wound may be captured in an absorbent element of the dressing, or a collection canister may be utilised. Where an absorbent element is utilised, it can be hard to determine when the absorbent element reaches capacity and needs to be replaced. Often the absorbent element is located under the dressing cover and it is undesirable to remove that cover to inspect the absorbent element for its fill level.

[0004] There is therefore a need for a negative pressure treatment system with an improved ability to determine when an absorbent element has reached capacity.BRIEF SUMMARY

[0005] Aspects of the following disclosure are set out in the following numbered clauses.

[0006] 1. A pump unit for a negative pressure treatment system, the pump unit comprising a body having an internal volume; a negative pressure pump mounted within the internal volume and having a pump inlet and a pump outlet; and an indicator fluidly coupled to the pump outlet and visible from outside of the body, the visual appearance of the indicator changing after exposure to a liquid; wherein there is no liquid barrier to prevent liquid reaching the indicator from a tissue site being treated by the pump unit via the pump.

[0007] 2. A pump unit according to clause 1, further comprising an exhaust port to atmosphere fluidly coupled to the pump outlet by an exhaust fluid path, wherein the indicator is fluidly coupled to the exhaust fluid path.

[0008] 3. A pump unit according to clause 1 or clause 2, further comprising an absorbent element configured to absorb liquid from fluids flowing through the pump outlet and bring absorbed liquid into contact with the indicator.

[0009] 4. A pump unit according to clause 3, wherein the absorbent element is positioned in the exhaust fluid path.

[0010] 5. A pump unit according to any of clauses 3 to 4, wherein at least part of the exhaust fluid path is formed by a first channel in an outer surface of the body and a fluid-impermeable label over the first channel.

[0011] 6. A pump unit according to clause 5, wherein the exhaust port is an aperture in the label.

[0012] 7. A pump unit according to any preceding clause, further comprising a lumen fluidly coupling the pump inlet to the internal volume.

[0013] 8. A pump unit according to clause 7, wherein the lumen has a length and cross section which prevents liquids passing through the lumen.

[0014] 9. A pump unit according to clause 7 or clause 8 wherein the lumen is a tortuous path which prevents liquid passing through the lumen.

[0015] 10. A pump unit according to clause 9, wherein at least part of the lumen is formed by a second channel in an outer surface of the body and a fluid-impermeable label covering the second channel.

[0016] 11. A pump unit according to any of clauses 7 to 10, further comprising a liquid barrier to prevent liquid passing through the lumen.

[0017] 12. A pump unit according to any of clauses 7 to 10, further comprising a one-way valve which allows fluids to flow from the internal volume to the pump inlet, but not in the reverse direction.

[0018] 13. A pump unit according to any preceding clause, further comprising a controller in the body, the controller being configured to control the pump and comprising a pressure sensor for sensing the pressure in the internal volume.

[0019] 14. A pump unit according to clause 13, wherein the controller is configured to detect liquid in the pump based on an increase in current draw of the pump when operating.

[0020] 15. A pump unit according to any preceding clause comprising a plurality of indicators, each indicator being configured to change its visual appearance after a different amount of liquid has passed through the pump outlet.

[0021] 16. A pump unit according to any of clauses 2 to 15, further comprising a filter to prevent liquid passing through the exhaust port.

[0022] 17. A pump unit according to any preceding clause, wherein a perimeter of a face of the body is for sealing around a perimeter of a tissue site to be treated, or to a cover layer over a tissue site to be treated, and the pump inlet is formed as an opening on the face within the perimeter to deliver negative pressure to the tissue site or to an aperture in the cover layer.

[0023] 18. A method of determining the fill status of a wound dressing in a negative pressure wound treatment system, the method comprising operating a pump to deliver negative pressure to a tissue site, wherein there is no liquid barrier to prevent liquid reaching the pump from the tissue site; and detecting liquid in an outlet of the pump using an indicator, wherein the visual appearance of the indicator changes after exposure to a liquid.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 shows a schematic diagram of a negative pressure treatment system;

[0025] Figure 2 shows a schematic diagram of a negative pressure pump unit according to the current disclosure;

[0026] Figures 3A, 3B, and 3C show an example of a negative pressure pump unit according to the current disclosure;

[0027] Figure 4 shows a further example of a negative pressure pump unit according to the current disclosure, with a larger absorbent element;

[0028] Figure 5 shows a further example a negative pressure pump unit according to the current disclosure; and

[0029] Figure 6 is a block diagram of components of a pump unit and a pressure sensor device.DESCRIPTION OF EXAMPLE EMBODIMENTS

[0030] The following description of examples provides information that enables a person skilled in the art to make and use the subject matter set forth in the appended claims, but it may omit certain details already well-known in the art. The following detailed description is, therefore, to be taken as illustrative and not limiting.

