GB2128882A - Drip-feed supply apparatus - Google Patents

Abstract

A drip-feed apparatus comprises a liquid container suspended from a support and having an outlet for gravitational supply of a drip feed liquid to a patient and a valve for adjusting the rate of supply, the apparatus having (a) for linking the container with the support, a weight-deformable linkage 16 having transducers, 28, 30, to provide an electrical output parameter which changes with deformation of the linkage, the weight-deformability of the linkage and the consequent changes of the output parameter both being continuously variable, as the weight of liquid in the container diminishes over the range from that required to fill the container, to zero and (b) electrical means for sensing the weight of liquid in the container. <IMAGE>

Description

SPECIFICATION Liquid supply apparatus This invention relates generally to liquid supply apparatus, and more especially to drip feed apparatus as used in hospitals and to a method of monitoring said drip feed apparatus.

Treatment of patients in hospitals frequently involvesthe use of drip feed apparatus for supplying a patient with liquid solutions such as liquid food, saline solution or the like. Forthis purpose a drip feed support, usually carried by a stand, is positioned adjacent the head of the patient's bed, and a liquid container, conveniently a bag, containing the liquid to be fed is suspended therefrom. Liquid in the bag is drip fed downwardly from the container to the patient.

It is often important to maintain a substantially continuous feed to the patient, involving minimum delays in replacement or replenishment ofthe container. It is thus often necessary to maintain a relatively constant watch on the apparatus, especially as the bag approaches the empty condition. Disadvantageously, this constant surveillance can be very time consuming, especially as the amount of liquid remaining in the container is often not readily apparent visually and even closer examination tends to afford only approximate indication ofthe amount of remaining liquid.

It is an object of this invention to provide a solution to the problem of monitoring the liquid supply in the container.

In accordance with the present invention, there is provided a drip feed apparatus which comprises a liquid container adapted to be suspended from a support and having an outlet conduit for the gravitational supply of a drip feed liquid from the containerto a patient and valve means for adjusting the rate of said supply said apparatus having (a) for linking the containerwith the support, a weight deformable linkage, the weight-deformability of the linkage and the consequent changes of the output parameter both being continuously variable as the weight of liquid in the container diminishes over the range from that required to fill the container to zero and (b) electrical means, responsive to the output parameter, for sensing the weight of liquid in the container.

The task of fitting the drip feed apparatus for supplying a patient with the liquid differs, at most, from that ofthe conventional fitting of a conventional apparatus only in thattheweight-deformable linkage requires to be interposed between the container and the support. Where as in some cases, the linkage is already carried bythesupport-eg. being leftthere from a previous operation - or the container is supplied with the linkage already attached-the task differs even less from the conventional. In addition, the presence ofthe linkage is readily visible. These points are important in practice.In at least a substan-- tial proportion of cases the fitting of the drip feed apparatus, supervision of its performance, and re placement of the container as required, are tasks for the nursing staff. They have to be carried out together with other importanttime-consuming duties and, by the present invention, they are given a task which besides being rapidly performed involves no more than a minordeviationfrom manoeuvreswhich have become virtually automatic from practice.

In a preferred arrangementtheweightdeformable linkage has at least one curved load-bearing part so arrangedthatthe curvaturethereofchanges continuously over said range and the transducer is responsive to the curvature of said curved part.

Especially when the deformable linkage has a general- ly circular or other ring shaped portion which provides two of said curved parts, the arrangement gives a compact structure which is readily accommodated between a conventional drip-feed bag and its support and which is progressively deformable overthe required range.

Convenientlythe linkage has an upper part for attachmentto the support and a lower part for attachment ofthe container, said upper and lower parts being interconnected only by said curved load bearing part or parts. In a simple construction, the upper and lower part or parts are provided in the form of a single integral moulding, conveniently of resinous material of appropriate rigidity.

The transducer aforesaid must provide its output parameter in such a manner that it changes continuously (preferably but not necessarily lineably) overthe appropriate range and it has been discovered that best results are provided by a piezo-electric transducer-eg. a transducer ofthequartz crystal type-which gives an E.M.F. as the output parameter or by a resistance-type transducer which provides the output parameter in the form of resistance. Resistance, like an E.M.F., can be measured by the use of appropriate circuitry and isto be regarded as an output parameter even though resistance and changes of resistance are not output signals in the sensethattheyareself4ransmitting along conductors.

A resistive-type tranducer of the strain-gauge type is preferred on grounds of its simple construction, its reliability and the simplicity of its incorporation in the apparatus. Such transducers are commercially available products and, of these, a transducer of the metallic alloy type is preferred. Best results have been obtained using a transducer ofthe copper-nickel alloy type and especially in the case where the alloy is incorportated in the form of a foil. Such a foil is usually supplied within, and installed within, a flexible protective coating of non-conductive material, eg. a flexible resinous material.

It will be noted thatthe preferred transducers are free from mechanical linkages, provided for example to bring the mechanical loading into the range required for response. They are consequently not readily damaged by mishandling.

