WO2014193246A1

WO2014193246A1 - Fluid metering apparatus and system

Info

Publication number: WO2014193246A1
Application number: PCT/NZ2014/000100
Authority: WO
Inventors: Murray Edward Fenton
Original assignee: Adept Limited
Priority date: 2013-05-31
Filing date: 2014-05-30
Publication date: 2014-12-04

Abstract

The invention relates to a device for metering fluids comprising: a metering chamber (606) for receiving fluid with first inlet/outlet pair (610, 613) and a second inlet/outlet pair (612, 611), and a movable membrane (608) disposed between the inlet/outlet pairs, the moveable membrane (608) being operable under pressure from fluid entering the chamber (606) from a first preformed shape state to a second preformed shape state wherein during movement the membrane (608) discharges fluid in the chamber out one of the outlets e.g. (613) and recharges a volume of fluid in the chamber (606) defined by the preformed shape of the membrane (608) and chamber (606).

Description

FLUID METERING APPARATUS AND SYSTEM

FIELD OF THE INVENTION

The invention relates to a device for use in a system, a system, and/or a method for the administration of fluids in a medical environment, and more particularly to a device, system and/or method for metering fluids to be administered to a patient.

BACKGROUND

Enteral feeding (also sometimes referred to as tube feeding or gavage) is the provision of nutrients directly to a patient's gastrointestinal tract. The food is most commonly supplied as a liquid and delivered through an enteral feeding tube. Enteral feeding is commonly used when a person cannot ingest, chew, or swallow food, but can digest and absorb nutrients or in cases of malnutrition where the patient cannot take enough food by mouth. Enteral feeding tubes generally bypass the patient's mouth and esophagus so that food is delivered directly to the patient's stomach. The tubes may be inserted through a patient's nostril (nasogastric feeding) or directly through a patient's abdomen wall (gastric feeding).

A percutaneous endoscopic gastrostomy (PEG) feeding tube is a particular type of feeding tube that passes through the wall of the outer abdomen and into the stomach of the patient. PEG tubes are commonly used for long term nutrition for patients who cannot maintain adequate nutrition with oral intake.

Enteral feeding may be administered continuously (where a constant flow of food is delivered to the patient) or by a method known as 'bolus' feeding. Bolus feeding emulates natural ingestion by introducing the feed in doses of similar size to what a patient would orally ingest (i.e. a mouthful)

The quantity of food delivered to a patient may be measured to ensure the patient is receiving sufficient nutrition.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved fluid metering device and/or an improved method of metering fluids for use in a medical system that will at least provide the public and/or medical practitioners/industry with a useful choice.

In a first aspect the present invention may be said to consist in a device for metering fluids comprising : a metering chamber for receiving fluid with a valve controlled first inlet/outlet pair and a valve controlled second inlet/outlet pair, and a movable membrane disposed between the inlet/outlet pairs, the moveable membrane being operable under pressure from fluid entering the chamber through one of the inlet valves to move between a first state where it resides against a first wall of the chamber and a second state where it resides against a second wall of the chamber, wherein during movement the membrane discharges fluid in the chamber out one of the outlets.

Preferably the membrane is not stretchable.

Preferably fluid fills and discharges alternatively on a first and second side of the membrane.

Preferably the membrane substantially seals the first wall from the second wall.

Preferably the metering chamber is elliptical or spherical in shape. Preferably the metering chamber is formed from two halves.

Preferably the metering chamber further comprises a ridge formation along the longitudinal length of the chamber, such that excess fluid or air may escape from the chamber. Preferably the valves are biased to close the fluid flow paths. Preferably the valves are elastomeric seal members.

Preferably the membrane is thicker at the centre than it is towards the edge. Alternatively, the membrane has a uniform thickness throughout its cross-section.

Preferably the membrane is non-permeable, and made from silicon, rubber or thermoplastic elastomer.

Preferably the membrane is configured to operate within a pressure range between lOKPa and 60KPa.

In another aspect the present invention may be said to consist in a fluid delivery system comprising a reservoir for fluid, a conduit to a metering device comprising: a metering chamber for receiving fluid with a valve controlled first inlet/outlet pair and a valve controlled second inlet/outlet pair, and a movable membrane disposed between the inlet/outlet pairs, the moveable membrane being operable under pressure from fluid entering the chamber through one of the inlet valves to move between a first state where it resides against a first wall of the chamber and a second state where it resides against a second wall of the chamber, wherein during movement the membrane discharges fluid in the chamber out one of the outlets. Preferably the embodiment further comprises an external casing configurable to receive the metering device. Preferably the external casing comprises a hinged lid operable to insert or remove the metering device.

Preferably the actuators for operating the valves are mounted on the external casing.

Preferably the embodiment further comprises a controller for determining an appropriate period to wait between each state change to match a desired fluid discharge rate from the chamber. Preferably the controller waits for a period of 5 seconds between each state change to discharge fluid from the chamber.

Preferably the controller does not wait between each state change to discharge fluid from the chamber.

Preferably the embodiment further comprises a user control interface for inputting the desired fluid discharge rate.

In a another aspect the present invention may be said to consist in a device for metering fluids comprising a metering chamber for receiving fluid with first inlet/outlet pair and a second inlet/outlet pair, and a movable membrane disposed between the inlet/outlet pairs, the moveable membrane being operable under pressure from fluid entering the chamber from a first preformed shape state to a second preformed shape state wherein during movement the membrane discharges fluid in the chamber out one of the outlets and recharges a volume of fluid in the chamber defined by the preformed shape of the membrane and chamber.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

The invention consists in the foregoing and also envisages constructions of which the following gives examples only. The term "comprising" as used in the specification and claims, means "consisting at least in part of". When interpreting a statement in this specification and claims that includes

"comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-sectional schematic representation of a patient being fed through a nasogastric feeding tube, the tube extends through the patient's nostril, past the esophagus and exits in the stomach.

Figure 2 is a schematic representation of a patient being feed through a percutaneous endoscopic gastrostomy (PEG) tube, the tube extends through an incision in the patient's abdominal wall to the stomach.

Figure 3 is a cross-sectional schematic representation of a patient being fed through a percutaneous endoscopic gastrostomy (PEG) tube showing the arrangement of the tube on either side the abdominal wall.

Figure 4 is a schematic representation of a patient being feed through a percutaneous endoscopic gastrostomy (PEG) tube using a similar setup to the system shown in Figure 2 with a inflatable cuff to increase the discharge pressure with the metering device.

Figure 5 is an isometric view of a fluid metering device specially configured for use in a feeding system.

Figure 6 is an isometric view of the metering device of Figure 5 coupled to a controller that regulates the quantity of fluid discharged from the device.

Figure 7 is a flow chart representation of a potential control sequence illustrating how the device of Figure 5 may be filled with fluid and subsequently discharged.

Figure 8 is a sectional view of a preferred embodiment of the metering cassette.

Figure 9 is a top perspective view of a preferred embodiment of the metering device, including a configuration of the metering cassette secured by a hinged door.

Figure 10 is a perspective view of a preferred embodiment of the metering cassette.

Figure 11A is a perspective view showing the metering device of the preferred embodiment without the metering cassette and the hinged door in an open state.

Figure 11B is a side perspective view showing the metering device without the metering cassette and the hinged door in an open state. Figure 12 is a cut-away view showing the internal components of a metering device of the preferred embodiment.

Figure 13 is a perspective view of a membrane/seal of the preferred embodiment.

