GB2147087A

GB2147087A - Parenteral fluid administration set

Info

Publication number: GB2147087A
Application number: GB08422232A
Authority: GB
Inventors: Robert Farmer
Original assignee: Smith and Nephew Associated Companies PLC
Current assignee: Smith and Nephew PLC
Priority date: 1983-09-10
Filing date: 1984-09-03
Publication date: 1985-05-01
Also published as: GB8422232D0; GB8324282D0; GB2147087B

Abstract

A shut-off device, for use in a burette for an administration set for delivering parenteral fluid comprising a cylindrical liquid holding chamber 8 having an inlet 9 capable of connection to a source of parenteral fluid and an outlet 12 capable of communicating with an infusion means attached to a patient, comprises a buoyancy means 1 having at or near its centre a bobbin-shaped means 3 which is capable of forming an air- tight seal with the outlet 12 of the chamber 8. Preferably the bobbin- shaped means 3 is made of soft rubber and is a snap fit in the buoyancy means 1, which may be made of medical grade polypropylene. <IMAGE>

Description

SPECIFICATION Parenteral fluid administration set The present invention relates to a burette for use in an administration set suitable for delivering parenteral solutions which is of the type which includes a calibrated liquid holding chamber and a free floating valve in the chamber which will close off the outlet from the chamber as the chamber empties so as to avoid the risk of air being delivered to the patient receiving the parenteral solution.

Parenteral solution administration sets of the type which include a calibrated liquid holding chamber or burette have been used for many years where the rate of infusion of the solution is measured in ml/hour rather than by counting drops. Such burette-type administration sets comprise a burette the top of which typically carries three inlets, one in communication with a source of infusion fluid, a second carries a filter and allows sterile air to pass into the burette as the solution is infused and the third covered with a septum cap allows for injection of medicament into the parenteral solution. The bottom of the burette has an outlet which leads via a steel needle to a drip chamber which is in turn connected to a means for delivering the solution to the patient for example an intravenous needle or catheter.In use the burette is filled with parenteral fluid and the drip chamber primed by expelling air from it through the burette. The solution is administered to the patient at a rate measured by the reduction in volume per unit time as measured in the burette. However, when the burette is empty air will continue to pass through the needle into the drip chamber and may if not noticed be infused into the patient with life threatening results. It has been recognised that a shutoff valve incorporated into the burette type of set to close the outlet as the fluid runs out would mitigate against this happening. However none of the valves disclosed to this date have been entirely successful. British Patent No. 1182016 discloses a burette type set in which a semipermeable membrane closes the outlet. Fluid may pass through the membrane but air will not.This has the disadvantage that priming the drip chamber may damage the membrane as air is forced through it under pressure. British Patent No. 1383975 describes a burette-type set which has inter alia a membrane valve which floats within a cage.

Whilst this will make priming easier the membrane may stick to its cage in a way which prevents it closing the outlet. British Patents Nos. 1523292 and 1523293 disclose a membrane permeable to fluid but not to air which allows air from the drip chamber to bypass the membrane valve during priming but the pressure of parenteral fluid causes an airtight seal to be formed during administration.

Such membranes also filter the parenteral fluid and may remove any medicament added by absorption on to the filter. British Patent No. 1600831 discloses a burette-type set in which the outlet may be closed by a ball valve retained within a cage which seats on a valve seat present in the outlet. This type of valve may have the disadvantage that as it is moulded from a polymeric material it may not be perfectly round and seat in a non-sealing manner in the outlet. Also by using a moulding technique certain irregularities known as split-lines and gate marks may be present on the surface of the ball which if they coincide with the valve seat will not seal correctly.

United States Patents Nos. 3216418 and 321641 9 disclose other types of membrane shut-off valves including a free floating disc membrane valve and a disc membrane which floats whilst being retained close to the outlet by means of a flexible strip attached to the bottom of the burette. In this type of device the size of the membrane valve must be carefully chosen to ensure that the membrane always settles over the outlet which is reentrant into the burette making moulding more complex. Such valves may suffer from the disadvantage that they may stick to the sides of the burette. This is particularly true of the flap membrane valve which tends to be up against the wall of the burette as the solution is administered. United States Patents Nos.