When the deformable linkage has more than one part designed to be deformable in response to the weight of the container and contained liquid, a transducer can be fitted to each part if desired. Thus two transducers can be fitted one to each of the curved parts of a linkage having a ring-shaped portion as aforesaid.

In cases where more than one transducer is provided,thetransducers need not be identical in type, have the same response range, or be connected with the same electrical apparatus. For example a separate tranducer connected with a second electrical apparatus may be provided foroperating a warning system when the first or its associated apparatus fails.

Adequately reliable results are, however, given by transducers ofthe same type connected with the same apparatus.

The responsive electrical means, besides responding to the parameter indicating the amount of liquid in the container, may be so constructed and arranged as to provide an output representing the drip-feed rate.

Such an output may be arranged to actuate an indicatorto facilitate adjustment by the operator and/orto control the rate, adjusting a clamp arranged to compress the outlet conduit ofthe drip feed apparatus.

The following description, in which reference is made to the accompanying drawings is given in order to illustrate the invention. In the drawings: Figure 1 shows the general layout of a drip feed apparatus; Figure 2 shows a suspension linkage; Figure 3 shows a meter; Figure 4 is a circuit diagram; Figure 5 is a circuit diagram of an alternative system, and Figure 6 shows the mechanical part of an automatic regulating arrangement.

In Fig. the reference 10 denotes a hospital bed and reference 12 a drip feed stand adjacent to the head of the bed.

A drip feed liquid container in the form of a bag 14 is suspended from a hook at the top of the stand 12 via linkage 16. A meter-type monitor 18for indicating the amount of liquid in the bag attaches to the foot rail of the bed, i.e. the rail from which the patient's records are conventionally hung. Reference 20 denotes a drip feedconduittothe patient and 22 denotes a four conductor electric cable which extends from the linkage 16to the meter 18.

The linkage 16 is shown in Figure 2. It has an attachment eye atthe top for engagementwith the hook on the stand and another eye 26for receiving the bag which is normally suspended from the hook on the stand. Opposite sides of the ring carry internally positioned quartz crystal transducers 28,30.

The linkage orthe ring part thereof may be in the form of resinous moulding or fabricated from metal, with at least the ring part being metal of spring-like quality and of cross-sectional dimensions arranged to give a convenient deformability overthe expected range of loads.

The ring 16, which is relatively rigid, undergoes limited deformation proportionatelyto the weight of the liquid bag suspended therefrom. The transducers 28,30 undergo corresponding deformation.

Thus, in use, thetransducers 28, 30 supply output signals through the cable 22 to the meter 18. The transducer outputs are preferably summed for max imisation ofthe magnitude ofthe deformation signal.

The meter 18, shown in Figure 3, has a scale 32 readingfrombag"replace"tobag"full",with adjustablecontrols34 & 6actuating,forexample, potentiometers for setting the bag-empty and bag-full indications ofthe needle 38 to match the scale. The cable 22 couples to the meter 18 th rough a five way "din" plug/socket coupling 40. Atwo-pole centre off-biased lever switch 42 has voltage check and scale read positions. A curved flange 44 on the backofthe metercasing enables attachment of the metertothe bed rail.

Figure4showsthecircuit layoutofthecomplete system. The combined outputs from the linkage 16 are fed on line 46 to an operational amplifier 48 powered from a 9V battery 50 via a 5V voltage regulator 52. The output of the amplifier 48 feeds the coil of the meter 18. Conveniently, the operational amplifier 48, the voltage regulator 52 and a compartmentfor housing the battery 50 are accommodated within the casing of the meter 18.

In use, after calibration ofthe meter, it is read simultaneously when the other patient records are inspected at the foot of the bed. Detailed examination of the drip feed apparatus is unnecessary, as the meter provides an accurate indication of when bag replacement is due. The scale can be calibrated, for example, on a time division, volume division orweight division basis. Preferably, an audio alarm is incorporated to alert the operator if the bag is allowed to reach the substantially empty condition, i.e. the needle drops close to the lower end ofthe range marked "replace".

Such an alarm device can be rendered operable through a needle actuated contact, or a threshold comparator can be incorporated in the operational circuitry.

The output of the transducers 28 and 30 may additionally, or alternatively, be fed to a central control console, along with corresponding outputs from other drip feed apparatus units in use in the hospital. Atthis console, a single operator can monitor all the drip feed units simultaneously. The console can include a logging system which will provide a read-out, poss idly via a printer, of the times at which drip feed bags have been changed, as well as the existing conditions thereof.

Figure 5 shows an arrangementformonitoring a plurality of drip feed bags at a central monitoring station. Outputs from the linkages 16a, 1 6b and 16care fed through operational amplifiers 48a, 48b and 48c respectively, powered from a 5-volt line 56 equipped with a monitor 57. Powerforthe line 56 is provided from a mains connection 58, through an AC/DC converter 60, a rechargeable battery 62 and a voltage regulator 64. The battery 62 provides stand by power if the mains fails.

