WO1997047339A1

WO1997047339A1 - Gravity infusion set for medical infusions

Info

Publication number: WO1997047339A1
Application number: PCT/IB1997/000702
Authority: WO
Inventors: Jan Willem Marinus Myers
Original assignee: Filtertek, S.A.
Priority date: 1996-06-14
Filing date: 1997-06-14
Publication date: 1997-12-18
Also published as: DE29610419U1; EP0812596A1

Abstract

A gravity infusion set for medical infusions having a drip chamber which by means of a hollow spike can be connected to a bottle containing the infusion liquid. A flexible line with one end is connected to the drip chamber and includes at its other end a coupling device for the infusion needle. Between the drip chamber and the coupling device in the flexible line there is provided a pressure compensator which includes at least one inlet and at least one outlet for the infusion liquid and which dependent on variations of the hydrostatic pressure at the inlet maintains the chosen flow rate at the outlet constant. The pressure compensator includes a compensator chamber having the inlet and the outlet. Between the inlet and the outlet there is provided a thin diaphragm being tensioned and clamped basically over the entire cross section of the housing, wherein a lateral bypass-opening is provided connecting the top side of the diaphragm with the bottom side thereof. The diaphragm adjusts the flow path during variations of the hydrostatic pressure existing on the side of the inlet in such a way that the flow rate on the side of the outlet remains constant.

Description

GRAVITY INFUSION SET FOR MEDICAL INFUSIONS

FIELD OF THE INVENTION

The invention relates to a gravity infusion set for medical infusions. A bottle containing the infusion fluid may be connected to a drip chamber. A flexible line connects the drip chamber with a coupling device for an infusion needle or catheter. Between the drip chamber and the coupling device there is provided a control device for controlling the flow rate of the infusion liquid.

BACKGROUND OF THE INVENTION

In the medical field there are generally two methods of treating patients by infusion therapy: gravity infusion, and infusion by motor driven pump.

In both methods, the infusion liquid may come from a container, for example, a bottle or a filled syringe. Gravity infusion is the cheaper method, but has the draw-back of being relatively imprecise for administering medicines. It is of extreme importance that the staff of the hospital adjusts the prescribed dose per duration of the infusion several times daily. Accordingly, to maintain a precise dose per duration motor driven systems are commonly used. The motor driven systems, however, are comparatively expensive. The common gravity infusion set, described above, generally includes, a drip chamber having a vented or non-vented hollow spike or hollow needle for punching the sterile closure of the container containing the infusion liquid to establish the connection simultaneously when opening the container in a sterile way. A flexible line connects the drip chamber with the distal end at which a coupling device is provided for connecting an infusion needle or catheter. The coupling device generally is a male Luer-lock-connection by the means of which a long term catheter for connecting to the patient may be attached. Between the drip chamber and the patient there additionally is provided a device for controlling the flow rate of the infusion liquid. Commonly a roller clamp or special control valves which operate as no return devices to achieve a still more precise adjustment of the flow rates may be used.

Alternatively, infusion sets may have motor driven pumps which include piston pumps and peristaltic pumps. These pump systems are connected to the patient in the manner discussed above.

Although gravity infusion sets are simple and cheap with regard to their use, they have the draw-back of being very inaccurate. Infusion pumps are far more accurate compared with gravity infusion sets, but are extremely expensive. Piston pumps are mainly used for small volumes. A combination of gravity infusion set with a electronic drip may be used to increase accuracy. These systems, however, are extremely expensive.