[0031] Figure 1 is a block diagram of an example therapy system 100 that can provide negativepressure therapy to a tissue site in accordance with this specification.

[0032] The term “tissue site” in this context broadly refers to a wound, defect, or other treatment target located on or within tissue, including, but not limited to, bone tissue, adipose tissue, muscle tissue, neural tissue, dermal tissue, vascular tissue, connective tissue, cartilage, tendons, or ligaments. A wound may include chronic, acute, traumatic, subacute, and dehisced wounds, partial thickness bums, ulcers (such as diabetic, pressure, or venous insufficiency ulcers), flaps, and grafts, for example. The term “tissue site” may also refer to areas of any tissue that are not necessarily wounded or defective but are instead areas in which it may be desirable to add or promote the growth of additional tissue. For example, negative pressure may be applied to a tissue site to grow additional tissue that may be harvested and transplanted. The surface of the patient within the tissue site being treated will be referred to as the tissue site bed.

[0033] The therapy system 100 includes a negative-pressure source 102 and a dressing 104. The dressing 104 comprises a tissue interface 108 and a cover 110 such that negative pressure can be coupled from the negative pressure source 102 and maintained at the tissue site under the cover 110. The tissue interface 108 comprises a manifold to distribute negative pressure to the tissue site bed and to collect exudate exuded by the tissue site. The manifold may comprise a combined interface and absorbent or may comprise separate elements to act as a wound layer, manifold, and absorbent. The absorbent element may be any suitable material, for example foams or superabsorbent materials. The cover is typically an elastomeric self-adhesive fdm, for example a polyurethane film, and is typically formed of a breathable, but liquid impermeable, material.

[0034] The therapy system 100 may also include a controller 112 to control the delivery of negative pressure by the negative pressure source 102. A pressure sensor 116 may be included to detect the pressure delivered by the negative pressure source 102. That pressure may be measured at the reduced pressure source 102, or at the tissue site. The pressure sensor 116 may be utilised by the controller 112 to control the negative pressure source 102. Other sensors may also be provided to monitor operating parameters of the system.

[0035] The components of therapy system 100 may be combined into integrated elements and may be co-packaged or provided separately. The negative pressure source 102, controller 112, and sensor 116 may be provided in a device remote from the dressing 104 at the tissue site, and connected via a lumen, or those components may be a single device with the dressing. For example, a pump unit comprising those components may be mounted on the cover 110 to provide an integrated device.

[0036] The controller 112 comprises a microprocessor or computer programmed to operate one or more components of the therapy system 100, such as the negative pressure source 102. The controller 112 may be a microcontroller, which generally comprises an integrated circuit containing a processor core and a memory programmed to directly or indirectly control the one or more elements of the therapy system 100. A function of the controller 112 is to control the negative pressure source 102 to deliver the desired negative pressure to the tissue site for which signals from the pressure sensor 116 may be utilised in addition to settings made by the user.

[0037] In operation, the tissue interface 108 is placed within, over, on, or otherwise proximate to a tissue site and may partially or completely fill the tissue site. The cover 110 is placed over the tissue interface 108 and sealed to an attachment surface near a tissue site. For example, the cover 110 may be sealed to undamaged tissue (e.g. epidermis) peripheral to the tissue site. Thus, the dressing 104 can provide a sealed therapeutic environment proximate to the tissue site, substantially isolated from the external environment, and the negative-pressure source 102 can reduce pressure in the sealed therapeutic environment.

[0038] As will be appreciated only selected components have been shown and described in relation to Figure 1 to explain the principles of operation and construction of the treatment system, but other components may also be present in a complete system.

[0039] Figure 2 shows a schematic cross-section diagram of a pump unit 200 for positioning over a tissue site to apply negative pressure for treatment. The pump unit 200 may be attached directly to the patient, for example using a medically acceptable adhesive on perimeter 201 , or the perimeter 201 may be attached to a cover layer positioned over the tissue site and creating a sealed chamber at the tissue site. An aperture in the cover layer allows negative pressure from the pump unit to the tissue site.