Figure 14 is a schematic sectional view showing the metering cassette of the preferred embodiment from a reverse angle.

Figure 15 is a schematic sectional view showing the inverting membrane in both resting configurations.

Figure 16A is a side schematic sectional view showing a metering cassette of the preferred embodiment.

Figure 16B is a side schematic sectional view showing a metering chamber of the preferred embodiment

Figure 17 is a side schematic sectional view showing an inverting membrane of the preferred embodiment.

Figure 18 is a perspective view showing the internal workings of the metering device when the metering cassette is also loaded.

Figure 19 is a flow chart representation of a potential control sequence illustrating the metering device fill and discharge fluids in accordance with the preferred embodiment.

Figure 20 is a schematic sectional view showing the auto-flush reservoir tube and the flush valve configuration of the preferred embodiment.

Figure 21 is a schematic sectional view showing the flush valve of an alternative embodiment.

Figure 22 is an exploded view showing the flush valve of the alternative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various enteral feeding systems are illustrated in Figures 1 to 4. A gravity fed nasogastric system 1 is illustrated in Figure 1 and a gravity fed gastric feeding system 5 is illustrated in Figure 2 and 3. While shown and described in respect of feeding systems, it will be

appreciated that the embodiments described below can also be used for IV dispensing or other fluid dispensing. The description in relation to enteral feeding systems should not limit the present invention to just that application.

Both the nasogastric 1 and the gastric systems 5 comprise a fluid reservoir 14 that is elevated above the patient 2. The fluid reservoirs are maintained at a desired elevation on a bag stand 16. Each reservoir 14 comprises a flexible bag with a removable lid to enable filling and sealing of the reservoir 14.

The outlet of each reservoir 14 is coupled to a metering device 20. The metering device 20 regulates the delivery of fluid to the patient 2. Either a nasogastric (see Figure 1) or a percutaneous endoscopic gastrostomy (PEG) tube (see Figure 2)_is coupled to the metering device outlet and delivers the feeding fluid directly to the patient's stomach 4 (by-passing the patient's mouth and esophagus 3).

The percutaneous endoscopic gastrostomy (PEG) tube illustrated in Figures 2 and 3 is supported on either side of the abdominal wall by 'bumpers'. The external bumper 8 has a connection interface that is configured to receive a complimentary connector part 7. The connector part 7 is coupled to an external portion of the feeding tube. The external bumper 8 and complimentary connector part 7 enable the external feeding system to be releasably coupled to the patient 2. The internal bumper 9 may be coupled to an internal tube (not shown) or discharge directly to the stomach 4.

A modified gastric feeding system is illustrated in Figure 4. The system includes an inflatable cuff 22 around the reservoir that is connected to the hand pump 12. The inflatable cuff 22 enables the patient 2 or an assistant to apply air pressure to the system when a gravity fed arrangement is not being used or to compensate for low fluid pressure in the system. The inflatable cuff 22 may be used to compliment a gravity fed system. The nasogastric system illustrated in Figure 1 may also be modified to incorporate an inflatable cuff arrangement.

Metering device

A device for metering enteral feeding fluids is illustrated in Figure 5. The device 100 comprises a casing 101 with a fluid inlet 102 and outlet 104. The inlet 102 and the outlet 104 are located at opposing ends of the casing 101 and each comprise a single opening in the illustrated embodiment. The openings are configured to receive a fluid conduit A metering compartment 106 is situated within the device 100 between the inlet 102 and the outlet 104. The geometry and volume of the metering compartment 106 is defined by the casing 101 in the illustrated embodiment. Two inlet channels 114, 115 are illustrated extending from the metering compartment 106 toward the inlet 102. Similarly, two outlet channels 116, 117 are illustrated extending from the metering compartment 106 toward the outlet 104. All of the channels are arranged generally parallel in the illustrated embodiment.

Two flexible tubes 108, 109 extend through the metering compartment 106. The tubes 108, 109 are coupled to the casing inlet 102 and outlet 104. Each tube 108, 109 extends through one of the inlet channels 114, 115 and one of the outlet channels 116, 117 at either end of the metering compartment 106 and couple to an inlet/outlet 102/104 as appropriate. The tubes 108, 109 ideally have a high flexibility so that they can expand to several times their unexpanded cross-section either along the length of the tube 108, 109 or at localised regions. In the illustrated embodiment, the tubes 108, 109 are generally flat and unexpanded. The tubes could be made from any suitable flexible material, such as silicon or polyurethane. The flexible 108, 109 tubes are configured to expand and contract within the metering compartment 106 as the device 100 is filled with fluid and the fluid within the device 100 is discharged. The metering compartment 106 is sized and shaped to constrain expansion of each flexible tube 108, 109 during filling so as to define a maximum discharge volume for each tube. The maximum discharge volume for each tube 108, 109 is substantially equivalent to the metering compartment 106 volume.

Each tube 108, 109 is filled and discharged. As one tube fills, the other discharges so that the filling tube inflates within the constraints of the metering compartment 106 and bears against the discharging tube, effectively transferring the hydrostatic pressure head of the fluid reservoir through the device to the discharging tube. The pressure created by the filling tube bearing against the discharging tube coerces or urges fluid from the discharging tube. Each tube is flexible and changes shape as it is filled/discharged. During a fill cycle, a tube changes from being "squashed" against the wall of the metering compartment 106 to being "inflated" into the full shape of the metering compartment 106. In doing this, the discharge tube is "deflated" against the wall of the metering compartment 106.

The inlet channels 114, 115 and outlet channels 116, 117 may have a narrow cross-section (such as a slender rectangular geometry) to retain the tubes 108, 109 generally flat when not filled with fluid. The cross-sectional area of each channel is limited to a narrow width to provide sufficient flow rate with viscous fluids while minimising the length of stroke required of the valve actuators. Each tube 108, 109 is associated with an inlet valve 110, 112 and outlet valve 111, 113. The valves are operable to enable and/or control filling and discharge of the tubes with fluid. The valves may operate as clamps (as illustrated), compressing a localised region of the tube to close or occlude the tube lumen. As the valves bear against and compress the tubes 108, 109, the valve components do not directly contact the fluid being administered to the patient.

Separating the valves from the fluid within the device improves sterility and simplifies cleaning, which can be achieved by simply flushing the tubes after use. In the illustrated embodiment, the tubes 108, 109 are pinched against an internal surface of the casing (an internal surface or wall of a channel). The illustrated clamp valves may be substituted for other types of valves. Some alternative valves that may be incorporated in place of some or all of the illustrated clamp valves include ball valves, butterfly valves, gate valves and other suitable two port valves. The illustrated valves 110, 111, 112, 113 each comprise a valve member that is disposed adjacent a corresponding channel 114, 115, 116, 117. Each valve member is disposed to one side of the respective channel and intermediate the channel ends so that the flexible tube extending through the channel is situated between the valve member and the opposing surface or wall of the channel. When a valve is closed, the valve member extends into the channel and compresses a localised region of the corresponding flexible tube against the channel wall to restrict flow through the tube. Each valve member has an impinging edge that is situated adjacent the respective flexible tube 108, 109. The impinging edge is complimentarily shaped and sized with the opposing channel section so that the valve member is able to sufficiently occlude the tube lumen when the valve is closed.

The device valves are ideally actuated in an alternating sequence, with opposing inlet 110, 111 and outlet 113, 112 valves actuated concurrently, so that the flexible tubes 108, 109 are sequentially filled and discharged. In the sequence, the tubes 108, 109 fill and discharge substantially in unison so that expansion of the filling tube creates a pressure within the discharging tube to urge or coerce fluid out of the device.