DE 27 13 618 C2 discloses a flow control device which, for example, may be used for the intravenous administering of liquids. This device, however, is a combination of a check valve with a pressure regulator which maintains the pressure constant. The pressure regulator divides the flow into two separate portions, one of which is used as a control pressure for the diaphragm of the pressure regulator. Accordingly, this flow control device is of a comparatively complex construction. A further comparatively complicately constructed flow control apparatus for infusion purposes is disclosed in U.S. Patent No. 4,343,305. In this apparatus, the adjustment of the flow rate occurs within the same apparatus containing the pressure regulator. The pressure regulator which is a pressure compensator designed to maintain the pressure constant at a given constant flow rate, contains a freely movable diaphragm as the control means. This design, however, may lead to substantial inaccuracies. SUMMARY OF THE INVENTION

The present invention therefore has the objective to improve a gravity infusion set of the above-defined kind such that with extremely simple and cheap means a high accuracy may be achieved. The inaccuracy of known gravity infusion sets mainly is caused by the fact that the hydrostatic pressure is changing during the emptying of the container or bottle containing the infusion liquid. The inaccuracy may further be caused by the fact that when using roller clamps, the adjusted flow cross-sectional area of the line is changed by cold flow of the plastics material from which such roller clamps are produced. The inaccuracy may further be caused by a shift in position by the patient.

In a gravity infusion set of the above defined kind, these problems are solved by the use of a pressure compensator having at least one inlet and at least one outlet for the infusion liquid. The variations of the hydrostatic pressure at the inlet are compensated for and the flow rate at the outlet is maintained at a constant rate. The pressure compensator includes a compensator chamber communicating with the inlet and the outlet. Between the inlet and the outlet, a thin flexible diaphragm is provided which adjusts the flow path based on variations of the hydrostatic pressure being present on the side of the inlet, in such a way that the flow rate on the side of the outlet is remaining constant. The diaphragm basically is clamped between a cover part and bottom part; over the entire cross-section of the housing. The housing includes a lateral bypass-opening which connects the inlet side of the diaphragm with the outlet side.

Decreasing hydrostatic pressure due to the emptying of the infusion container, as well as variations of the flow opening in the roller clamp may be compensated by the movement of the diaphragm which automatically adjusts the interior flow path to keep the flow rate constant.. This adjustment is in direct response to the decrease of the hydrostatic pressure due to line being compressed in the roller clamp. The diaphragm moves to provide a larger cross-section of the interior control opening, if the hydrostatic pressure is decreasing The interior control opening may also be adjusted due to changes in hydrostatic pressure when the patient changes position. The diaphragm may simultaneously compensate for each of these actions. A further aspect of the invention is that the inlet is connected to a first section of the flexible line coming from the drip chamber, and the outlet is connected to a second section of the flexible line leading to the coupling device. The control device is provided in the second line section. By this, it is assured that the total volume of the infusion to be administered is flowing through the pressure compensator.

Further, it is preferred that the inlet and the outlet are oriented as coaxial connecting pieces at the cap and bottom housing, respectively, of a cylindrical housing forming the compensator chamber. By this, the pressure compensator simply may be assembled with existing infusion sets by cutting the present flexible line and by reconnecting the two line sections by means the connection pieces

Further in this connection it is preferred that oriented coaxially to, and surrounding the connection piece forming the exit within the compensator chamber in the housing there is provided a projecting hub which includes a seat opposite to the diaphragm

Further it is preferred that within the inlet of the compensator chamber there is provided a throttle restriction

According to a further aspect of the invention, the outlet of the compensator chamber includes, a funnel-shaped throttle reduction. In a further aspect of the invention, the pressure compensator operates as a one way or no return item The housing of the pressure compensator includes a cover part or cap and a bottom part or base. Advantageously, the cover part is unitary with the connection piece and the bypass-opening and the bottom part is unitary with the connection piece and the hub having the seat

A further improvement of this embodiment provides a diaphragm clamped between the cover part and the bottom part by means of suitable

- A - unitary formations. In this embodiment, the achieved advantage resides in that the entire pressure compensator merely consists of three parts- the bottom part, the cover part and the diaphragm, which can be produced and mounted at low costs to operate the entire unit as a one-way or non- return item

A further aspect of the invention provides a pressure compensator as having one or more of the above-mentioned features. The pressure compensator may include a ring protruding from the cover part in the direction of the diaphragm and surrounding the inlet. Preferably, the ring has a V-shaped cross-section, and provides a valve set The valve set preferably cooperates with the diaphragm to form a check valve

The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of a preferred embodiment gravity infusion set according to the invention,

FIG. 2 is a sectional view of a preferred embodiment of the pressure compensator according to the invention;

