Pumping Arrangement for Intravenous Supply of Fluids

1. Field of the Invention

This invention relates to pumping arrangements and in particular to pumping arrangements for use in medical applications such as the intravenous supply of fluids to a patient.

This case also relates to the subject matter disclosed is commonly owned U.S. applications Ser. No. 07/430,851 filed Nov. 2, 1989, now U.S. Pat. Pat. No. 5,151,019 Ser. No. 07/744,350 filed Aug. 13, 1991, now U.S. Pat. No. 5,154,700 and Ser. No. 07/775,449 filed Oct. 15, 1991, which are hereby incorporated by reference into the present application.

2. Discussion of Background

In pumping applications involving intravenous supply of fluids it is common for deformable tubing, such as p.v.c. tubing, to be used to deliver the required fluid to the point of application. Where the supply rate and pressure is required to be carefully controlled, as is generally the case in medical applications, a serious problem can arise if the delivery tubing is restricted in any way (for example, by a patient rolling over onto it). Means can be provided to detect the resultant increase in pressure in the delivery tubing and disable the pumping action. However, if the restriction is removed (in the example given, by the patient rolling over again, off the tubing, or more likely by a nurse responding to an alarm also initiated by the means for detecting the increase in pressure) an undesirable surge of fluid to the point of application can result due to pressure retained in the delivery tubing.

Accordingly, one object of this invention is to provide a new and improved pumping arrangement in which the undesirable surge of fluid to the point of application, characteristic of the conventional pumping arrangement, is mitigated.

The above object, and others, are achieved according to the present invention by providing a novel pumping arrangement including means for subjecting fluid to pressure, input and output controllable valve means for restricting fluid flow provided on input and output sides of the fluid pressure subjecting means, means responsive to fluid pressure in delivery tubing connected in operation between the output controllable valve means and the point of application of the required fluid for detecting an increase in fluid pressure, and means responsive to increases in pressure detected by said fluid pressure responsive means for controlling both the input and output controllable valve means to open, whereby fluid under excess pressure in the delivery tubing is released back towards a source of fluid connected in operation to the input controllable valve means.

Normally means are also provided for disabling the fluid pressure subjecting means in response to increases in pressure detected by the fluid pressure responsive means.

Preferably the controllable valve means each includes means operable to squeeze the tubing to produce occlusion.

Preferably the pumping arrangement is also in accordance with the invention described in the above cross-referenced copending application Ser. No. 07/430,851, now U.S. Pat. No. 5,151,019.

Preferably again the fluid pressure responsive means includes a device as described in the above cross-referenced related co-pending application Ser. No. 07/744,350 which has issued as U.S. Pat. No. 5,154,700.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic block diagram of a pumping arrangement in accordance with the present invention;

FIG. 2 is a view in elevation of one pressure responsive device in accordance with the present invention;

FIG. 3 is a cross-sectional view along the line x--x in FIG. 2; and

FIG. 4 is a schematic block diagram of a liquid flow monitoring arrangement associated with the pressure responsive device of FIGS. 2 and 3 in accordance with the present invention.

Referring to the drawing, a length of standard pliant p.v.c. tubing 1 of approximately 4.1 mm outside diameter and 0.5 mm wall thickness is connected at one end to a source of fluid 2. From that end, tubing 1 passes through a pumping device 3 to a point of application 4. The point of application in this case is a patient and the fluid is a fluid required to be supplied intravenously. The means at the point of application for achieving this is not represented, but may be taken to be conventional.

Between the source of fluid 2 and pumping device 3 the tubing 1 may be regarded as supply tubing, whilst between pumping device 3 and the point of application 3 the tubing 1 may be regarded as delivery tubing, although in this example the length of tubing is continuous.

Pumping device 3 includes a squeezing device 5 through which tubing 1 passes. Squeezing device 5 is arranged to deform tubing 1, first in one direction locally to reduce its volume and thereafter in another direction tending to restore the original cross-sectional shape of the tubing 1.

On the supply or input side of squeezing device 5 is a controllable input valve 6 which is operable to block the passage of fluid between the squeezing device 5 and the fluid source 2 by squeezing tubing 1 to produce occlusion.

On the delivery or output side of squeezing device 5 is a controllable output valve 7 which is operable to block the passage of fluid between the squeezing device 5 and the point of application 4.

For more detail of the pumping device 3 reference may be made to the specification of co-pending application Ser. No. 07/430,851 now U.S. Pat. No. 5,151,019. Squeezing device 5 and controllable valves 6 and 7 described herein corresponding to squeezing device 2 and inlet and outlet valves 3 and 4 described in detail in the specification of the co-pending application Ser. No. 07/430,851 now U.S. Pat. No. 5,151,019.