The device may be configured to accommodate more than two tubes. The device casing may be modified to include additional valve arrangements and suitable channels to receive the additional tubing if required.

A fluid divider is provided adjacent the device inlet 102 and outlet 104 in the illustrated embodiment. The inlet fluid divider 118 splits supply fluid from a single source amongst the flexible tubes 106, 108. The outlet fluid divider 120 receives fluid from the flexible tubes 108, 109 to form a single discharge from the device 100. Both the device inlet 102 and outlet 104 comprise a single opening configured to receive a fluid conduit in the illustrated embodiment.

The device inlet 102 and/or outlet 104 may comprise more than one opening each. In particular, the inlet 102 and/or outlet may comprise an opening for each flexible tube 108, 109 so that fluid can be supplied/discharged directly to/from the tubes 108, 109 without the fluid dividers 118, 120.

Valve actuator and controller

One exemplary embodiment of controller that can be used with the device 100 is disclosed in relation to Figure 6. Other forms of controller may be used to actuate the device valves and regulate filling and discharge of the device 100. A high level control sequence that a suitable controller may employ to control the device 100 is illustrated in Figure 7. The device 100 is illustrated in Figure 6 coupled to a controller 200. The controller operates each valve within the device to control filling and discharge of the flexible tubes 108, 109 and the overall discharge of the device 100. The controller and device 300 may be individual modular components (as illustrated in Figure 6) or integrated within a common housing.

The controller 200 is configured to alternately actuate opposing inlet 110, 111 and outlet 113, 112 valves so that the flexible tubes 108, 109 are sequentially filled and discharged. The controller 200 fills and discharges the tubes 108, 109 substantially in unison (concurrently opening opposing inlet 110, 111 and outlet 113, 112) so that expansion of the filling tube creates a pressure within the discharging tube to urge or coerce fluid out of the device.

The discharge volume of each tube 108, 109 is generally limited to the maximum discharge volume defined by the metering compartment 106. The illustrated controller 200 comprises a mechanical linkage that couples the valves together. The linkage includes a cam arrangement having a cam shaft 206 with a pair of axially spaced cam lobes 207, 208 and a plurality of cam followers 210, 211, 212, 213 . The cam followers 210, 211, 212, 213 are coupled to the device valvesl lO, 111, 112, 113. Each cam lobe 207, 208 is associated with two cam followers 210, 211, 212, 213. The cam shaft 206 is supported by axially spaced bearing 222, disposed at either end of the shaft 206 in the illustrated embodiment.

The cam followers are arranged in two rows, with the cam shaft 206 disposed substantially equidistant between the two rows. The cam shaft 206 and the cam followers are disposed to one side of the device 100, so that the cam arrangement is nearer one flexible tube 108 (the near tube) then the other 109 (the distant tube). An intermediate row of cam followers 211, 213 is disposed between the cam shaft 206 and the flexible tubesl08, 109. The intermediate row of cam followers 211, 213 is coupled to the inlet 111 and outlet 113 valve of the distant tube 109. A far row of cam followers 210, 212 is disposed on an opposing side of the cam shaft 206 away from the flexible tubes 108, 109. The far row of cam followers 210, 212 is coupled to the inlet 110 and outlet 112 valves of the near flexible tube 108.

The cam arrangement (including the cam shaft 206 and cam followers) is arranged generally parallel with the device inlet 114, 115 and outlet 116, 117 channels. The cam lobes 207, 208 are axially spaced along the cam shaft 206 to coincide with a cam follower from each row and the device inlet 110, 111 and outlet 112, 113 valves. One cam lobe 207 and set of cam followers 210, 211 (the inlet lobe and cam followers) are generally aligned with the device inlet valves 110, 111 and the other lobe 208 and cam followers 212, 213 (the outlet lobe and cam followers) are generally aligned with the outlet valves 112, 113. The cam lobes 207, 208 are out of phase by about 180°, so that the lobes 207, 208 concurrently engage cam followers from the different rows to actuate the inlet valve of one tube and the outlet valve of the other tube. The two rows of cam follower 210, 211, 212, 213 are sufficiently spaced from the cam shaft 206 so that the inlet valve 110, 111 and outlet valve 112, 113 of each tube are momentarily closed while transitioning between valve states. A spring 224 is disposed between each cam follower and the associated valve. The spring 224 biases the valves closed. The cam shaft 206 is driven by an electric motor 220 in the illustrated embodiment. A gearbox 226 (illustrated comprising a cam shaft gear and a complimentary gear on the motor 220) converts the rotation drive of the motor to a suitable angular speed for driving the device valves. The shaft angle sensor allows the cams to be positioned and stopped with the valves in their fully open state.

The volume flow rate is dependent upon the valve sequence time (the fill and discharge duration of the tubes 108, 109) and the quantity of fluid discharged from the device 100 per cycle. The volume flow rate = ( V_Cy_Cie/ tcycle)- For bolus feeding applications the bolus feeding volume is equivalent to the cycle volume

(Vcycle)_/ and the total number of cycles (Ntotai) for a desired feeding volume can be determined using equation 2.

Ntotai = Vtotal / V_cycle (1)

The controller 200 incorporates a sub-control system that operates the motor 220. The sub- control system may be programmable with a desired feeding volume, a feeding administration method and other feeding variables as desired. Other possible variables the sub-control system may regulate include: motor speed, supply reservoir pressure head compensation, the volume of fluid discharged per cycle and bolus feeding intervals. The sub control system and motor 220 may receive power from a mains supply, have a battery supply or have the option of both battery and mains power. The sub control system may include a micro-controller or other suitable logic based controller (such as suitable control circuitry). A sensor 228 provides an indication of rotational displacement of the cam shaft to the sub- control system. The sensor may comprise a rotating disc that is coupled to the cam shaft 206 and a transducer that is coupled to the sub-control system. The sub-control system is configured to equate the rotation displacement of the cam shaft 206 to the state of the device valves. The sub-control system may also be able to determine the cam shaft 206 position from the motor 220 run time.

Device operation and metering function

The controller executes a sequence that opens the inlet valve 110, 111 of one tube (the filling tube) concurrently with the outlet valve 113, 112 of the other tube (the discharging tube) so that expansion of the filling tube within the metering compartment urges or coerces fluid from the discharging tube. A possible controller sequence is provided below: 1. Controller standby: All valves closed.