FIG. 3 is a sectional view of an alternative preferred embodiment of the pressure compensator with check valve function according to the invention;

FIG. 4 is a sectional view of the bottom part or base of the pressure compensator of FIG. 3,

FIG. 5 is an end view of the bottom part of FIG. 4, FIG. 6 is a sectional view of the cap or cover part of the pressure compensator of FIG. 3,

FIG. 7 is an end view of the cover part of FIG. 6, and FIG. 8 is a graph showing test results of a standard prior art gravity infusion set versus a gravity infusion set according to the invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

As shown in FIG. 1, the infusion set for medical infusions includes a bottle 1 containing the infusion liquid which usually is suspended at a higher level. By use of a hollow spike or needle 2, which is a part of the usual drip chamber 4, a flexible line 6 is connected to the bottle 1 The flexible line 6 includes a first end 8 connected to the bottom end of the drip chamber 4, and a second end 10 provided with a coupling device 12, which has the function to be connected to an infusion needle or catheter connected to the patient Usually the coupling device 12 is a male Luer-lock-connection Between the drip chamber 4 and the coupling device 12 is a control device 14 for controlling the flow rate of the infusion liquid to the patient which usually is a roller clamp 15.

According to the invention, a pressure compensator 16 may be positioned in the flexible line 6 between the drip chamber 4 and the control device 14 The pressure compensator 16 includes an inlet 18 and an outlet 20 for the infusion liquid The pressure compensator 16 operates to compensate for the hydrostatic pressure at the inlet 18 and maintain the chosen flow rate from the outlet 20 at a constant rate.

As especially shown in FIGS. 2 and 3, the pressure compensator 16 includes a compensator chamber 22 having the inlet 18 and the outlet 20. Between the inlet 18 and the outlet 20 there is mounted a thin flexible diaphragm 24 being pressurized by the fluid column above the inlet 18. The diaphragm 24 is deformed by variations of the hydrostatic pressure existing on the side of the inlet 18 in such a way that the flow rate on the side of the outlet 20 is maintained constant

The inlet 18 is connected to a first line section 6A of the flexible line leading from the drip chamber The outlet 20 is connected to a second line section 6B of the flexible line 6 leading to the coupling device 12, wherein the control device 14 is positioned in the second line section 6B (compare FIG. 1).