3625211 and 3774603 describe burette sets in which the membrane valve is retained in a cage. Such cage devices may cause the valve to stick open and may retain air bubbles preventing the valve from closing, particularly if the fluid is viscous. United States Patent No. 4078563 described a membrane disc valve in which the cage retainer is replaced by posts which have disc retaining stops so that the disc floats just above the outlet as fluid is dispensed and slides down the post to seat over the outlet when the burette empties. In such a device the valve may stick open even when the fluid is exhausted.

European Patent Application No. 102141 published after the priority date of the present application describes a burette device in which the shut-off device is restrained over the outlet of the burette set. A portion of the shut-off device frictionally engages the walls of the outlet tube risking the possibility of the shut-off device sticking open.

It has been found that by using a free floating disc which comprises a bouyancy means and a bobbin-shaped means held at the centre of the bouyancy means, a shuft-off device may be manufactured which is free from dangerous manufacturing flaws such as gate marks, can not stick to the walls of the burette, may be simply made and will not require special moulding or seating at the outlet of the burette.

Accordingly the present invention provides a burette for use in an administration set suitable for delivering parental fluid which burette is of the type which comprises a cylindrical liquid holding chamber which has an inlet capable of being placed in fluid communication with a source of parenteral fluid and an outlet capable of being placed in fluid communication with a means for delivering parenteral fluid to a patient and which has within the chamber a shut-off device which is free to float on the parenteral fluid when present but will form an air-tight seal with the outlet when the chamber is empty characterised in that the shut-off device comprises a buoyancy means having at or near its centre a bobbin-shaped means which is capable of forming an air-tight seal with the outlet of the chamber.

By bobbin-shaped is meant a piece which comprises of two plates each having at least one flat surface, the other being flat or arcuate, joined at the centre of the flat surface by means of a cylinder of material.

The shut-off device used in the present invention will have adequate buoyancy in order to lift off the seating at the outlet of the fluid chamber when liquid is added to the chamber and to float freely on the liquid during use. As the liquid level falls, the shutoff device floating on the liquid falls correspondingly, whilst lying in a generally horizon- tal plane. The liquid level falls until such time as the bobbin-shaped means locates itself onto the seating at the outlet to produce a seal which prevents any further fluid (liquid or air, but particularly air) from passing out of the chamber.

The shut-off device of the present invention is suitably made of two parts, one part giving buoyancy to the whole device and the other a means for achieving the air-tight seal at the outlet of the fluid chamber. In order to obtain an adequate sealing effect it is necessary that at least one of the mating components should be made in a soft pliable material. It is advantageous from the point of view of simplicity and cost effectiveness that the bobbinshaped means should be formed from a soft and pliable means whilst the seating can be integrally moulded into the outlet end of the fluid chamber and is made of a rigid plastics material. Suitably therefore the bobbin-shaped means is formed from a soft pliable material which includes medical grades of soft rubber.

The bobbin-shaped means can be moulded from soft rubber in a way which avoids the presence of split lines or gate marks on critical surfaces, which has been a disadvantage found with previously known plastics devices, especially those involving ball valves.

Aptly the specific gravity of material used in the bobbin-shaped means may be greater than 1.0 so to use more of the weight of the device to provide the force to achieve the airtight seal. However, it is preferred that the bobbin-shaped means has a specific gravity of less than 1.0 to ensure that the shut-off device floats freely when fluid is present.

Aptly the surface of the bobbin-shaped means which is to seat onto the seating will be flat, however it is envisaged with the invention that the surface may be arcuate or any other shape which is capable of forming an air-tight seal with the seating at the outlet of the fluid chamber.

Suitably the bobbin-shaped means is symmetrical so that no restrictions are required in the chamber to keep it in the correct alignment and should the device turn over during the filling or priming operations, the effectiveness and safety of the device is not compromised.

The second part of the device comprises the buoyancy means which is capable of raising the bobbin-shaped means onto the surface of the fluid. Suitably the buoyancy means is formed from a rigid polymeric material. Suitable polymeric material includes polyethylene, polypropylene, polyamide. A preferred polymer is a medical grade polypropylene.

The buoyancy means will be capable of accepting the bobbin-shaped means at or near its centre. Suitably a circular hub is present which adapts to accept the cylindrical part of the bobbin-shaped means in a snap fit.