2. Activate controller.

3. Start control sequence:

a. Fill the first tube 108: The inlet valve 110 of the first tube 108 and the outlet valve 113 of second tube 109 are opened to allow the first tube 108 to fill with fluid. The outlet valve 112 of the first tube 108 and the inlet valve 111 of the second tube 109 are closed during this step. Then, the motor is held stationary until the cycle time has elapsed and then the motor is started again b. Transition : The first tube inlet valve 110 and the second tube outlet valve 113 are closed after a predetermined time (corresponding to a predetermined fill volume in the first tube 108). All the device valves are simultaneously closed during transition.

c. Empty the first tube 108 and fill the second tube 109: The outlet valve

112 of first tube 108 and the inlet valve 111 of the second tube 109 are opened to allow the first tube 108 to discharge the fluid accumulated during filling (step 3a or 3e) and the second tube 109 to fill with fluid. The fluid filling the second tube 109 causes the tube 109 to expand and bear against the first tube 108, coercing fluid to discharge from the first tube 108. The outlet valve 113 of the second tube 109 and the inlet valve 110 of the first tube 108 are closed during this step. Then, the motor is held stationary until the cycle time has elapsed and then the motor is started again

d. Transition: The second tube inlet valve 111 and the first tube outlet valve 112 are closed after a predetermined time (corresponding to a predetermined discharge volume for the first tube 108 and a fill volume for the second tube 109). All valves are simultaneously closed during transition.

e. Empty the second tube 109 and fill the first tube 108: The outlet valve

113 of the second tube 109 and the inlet valve 110 of the first tube 108 are opened to allow the second tube 109 to discharge the fluid accumulated during filling (step 2d) and the first tube 108 to fill with fluid. The fluid filling the first tube 108 causes the tube 108 to expand and bear against the second tube 109, coercing fluid to discharge from the second tube 109. The outlet valve 112 of the first tube 108 and the inlet valve 111 of the second tube 109 are closed during this step. Then, the motor is held stationary until the cycle time has elapsed and then the motor is started again

f. Transition : The first tube inlet valve 110 and the second tube outlet valve 113 are closed after a predetermined time (corresponding to a predetermined fill volume in the first tube 108). All the device valves are simultaneously closed during transition.

4. Loop through fill and discharge sequence: Repeat steps 3c to 3f

5. Flush flexible tubes: Execute control sequence in step 3 to flush sterilizing fluid

through device prior to storage.

6. Place controller in standby: All valves closed.

Generally the fill and discharge time for each flexible tube 108, 109 (steps 3a, 3c and 3e) is the same, so that each cycle discharges approximately the same quantity of fluid.

The expansion of the filling tube within the metering compartment during steps 3a, 3c and 3e coerces fluid from the discharging tube by creating a pressure within the discharging tube. The hydrostatic pressure head from the elevated or pressurised fluid reservoir is transmitted between the tubes as the tubes 108, 109 are arranged in the metering compartment and the metering compartment is sized such that the filling of one tube coerces the other tube to discharge fluid.

Other valve arrangements are possible.

Second embodiment

A further embodiment of a fluid metering device is illustrated in Figures 8 to 22. The fluid metering device embodiment is compatible with various enteral feeding systems as illustrated in Figures 1-4, and can be used as the metering device 20 depicted in and described with reference to those Figures. A gravity fed nasogastic system 1 is illustrated in Figure 1 and a gravity fed gastric feeding system 5 is illustrated in Figures 2 and 3. While shown and described in respect of feeding systems, it will be appreciated that the embodiments described below can also be used for IV dispensing or other fluid dispensing. The description in relation to enteral feeding systems should not limit the present invention to just that application.

Overview of the metering device A metering device of the second embodiment for metering enteral feeding fluid is illustrated in Figures 8 and 9. The metering device 500 comprises a device casing 501 that is adapted and configured to accommodate a fluid metering cassette 600. The cassette 600 comprises a fluid inlet 602 and fluid outlet 604 located at or proximate opposing ends of the cassette 600, where the inlet 602 is connected to the fluid reservoir 14 (via tubes) and the outlet 604 is connected to the patient through an enteral feeding tube system.

The cassette 600 has an internal metering chamber 606 capable of storing a predetermined volume of fluid. The metering chamber 606 comprises a movable pre-formed membrane 608 configured to operatively move or "flip" between two pre-formed resting states to expel fluid from the chamber 606; a first state where the inverting membrane 608 resides against a first wall of the chamber, and a second state where the inverting membrane 608 resides against an opposing second wall of the chamber. The cassette 600 further comprises a first valve controlled inlet/outlet pair 610, 613 and a second valve controlled inlet/outlet pair 612, 611 operable by mechanical actuators for regulating the flow of fluid inside the metering device. The membrane 608 is disposed within the chamber 606 between the inlet/outlet pairs.

The device casing 501 receives the cassette 600 and secures it in place, while having internal mechanical actuators for controlling the first and second inlet/outlet pairs. The inlet valve and outlet valve on opposing sides of the membrane 608 may be considered a valve pair. The device casing 501 preferably further comprises a hinged door 502 which closes onto the casing to secure the cassette 600 in place during use.

In use, the cassette 600 regulates the flow of fluid through the metering device 500 by changing configurations of the valves to alternate the inverting membrane 608 between the first and second states. In a first configuration, the valves are configured to allow fluid to fill one side of the chamber 606, causing the inverting membrane 608 to move or "flip" from a first pre-formed state of lying against the first side of the chamber to a second pre-formed state of lying against the opposing side of the chamber, this movement of the inverting membrane 608 displaces or expels fluid from the chamber 606. In a second configuration, the valves are configured to allow fluid to fill the opposing side of the chamber 606, causing the inverting membrane 608 to move or "flip" from a second state of lying against the opposing of the chamber to a first state of lying against the first side of the chamber, this movement of the inverting membrane 608 displaces or expels fluid from the chamber 606.

Fluid metering cassette

Referring to Figures 8, 9 and 15, the metering cassette will be described in more detail. The metering cassette 600 is made from two halves 609A and 609B assembled having linked channels and defines the metering chamber 606. The two halves 609A and 609B may be clamped together or otherwise sealingly coupled to one another. The cassette 600 may be made from substantially opaque or transparent material. The cassette 600 comprises a fluid inlet 602 and fluid outlet 604 located at opposing ends of the cassette 600. The inlet 602 is connected to the fluid reservoir 14 through a connecting tube 21 and the outlet 604 is connected to the patient through an enteral feeding tube 10. Tubes 21, 10 connecting to the fluid inlet 602 and outlet 604 may be connected at or proximate the opposing ends of the cassette 600. In one embodiment, the inlet 602 and outlet 604 extend at right angles, so that the tubes 21, 10 connecting to the fluid inlet 602 and outlet 604 may extend substantially perpendicular to the longitudinal axis of the cassette 600 to aid with assembly of the metering device 500 and reduce likelihood of kinking for tubes connecting into the fluid inlet 602 and outlet 604.

The metering chamber 606 within the cassette 600 is capable of storing a predetermined volume of fluid (nominal volume of 5 ml). The metering chamber 606 formed from the two halves 609A, 609B and is preferably elliptical or spherical in shape. The chamber 606 further comprises a ridge formation 650 (see Figure 10) along the longitudinal length of the chamber 606, the ridge formation 650 forms a channel between the chamber 606 and the movable membrane 608, such that excess fluid or air may escape through a channel 650C formed between the ridge 650 and the membrane 608 (in a manner to be described later with reference to Figure 16A). In one embodiment, the chamber 606 further comprises a rib formation 650A channels connecting with the ridge 650 across the walls such that excess fluid or air may escape. The cassette inlet 602 to the cassette comprises a channel that extends to and is fluidly connected to metering chamber inlets 670, 672 (via valves 610, 612 to be described below). The cassette outlet 604 comprises a channel that extends to and is fluidly connected to metering chamber outlets 671, 673 (via valves 611, 613 to be described below). The two chamber inlets 670, 672 and the two chamber outlets 671, 673 could be formed from separate channels, or could each be a single moulded channel that is separated in some manner, by for example a seal. In the present embodiment, the chamber inlets 670, 672 are actually a single moulded channel formed from the moulded halves 609A, 609B that are separated by a seal 601 to form two inlets. Likewise, the chamber outlets 671, 673 are actually a single moulded channel formed from the moulded halves 609A, 609B that are separated by a seal 601 to form outlets. In an alternative embodiment, the outlets 671, 673 may form a single outlet. The metering chamber 606 is connected to inlets 670, 672, and the outlets 671, 673.

