WO1989003697A1

WO1989003697A1 - Collapsible solution container

Info

Publication number: WO1989003697A1
Application number: PCT/AU1988/000413
Authority: WO
Inventors: Leonard Barry French
Original assignee: Leonard Barry French
Priority date: 1987-10-22
Filing date: 1988-10-21
Publication date: 1989-05-05

Abstract

This invention relates to a container (1) suitable for holding parenteral fluid while it is administered to a subject. The container being sealed to enclose the fluid from the atmosphere, and at least a portion of the container having flexible sidewalls which, in use, allow the container to collapse as the fluid is administered. The container is associated with a hollow cage (5) which determines the minimum volume to which the container can collapse as the parenteral fluid is used. The cage may be internal or external to the container, or may even be incorporated into part of the walls of the container. The container typically is a collapsible drip bag (2), but may also be embodied in any part of a parenteral fluid administration set either alone or in combination with other parts of such a set.

Description

COLLAPSIBLE SOLUTION CONTAINER

Technical Field

This invention relates to improvements in parenteral fluid administration sets, and particularly to a container suitable for holding parenteral fluid while it is administered to a subject, the container being sealed to enclose the fluid from the atmosphere and having flexible sidewalls which, in use allow the container to collapse as the fluid is administered.

Parenteral fluid administration sets commonly include a parenteral fluid container and a length of flexible drip tubing. A hollow needle is attached to the lower end of the drip tubing, and a drip chamber is included near the upper end.

In use the drip tubing and drip chamber are primed with the parenteral fluid. Then a venipuncture is made in a subject with a hollow needle and the drip tubing connected to the needle. A clamp, which is usually included in the drip chamber assembly, constricts the drip tubing to control the rate of administration of the parenteral fluid. Background Art

Where a rigid parenteral fluid container is used the air space within the container may be vented to the atmosphere so that the parenteral fluid is allowed to feed into the patient under the influence of gravity. When a high rate of flow is required the air space may^¬ be pressurised to assist in driving the fluid into the subject. It is important that the administration set is closely monitored to ensure that once the parenteral fluid supply is exhausted air is not allowed to enter the subject since air embolism may cause coronary occlusion, stroke or even death.

It is also desirable to monitor the rate of administration to ensure that when the supply of parenteral fluid is nearly exhausted the level does not fall to allow air to enter the drip tube. This is because if air enters the drip tube it is necessary to reprime the tube before it is possible to recommence administration. This is time consuming for the medical staff and possibly uncomfortable for the subject.

Similar difficulties arise where sealed flexible parenteral fluid containers are employed. These containers are commonly used to administer parenteral fluids under the influence of gravity, and they are designed to collapse as they are emptied. When the flexible containers are filled with parenteral fluid a small air space often remains, and in addition to this volume of air a further volume of air, is often introduced into the container when the drip chamber is primed.

In the past when all the liquid had flowed out of the container the container was almost completely collapsed and subsequently, unless appropriate action was taken, the liquid level would fall down the lengt of the drip tube under the influence of gravity until the remaining air was sucked out of the container and it was completely collapsed. It was in fact possible for all the parenteral fluid to enter the subject and the subject's vein to be placed in communication with the air remaining in the administration set. This result will also occur if all the air is not removed from the drip tube before a fresh container is utilized.

The only forces which are liable to retard the falling of the liquid level in the drip tubing are the force which results from the reduction in pressure of the air remaining in the drip tubing as the liquid level falls, and the force arising from the subject's tissue hydrostatis pressure. These forces on the fluid oppose the downward force of gravity, and if large enough could cause the flow of liquid into the subject to cease. However, it is not adviseable to rely upon these forces to prevent air embolism because the volume of air initially present in the container varies considerably and is often greater than the internal volume of the drip tubing. Usually there is also a volume of air trapped within the drip chamber which complicates the problem.