[0040] An inlet 203 of a pump 202 is fluidly coupled to space 204 to provide negative pressure to the tissue site. As will be appreciated space 204 may be any shape or configuration to couple negative pressure as required by a particular unit’s configuration.

[0041] A lumen 205 is provided between the pump inlet 203 and the interior volume 206 of the pump unit. Lumen 205 has a small cross-sectional area compared to inlet 203 such that when the pump is active fluid is pulled from the space 204 in preference to through the lumen 205 from the interior volume 206. However, sufficient air flow is possible through lumen 205 such that in steady state the pressure in the interior volume 206 approximates the pressure in pump inlet 203.

[0042] A fdter 207 may be provided across the lumen 205 to prevent liquids passing between pump inlet 203 and the interior volume 206 of the pump unit 200.

[0043] The outlet of the pump 202 is fluidly coupled to an indicator 208. Indicator 208 is visible from outside of the pump unit 200 and is configured to provide a visual indication of the presence of liquids in fluids leaving the pump outlet. The pump outlet is also fluidly coupled to exhaust 209 which permits fluids to from the pump outlet to exist the pump unit.

[0044] The pump unit also comprises a controller 210 for controlling the pump 202 and providing a user interface (not shown) to enable a user to control the pump unit 200. The controller 210 may include a pressure sensor 211 for sensing pressure in the interior volume 206.

[0045] It is usual in negative pressure treatment systems to utilise a liquid barrier to prevent liquids, specifically exudate, from reaching the pump. However, the pump unit 200 of Figure 2 does not have any such component and liquid reaching the pump inlet 203 can enter the pump 202. Liquid entering the pump will be drawn through the pump by its normal operation and pushed out of the pump outlet to exhaust 209 and indicator 208. As introduced previously, indicator 208 is configured to provide a visible indication when liquid is detected at the pump outlet. The user is thus made aware of the presence of liquid at the pump inlet 203 which typically occurs when the absorbent components of the dressing are full. The user is thus notified when the absorbent components are full and need changing. The configuration of Figure 2 therefore enables the user to determine that a dressing change is required without opening the dressing to inspect the absorbent component as was necessary with previous systems. In an example, l-2ml of liquid per day may move past the absorbent component and reach the indicator. Such a dressing may be expected to last 7 days such that the indicator should change appearance when 7-14ml of liquid have reached the indicator. However, these values are given for example only and the volume at which the indicator changes appearance is selected based on the specific dressing characteristics as understood by the Skilled Person.

[0046] The indicator 208 may be material which changes colour when exposed to liquid. The indicator 208 and exhaust 209 may be a single element such that fluids from the pump outlet pass through the indicator 208 as they exit through the exhaust 209, or the components may be separate such that the fluids pass through or over the indicator and then exit through the exhaust 209. A further example of an indicator structure suitable for use as indicator 208 (or any indicators discussed herein) has an outer layer of material which transitions from opaque to translucent in response to exposure to water (or vice versa) and an inner layer with a visible indicator. When viewed from the side of the outer layer the indicator has the appearance of the outer layer when that layer is opaque, and theappearance of the inner layer when the outer layer is translucent. That is, the inner layer can be seen through the outer layer when the outer layer is translucent. The outer layer may be formed of materials which easily absorb and desorb liquid such that the indicator is reversible. For example, the outer layer may be a microporous hydrophilic polymer. An indicator of this type is positioned behind a transparent fluid-impermeable region of the case, shell, or outer structure of the pump unit 200 such that it is visible from outside of the pump unit.

[0047] As will be appreciated during use the interior of the pump unit is likely to become contaminated with liquids from the patient (principally exudate from the tissue site being treated) and so may not be suitable for re-use without cleaning and sterilising, and / or replacement of exposed parts. The principles discussed herein may therefore be most applicable to pump units intended for single-use and disposal.

[0048] The exhaust 209 may be provided with a fdter to prevent liquids existing with gases, thereby retaining all liquids within the pump unit. Other fdters, for example an odour fdter, may also be provided across the exhaust to treat fluids leaving through the exhaust 209.

[0049] The indicator 208 and / or exhaust 209 may include an absorbent material to absorb any liquid present in fluid flowing in the pump outlet.