Fluid flow from the cassette inlet 602 through the channel and into the chamber via each chamber inlet is controlled by a valve 610, 612. Likewise, fluid egress from the chamber via each chamber outlet to the channel and out the cassette outlet is controlled by a valve 611, 613. Each valve is an elbow-shaped lever with an actuation portion and a blocking portion. Each blocking portion resides adjacent the inlet/outlet port encased in a resilient seal that holds the valve in place within the cassette. The valves levers are configured to have a resting or closed state and an open state. At a closed state, the lever end of having the soft and flexible material is biased to close one of the cassette's 600 four internally sealed flow paths. While the external end of the respective levers 620, 621, 622, 623 are configured to be actuated by any external force. The inlet and outlet valves 610, 611, 612, 613 are configured such that the valves are biased to close the flow paths from the fluid inlet 602 and outlet 604, and prevent the flow of fluid into or out of the metering chamber 606 at a resting state. In an open state, the valve levers are raised to open an aperture to the inlet and outlet conduits to allow fluid to enter or exit the metering chamber 606. When the valve is closed, the blocking portion sits as shown in Figure 8 and blocks the inlet/outlet. When the lever/actuation portion is pushed, the blocking portion levers away from the inlet/outlet port/opening thereby allowing fluid to flow through the inlet/outlet port/opening. Upon removing the pushing force, the resilient seal is biased to return the blocking portion to its resting state. Control of fluid into and out of the chamber is controlled by controlled combinations of opening and closing the valves in a manner to be described later. Figure 13 shows the seal 601 that is disposed between the two moulded halves 609A, 609B to form a seal. A flange 651 of the seal 601 sits between the halves 609A, 609B and also bisects the chamber inlet channel to create the two chamber inlets 670, 672 and also bisects the chamber outlet channel to create the two chamber outlets 671, 673. The seal 601 has the curved movable membrane 608 that extends between the flanges 651.

The curved membrane 608 has a pre-formed shape (e.g. elliptical bubble shape) that is substantially the same as one half of the chamber, so that it can reside snugly against and be cupped by a half of the chamber. The pre-formed shape has a known reliable volume. Referring to Figures 8 and 14-17, the movable membrane 608 is configured to operatively move to invert ("flip") between two resting states to expel fluid from the chamber 606; a first pre-formed state where the inverting membrane 608 resides against and is cupped by a first wall/half of the chamber, and a second pre-formed state where the inverting membrane 608 resides against and is cupped by an opposing second wall/half of the chamber. The movable membrane 608 is invertible. In each state, the membrane has a pre-formed shape of a known reliable volume. In one embodiment, the membrane is a non-permeable membrane. The membrane 608 has a pre-formed shape that is configured to substantially match the interior of the chamber 606. The membrane 608 may fittingly reside against the interior contour of the first and opposing second wall of the chamber 606. The membrane 608 may be made from any suitable material including silicon, rubber or suitable thermoplastic elastomer (TPE), such as Crayton™.

In a preferred embodiment in a cross sectional view, the membrane is shaped to have a first end 608A and a opposing end 608B and a gradual arch rising from each end. The membrane 608 preferably does not substantially change or alter shape before, during or after operation so that the volume of fluid inside the metering chamber 606 stays consistent. The seal flange 651 has a thicker layer (for example about 1mm) to seal and sandwich between the cassette halves 609A, 609B. It is relatively thinner for regions where the membrane 608 is conforming to the interior of the first and second walls 605A, 605B of the chamber 606. In a preferred embodiment, the thickness of the membrane 608 is reduced to about 0.5 mm around its outer extremity where it joins the flange 651, while the thickness of the membrane 608 transitions to be 0.6 mm thicker than the outer extremity towards the central portion of the membrane 608 curve. This thinner portion provides a hinge that enables the membrane 608 to invert.

In a further preferred embodiment, a raised ridge formation 690 is centrally located intermediate the membrane 608. The ridge formation 690 may be an elliptical section dimensioned about 1 mm thick, about 3 mm high and about 6 mm long. This enables material to flow through the mould through the very thin section and out to the thicker extremities of the seal mould during injection moulding. In an alternative embodiment, the thickness of the membrane 608 is uniform throughout its entire cross-section. In a further embodiment, thicker layer regions of the membrane 608 as described above may further comprise apertures or holes to allow air to escape. The membrane 608 has a pre-formed shape and is configured to rest or bias initially against the first or second wall of the metering chamber 606, and configured to move between two resting positions under pressure from ingressing fluid (see Figure 15) within the metering chamber 606. When the membrane is in a first position against the first wall 605A, fluid can enter the chamber via the second chamber inlet 672 (with the second chamber outlet 673 closed) to fill the chamber. Then the first inlet 670 and second outlet 673 open, while the second inlet 672 and first outlet 671 close - all under valve control. This causes fluid to flow in between the membrane and the first wall 605A. The membrane may move, invert or "flip" between the two resting positions under the pressure, and in doing so, fluid already in the chamber on the other side of the membrane will expel out of the second outlet 673. This may work under various pressures, including quite low pressures.

It is to be understood that the membrane can accurately conform to the walls of the chamber 606 and displace fluid from the chamber 606 across a range of pressure conditions and fluid viscosity due to the pre-formed nature of the membrane shape. Below is a table of fluid typically displaced by the pre-formed membrane for a range of test pressure within a chamber volume of 5.5ml.

Pressure (KPa) Expelled Volume (ml)

10 5.47

20 5.46

30 5.55

40 5.42

50 5.59

60 5.49 The pre-formed shape of the membrane 608 has two natural resting states which allow the membrane 608 to reliably invert or flip between the first and second pref-formed states to displace fluid from the chamber 606 across a range of pressure conditions and / or fluid viscosity. For example, even under relatively low pressure conditions (e.g. lOKPa), once the membrane starts to move from a first state, there is a biasing force for the membrane to complete the transition to a second pre-formed resting state, and to consequently complete the 'flip' to the second state and displace fluid from the chamber 606. In this manner, a reliable volume can be dispensed even under relatively low pressures.

In one embodiment, the membrane 608 may move due to hydrostatic pressure created by the fluid reservoir 14 positioned above the metering cassette 600 as that fluid enters the chamber 606 via the cassette inlet 602 and one of the chamber inlets 670, 672. In one embodiment, the pressure provided by the fluid reservoir 14 varies between lOKPa to 60Kpa, however one would appreciate that the pressure ranges are not limiting and the membrane may move under pressure conditions outside of this range. It is to be understood that the movement speed of the membrane may differ depending on the pressure exerted. For example if fluid ingresses into a the chamber 606 via an inlet 670, 672 at higher pressure (such as 60KPa) the membrane 608 may move quicker or "snaps" from one state to another, while at lower pressure (such as lOKpa) the membrane 608 may not move as quickly. It will be appreciated that the resting position of the membrane 608 may be independent from the operational states of the metering cassette 600. For example, while the inlets and outlets are configured by the valves to allow fluid to flow into and out of the metering chamber 606, the membrane 608 may be in either first or second resting positions. The movement of the membrane 608 is controlled by the configuration of the inlet/outlet pairs as will be described further below. The movement of the membrane 608 in moving fluid through the metering chamber 606 may be described as peristaltic motion. In one embodiment, each successive movement of the membrane 608 displaces a set amount of fluid from the chamber 606 through the outlet 604.