As shown in FIGS. 2 and 3, the inlet 18 and the outlet 20 are positioned as coaxial connecting pieces 28 and 30 on the top side and bottom side, respectively, of a cylindrical housing 26. Formed within the housing 26 is the compensator chamber 22. The respective ends of the line sections 6A and 6B, may be pushed onto the connecting pieces 28 and 30. The diaphragm 24 partially covers the entire cross-section of the housing 26, wherein a lateral bypass-opening 32 is provided to connect the top or inlet side 34 of the diaphragm 24 with the bottom or outlet side 36, thereof. As shown in FIG. 3, with reference arrows 37, the infusion liquid entering through the inlet 18 flows from the top side 34 of the diaphragm 24 via the bypass-opening 32 to the bottom side 36 of the diaphragm 24 and from there to the outlet 20 and finally to the patient. Positioned coaxially to the connecting piece 30 forming the outlet 20 there is provided a hub 34 projecting into the compensator chamber 22 of the housing 26. The hub includes seat 40 opposite to the bottom side 36 of the diaphragm 24. The seat 40 together with the opposed bottom side 36 of the diaphragm 24 forms the opening controlled by the hydrostatic pressure which assures that constant flow conditions are existing on the downstream side in spite of the fact that on the inlet side there are variations of the hydrostatic pressure. Formed in the inlet 18 of the compensator chamber 22 there may preferably be a throttle reduction 42. A further throttle reduction 44 may be provided in the outlet 20 of the compensator chamber. In the embodiment of FIG. 2, the throttle reduction 44 has a funnel-shape. As shown in FIGS. 2 and 3, the pressure compensator 16 preferably is constructed as a one-way or no-return item. To this end, the housing 26 of the pressure compensator 16 may be preferably formed of a plastic material and may be formed by a cover part or cap 46 and a bottom part or base 48 which are mounted to each other Referring to FIGS. 4 and 5, the bottom part 48 may in a preferred embodiment include the following dimensions: A = 26 0 mm, B = 25 0 mm, C = 24 0 mm, D = 2.50 mm, E = 2.0 mm, F = 2.45 mm, G = 2.70 mm, H = 4 0 mm, I = 6.0 mm, J = 14.9 mm, K = 4.9 mm, L = 4.65 mm, M = 3.70 mm, N = 28.5 mm and O = 30.0 mm. The bypass-opening 32 leads to channel 35 formed in the cap 46 which may communicate with a channel 35 formed in the base 48. It is contemplated that more than one channel may be formed in the housing 26. Referring tσFIGS. 6 and 7, the cover part 46 may include the following dimensions to lock in place a silicon rubber membrane or diaphragm 24 having, for example, a thickness of 0.30 mm and a diameter of 26 mm to the bottom part 48 having the dimensions specified above P = 26.0 mm, Q = 6.0 mm, R = 4 0 mm, S = 17 55 mm, T = 6 8 mm, U = 4.0 mm, V = 2.5 mm, W = 5.25 mm, X = 4 0 mm, Y = 2.2 mm, Z = 24 0 mm, AA = 28.5 mm, BB = 10 0 mm, CC = 2 0 mm, DD = 2.0 mm and EE = 30.0 mm. The cover part 46 and bottom part 48 may be made of a thermoplastic polymer with a Shore D hardness of a minimum 65 degrees The material may preferably be ultrasonically weldable Preferably, the cover part and bottom part may be made of A B S -type Terlux KR2802 available from BASF, or a polycarbonate-type Makrolon 2858 available from Bayer. The cover part 46 is unitary with the connection piece 28 and the bypass-opening 32 and the bottom part 48 is unitary with the connection piece 30 and the hub 38, which includes seat 40 The diaphragm 24 may be clamped between the cover part 46 and the bottom part 48 by means of suitable formations 50 and 52. Preferably, the formations 50, 52 may be configured in the stepped configuration shown in FIGS. 3, 4 and 6 to secure the diaphragm 24 in the housing Preferably, the diaphragm 24 may be a flexible membrane made from silicone rubber with a Shore A harness of 40 (minimum) to 50 (maximum) degrees. The thickness of the diaphragm 24 may preferably range from 0.3 mm to 0.4 mm. In practical use of the above described embodiment, the infusion liquid from the bottle 1 via the drip chamber 8 and the first line section 6A flows through the inlet 18 of the pressure compensator 16 and through the inner bypass-opening 32 to the outlet 20. The outlet 20 may be connected via the second line section 6B of the flexible line 6 to the patient. After venting or after filling the entire infusion set with liquid, the fluid column above the thin diaphragm 24 deflects the diaphragm and, in turn, decreases the flow cross-sectional area between the bottom side 36 of the diaphragm 24 and the seat 40. The decrease of this flow cross-sectional area in turn provides a lower flow rate. When the liquid level in the system decreases, the deflection of the diaphragm also decreases. Accordingly, the flow cross-sectional area or gap 41 between the bottom side 36 of the diaphragm 24 and the seat 40 is increased. More^' liquid may then flow through this flow cross-sectional area, in spite of the fact that the hydrostatic pressure is decreasing, therefore the flow rate remains constant. The relationship between flow rate, decrease of pressure and area of the gap 41 may be understood from the Poiseuille equation:

wherein

Q = flow rate, C = the constant, p = the pressure variation, d = the opening cross-section, and

I = the length of the opening.