Suitably the buoyancy means will be in the form of a flat disc which lies in a parallel plane to those of the ends of the bobbin and is positioned between ends of the bobbinshaped means, around the cylinder of material joining the ends together. The dimensions of the disc are such that it is free to move up and down inside the fluid chamber as the liquid level rises and falls, that is to say that the diameter of the flat disc is from 1 to Smm less than that of burette chamber.

The buoyancy means suitably is shaped as an annular flat ring which has at least two radial arms extending from a hub at the centre to provide rigidity and a means for holding the bobbin-shaped means. Aptly the buoyancy means will have three radii symetrically placed around the hub. This arrangement means that the chamber can be filled quickly either by priming or from the parenteral fluid container without causing undue turbulence. This arrangement also avoids the risk of trapping air-bubbles beneath the buoyancy device which could affect the efficiency of the seal.

Alternatively the buoyancy means can be in the form of a central incomplete annular ring which is adapted to accommodate the bobbinshaped means. At least two radial arms join this central hub to an annular ring which has a diameter substantially less than that of the burette chamber. At least two triangular pieces, and preferably three, issue from this annular ring. The outer points of each of the triangular pieces are arranged to fall on a circle whose radius is substantially the same as that of the burette chamber. This allows the shut-off device to rise and fall freely even if the burette chamber has slight imperfections arising from manufacture, sterilisation or caused by the priming operation, as the buoy ancy means will touch the chamber at only three points instead of around a circumference of a circle.

The buoyancy means also serves as a visual aid to follow the liquid level as the liquid leaves the chamber.

The shut-off device may rest either on a specially moulded seating or may rest over the outlet of the fluid chamber. The seating may be a raised annular ring extending around the outlet to the fluid chamber.

In a further aspect the present invention provides an administration set for use in delivering parenteral fluid which administration set comprises a burette as herein before described in fluid communication with a source of parenteral fluid and with the patient.

By parenteral fluid is meant any fluid which may be given parenterally such as saline, nutritional solutions, medicament containing solutions and the like.

In a further aspect of the present invention the burette and administration set will be sterile and will be packaged in a bacteriaproof pack. The device may be sterilised by conventional means.

The burette device may be made by conventional means of forming each end cap by moulding and the body of the device by extrusion. The shut-off valve may be made as its two constituent parts by moulding and then manually assembled. The shut-off device is placed in the body of the burette and the end cap of the burette sealed in place using adhesive.

In a further aspect the present invention provides a shut-off device suitable for use in a burette as herein before described.

The shut-off device and the burette for use in the administration sets comprising the present invention will now be described by way of example only with reference to the accompanying drawings in which, Figure 1 shows a top view of the shut-off device.

Figure 2 shows a cross section of the cut-off device taken through two radial arms.

Figure 3a, b shows the shut-off device separated into its component parts.

Figure 4 shows an administration set with the shut-off device seating on a projecting ring about the outlet of the fluid chamber.

Figure 5 shows an administration set with the shut-off device seating over the outlet.

Figure 6 shows a top view of an alternative buoyancy means.

Fig. 1 shows a top view of the shut-off device. The buoyancy means comprises an annular ring (1) formed from a medical grade polypropylene which is capable of floating on the fluid in the chamber with the bobbinshaped means in position. The annular ring (1) has three symmetrically arranged radial arms (2) radiating from a hub in the centre of the ring (not shown). The bobbin-shaped means (3) passes through hub.

Fig. 2 shows a cross-section through the shut-off device taken through two of the radial arms (2). The annular ring (1) and the radial arms (2) are moulded from a single piece of plastics material. The bobbin-shaped means (3) which fits into the hub at the centre of the annular ring, is formed from a single piece of soft rubber. The bottom has two flat plates (4) which are joined at their centre by a cylindrical piece (5). This piece is adapted to fit into the hub portion at the centre of the annular ring (1).

Figs. 3a and 3b show each of the components separately. The hub (6) is shown at the centre of the annular ring as an incomplete circle having a space (7) into which the cylindrical piece (5) fits so that it is free to move up and down and if need be rotate and it is also capable of tilting if the burette is not set up vertically so that it provides a good seat even if the burette is inclined.

Fig. 4 shows an administration set in which the top of the fluid containing chamber (8) has three openings. The centre opening (9) is the inlet for the fluid and is usually in communication with a source of parenteral fluid.

