GB1568414A

GB1568414A - Automatic intravenous flow regulator

Info

Publication number: GB1568414A
Application number: GB26183/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-07-02
Filing date: 1977-06-22
Publication date: 1980-05-29
Also published as: AR213208A1; IT1084566B; JPS535892A; AU2622577A; SE7707506L; BR7704338A; BE856391A; FR2356988B1; DE2729642B2; ES460247A1; IE45146L; DE2729642A1; AU500155B2; PH13801A; DE2729642C3; JPS5718895B2; GR63661B; FR2356988A1; ZA773845B; IE45146B1

Description

(54) AUTOMATIC INTRAVENOUS FLOW REGULATOR (71) I, KARL EDMUND BECKER, JR., a Citizen of the United States of America of 4247 Crane Boulevard, Jackson, Mississippi 39216, United States of America, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates primarily to a flow regulator for use in a parenteral administration set, and more particularly to a flow regulator for sustaining fluid flow to a patient after his IV bottle has become empty.

Parenteral administration sets are used to intravenously infuse parenteral solutions. A container of parenteral solution, typically a glass bottle or a collapsible plastic bag, feeds fluid to the administration set and then to the patient's circulatory system through an intravenous catheter. Infusion of the parenteral solution is currently achieved by piercing a membrane stopper at the mouth of the container, suspending the container in an inverted condition, and delivering the parenteral solution to the patient through flexible infusion tubing and an intravenous catheter.

The tubing generally includes a clamp for regulating the infusion rate, and a drip chamber is customarily provided in the fluid circuit to enable observation of the infusion rate.

A patient is frequently scheduled to receive more than a single container of parenteral solution. Therefore, when one container of solution is infused, the empty container must be removed and replaced by a fresh container so that the scheduled infusion can be completed. Obviously, it is desirable to replace the empty container immediately upon becoming exhausted, and if this is accomplished, no difficulties arise. If the empty container is not promptly replaced, on the other hand, the intravenous infusion catheter is susceptible to becoming clotted. If clotting results, a new catheter must be fitted, at considerable cost in materials, employee time, and patient discomfort.

The problem of clotting has been recognized, and a proposed solution can be found in U.S. Patent No. 3,738,361, issued to Price on June 12, 1973. The Price patent discloses a float-controlled valve, residing in the IV bottle, and serving to gradually close off the main supply line between the IV bottle and the flexible infusion tubing when the volume of parenteral solution in the bottle becomes low. The stated purpose for the Price mechanism is to provide an extended time for attendant personnel to change an IV container with an insufficient volume of parenteral solution.

While the Price flow regulator should operate as disclosed, several potential problem areas come to mind. Because the flow regulating valve is in the sole supply line, malfunction of the valve would necessarily have a significant effect on steady-state infusion rate. Next, mechanical tolerances for the Price valve elements are likely to be extremely difficult to maintain, and therefore variations can be expected between one flow regulator and another. Also, misalignment and surface tension could cause the Price valve to stick, in either its open or its closed condition. Finally, the Price mechanism fits directly into the IV bottle, a condition no longer feasible with current intravenous technology.

The elimination of the foregoing drawbacks and the provision of an efficient automatic flow regulator for an intravenous infusion set, are effected by the present invention.

The present invention relates to a device for use as part of a parenteral administration set, which serves the function of regulating the flow of parenteral solution to a patient.

The device automatically controls fluid flow between a first rate when the IV bottle con tains a supply of fluid, and a second reduced rate when the IV bottle is empty. Low-rate flow continues with a particular embodiment, for approximately two hours.

The flow regulator is adapted for direct connection to an IV bottle. Parenteral solution from the bottle fills a reservoir chamber having a capacity of approximately 50 cc.

When the bottle contains fluid, fluid from the reservoir chamber enters a primary flow path and is fed to the patient through conventional infusion tubing, the infusion rate being adjusted by any known type of slide or pinch clamp. At the same time, the bottle replenishes the parenteral solution which was discharged from the reservoir chamber.

When the IV bottle becomes empty, the fluid level in the reservoir chamber drops, and the entire infusion is through a secondary flow path. The secondary flow path defines a channel of communication between the bottom of the reservoir chamber and the primary flow path, and is designed to limit fluid flow to a reduced rate on the order of 25 cc/hour. When the IV bottle becomes empty the supply end of the primary flow path is automatically closed to fluid flow.