Squeezing device 5 and inlet and outlet valves 6 and 7 shown in the accompanying drawing are controlled by a microprocessor control unit 8 corresponding to control unit 52 as described in co-pending application Ser. No. 07/430,851 now U.S. Pat. No. 5,151,019 to produce pumping action as described in detail therein. Briefly, with squeezing device 5 relaxed, output valve 7 closed and inlet valve open, fluid passes into the region of the tubing encompassed by squeezing means 5. With squeezing means 5 activated locally to reduce the volume of tubing 1, inlet valve 6 closed and outlet valve 7 open, fluid is passed towards the point of application 4. The process then repeats. Normally, it will be noted, inlet valve 6 is shut when outlet valve 7 is open and vice versa.

Beyond outlet valve 7 is a pressure responsive device 9 which in this particular case is an adaptation of the pressure responsive device described in detail in the specification of co-pending application Ser. No. 07/744,350 now U.S. Pat. No. 5,154,700. Pressure responsive device 9 is connected to microprocessor control unit 8. When the signal from pressure responsive device 9 exceeds a given threshold indicating that the pressure in the delivery portion of tubing 1 had risen beyond a predetermined value indicative of a restriction caused, for example, by the patient rolling over onto the tubing 1, control unit 8 acts to cause squeezing device 5 to be disabled and both input and output valves to be opened together so as to enable excess fluid in the delivery portion of tubing 1 to pass back towards the fluid source 2 and thus relieve the excess pressure caused by the restriction. At the same time an alarm is caused to be activated to call the attention of a nurse to the restriction.

It will be appreciated that the arrangement may be such that normal operation of the pumping device 3 recommences as pressure in the delivery portion of tubing reduces. In that case, however, "hunting" may occur since a reduction in pressure will occur not only because of a removal of the causative restriction, but also by the very opening of valves 6 and 7 upon device 9 detecting an increase in pressure.

If "hunting" as described is undesirable, renewed pumping may be subject to a reset control, operable by the nurse upon removing the cause of the restriction.

FIGS. 2 and 3 illustrate details of the pressure responsive device 9, as disclosed in the noted related U.S. Pat. No. 5,154,700. As shown in FIGS. 2 and 3, the device 9 includes a hard bed member 11 across the surface of which may be positioned a length of the pliant tubing 1.

Hinged to the bed member 11 by hinge 13 is a main body 14 which has a circular cylindrical passage 15 extending orthogonally away from the surface of the bed member 11 across which the tubing 1 is positioned. The passage 15 exits from main body member 14 towards tubing 1 through a tubular projection 16 which, when the main body member 14 is closed up towards the bed member 11, flattens the tubing 1 against the surface of the bed member 11 over a short length 17 thereof. The extent to which tubular projection 16 projects towards bed member 11 is such that when the main body member 14 is fully closed up to the bed member 11 (and held by means of a suitable catch, not represented) the tubing 1 is flattened against the bed member 11 without occlusion occurring and without unduly impeding the flow of liquid through the tubing 1.

Inserted within the passage 15 is a linear voltage displacement transducer 18 of known form. As know per se transducer 18 has a spring-loaded plunger 19 and produces an output digital voltage signal which is indicative of the extent to which plunger 19 extends beyond the body of the transducer 18. The output voltage signal of transducer 18 will thus vary with the displacement of a surface against which plunger 19 is pressed in the direction of action of the plunger 19.

Transducer 18 is entered into and fixed within the passage 15 to an extent such that plunger 19 is spring-biased against the flattened surface of the tubing 1 when the main body member 14 is closed up and secured to the bed member 11, as previously described.

In operation, any variation in the pressure of fluid passing through the tubing 1 will tend to cause expansions and contractions. It is believed that flattening the tubing as above described magnifies the resultant displacement of the relatively flat portion of the wall of the tubing with which the plunger 9 is in contact, thus enabling the transducer 8 to respond to such variations with a higher degree of sensitivity than would otherwise be the case.

FIG. 4 is a schematic block diagram illustrating functional operation of the pressure responsive device 9 in conjunction with the microprocessor 8 of the present invention.

Referring to FIG. 4 only transducer 18 and plunger 19 of the pressure responsive device 9 of FIGS. 2 and 3 are represented. The analog output voltage of transducer 18 is arranged to be sampled at the rate of once per second by a sampling circuit 20.

The output of sampling circuit 20 is connected to the input of an analog-to-digital converter 21.

The output of analog-to-digital converter 21 is connected to a unidirectional "count down" only shift register 22, where it is stored, and in parallel to one input of a comparator circuit 23. A second input for comparator circuit 23 is derived from the output of shift register 22 so that comparator circuit 23 compares the digital signal output of analogue-to-digital converter 21 derived from one sample taken by sampling circuit 20 with that derived from the sample taken one second before.

The output of comparator circuit 23 is connected via a positive threshold circuit to a suitable visual and/or aural alarm 25.

For a further understanding of the operation of the arrangement illustrated in FIG. 4 reference is made to the above-noted U.S. Pat. No. 5,154,700.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.