GB2183014A

GB2183014A - Flow regulating device

Info

Publication number: GB2183014A
Application number: GB08626242A
Authority: GB
Inventors: David Alan Rawlings
Original assignee: Smith and Nephew Associated Companies PLC
Current assignee: Smith and Nephew PLC
Priority date: 1985-11-01
Filing date: 1986-11-03
Publication date: 1987-05-28
Also published as: GB8527020D0; GB8626242D0

Abstract

A compensating flow regulating device for the parenteral administration of liquid at a constant and controllable flow rate comprises a chamber which has a tubular inlet passage 3 for connection to a liquid supply means, a tubular outlet passage 4 for connection to an infusion means and a flexible membrane 5 which closes off the chamber and which removably covers the end of the tubular outlet passage 4 within the chamber. The flexible membrane 5 is exposed on its outside surface to a reference pressure which by acting on the membrane provides a means for compensating for fluctuations induced in the flow rate, for example by changes in venous blood pressure. The tubular inlet passage 3 has a variably adjustable flow constricting means 10. An apparatus including the compensating flow regulating device is also described. <IMAGE>

Description

SPECIFICATION Flow regulating device The invention relates to a compensating flow regulating devfce for parenteral administration of liquids apparatus comprising the device and process employfng the device.

Parenteral administration of liquids for example by intravenous infusion, is a common practice in medicine. Such liquids can include medicament solutions such as antibiotic solutions, saline solutions, glucose solutions, blood, anaesthetic solutions and the alike. The administration of these liquids to a patient by intavenous infusion usually employs an apparatus which comprises a liquid supply means in the form of a rigid or flexible container connected to a drip chamber to remove trapped air bubbles from the liquid, a liquid infusion means in the form of a cannula or needle which can be inserted in a vein and an intermediate flexible tube made of a plastics material such as plasticised polyvinyl chloride which interconnects the liquid supply and infusion means.The liquid supply container during administration of the liquid is fixed in an elevated position above the needle entry point in the patient so that liquid flows by gravity from the container via the intermediate flexible tube into the patient's vein.

It is an important requirement in the treatment of patients by the administration of a liquid such as a medicament solution that the liquid be administered at a constant and con trollabie flow rate. The flow rate of a given infusion liquid through an infusion apparatus will depend mainly on the height of the container above the entry point of the liquid into the patient i.e. the liquid supply pressure and the resistance to liquid flow provided by the individual components of the apparatus. A convenient method of varying the resistance of liquid flow through the infusion apparatus is to vary the internal diameter of the flexible tube.It is, therefore, common practice to suspend the liquid supply container at an appropriate height above the patient and to regulate the flow of liquid through the apparatus by constricting the flexible tube by a fixed amount using a roller clamp attached thereto.

The rate of liquid flow, normally determined by timing the frequency of drops occurring in the drip chamber, can be regulated by adjusting the roller clamp to the correct pressure. It has been found, however, that these roller clamps need frequent adjustment in order to provide a constant flow rate. This is due in part to the creep behaviour of the plastics tube material under compression which can gradually alter the tube constriction. Such compression can also cause the plastics tube material to lose elasticity or crack if the roller clamp is used frequently in the same area of the tube. Furthermore, these roller clamps cannot provide for a fine regulation of the flow to compensate for fluctuations therein due to random changes in the venous blood pressure.

To overcome these problems flow regulating devices have been developed which do not employ roller clamps. United Kingdom Application GB No.2, 012,393A discloses an apparatus for the microregulating and stabilisation of the flow of a liquid which device comprises a body formed with a cavity therein which has a tubular capillary inlet passage for connection to a liquid supply means, a tubular outlet passage for connection to an infusion means and a flexible membrane which closes off the chamber against ambient air and which removeably covers the end of the tubular outlet passage within the cavity.

United Kingdom Application GB No.2,012,393A explains that the overall flow rate of the liquid through the device is controlled by the height of the liquid supply means above the device and the hydraulic resistance of the capillary inlet tube whilst minor variations in flow rate due to variations in pressure load in the outlet tube can be compensated by the tubular passage. Such a device therefore can regulate the liquid flow at a constant rate. This device, however, had a disadvantage in that in order to change the overall flow rate of the liquid through the device, the device has to be moved in a vertical relationship to the liquid supply means because of the fixed dimensions of the capillary inlet tube.

The hereinbefore mentioned patent further explains that vertical movement of the device can be achieved by means of a clamp attached to the device which is slideably connected to a graduated scale. Such clamp means, however, are relatively expensive and inconvenient in use.

A compensating flow regulating device has now been found which can be adjusted to alter the liquid flow rate through an infusion apparatus without altering the position of the device in relation to the liquid supply means.

The present invention provides a compensating flow regulating device for the parenteral administration of liquid at a constant and controllable flow rate which comprises a chamber which has a tubular inlet passage for connection to a liquid supply means, a tubular outlet passage for connection to an infusion means and a flexible membrane which closes off the chamber and which removeabiy covers the end of the tubular outlet passage within the chamber, said flexible membrane being exposed on its outside surface to a reference pressure, said tubular inlet passage having a variably adjustable flow constricting means.