It is accordingly a main object of the present invention to provide an intravenous flow regulator which minimizes the possibility of catheter clotting.

According to the present invention there is provided an automatic flow regulator for delivering a liquid, such as a parenteral solution, from a source to a patient, the flow regulator comprising: a reservoir chamber for receiving liquid from the source; inlet means at one end of said reservoir chamber for associating with said source, and for delivering liquid from said source to said reservoir chamber; primary delivery means within said reservoir chamber for delivering liquid from said reservoir chamber to an outlet at a first flow rate, said primary delivery means including means for discontinuing the conveyance of liquid from said reservoir chamber to the outlet when the level of liquid in said reservoir chamber drops, by continued infusion, below a predetermined threshold level; and secondary delivery means for continually conveying liquid from said reservoir chamber to the outlet at a second flow rate less than said first flow rate.

The present invention, as well as many of the attendant advantages thereof, will become more readily apparent when reference is made to the following exemplary description, taken in conjunction with the accompanying drawings, in which: Figure 1 illustrates a first embodiment of the inventive automatic intravenous flow regulator; Figure 2 is a cross section of the inventive flow regulator taken along site line 2-2 of Figure 1; Figure 3 is a cross section of the inventive flow regulator taken along site line 3-3 of Figure 1; Figure 4 is an illustration of a second embodiment of the inventive flow regulator; Figure 5 is a cross section of the inventive flow regulator taken along site line 5-5 of Figure 4; Figure 6 is a cross section of the inventive flow regulator taken along site line 6-6 of Figure 4; Figure 7 is an illustration of a third embodiment of the inventive flow regulator employing a collapsible reservoir chamber; Figure 8 is a cross section of the inventive flow regulator taken along site line 8-8 of Figure 7; Figure 9 is a cross-section similar to that of Figure 8, but showing the condition of the inventive flow regulator after its reservoir chamber has been collapsed upon the IV bottle becoming empty; Figure 10 is an illustration of still another embodiment of the inventive flow regulator; Figures 1 la and Figure 1 lib show an alternate primary flow path valve in respective open and closed operating conditions; Figure 12 illustrates another mechanism for communicating the secondary flow path with the infusion tubing; Figure 13 shows a mechanism for supporting the secondary flow membrane utilized in the flow regulator of Figure 4; and Figure 14 is a cross section through site line 14-14 of Figure 13.

With reference to Figures 1 through 3, the first embodiment of the inventive intravenous flow regulator will be described. The flow regulator is shown generally at 10, associating, at one end, with a conventional IV bottle 12, and at the other end, with a length of flexible infusion tubing 14. A conventional piercer 16, extending through a membrabe stopper 18 and into the bottle 12, receives parenteral solution 22 at an entry bore 20.

An inlet tube 24 continuous with bore 20, supplies parenteral solution to a reservoir chamber 26, and fills the same up to a level indicated at 28. A primary delivery tube 30 is supported by a spider 29, and communicates with an optional drip chamber 32 through an opening 34 at the bottom of the delivery tube. A drop of the parenteral solution can be seen at 36.

A secondary delivery tube 38 is positioned at the discharge end of the primary delivery tube 30, and enables secondary fluid communication between the reservoir chamber 26 and the interior of delivery tube 30. A small-diameter orifice could be used, as will be explained below, instead of the tube 38.

Primary fluid communication between reservoir chamber 26 and principal delivery tube 30 is accomplished by means of a valve 40 mounted at the supply end of the delivery tube.

As best seen in Figure 2, the secondary delivery tube 38 pierces the surface of primary delivery tube 30. Tube 38 can be held in place by means of any conventional mounting mechanism. The orifice of secondary delivery tube 38 is much restricted from that of the primary delivery tube 30, and is designed to pass the parenteral solution at a rate of approximately 25 cc/hour. Also, to serve as a natural filter, the inlet to secondary delivery tube 38 is slightly elevated relative to the base of the reservoir chamber 26. Of course, as will be discussed below an actual filtering membrane having a selected pore size may also be used as a means to control the rate at which the parenteral solution is passed.

The construction of valve 40 can be seen in Figures 1 and 3. This valve includes a cage 44 of a cylindrical configuration, having a plurality of spaced openings 46 around the periphery thereof. Four such openings are illustrated. A floating disc 48 is housed within the cage 44, and is free to move from the top 50 to the bottom 52 of cage 44, depending upon fluid level in the reservoir chamber 26. When the fluid level is high, floating disc 48 takes the position shown in solid lines in Figure 1 and, when the level is low, such as that illustrated at 54, the disc takes the position shown in Figure 1 at 48'.