[0050] As described above lumen 205 provides a fluid connection between the pump inlet 203 and the interior volume 206 of the pump unit 200. In steady state the pressure in the interior volume 206 thus approximates the pressure at the pump inlet 203 (which in turn approximates the pressure at the tissue site). The pressure sensed by pressure sensor 211 is thus indicative of the pressure delivered by the pump unit 200 to the tissue site. The fdter 207 prevents liquids which enter the pump inlet 203 from entering the interior volume 206. If such liquids entered volume 206, they may interfere with, or damage, components of the pump unit, particularly the electronics of controller 210. The fdter 207 may be a hydrophobic fdter, or any component which prevents the passage of liquid but permits gas to pass through. The fdter could also be omitted where other means are provided to prevent passage of liquids. For example, the lumen 205 could be formed as a small cross-section tortuous path which prevents the passage of liquid due to its dimensions.

[0051] A one-way valve could also be utilised instead of fdter 207 such that fluids can flow from the interior volume 206 to the pump inlet 203, but not in the reverse direction. In such configurations, or in any described example, a small vent to atmosphere may be provided from the interior volume 206 to return the interior volume to atmospheric pressure over time. The flow rate of such a vent is selected to be sufficiently low to prevent interference with correct operation of the pump unit when delivering negative pressure.

[0052] Figures 3A-C show cross-section, perspective, and partially exploded views respectively of an exemplary pump unit 300 to provide the functionality described with reference to Figure 2. To avoid a loss of clarity not all elements are numbered in all of the figures, but this does not imply there is a difference between the three parts, Figures 3A-C.

[0053] The base of the pump unit 300 comprises a perimeter region 301 which may seal around the edge of a tissue site being treated, or to a cover layer over the tissue site. Where a cover layer is utilised one or more apertures are provided in the cover layer to allow fluid communication between the tissue site and the inlet space 302 of the pump unit 300. Inlet space 302 is in fluid communication with pump inlet chamber 303 which is fluidly connected to the pump inlet 304. The inlet space 302 enables negative pressure to disperse across a larger area and may be omitted, or its shape varied as desired for each pump unit design.

[0054] A lumen fluidly connects the pump inlet chamber 303 to the interior volume 305 of the pump unit 300. A fdter 306 may be provided across that lumen to prevent liquids passing between the pump inlet chamber 303 and the interior volume 305. Filter 306 may be omitted if entry of liquids to the volume 305 is not a concern, or if the lumen is designed such that under normal operating conditions liquids cannot pass through the lumen. For example, the diameter and length of the lumen may be selected such that gasses can flow through the lumen, but liquids cannot pass. When a fdter is utilised, any suitable construction may be employed, for example a hydrophobic fdter may be used.

[0055] Controller 307 is electrically connected to the pump 308 and may also comprise or be connected to a user interface. In the example of Figures 3A-C the user interface comprises only an on / off button 309 which may be mechanically or electrically connected to the controller 307 to allow a user to turn the pump unit 300 on or off. The controller 307 is provided with a pressure sensor (not show) to measure the pressure in the interior volume 305. As will be appreciated the pressure sensor can be mounted in any convenient location based on usual mechanical and electrical design principles. The interior volume 305 is in fluid communication with the tissue site being treated via the lumen, inlet chamber 303 and inlet space 302 such that in steady state the pressure sense can measure the pressure being supplied to the tissue site. Changes in pump operation or a fluid leak in the system may create a pressure gradient meaning the pressure at the pressure sensor does not accurately match that at the tissue site. The pressure sensor could also be mounted to directly measure the pressure in the inlet chamber 303 in which case the lumen and fdter 306 are not required. However, PCB-mounted pressure sensors may offer price and installation simplicity advantages.

[0056] Pump outlet 310 is fluidly coupled to outlet chamber 311 which is fluidly coupled to indicator 312 and exhaust port 313. As can be seen in Figure 3C the outlet chamber 311 is fluidly coupled to the indicator 312 and exhaust port 313 by an aperture in the body of the pump unit 300, and a lumen 314 formed by a channel in the outer surface of body & a fluid impermeable label 315 sealed to the outside of the body. This is an example construction only and as will be appreciated any suitable mechanical arrangement may be utilised.