The other two openings (10, 11) are generally available for adding a medicament to the parenteral fluid when it is closed by a septum cap and for allowing air to pass into the chamber as the fluid is administered and this opening is usually closed with a cap containing a filter capable of removing dust and bacteria. The fluid chamber (8) can have a volume of between 25 ml., 100 ml. and 150 ml. or even larger depending on the type of fluid to be administered.

The bottom of the fluid chamber (8) has a single outlet (12) leading to a drip chamber (13)which is fluid communications with the patient receiving the fluid, usually by a tube and cannular or an indwelling catheter (not shown). The shut-off device is shown with the bobbin-shaped device resting on a raised ring (14) around the outlet of the fluid chamber to form an air-tight seal. The spaces between the radial arms of the shut-off device avoids the risk of trapping air between the device and the bottom of the fluid chamber and compromising the air-tight seal.

Fig. 5 shows a similar administration set to that shown in Fig. 4 except that the shut-off device rests directly on the bottom of the fluid chamber on a valve seat (15).

Fig. 6 shows a top view of an alternative buoyancy means which shows a central hub (16) as an incomplete annular ring which has a space (17) to accommodate the bobbin shaped means shown in Fig. 3a. Radial arms (18) join the central hub (16) to an annular ring (19)which has a diameter substantially smaller than that of the burette chamber.

Three triangular shaped pieces (20) issue from the annular ring (19). The points of the triangular pieces lie on a circle which has a diameter approximately equal to that of the burette chamber, so that the shut-off device may rise and fall with the level of liquid in the burette. This form of device will operate successfully even if the burette has slight imperfections in its cross-section because the shutoff device is only required to touch the burette walls at three points to keep it in correct orientation.

Claims

1. A burette for use in an administration set suitable for delivering parenteral fluid which burette is of the type which comprises a cylindrical liquid holding chamber which has an inlet capable of being placed in fluid communication with a source of parenteral fluid and an outlet capable of being placed in fluid communication with a means for delivering parenteral fluid to a patient and which has within the chamber a shut-off device which is free to float on the parenteral fluid when present but will form an air tight seal with the outlet when the chamber is empty characterised in that the shut-off device comprises a buoyancy means having at or near its centre a bobbin-shaped means which is capable of forming an air-tight seal with the outlet of the chamber.

2. A burette as claimed in claim 1 in which the bobbin-shaped means comprises two plates each with two flat surfaces joined at their centres by a cylindrical portion.

3. A burette as claimed in either of claims 1 or 2 in which the bobbin-shaped means is formed from a material having a specific gravity of less than 1.

4. A burette as claimed in claim 3 in which the bobbin-shaped means is formed from soft rubber.

5. A burette as claimed in any of claims 1 to 4 in which the buoyancy means comprises an annular flat ring which has at least two radial arms linking the ring with a central hub adapted to receive the bobbin-shaped means.

6. A burette as claimed in claim 5 in which the buoyancy means has a diameter 1 to Smm less than that of the burette chamber.

7. A burette as claimed in any of claims 1 to 4 in which the buoyancy means comprises a small annular ring joined to a central hub adapted to receive the bobbin-shaped means, said annular ring having three projecting annular pieces whose outer points lie in a circle whose diameter is substantially the same as that of the burette.

8. A burette as claimed in any of claims 5 to 7 in which the buoyancy means is formed from a rigid polymeric material.

9. A burette as claimed in claim 8 in which the buoyancy means is formed from polypropylene.

10. A burette as claimed in any of claims 1 to 9 which is sterile and packaged in a bacteria proof pack.

11. A shut-off device for use in the burette of an administration set for parenteral fluid characterised in that the shut off device comprises a buoyancy means having at or near its centre a bobbin-shaped means which is capable of forming an air-tight seal with the outlet chamber of the burette which contains it.

12. A shut-off device as claimed in claim 11 in which the bobbin shaped means comprises two plates each with two flat surfaces joined at their centres by a cylindrical portion.

13. A shut-off device as claimed in either of claims 11 or 12 in which the buoyancy means comprises an annular flat ring which has at least two radial arms linking the rink with a central hub adapated to receive the bobbin-shaped means.

14. A shut-off device as claimed in either of claims 11 or 12 in which the buoyancy means comprises a small annular ring joined to a central hub adapted to receive the bobbin-shaped means, said annular ring having three projecting triangular pieces whose outer points lie on a circle whose diameter is substantially the same as that of the burette.