The amplifiers48a,48b,48care connected to respective comparators 66a, 66b, monitoring a bag low condition. When this condition is reached on any channel, a corresponding red light 68b, is illuminated and an alarm 70 is sounded and a lamp 72 flashes. A mute switch 748, 74b, 74cis included to mute the alarm 70, eg. during bag changing.

Atthe central monitoring station there isa bank 78 of interlocked switches, and a meter display 80.

Depression of a switch corresponding to a selected channel (ie. to a selected bag) causes the display 80 to indicate the amount of liquid in that bag. Amulti-way socket 82 is provided for connection to a data-logger analogue/digital converter (not shown).

Improved results are obtained by substituting resistors of the strain-gauge typeforthe piezo-electric transducers 28 and 30. Such resistors do not, in themselves, provide electric signals as an output.

They are readily arranged howeverto provide signals in the form of a modified output of an auxiliary circuit and in a preferred arrangement one or more of them is connected to form a part or parts of a bridge circuit, the current or voltage output of which provides the required signal.

As indicated hereinbefore, an electrical circuit may be arranged to maintain theflowconstant. This circuit may be responsivetothe rate of change of weight in the bag orothercontainerortoa rate of flow measured by reference to a photocell and sig ht-glass arrangementthrough which the liquid passes in drips.

lncorporatingasight-glassis in any case useful for visual checking purposes.

Fig. 6 shows a form of adjusting apparatus suitable for response to the circuit. The drip-feed tube 20, or a tube of deformable material connected between the fluid-container and the tube 20 itself, is clamped to a rigid backing 87, which may be part of the stand 12. A compressing member88 pivotally mounted and movable by a spindle 89 bears upon the 20 at end 90 which is of rounded cross-section.

Rotation ofthespindletoadjustcompression of the tube by end 90 is by a reversible electric motor 91 operating via a gearbox 92.

It will be understood that the specific embodiments described herein are described for purposes of illustration only and that various modifications may be made bythose skilled in the artwithoutdeparting from the scope of the i nvention.

Claims (19)

1. A drip-feed apparatus which comprises a liquid container adapted to be suspended from a support and having an outlet conduitforthe gravitational supply of a drip feed liquid from the container to a patient and valve means for adjusting the rate of said supply said apparatus having (a) for linking the containerwith the support, aweight-deformable linkage having a transducer operable to provide an electrical output parameterwhich changes with deformation of the linkage, the weight-deformability of the linkage and the consequent changes of the output parameter both being continuously variable as the weight of liquid in the container diminishes overthe range from that required to fill the container to zero and (b) electrical means, responsive to the output parameter, for sensing the weight of liquid in the container.

2. Apparatus according to Claiml in which the linkage has at least one curved load-bearing part so arranged that the curvature thereofchanges continuously over said range and the transducer is responsive to the curvature of said curved part.

3. Apparatus according to Claim 2 in which said linkage has a ring-shaped portion which provides two of said curved parts.

4. Apparatus according to Claim 3 in which said ring-shaped portion is of generally circularform.

5. Apparatus according to any one of Claims 2 to 4 in which the linkage has an upper partforattachment to the support and a lower part for attachment of the container, said upper and lower parts being interconnected only by said curved load bearing part or parts.

6. Apparatus according to any one of Claims 2 to 5 in which the transducer is a piezo-electric transducer and the output parameter is an E.M.F.

7. Apparatus according to Claim 6 in which the transducer isa quartz-typetransducer.

8. Apparatus according to any one of Claims 1 to 5 in which the transducer is a resistance-type transduc erandtheoutputparameteris resistance

9. Apparatus according to any one of Claims 1 to 8 in which the container is a bag.

10. Apparatus according to any one of Claims 1 to 9 having means responsive to the output parameter for indicating, at least,when thefluid content of the container has emptied or been reduced to a predetermined minimum.

11. Apparatus according to any one of Claims 1 to 10 having means responsive to the output parameter for providing a continuous indication ofthe amount of fluid present in the container.

12. Apparatus according to Claim 10 having means responsivetotheoutputparameterfor providing a visual or audible warning when the container has emptied or been reduced to said minimum.

13. Apparatus according to any one of Claims 10 to 12 in which said responsive means is adapted for attachmenttothefoot rail of a bedfora patient being drip fed from said conduit.

14. Apparatus according to any one of Claims 10 to 12 in which said responsive means is a central processing unit common to said apparatus and at least one other similar apparatus.

15. Apparatus according to any one of Claims 1 to 14 in which the outlet conduit is provided with valve means operable in response to the output parameter to maintain the supply rate substantially constant.

16. Apparatus according to any one of Claims 1 to 15 having means responsive to the output parameter to indicate when the container is empty and/or full.

17. Apparatus according to Claim 16 in which said responsive means is operable to operate an audible warning when the container is substantially empty.

18. Apparatus according to any of Claims 1 to 17 having a central processing unit for receiving the outputs from the transducers of a plurality of drip feed apparatuses.

19. A drip feed apparatus substantially as hereinbefore described and illustrated by reference to the accompanying drawings.