[0057] Exhaust port 313 is covered by a fdter 316 to prevent liquids exiting the pump unit 300, while enabling such liquids to contact the indicator 312. The fdter 316 allows gasses to exit but blocks liquids and may be formed of any suitable element, for example a hydrophobic fdter. The fdter 313 may also provide other functionality such as an odour fdter.

[0058] Absorbent 317 is provided to absorb liquids from exhaust fluids and bring them into contact with the indicator 312. The absorbent may utilise any appropriate absorbent material, such as foams, fabrics, superabsorbent materials, or a combination thereof. The absorbent 317 functions to ensure liquids are reliably brought into contact with the indicator 312, and to avoid liquids moving around the exhaust passages. The absorbent 317 may also increase the amount of liquid in the exhaust before the indicator changes visual appearance because not all liquid entering the absorbent will be brought into contact with the indicator 312. Appropriate design of the absorbent and indicator will thus provide an indicator which changes visual appearance when the desired amount of liquid has reached it. That desired amount of liquid is determined based on the amount of liquid expected to leave the absorbent dressing as it approaches capacity such that the indicator provides an indication that the absorbent of the dressing is full or approaching full. The indicator may be formed as described hereinbefore in relation to Figure 2. In such implementations an additional fluid-impermeable transparent layer is formed outside of the indicator, for example as part of the label 315. The absorbent layer 317 may be formed as the outer layer of the indicator described above.

[0059] The indicator may also be configured to change appearance in proportion to the amount of liquid it has detected such that the indicator provides a quantitative indication of remaining absorbent capacity of the dressing absorbent. Similarly, a plurality of indicators may be provided, changing appearance at different exposures to liquid.

[0060] Figure 4 shows a cross-section of an alternative construction for the pump unit of Figures 3A-C. In this example the absorbent element 316 is larger than shown in Figure 4 and is located in the outlet chamber of the pump. Functionally the arrangement of Figure 4 is the same as Figures 3A-C, but with an increased absorbent capacity.

[0061] In the foregoing description the pump units have been configured to attach either directly to a patient, or to a cover over a tissue site. The principles discussed herein can also be applied to pump units which are remote from the tissue site being treated and which are connected to the dressing by a tube or other lumen. In such examples the pump inlet 203 is fluidly connected to the dressing by a tube and the principles of operation of the system are identical to when a pump unit is mounted on a tissue site or cover.

[0062] Figure 5 shows a further modified design of the pump units discussed hereinbefore, which also provides the functionality described above. The pump unit of Figure 5 has a long, tortuous, lumen coupling the pump inlet chamber to the interior volume of the pump unit to avoid the need for a liquid barrier to prevent liquid flowing through that lumen. Other than the features described in relation to Figure 5 other aspects are the same as described hereinbefore.

[0063] A channel 500 is formed in the outer surface of the pump unit, underneath the label 501. As discussed previously the label 501 is impermeable to fluids and accordingly seals the channel 500 from the surrounding atmosphere. At one end channel 500 is fluidly coupled, via a lumen 502 throughthe pump unit body to the interior volume 503 of the pump unit. At the other end the channel 500 is fluidly coupled to the pump inlet chamber 504 via a lumen 505 in the pump unit body.

[0064] The fluid path between the interior volume 503 and the pump inlet chamber 504 therefore passes through lumen 502, around channel 500, and back through lumen 505, thus forming a tortuous path with numerous direction changes. The combination of the tortuous direction changes, and cross-sectional area of the path, makes it difficult for liquids for travel through the path from the pump inlet chamber 504 to the interior volume 503. The liquid barrier discussed hereinbefore is therefore replaced by the tortuous path.

[0065] When liquid enters a negative pressure pump the load on the motor typically increases. The controller may detect that increase in load, for example due to an increase current draw, and utilise that detection to activate an indicator that liquid is reaching pump. As disclosed hereinbefore, liquid reaching the pump unit may be an indication that an absorbent dressing is full and needs to be replaced. The increase in load may be correlated to the amount of liquid reaching the pump thereby providing a quantitative indication.

[0066] Figure 6 shows a simplified schematic diagram of the electronic elements of a pump unit 900. The components included in Figure 6 are selected to explain the general structure and configuration of the system by reference to the main elements such that the skilled person can implement the examples using known techniques. The pump unit 900 comprises a negative pressure pump 904 for supplying negative pressure to a tissue site via a suitable fluidic connection. The pump 904 is controlled by processor 906 based on settings made by the user via user interface 908, data held in memory 910, programming executed by the processor 906, sensors 912 (for example the ambient pressure sensor discussed hereinbefore). Communications interface 914 is a wireless communication interface capable of establishing a wireless connection with external devices.