In a preferred embodiment, the amount of fluid displaced by the membrane 608 is

substantially the same as the volume of the chamber 606. In an alternative embodiment, the amount of fluid displaced by the membrane 608 is less than the volume of the chamber 606. The flow rate of liquid displaced by the membrane 608 from the chamber 606 is a function of rate of state change between the first and second pair of inlet/outlet valves. It is to be appreciated that faster state of change between the first and second pair of inlet/outlet valves results in more frequent movement of the membrane 608 from one resting state to another, thereby increasing the volume of liquid displaced by the chamber 606 within a given period of time. In one embodiment there is a waiting period of 5 seconds between state change of the first and second pair of inlet/outlet valves for the membrane 608 to change state and displace liquid from the chamber 606. In another embodiment there is no waiting period between state changes of the first and second pair of inlet/outlet valves. It is to be appreciated at the waiting period between states changes of the first and second pair of inlet/outlet valves can be any suitable time frame.

Referring to Figure 8, as previously mentioned, mechanical inlet valves 610, 612 and outlet valves 611, 613 control fluid flow into and out of the chamber inlets/outlets. Inlet valve 610 and outlet valve 613 regulates fluid passing (via the first inlet 670 and outlet 673) between the membrane 608 and the first wall 605A of the metering chamber 606, while inlet valve 612 and outlet valve 611 regulates fluid passing (via second inlet 672 and outlet 671) between the membrane 608 and the second wall 605B of the metering chamber 606. Inlet valve 610 and outlet valve 613 form a first valve pair, while the inlet valve 612 and outlet valve 611 form a second valve pair. These respectively control the fluid entering and existing regions between the membrane 608 and respective first or second wall 605A, 605B of the chamber 606.

In operation, the valves are controlled to in one configuration open the first inlet valve 610 and second outlet valve 613; and close the second inlet valve 612 and first outlet valve 611; and in a second configuration, open the second inlet valve 612 and first outlet valve 611, and close the first inlet valve 610 and second outlet valve 613. For example, in a first configuration the first inlet/second outlet valve pair is closed and the second inlet/first outlet valve pair is open; fluid is restricted from entering into the region between the membrane 608 and the first wall 605A of the metering chamber 606, while fluid enters and fills the region between the membrane 608 and a second wall 605B of the metering chamber 606. In this configuration, the inverting membrane 608 may initially sit substantially against the first chamber wall 605A of the metering chamber 606. In a second configuration, the first inlet/second outlet valve pair is open while the second inlet/first outlet valve pair is closed, such that fluid enters the region between the membrane 608 and the first chamber wall 605A only while restricted from flowing into the region between the membrane 608 and the second chamber wall 605B.

The hydrostatic pressure from the fluid entering into the region between the membrane 608 and the first chamber wall 605A will apply a force on the surface of the inverting membrane 608 and subsequently inverts the membrane 608 to a second resting position where the membrane 608 sits substantially fully against the opposing second chamber wall 605B- thus making substantially the entire chamber available for fluid ingress. The shape of the inverting membrane 608 does not change before or after the change of state and matches the wall of the chamber to keep the volume of fluid inside the metering chamber consistent and accurate.

In a preferred embodiment, the membrane 608 preferably keeps its shape and does not deform in either resting states. The valves pairs are accordingly configured to control the position of the inverting membrane 608 from the first resting position to the second resting position, and back to the first position and so on and so forth. The movement of the inverting membrane 608 from one resting position to another may be substantially instant, such that there are no intermediate resting positions in between.

In one embodiment, the amount of fluid passing through the metering device 500 is controlled by opening valves pairs for a time duty cycle (for example 5 seconds) such that it is long enough to allow the metering chamber regions between the membrane 608 and a first or second wall of the metering chamber 606 to be filled and emptied.

Device casing

Referring to Figures 9, 11A and 11B, the metering device 500 comprises a device casing 501 that is adapted and configured to accommodate the fluid metering cassette 600. In a preferred embodiment, the device casing 501 is assembled from two halves forming an internal enclosure for housing a flow control mechanism 550. The flow control mechanism 550 includes a set of four mechanical lever actuators 530, 531, 532, 533 which will be described in detail further below. The casing may be of any suitable shape and made from any plastic or metallic materials. In a preferred embodiment, the device casing 501 is constructed from a suitable waterproof material. In one embodiment the device casing 501 is substantially rectangular in shape. In a further embodiment, the device casing 501 is injection moulded.

In a preferred embodiment, the device casing 501 may be said to have a first half 505 and a second half 506. The first half 505 and/or second half 506 may be configured and dimensioned with an engaging formation 510 to receive and engage substantially an entirely of the metering cassette 600. In one embodiment the engaging formation 510 may be of a concave or recess formation. In a preferred embodiment, the device casing 501 may also comprise a seal over-moulded around the joint between the first half 505 and second half 506 casing parts.

In one embodiment, the device casing 501 comprises a lid 502 that may be closed in use to substantially enclose the cassette 600 against the engaging formation 510 during use. In a preferred embodiment, the lid 502 is a hinged lid. The lid 502 serves as a door to the engaging formation 510 and secures the removable metering cassette 600 to the device casing 501. The lid is further designed to protect the cassette 600 once the cassette 600 is inserted into the casing's 501 engaging formation 510. In one embodiment, the lid 502 may be "L" shaped and hinges on one side of the device casing 501. The metering casing 501 also comprises four windows 520, 521, 522 and 523 over-moulded with a soft material skirt. The windows 520, 521, 522, 523 are configured and dimensioned to sit adjacent or proximate the inlet and outlet valves levers 620, 621, 622, 623 of the cassette 600. The windows/skirt 520, 521, 522, 523 may have a three-dimensional form that allows them to flex resiliently without stretching the material. In a preferred embodiment, the windows/skirt 520, 521, 522, 523 are configured to be positioned intermediate the respective valve levers 620, 621, 622, 623 and mechanical lever actuators 530, 531, 532, 533 internal to the metering casing 501. Mechanical lever actuators 530, 531, 532, 533 may apply force to activate the respective valve levers 620, 621, 622, 623 on the cassette 600 such that the respective inlet and outlet valves 610, 611, 612, 613 shifts between the open and the closed or resting states. In one embodiment, the lever actuators 530, 531, 532, 533 is configured to deform the respective windows 520, 521, 522, 523 as it actuates the valve levers 620, 621, 622, 623 while not permanently stretching the soft material of the windows 520, 521, 522, 523. One purpose of the windows 520, 521, 522, 523 is to reduce the energy required to activate the valve levers.

The device casing 501 further comprises a user control interface 540. The user control interface 540 comprises a power control 541 for turning on/off the metering device 500 and a flow control 542 for regulating the flow rate or time cycle of the fluid dispensed from the fluid outlet 604. The user control interface may be located anywhere on the metering device 500. In a preferred embodiment, the user control interface is located in an area on the device casing 501 that is adjacent or proximate the cassette 600 in use.

Referring to Figure 12, the flow control mechanism 550 comprises a controller 700, mechanical lever actuators 530, 531, 532, 533, a mechanical cam shaft arrangement 560 driven by a geared motor 590, and a power source 595. The geared motor 590 drives the shaft arrangement 560 that controls the movement of lever actuators 530, 531, 532 and 533. The lever actuators comprise arms having projections that engages and deforms windows 520, 521, 522, 523 of the device casing 501.