The flow regulator 10 is illustrated as having an air entry port 56 with a filter 58. This is optional, since many of the new piercer pins have their own air entry ports. The drip chamber 32 is also optional. Many drip chambers are today on the market, many are even made a part of the piercer pin design, and any could be used with the inventive flow regulator 10. If constructed without a drip chamber, the base of reservoir chamber 26 could be made to terminate in a fitting for attachment to a conventional drip chamber or to a length of flexible plastic infusion tubing. Also illustrated is a conventional slide clamp 60, having a thumb wheel 62 to control crimping of the infusion tube 14 and hence to regulate the rate of fluid flow into the patient.

With continued reference to Figure 1, the operation of the inventive flow regulator 10 will be described. Initially, the flow regulator 10 is connected to appropriate, well-known intravenous apparatus to make up a complete infusion, or administration set. Then, the membrane 18 of a fresh IV bottle 12 is pierced by the piercer pin 16, and the IV bottle is inverted and suspended on a support stand (not shown). The slide clamp 60 is closed, and then the flexible wall of the reservoir chamber 26 is pumped by manually squeezing and relasing the same so that air is forced into the top of IV bottle 12. Parenteral solution 22 is in this manner delivered to the reservoir chamber 26 through inlet tube 24. The reservoir chamber 26 is continually filled until the parenteral solution 22 takes a level such as that shown at 28, above the top of valve 40.

The parenteral solution also drops into the drip chamber 32 and takes a level such as that shown at 64. Slide clamp 60 is then relieved until fluid flows out of the infusion catheter at the distal end, ensuring that no air is in the infusion tube 14, and that the administration set is ready for the start of an infusion. Slide clamp 60 is then again closed, the catheter introduced into the circulatory system of the patient, the administration set connected to the catheter,and the slide clamp 60 finally adjusted so that the desired number of drops per unit time is counted through the transparent wall drip chamber 32 or a drip chamber incorporated in the piercer.

With parenteral solution in the IV bottle 12, the reservoir chamber 26 remains filled to the level shown at 28. The floating disc 48 therefore maintains the position illustrated in solid lines in Figure 1, and parenteral fluid flows through the openings 46 in the cage 44 of valve 40. This parenteral solution then flows down through the primary delivery tube 30, and results in the formation of drops 36 entering the drip chamber 32. At the same time, a limited amount of parenteral solution enters the primary delivery tube 30 through the secondary delivery tube 38. Because of relative sizing, however, the contribution of secondary delivery tube 38 to the formation of drops 36 is minimal.

When the IV bottle 12 first becomes empty, the fluid level in the reservoir chamber 26 begins to fall from its initial level at 28. The parenteral solution is discharged through openings 46, primary delivery tube 30, drip chamber 32 and infusion tubing 14, ultimately to reach the patient; since the bottle 12 is empty, liquid lost from reservoir chamber 26 is not replenished. As the fluid level drops from that shown in 66, the floating disc 48 falls, until taking the position shown in phantom at 48'. Here, the supply end of primary delivery tube 30 is closed to fluid flow and air entry. With no further flow of parenteral solution through the openings 46 of valve 40, all the infused fluid originates through secondary delivery tube 38.

As mentioned above, the orifice in secondary delivery tube 38 is sized so as to permit only on the order of 25 cc/hour of parenteral solution to flow into drip chamber 32 and hence into the circulatory system of the patient. The volume of the reservoir chamber 26 is designed to be somewhere in the neighbourhood of 50 cc (diameter of reservoir being approximately 2.6cm), and hence once the IV bottle 12 is empty, the attendant personnel have approximately 2 hours in which to replace the empty IV bottle before clotting of the intravenous infusion catheter becomes a problem.

With reference now to Figures 4 through 6, another embodiment of the inventive flow regulator will be described. The flow reg ulator of this embodiment is indicated at 10' and is similar in most respects to the flow regulator 10 shown in Figures 1 through 3.

Accordingly, common reference numbers have been utilized, and only the differences will be described.