[0067] While shown in a few illustrative embodiments, a person having ordinary skill in the art will recognize that the systems, apparatuses, and methods described herein are susceptible to various changes and modifications that fall within the scope of the appended claims. Moreover, descriptions of various alternatives using terms such as “or” do not require mutual exclusivity unless clearly required by the context, and the indefinite articles “a” or “an” do not limit the subject to a single instance unless clearly required by the context. Components may also be combined or eliminated in various configurations for purposes of sale, manufacture, assembly, or use.

[0068] The appended claims set forth novel and inventive aspects of the subject matter described above, but the claims may also encompass additional subject matter not specifically recited in detail. For example, certain features, elements, or aspects may be omitted from the claims if not necessary to distinguish the novel and inventive features from what is already known to a person having ordinary skill in the art. Features, elements, and aspects described in the context of some embodiments may also be omitted, combined, or replaced by alternative features serving the same, equivalent, or similar purpose without departing from the scope of the invention defined by the appended claims.

Claims

Claims1. A pump unit for a negative pressure treatment system, the pump unit comprising:a body having an internal volume;a negative pressure pump mounted within the internal volume and having a pump inlet and a pump outlet; andan indicator fluidly coupled to the pump outlet and visible from outside of the body, the visual appearance of the indicator changing after exposure to a predetermined volume of a liquid;wherein there is no liquid barrier to prevent liquid reaching the indicator from a tissue site being treated by the pump unit via the pump.

2. A pump unit according to claim 1, further comprising an exhaust port to atmosphere fluidly coupled to the pump outlet by an exhaust fluid path, wherein the indicator is fluidly coupled to the exhaust fluid path.

3. A pump unit according to claim 1, further comprising an absorbent element configured to absorb liquid from fluids flowing through the pump outlet and bring absorbed liquid into contact with the indicator.

4. A pump unit according to claim 3, wherein the absorbent element is positioned in the exhaust fluid path.

5. A pump unit according to claim 3, wherein at least part of the exhaust fluid path is formed by a first channel in an outer surface of the body and a fluid-impermeable label over the first channel.

6. A pump unit according to claim 5, wherein the exhaust port is an aperture in the label.

7. A pump unit according to any preceding claim, further comprising a lumen fluidly coupling the pump inlet to the internal volume.

8. A pump unit according to claim 7, wherein the lumen has a length and cross section which prevents liquids passing through the lumen.

9. A pump unit according to claim 7 wherein the lumen is a tortuous path which prevents liquid passing through the lumen.

10. A pump unit according to claim 9, wherein at least part of the lumen is formed by a second channel in an outer surface of the body and a fluid-impermeable label covering the second channel.

11. A pump unit according to claim 7, further comprising a liquid barrier to prevent liquid passing through the lumen.

12. A pump unit according to claim 7, further comprising a one-way valve which allows fluids to flow from the internal volume to the pump inlet, but not in the reverse direction.

13. A pump unit according to claim 1, further comprising a controller in the body, the controller being configured to control the pump and comprising a pressure sensor for sensing the pressure in the internal volume.

14. A pump unit according to claim 13, wherein the controller is configured to detect liquid in the pump based on an increase in current draw of the pump when operating.

15. A pump unit according to claim 1 comprising a plurality of indicators, each indicator being configured to change its visual appearance after a different amount of liquid has passed through the pump outlet.

16. A pump unit according to claim 2, further comprising a filter to prevent liquid passing through the exhaust port.

17. A pump unit according to claim 1, wherein a perimeter of a face of the body is for sealing around a perimeter of a tissue site to be treated, or to a cover layer over a tissue site to be treated, and the pump inlet is formed as an opening on the face within the perimeter to deliver negative pressure to the tissue site or to an aperture in the cover layer.

18. A method of determining the fill status of a wound dressing in a negative pressure wound treatment system, the method comprisingoperating a pump to deliver negative pressure to a tissue site, wherein there is no liquid barrier to prevent liquid reaching the pump from the tissue site; anddetecting liquid in an outlet of the pump using an indicator, wherein the visual appearance of the indicator changes after exposure to predetermined quantity of a liquid.

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