The shaft arrangement 560 comprises a cam shaft 561 having a gear between two cam arrangements 565, 575 spaced axially and generally configured at opposite parallel ends of the shaft 561. The first cam arrangement 565 has a cam lobe 566 and a cam follower 567, the cam follower is connected to lever actuators 530 and 532. While the second cam arrangement 575 is substantially symmetrical to the first arrangement 565; the second cam arrangement 575 has a cam lobe 576 and a cam follower 577, where the cam follower 577 is connected to lever actuators 531 and 532. In a preferred embodiment, the cam followers 567, 577 are cam rollers; the cam rollers push on an internal track to actuate the cam followers, such that energy used is reduced.

The cam arrangements 565, 575 (including the cam shaft 561, cam lobes 566, 576 and cam followers 567, 577), is arranged generally parallel with the inlet valves 610, 612 and outlet valves 611, 613. One set of cam lobe 566 and cam follower 567 are generally aligned with the inlet valves 610, 612 and the other set of cam lobe 576 and cam follower 577 are generally aligned with the outlet valves 611, 613.

The cam lobes 566, 576 are configured to be out of phase by about 180°, so that the lobes 566, 576 engage respective cam followers 567, 577 from different rows to actuate the inlet valves 610, 612 and the outlet valves 611, 613. In other words, the cam arrangements 565, 575 push and retract the cam followers 567, 577 in opposite timing to each other. The two rows of cam follower 567, 577 are sufficiently spaced from the cam shaft 561 so that the inlet valves 610, 612 and outlet valves 611, 613 momentarily reaches a closed or resting state while transitioning between valve states. As described earlier, the inlet and outlet valves 610, 611, 612, 613 are biased to the closed or resting position.

The cam shaft 561 is driven by a geared motor 590 in the illustrated embodiment. The geared motor 590 may be an electric motor powered by a suitable power source such as batteries 595. A gearbox 591 (illustrated comprising a cam shaft gear 592 and a complimentary gear on the motor 590) converts rotation drive of the motor to suitable linear motion for driving the inlet and outlet valves 610, 611, 612, 613. The shaft angle sensor allows the cams to be positioned and stopped with the valves in their open or closed state. There are four possible shaft angle positions at 90° to each. There are also four cams triggers for actuating two limit switches 580, 581 to ensure accurate timing and movement of the cam shaft 561 at 90° increments. Referring to Figure 12, the controller 700 comprises a PCB with an onboard sub-control system that operates the motor 590. The sub-control system may be programmable with a desired feeding volume, a feeding administration method and other feeding variables as desired.

Other possible variables the sub-control system may regulate include: motor speed, duty cycle, supply reservoir pressure head compensation, the volume of fluid discharged per cycle and bolus feeding intervals. The sub control system and motor 590 may receive power from a mains supply, have a battery supply or have the option of both battery and mains power. The sub control system may include a micro-controller or other suitable logic based controller (such as suitable control circuitry).

A sensor 596 provides an indication of rotational displacement of the cam shaft to the sub- control system. The sensor may comprise a rotating disc that is coupled to the cam shaft 206 and a transducer that is coupled to the sub-control system. The sub-control system is configured to equate the rotation displacement of the cam shaft 561 to the state of the device valves. The sub-control system may also be able to determine the cam shaft 561 position from the motor 590 runtime.

In operation, the metering device 500 turns on via 90 degree activation of a rotary switch 542 on the PCB. In one embodiment, LEDs may begin to flash to confirm that the device is "ON". Also the device may have an LED to indicate status of the power or battery. The controller 700 checks the valve open and valve close limit switches 701, 702 to confirm that the motor 590 is in a rest state. The motor 590 drives on to the valve open state stops when the shaft triggers the valve open limit switch. The valve open limit switch is checked to confirm that the motor stopped in the correct position, i.e., the controller 700 still senses the switch. After a set optional time interval, the motor drives the arms on to the valve resting state where the motor senses the valve resting limit switch. The valve resting limit switch is checked to confirm that the motor stopped in the correct position, i.e., the controller 700 still senses the switch. Flow controller

One exemplary embodiment of controller that can be used with the metering device 500 is disclosed in relation to Figure 18. Other forms of controller may be used to actuate the device valves and regulate filling and discharge of the metering device 500. A high level control sequence that a suitable controller may employ to control the metering device 500 is illustrated in Figure 20.

The metering device 500 is illustrated in Figure 18 coupled to a controller 700. The controller operates each inlet and outlet valves 610, 611, 612, 613 within the cassette 600 to control filling and discharge of the metering chamber 606, and the overall discharge of the metering device 500. The controller 700 and metering device 500 may be individual modular components or integrated within a common housing. The controller 700 is configured to alternately actuate opposing first inlet/second outlet valve pair 610, 613 and second outlet and first inlet valve pair 612, 611 so that the metering chamber 606 (more particularly, the regions between the membrane 608 and a first and second wall 605A, 605B of the metering chamber 606 within the metering chamber 606) are sequentially filled and discharged. That is, when one valve pair is open, e.g. 610, 613, the other valve pair is closed, e.g. 612, 611. The controller 700 controls the valves to fill and discharge the regions between the membrane 608 and a first or second wall of the metering chamber 606 within the metering chamber 606 substantially in unison (concurrently opening opposing valve pair 610, 613 and closing valve pair 612, 611, or vice versa) so that the hydrostatic pressure entering either metering chamber 606 regions between the membrane 608 and a first or second wall of the metering chamber 606 will actuate the inverting membrane 608 from one resting position to the other to urge or coerce fluid out of the metering device 500 through the fluid outlet 604.

The discharge volume of the metering device 500 is generally limited to the maximum discharge volume defined by the metering chamber 606.

The volume flow rate is dependent upon the valve sequence time (the fill and discharge duration of the metering chamber regions between the membrane 608 and a first and second side of the metering chamber 606) and the quantity of fluid discharged from the metering device 500 per cycle. The volume flow rate = (V_Cy_C|e/ t_Cycle)-

For bolus feeding applications the bolus feeding volume is equivalent to the cycle volume (Vcycie)_/ and the total number of cycles (Ntotal) for a desired feeding volume can be determined using equation 2.

Ntotal = Vtotal / V_Cy_C|e (1)

Device operation and metering function The controller 700 executes a sequence that opens the first valve pair 610, 613 sequentially with the second valve pair 612, 611 so that the inverting membrane 608 switches position to alternatively fill and empty metering chamber regions between the membrane 608 and a first and second side of the metering chamber 606 and urges or coerces fluid to discharge from metering device 500. A transition step between the state changes of the membrane 608 where all valves are closed is optional. Referring to Figure 19, a possible controller sequence is provided below:

Controller standby: All valves closed.

Activate controller.