Disclosure of Invention

According to the present invention there is provided a container suitable for holding parenteral fluid while it is administered to a subject, the container being sealed to enclose the fluid from the atmosphere, and at least a portion of the container having flexible sidewalls which, in use, allow the container to collapse as the fluid is administered; wherein the container is associated with a hollow cage which determines the minimum volume to which the container can collapse as the parenteral fluid is used.

Advantageously the hollow cage is positioned inside the container. In a preferred embodiment the hollow cage comprises a hollow sphere punctured by a plurality of holes (evenly) distributed over its surface.

The cage may prevent complete collapse of the container as it empties. After the fluid has been used to the extent that the container has completely collapsed to the minimum volume defined by the cage, administration of further fluid causes the air remaining in the container to be expanded. The size of the minimum volume defined by the cage, is advantageously calculated to be sufficiently great to stop the administration of parenteral fluid to the subject as or before the fluid supply is exhausted. It is even more advantageous to make the minimum volume defined by the cage sufficiently large that the fluid supply is stopped before the last of the fluid is emptied from the container. In this way it becomes unnecessary to reprime the drip tubing when an exhausted container is to be replaced by a full one.

The container may be used in combination with a drip chamber and tube or in combination with a drip bag, drip chamber and tube, in which case the container may be positioned at any convenient location in a fluid circuit to a subject. For example, the invention may perform the functions of a paediatric burette without valves to prevent air entrainment in the drip tubing. The container may, of course, include air bleed vents and other valves such as may be necessary or desirable in any particular working configuration. Breif Description of the Drawings

The invention will now be described by way of example only with reference to the accompanying drawings, in which: figure 1 shows part of a parenteral fluid administration set including a container embodying the present invention; figure 2 shows an alternative container embodying the present invention; and figure 3 shows another alternative container embodying the present invention. Best Modes of carrying out Invention

Referring now to figure 1 parenteral fluid container 1 comprises a transparent flexible plastic bag 2 filled with parenteral fluid. Bag 2 has a reinforced hole 3 at one end from which it may be hung, and at the other end there is an outlet pipe 4. Bag 2 is filled with parenteral fluid and also contains a cage 5 which has the form of a hollow sphere penetrated by a number of holes 6. Holes 6 allow the parenteral fluid to circulate through cage 5, and one of the holes 6 is connected by a rigid tubular attachment 7 to outlet 4. Attachment 7 ensures liquid communication between the interior of cage 5 and outlet 4 even when bag 2 is completely collapsed about cage 5. When bag 2 is manufactured and filled outlet pipe 4 is sealed with a frangible seal 8. This seal prevents the contents of bag 2 from escaping or becoming contaminated before use. In use a drip chamber assembly, indicated generally at 9, is attached to outlet tube 4 and a pin 10 associated with the drip chamber assembly penetrates frangible seal 8 allowing the parenteral fluid to escape from bag 2 through drip chamber 9 and into drip tube 11. The lower end of drip tube 11 is equipped with a hollow needle 12 which in use is inserted into the vein of a patient.

Often after manufacture a small amount of air remains inside sealed bag 2. When pin 10 punctures frangible seal 8 more air is admitted to bag 2 from the upper portion of drip chamber 9 and pipe 4. It should be appreciated that drip chamber 9 is not completely flooded with parenteral fluid, but contains an air space through which the parenteral fluid is dripped in order, to allow the rate of delivery to be monitored. A clamp, not shown, is used to constrict drip tube 11 and control the rate of delivery.

As the parenteral fluid is delivered to the patient bag 2 collapses and its volume is reduced until the bag is fully collapsed about cage 5. Infusion will then continue and the fluid level will fall under the influence of gravity until the gas pressure in the volume above the fluid becomes low enough to stop flow. By suitably dimensioning cage 5 flow may be stopped when the liquid level is at at any convenient point in the circuit, and ideally before air enters outlet port 4. When delivery of the parenteral fluid is complete tube 11 is clamped shut and bag 2 removed; a new bag may then be attached to drip chamber 8 if desired.

For a bag containing 1,000 ml of parenteral fluid a cage of approximately 4 cm in diameter has been found to prevent the fluid level from falling below the level of the bag and air from entering the drip tubing under normal operating conditions. This result can be confirmed by a simple calculation.