The Poiseuille equation accounts for laminar fluid flows through very small channels. Bernoulli's equation may also be used to explain the action of the pressure compensator:

wherein

Q = flow rate, A = surface area, p = the pressure variation, g = density of the fluid

Accordingly, the flow rate in the different conditions of the pressure compensator is directly proportional to the square root of the pressure differential and is practically not dependent on the fluid viscosity The equations show that the flow rate may be influenced by the decrease of pressure because of the emptying of the infusion bottle 1 Since the flexible diaphragm 24 is deflected by the hydrostatic pressure it is decreasing the flow cross-section and is leaving the narrow gap 41 through which the fluid flows to the outlet or exit 20 of the pressure compensator 16 If the hydrostatic pressure during the infusion is decreasing the force exerted by this pressure on the flexible diaphragm or membrane 24, the deflected diaphragm 24 slowly returns to its original set position and increases the flow cross-section or gap 41 to allow increased fluid flow Accordingly, the decrease of the hydrostatic pressure is automatically compensated for and the flow from the outlet 20 remains constant

To assembly the pressure compensator 16, the diaphragm 24 may be positioned on the bottom part 48 Next, the cover part 46 is placed on the diaphragm/bottom part subassembly and welded to the bottom part by ultrasonics During the welding step, the diaphragm 24 may be slightly stretched due to the chosen geometry of the suitable formation 50, 52 of the cover part 46 and bottom part 48

The pressure compensator 16 will compensate for changes in the set drip rate of an infusion due to 1 change or hydrostatic pressure when the infusion container is emptying, 2 reduction of the lumen of the soft plastic tubing, when it is pinched by the roller clamp which is used in the infusion set for flow regulation This reduction is caused by cold plastic flow due to compression of the soft tubing by the roller clamp, and 3 change of hydrostatic pressure, when the patient changes his or her body position

As shown in FIG. 3, the hydrostatic pressure of the infusion system will flex the thin rubber-like membrane 24 off its check valve seat 54 in the direction of the small hub 38 of the bottom part 48, so reducing or enlarging the gap 41 between the membrane 24 and the seat 40 of the hub 38 depending on the changes of the hydrostatic pressure, and thus influencing the flow The check valve seat 54 may preferably be located on a ring 56, which surrounds inlet 18 The ring 56 preferably has a V- shaped cross-section Tests conducted with the embodiments shown, demonstrate that a preferred height of the gap 41 between the bottom side 36 of the diaphragm 24 and the seat 40 of the hub 38 may preferably be in a range between about 0 3 to 0 5 mm, also taking into account any manufacturing tolerances In the tests conducted, a most preferred height of gap 41 may be about 0 4 mm

The pressure compensator 16 may also preferably include an integrated check valve function This function is activated only when, due to certain circumstances, the counterpressure in the infusion line becomes higher than the total hydrostatic pressure in the infusion line connected to the patient Under these conditions, the flexible membrane 24 will seal against check valve seat 54 and immediately shut-off the line to the bottle 1 This check valve function will prevent the possibility of contammg the infusion line with, for example, blood from the patient, or in case of an occlusion, with a medicament coming from for example, an infusion pump

Tests were conducted with a B Braun standard roller clamp set with a 1 liter bottle of Isotonis salt solution A first test was conducted with the drip rate (drops per minute) set initially at about 27 drops/mm. A second test was conducted with an initial drip rate of about 55 drops/mm Referring to the graph of FIG. 8, the prior art gravity infusion set without pressure compensation for the first test is indicated by line 1 A, and the gravity infusion set with pressure compensation in accordance with the invention is indicated by line 1 B. The prior art gravity infusion set for the second test is indicated by line 2A, and the gravity infusion set in accordance with the invention is indicated by line 2B. As is clear from the graph results, the prior art sets had a noticeable rise in drip rate over the test periods, which ranged from 4 to 6 hours The drip rates of the gravity infusion sets with pressure compensator 16 remained relatively constant over the test period.