The device of the invention has the advantage that the overall liquid flow rate through the device can be changed by adjusting the flow constricting means without the need to reposition the device in relation to the liquid supply means.

The flow constricting means should be capable of adjustment to give an overall constant liquid flow rate through the device. Suitable variable adjustable flow constricting means include taps and like liquid flow regulators which have a passage for liquid flow which can be changed to vary the rate of liquid flow through the passage. Preferably the liquid flow rate through such flow regulators can be varied from a nil flow rate to a maximum flow rate to enable the device to be primed before use and flushed after use. Taps with these features are well known in the art.

Apt flow constricting means for use in the device are taps of this type of a pharmaceutically acceptable material which are of appropriate size for use in an intravenous infusion apparatus. Another flow constricting means for use in the device is a helical flow regulator. Such regulators are described in British Patent No. 1,551,170. Suitable helical flow regulators are available from Van Leer (UK) Limited.

The flexible membrane for use in the device will usually be a flexible film. Such films are preferably impermeable and insensitive to liquids commonly used for intravenous infusions in particular aqueous liquids. Suitable flexible films include films made of a water insensitive flexible polymer which is pharmaceutically acceptable, for example, silicone or polyurethane elastomer. Such flexible films can be a plain film or a film with a moulded flexible portion, for example a flexible portion moulded in the form of a bellows. The flexible membrane used in the device will be fixed in position at an end of the chamber to close off the chamber. In the position the flexible membrane can form a flexible wall between liquid inside the chamber and the reference pressure material outside the chamber.The flexible membrane will be fixed in position in a tension-free state so that it is free to move when exposed to small liquid volume changes within the chamber.

The flexible membrane can be fixed in position over an end of the chamber by any convenient method for example by heat sealing, adhesive bonding or mechanical fixing.

The device of the invention can be adapted according to the reference pressure to which the flexible membrane is exposed. When the reference pressure is ambient atmospheric pressure the flexible membrane can be exposed to ambient air without any form of cover. It is preferred, however, the flexible membrane is provided with a cover which has an opening for communication with a reference pressure. Such a cover can act as a protective cover for the flexible membrane.

Advantageously, a space can be provided between cover and the flexible membrane in the form of a compartment above the membrane which can accommodate a liquid reference pressure thus, the reference pressure can be a manometer which contains liquid such as water which is attached to the opening in the cover. Such a device can, if required, be connected via the opening in the cover over the flexible membrane to the air space in a drip chamber under a plastics infusion bag so that the reference pressure to which the membrane is exposed will gradually change as the level of the liquid in the bag falls.

In the device of the invention the flexible membrane is positioned in close proximity to the end of the tubular outlet passage within the chamber so that it can cover the outlet passage end. The membrane in this position can respond to a change in liquid flow rate in the outlet passage end to increase or reduce the flow of liquid through the outlet passage and thus to maintain it at a constant rate.

This enables the device to compensate for changes in flow due to variations in the venous blood pressure.

The chamber of the device of the invention can conveniently be made of pharmaceutically acceptable rigid or semi-rigid plastics material.

The tubular inlet passage of the device of the invention will have means for connecting the passage to a liquid supply means. Similarly, the tubular outlet passage of the device will have means for connecting the passage to a liquid infusion means. Such means can comprise a flexible plastics tube conventionally used for liquid infusion apparatus. The internal diameter of the inlet and outlet passages can suitably be similar to and preferably not less than that of the flexible plastics connecting tube to prevent undue restriction of liquid flow. Thus, it is clear that, for example, the inlet passage cannot be of capillary dimensions.

The device of the invention can form part of liquid infusion apparatus which will allow the parenteral administration of liquid at a constant and controllable flow rate.

Therefore, in another aspect the invention provides an apparatus for the parenteral administration of liquid at a controllable flow rate which apparatus comprises (a) a liquid supply means connected to a drip chamber, (b) a compensating flow regulating device which comprises a chamber which has a tubular inlet passage connected to the liquid supply means via the drip chamber, a tabular outlet passage connected to an infusion means and a flexible membrane which closes off the chamber and removably covers the end of the tubular outlet passage within the chamber, said flexible membrane being exposed on its outside surface to a reference pressure, said tabular inlet passage having a variably adjustable flow constricting means and (c) an infusion means for delivering the liquid to a patient.

In a preferred embodiment the device used in the apparatus is provided with a cover which has an opening which is adapted to be connected via a flexible tube to the air space above the liquid level in the drip chamber so that the reference pressure to which the flexible membrane is exposed gradually reduces as the level of liquid in the liquid supply means falls relative to the membrane.

In a further aspect the present invention provides a process for the parenteral administration of a liquid at a constant and controllable flow rate which process employs a compensating flow regulating devices which comprises a chamber which has a tubular inlet passage for connection to a liquid supply means a tubular outlet passage for connection to an infusion means and a flexible membrane which closes off the chamber and which removably covers the end of the tubular outlet passage within the chamber, said flexible membrane being exposed on its outside surface'to a reference pressure, said tubular inlet passage having a variably adjustable flow constricting means which process comprises passing a liquid to be infused through the compensating flow regulating device at a rate determined by the variably adjustable flow constricting means and the reference pressure acting on the flexible membrane.