Commonly when a 1,000 ml bag is filled a residual volume of air of approximately 50 mis remains in the bag when it is sealed. When the frangible seal 7 is penetrated by pin 9 of the drip chamber and the drip tube and drip chamber primed or reprimed the volume of air in the bag typically increases to about 100 ml. It can be estimated that this volume will not be increased to more than 150 ml by pressure reduction as the level of fluid falls under the influence of gravity. Accordingly the internal volume of the spherical cage may be calculated from the equation which gives the volume of a sphere V = 4/3 tr R³ inserting 150 mis as the volume V to give a radius R of 3.3 cm.

Since the fluid level may be stopped anywhere within the administration set to prevent air embolism it will be appreciated that it is possible to vary the size of the cage between wide limits. By experiment it has been determined that the diameter of a spherical cage may vary between about 2.0 cm to about 8.0 cm for a 1000 ml bag.

Referring now to figure 2 there is illustrated an alternative bag 2 containing a cage 5' of cylindrical shape. In this case bag 2 will collapse about both the upper and lower ends of cage 5. Figure 3 illustrates a bag containing yet another cage 5'' which comprises a grid 13 wedged in position or fixed to the interior of bag 2 above a rigid end portion 14. In this case only the upper portion of bag 2 is collapsible. Another variation embodying the invention involves the cage being wholly incorporated into part of the sidewalls of the container. In all cases it is necessary to ensure that the collapsible part of the container cannot enter the minimum volume defined by the cage as it collapses, even though it may partially enter the volume defined by cage.

It will be realised that although the invention has been illustrated with reference to embodiments where the minimum volume defining cage has been within the drip bag 2 the invention may be embodied with the cage anywhere in the fluid pathway to the patient, even say in an enlarged portion of the drip tube. It is, however, preferred that the cage is located at the upper end of the drip tube, and it is particularly preferred that the cage is above the drip chamber.

It should, of course, also be appreciated that the term "container" is not limited to a drip bag or equivalent container, and extends to include a drip bag or equivalent container in combination with other parts of a parenteral fluid administration set such as the drip tube. Furthermore the invention may be embodied by. providing the volume restricting means externally of a portion of the fluid path. For example, a suitable external cage may be attached to the outside of the drip bag to maintain the bag or a portion of it in a predetermined geometry and so prevent collapse of the bag beyond a predetermined minimum volume.

Although the above description has been given by way of an illustrative example of the invention many modifications and variations may be made by persons skilled in the art without exceeding the scope of the invention described.

Claims

1. A container suitable for holding parenteral fluid while it is administered to a subject, the container being sealed to enclose the fluid from the atmosphere, and at least a portion of the container having flexible sidewalls which, in use, allow the container to collapse as the fluid is administered; wherein the container is associated with a hollow cage which determines the minimum volume to which the container can collapse as the parenteral fluid is used.

2. A container as claimed in Claim 1 wherein the hollow cage is positioned inside the container.

3. A container as claimed in Claim 2 wherein the hollow cage comprises a hollow sphere punctured by a plurality of holes distributed over its surface.

4. A container as claimed in any preceding claim wherein the cage prevents complete collapse of the container as it empties.

5. A container as claimed in Claim 1 wherein the minimum volume defined by the cage is calculated to be sufficiently great to stop the administration of parenteral fluid to the subject before the fluid supply is exhausted.

6. A container as claimed in Claim 1 wherein the minimum volume defined by the cage is calculated to be sufficiently large that the administration of parenteral fluid to the subject is stopped before the last of the fluid is emptied from the container.

7. A container as claimed in any preceding claim wherein the container is used in combination with a drip chamber and tube.

8. A container as claimed in any preceding claim wherein the container is used in combination with a drip bag, drip chamber and tube.

9. A container as claimed in any preceding claim wherein the container may be positioned at any convenient location in a fluid circuit to a subject.

10. A parenteral fluid container substantially as herein described with reference to the accompanying drawings.