Start control sequence:

a. (Stage 1) Fill the region between the membrane 608 and a first wall of the metering chamber 606: The valve pair 610, 613 is opened to allow the region between the membrane 608 and a first wall of the metering chamber 606 to fill with fluid. The valve pair 612, 611 is closed during this step. Then, the motor is held stationary until the cycle time has elapsed and then the motor is started again. At the point of completely filling the region between the membrane 608 and a first wall of the metering chamber 606, the opposing region between the membrane 608 and a second wall of the metering chamber 606 has substantially zero volume.

b. Transition (optional) : The valve pair 610, 613 and the valve pair 612, 611 are closed after a predetermined time (corresponding to a predetermined fill volume). All the inlet and outlet valves 610, 611, 612, 613 are simultaneously closed during transition.

c. (Stage 2) Empty the region between the membrane 608 and the first wall of the metering chamber 606 and fill the region between the membrane 608 and the second wall of the metering chamber 606: The valve pair 612, 611 is opened to allow some fluid to enter the region between the membrane 608 and the second wall of the metering chamber 606. As fluid enters the region between the membrane 608 and the second wall of the metering chamber 606, hydrostatic pressure of the fluid acts upon the inverting membrane 608, resulting in the inverting membrane inverting or "flipping" to the other resting state where the inverting membrane coercing fluid to discharge from the region between the membrane 608 and the first wall of the metering chamber 606 out the first outlet. The fluid continues to fill the region between the membrane 608 and the second wall of the metering chamber 606 until the entire membrane has flipped and the chamber fills. The valve pair 610, 613 is closed during this step. Then, the motor is held stationary until the cycle time has elapsed and then the motor is started again.

d. Transition (optional): The valve pair 610, 613 and the valve pair 612, 611 are closed after a predetermined time (corresponding to a predetermined fill volume). All the inlet and outlet valves 610, 611, 612, 613 are simultaneously closed during transition. e. Empty the region between the membrane 608 and the second wall of the metering chamber 606 and fill the region between the membrane 608 and the first wall of the metering chamber 606: The valve pair 610, 613 is opened to allow some fluid to enter the region between the membrane 608 and the first wall of the metering chamber 606. As fluid enters the region between the membrane 608 and the first wall of the metering chamber 606, hydrostatic pressure of the fluid acts upon the inverting membrane 608, resulting in the inverting membrane inverting or "flipping" to the other resting state where the inverting membrane coercing fluid to discharge from the region between the membrane 608 and the second wall of the metering chamber 606 out the second outlet. The fluid continues to fill the region between the membrane 608 and the first wall of the metering chamber 606 until the membrane has fully flipped and the chamber is filled. The valve pair 610, 613 is closed during this step. Then, the motor is held stationary until the cycle time has elapsed and then the motor is started again.

f. Transition (optional) : The valve pair 610, 613 and the valve pair 612, 611 are closed after a predetermined time (corresponding to a predetermined fill volume). All the inlet and outlet valves 610, 611, 612, 613 are simultaneously closed during transition.

Loop through fill and discharge sequence: Repeat steps 3c (stage 2) to 3f (stage 3). The device is intended to run continuously and repeating steps 3c to 3f until turned off.

Flush flexible tubes: Execute control sequence in step 3 to flush sterilizing fluid through device prior to storage.

Place controller in standby: All valves closed.

Generally the fill and discharge time for each metering chamber region between the membrane 608 and a first or second wall of the metering chamber 606 (steps 3a, 3c and 3e) is the same, so that each cycle discharges approximately the same quantity of fluid.

Referring to Figures 20-22, the device may also initiate an auto-flush programme of the feedset with water at the end of an enteral feeding cycle. This would work by adding a second bag of water that would also sit within the pressure cuff alongside the fluid formula. Both bags would be plumbed in to the feedset tubing 801. There would be lightly sprung enteral feeder flush valve 800 closing the water supply off so that when both bags have external pressure applied to them the formula bag empties first and then when empty the pressure within the water bag is such that it overcomes the sprung valve and allows the water to flush through. The enteral feeder flush valve 800 comprises a housing assembly 810 including a first valve cap 811, a compression spring 812, a shuttle 813, a second valve cap 814 and a nozzle 820. The flush valve 800 acts as a gate for food and water delivery. The user puts liquidised food & water into separate bags; the bags are connected to either end of the valve via tubes that push onto the nozzles (see figure 1). Normally the water and food is pressurised using a pressure cuff. When the pressure cuff reaches a specific pressure the large valve cap is forced back and the valve 800 is then open. The large valve 800 will always open first because the pressure acting on a larger surface area creates a greater force. As a result of the large valve 800 opening the force is transferred through the spring and onto the small valve cap, forcing that closed.

As the food bag empties the pressure subsides with it, when this happens it will reach a point when there is not enough force acting against the large valve cap to keep it open and subsequently to keep the small valve shut. Assuming there is enough pressure in the cuff, the water bag the valve will automatically open the small valve cap (water side), because now all the remaining pressure is acting on the small valve cap and spring. Water then fills the housing and drains out to the user. This is used as a flush for the system and as an automatic way of delivering water after a meal.

Claims

What we claim is:

1. A device for metering fluids comprising :

a metering chamber for receiving fluid with a valve controlled first inlet/outlet pair and a valve controlled second inlet/outlet pair, and a movable membrane disposed between the inlet/outlet pairs, the moveable membrane being operable under pressure from fluid entering the chamber through one of the inlet valves to move between a first state where it resides against a first wall of the chamber and a second state where it resides against a second wall of the chamber, wherein during movement the membrane discharges fluid in the chamber out one of the outlets.

2. A device according to claim 1, wherein the membrane is not stretchable.

3. A device according to claims 1 or 2, wherein fluid fills and discharges alternatively on a first and second side of the membrane.

4. A device according to any one of claims 1 to 3, wherein the membrane substantially seals the first wall from the second wall.

5. A device according to any one of claims 1 to 4, wherein the metering chamber is elliptical or spherical in shape.

6. A device according to claims 5, wherein the metering chamber is formed from two halves.

7. A device according to any one of claims 1 to 6, wherein the metering chamber further comprises a ridge formation along the longitudinal length of the chamber, such that excess fluid or air may escape from the chamber.

8. A device according to any one of claims 1 to 7, wherein the valves are biased to close the fluid flow paths.

9. A device according to any one of claims 1 to 8, wherein the valves are elastomeric seal members.

10. A device according to any one of claims 1 to 9, wherein the membrane is thicker at the centre than it is towards the edge.

11. A device according to any one of claims 1 to 9, wherein the membrane has a uniform thickness throughout its cross-section.

12. A device according to any one of claims 1 to 11, wherein the membrane is non- permeable, and made from silicon, rubber or thermoplastic elastomer.

13. A device according to any one of claims 1 to 12, wherein the membrane is configured to operate within a pressure range between lOKPa and 60KPa.

14. A fluid delivery system comprising

a reservoir for fluid,

a conduit to a metering device comprising :

15. A system according to claim 14, further comprises an external casing configurable to receive the metering device.

16. A system according to claim 15, wherein the external casing comprises a hinged lid operable to insert or remove the metering device.

17. A system according to any one of claims 15 or 16, wherein actuators for operating the valves are mounted on the external casing.

18. A system according to any one of claims 14 to 17, further comprising a controller for determining an appropriate period to wait between each state change to match a desired fluid discharge rate from the chamber.

19. A system according to claim 18, wherein the controller waits for a period of 5 seconds between each state change to discharge fluid from the chamber.

20. A system according to claim 19, wherein the controller does not wait between each state change to discharge fluid from the chamber.

21. A system according to claim 18, further comprising a user control interface for inputting the desired fluid discharge rate.

22. A system according to any one of claims 14 to 21, wherein the membrane is configured to operate within a pressure range between lOKPa and 60KPa.

23. A device for metering fluids comprising:

a metering chamber for receiving fluid with first inlet/outlet pair and a second inlet/outlet pair, and a movable membrane disposed between the inlet/outlet pairs, the moveable membrane being operable under pressure from fluid entering the chamber from a first preformed shape state to a second preformed shape state wherein during movement the membrane discharges fluid in the chamber out one of the outlets and recharges a volume of fluid in the chamber defined by the preformed shape of the membrane and chamber.