The invention will now be illustrated by reference to the following drawing: Figure 1 is a cross-sectional representation of a compensating flow regulating device of the invention.

Figure 1 shows a compensating flow regulating device of the invention (1) which has a chamber (2) of cylindrical shape.

The chamber has an inlet tube (3) which can be connected to a liquid supply means such as a conventional infusion bottle or bag (not shown), and an outlet tube (4) which can be connected to a infusion means such as conventional infusion needle or cannula (not shown) and a flexible membrane (5). The flexible membrane (5) is shown in Figure 1 draped in a tension free state over an end of the chamber (2). In such a position the flexible membrane (5) closes off the chamber (2) and is in close proximity to and covering the end (6) of outlet tube (4). The flexible membrane (5) is provided with a cover (7) in the form of a close fitting lid which holds the edges of the membrane (5) by frictional forces. The cover (7) has an opening (8) which communicates with the air at ambient atmospheric pressure.

The inlet tube (3) has a variable adjustable flow constricting means in the form of a tap (9) of the screw type which has a washer (10) which can be moved in or out to widen or narrow the inlet tube (3). When the device (1) of the invention forms part of an apparatue for the intravenous infusion of a patient the inlet tube (3) is connected to a liquid supply means which is fixed in an elevated position above the device and the outlet tube (4) is connected to a liquid infusion means inserted in a patient's vein. When connected up the infusion liquid will flow into the inlet tube in the direction of Arrow A into chamber (2) and out of the outlet tube (4) in the direction of Arrow B to the infusion means. The overall flow of the infusion liquid can be controlled by tap (9) in the inlet tube. Variations in liquid flow out of the outlet tube (4) which can be caused by variations in the venous pressure, can be compensated by movement of the flexible membrane (5) which alters the distance between the membrane and the end of the outlet tube (6).

The device of the invention can allow the parenteral administration of liquids at a constant and controllable flow rate. Furthermore, the overall flow rate of the liquid through the device can be changed by simply adjusting the tap setting and, therefore, eleminates the need to change the height of the device in relation to the liquid supply means.

Claims

1. A compensating flow regulating device for the parenteral administration of liquid at a constant and controllable flow rate which comprises a chamber which has a tubular inlet passage for connection to a liquid supply means, a tubular outlet passage for connection to an infusion means and a flexible membrane which closes off the chamber and which removably covers the end of the tubular outlet passage within the chamber, said flexible membrane being exposed on its outside surface to a reference pressure, said tubular inlet passage having a variably adjustable flow constricting means.

2. A device as claimed in claim 1 in which the flexible membrane is formed from a pharmaceutically acceptable silicone elastomer.

3. A device as claimed in claim 1 in which the flexible membrane is formed from a pharmaceutically acceptable polyurethane elastomer.

4. A device as claimed in any one of claims 1 to 3 in which the reference pressure is provided by ambient atmospheric pressure.

5. A device as claimed in any one of claims 1 to 4 in which the flexible membrane is provided with a cover which has an opening for communication with a reference pressure.

6. A device as claimed in claim 5 in which the reference pressure is provided by a manometer containing a liquid.

7. A device as claimed in claim 5 in which the opening in the cover is connected, in use, by means of flexible tubing to the air space in a drip chamber under the liquid supply means whereby the reference pressure to which the membrane is exposed will gradually reduce as the level of liquid in the liquid supply means falls relative to the membrane.

8. A device as claimed in any one of claims 1 to 7 in which the variably adjustable flow constricting means is a tap.

9. An apparatus for the parenteral adminis tration of liquid at a controllable flow rate which apparatus comprises (a) a liquid supply means connected to a drip chamber, (b) a compensation flow regulating device which comprises a chamber which has a tubular inlet passage connected to the liquid supply means via the drip chamber, a tubular outlet passage connected to an infusion means and a flexible membrane which closes off inlet passage having a variably adjustable flow constricting means and (c) an infusion means for delivering the liquid to a patient.

10. An apparatus is claimed in claim 9 in which the chamber of the compensating flow regulating device is provided with a cover which has an opening which is connected via a flexible tube to the air space above the liquid level in the drip chamber whereby the reference pressure to which the membrane is exposed will gradually reduce as the level of liquid in the liquid supply means falls relative to the membrane.

11. A process for the parenteral administration of a liquid at a constant and controllable flow rate which process employs a compensating flow regulating device which comprises a chamber which has a tubular inlet passage for connection to a liquid supply means, a tubular outlet passage for connection to an infusion means and a flexible membrane which closes off the chamber and which removably covers the end of the tubular outlet passage within the chamber, said flexible membrane being exposed on its outside surface to a reference pressure, said tubular inlet passage having a variably adjustable flow constricting means which process comprises passing a liquid to be infused through the compensating flow regulating device at a rate determined by the variably adjustable flow constricting means and the reference pressure acting on the flexible membrane.