While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein

Claims

I CLAIM:

1. Gravity infusion apparatus for medical infusion, having a drip chamber which by means of a hollow spike can be connected to a bottle containing the infusion fluid, wherein a flexible line with one end is connected to the drip chamber and having at its other end a coupling device for an infusion needle or catheter and, wherein between the drip chamber and the coupling device there is provided a means for controlling the flow rate of the infusion fluid, characterized in that in the flexible line there is provided a pressure compensator which includes a housing having at least one inlet and at least one outlet for the infusion fluid and which in dependence from variations of the hydrostatic pressure at the inlet maintains a chosen flow rate at the outlet constant, in that the pressure compensator includes a compensation chamber in communication with the inlet and the outlet, a thin flexible diaphragm is positioned within the compensation chamber, which on occurrence of variations of the hydrostatic pressure being present on the inlet side of the diaphragm, the diaphragm adjusts the flow path such that the flow rate from the outlet is maintained constant, in that the diaphragm is tensioned over the entire cross-section of the housing and in that there is provided a lateral bypass-opening connecting the inlet side of the diaphragm with an outlet side of the diaphragm.

2. Gravity infusion set according to claim 1 , characterized in that the entrance is connected to a first line section leading from the drip chamber and the outlet being connected to a second line section leading to the coupling device, wherein the control device is provided in the second line section.

3 Gravity infusion set according to claim 1 , characterized in that the inlet and the outlet are formed as coaxially positioned connection pieces formed on the top side and bottom side, respectively, of a cylindrically shaped housing forming the compensation chamber.

4. Gravity infusion set according to claim 1 , characterized in that there is provided a hub coaxially to the connection piece forming the outlet and projecting in the compensation chamber in the housing, said hub includes a seat opposite to the outlet side of the diaphragm.

5. Gravity infusion set according to claim 1 , characterized in that within the inlet of the compensator chamber there is provided a throttle reduction.

6. Gravity infusion set according to claim 1 , characterized in that the outlet of the compensator chamber includes a funnel-shaped throttle reduction.

7. Gravity infusion set according to claim 1 , characterized in that the pressure compensator operates as a one use or disposable item, in that the housing of the pressure compensator comprises plastic and, in that the housing is constructed from a cover part and a bottom part.

8. Gravity infusion set according to claim 7, characterized in that the cover part is unitary with a connection piece forming the inlet and the bypass-opening.

9. Gravity infusion set according to claim 7, characterized in that the bottom part is unitary with a connection piece forming the outlet and a hub provided with a seat

10. Gravity infusion set according to claim 7, characterized in that the diaphragm is clamped between the cover part and the bottom part by means of suitable unitary formations.

11. Gravity infusion set according to claim 1 , characterized in that formed around the inlet there is provided a check valve seat in the compensator chamber which in cooperation with the diaphragm operates as a check valve.

12. Gravity infusion set according to claim 11 , characterized in that the check valve seat is formed on a ring protruding from the cover part in the direction of the diaphragm, said ring surrounding the inlet.

13. Gravity infusion set according to claim 12, characterized in that the ring is unitary with the cover part and includes a V-shaped cross-section.

14. A pressure compensator for use in a gravity infusion set comprising: a housing including an inlet, an outlet, a compensation chamber, and a bypass-opening; a diaphragm positioned across the compensation chamber and attached to the housing; a hub surrounding the outlet and protruding into the compensation chamber, the hub including a seat, a gap formed between an outlet side of the diaphragm and the seat.

15. The pressure compensator of claim 14 wherein the height of the gap is initially set at between about 0.3 mm and 0.5 mm.

16. The pressure compensator of claim 14 wherein the housing comprises a cover part including the inlet and a bottom part including the outlet and hub.

17 The pressure compensator of claim 16 further comprising a formation formed on the cover part and a formation formed on the bottom part, the diaphragm secured between the formations

18. The pressure compensator of claim 14 further comprising a ring formed around the inlet, the ring including a check valve seat

19. The pressure compensator of claim 14 wherein the bypass-opening communicates with a bypass-channel to allow infusion fluid to flow from an inlet side of the diaphragm to the outlet

20 A method of operating a pressure compensator for use in a gravity infusion set comprising providing a housing including an inlet, an outlet, a compensation chamber, and a bypass-opening, a diaphragm positioned across the compensation chamber and attached to the housing, a hub surrounding the outlet and protruding into the compensation chamber, flowing infusion liquid through the inlet, through the bypass-opening, and through the outlet, and deflecting the diaphragm to increase or decrease a gap formed between an outlet side of the diaphragm and a seat formed on the hub