As in the previously-described embodiment, the primary delivery tube 30 of flow regulator 10' extends into the drip chamber 32 to form drops 36. Here, however, instead of utilizing a fixed orifice tube, the secondary flow path is defined by a metering membrane 68 and an oversized aperture 70. The membrane 68 is in the form of a disc with a central aperture, and is sized so as to extend from the exterior surface of the primary delivery tube 30 to the interior surface of the reservoir chamber 26. An outer support ring 72 and an inner support ring 74 maintain the position of metering membrane 68, and form seals with the membrane so that no fluid is able to pass from chamber 26 and through aperture 70 without first encountering the membrane.

Membrane 68 has a pore size and area which permit approximately 25 cc/hour of parenteral solution to pass therethrough. Aperture 70 is able to deliver a more substantial flow of fluid, but is not called upon to do so.

The embodiment of Figure 4 differs from the previously-described embodiment also in the construction of the valve 40. In Figure 4, the supply end of the primary delivery tube 30 is equipped with a valve 40'. Here, the upper end of the primary delivery tube 30 defines a support 76 on which is supported a filter membrane 78 of selected pore size and which is similar to membrane 68, the filter membrane being held in place by means of a mounting ring 80. Filter membranes 68 and 78 are of a well-known type which freely passes parenteral fluid at a rate dependant on pore size. but which blocks the passage of air; these are commercially available.

The operation of flow regulator 10' is quite similar to the operation of flow regulator 10.

When the associated IV bottle contains fluid, the majority of the infused fluid flows through primary delivery tube 30 from filter membrane 78. A small amount of fluid, on the order of 25 cc/hour, flows through the metering membrane 68 and combines with the fluid in delivery tube 30, through aperture 70. When the IV bottle becomes empty the fluid in reservoir 26 falls below the level of filter membrane 78. whereupon filter membrane 78 functions to block the passage of air into delivery tube 30. No further parenteral solution enters the supply end of the primary delivery tube 30; rather, the sole path of infused fluid is from reservoir 26, through metering membrane 68, into the collecting chamber 82 through aperture 70, and thence to the patient. Since membrane 68 passes parenteral solution at a rate of approximately 25 cc/hour, and since reservoir chamber 26 houses on the order of 50 cc of fluid, attendant personnel have about two hours from the emptying of the IV bottle in which to change bottles.

The previously-described embodiments have included reservoir chambers whose walls are flexible, but yet relatively rigid. In the embodiment of the invention illustrated in Figures 7 through 9, on the other hand, a collapsible reservoir chamber is utilized. This embodiment of the inventive flow regulator is indicated at 10". Here, a primary delivery tube 30 resides within a collapsible reservoir chamber 84. which is generally oval when filled with a parenteral solution. The supply end of the primary delivery tube 30 is expanded into a valve 86 conforming in shape to that of the reservoir chamber 84.

The top of valve 86 is closed, at 88, and the valve body is apertured, as shown at 90. The discharge region of the primary delivery tube 30 contains a small-diameter secondary delivery aperture 92, designed to pass parenteral fluid from the interior of reservoir chamber 84 to the flexible infusion tubing 14 at a rate of approximately 25 cc/hour.

When the IV bottle contains parenteral solution, the reservoir chamber 84 remains filled to a level approximately that indicated at 94 in Figure 7. The parenteral solution then enters the apertures 90 in valve 86, flows down the primary delivery tube 30, and enters the flexible tubing 14 for infusion at a rate set by a side clamp such as that shown at 60 in Figure 1. A small amount of parenteral solution enters the primary delivery tube 30 through secondary delivery aperture 92, but this contribution of parenteral solution is minimal.

When the IV bottle is empty, the level of parenteral solution in the chamber 84 drops, and the chamber begins to collapse. During the initial stages of the collapse, the level of parenteral solution remains above the level of apertures 90, and therefore fluid continues to flow into valve 86 and down through primary delivery tube 30. Further collapse of the chamber 84, however, results in the walls of the chamber itself closing the apertures 90 of valve 86- this is illustrated in Figure 9. With valve 86 closed, the sole source of parenteral solution which enters the infusion tube 14 is through the secondary delivery aperture 92. The flow rate of parenteral solution therefore approximates 25 cc/hour, so that with a 50 cc reservoir chamber, the attendant personnel have about 2 hours after an IV bottle is exhausted, in which to fit a fresh bottle.

Figure 10 illustrates still another embodiment of the inventive flow regulator, at 10".

In this embodiment,the regulator is equipped with a primary delivery tube 96. A valve seat 98, within the confines of delivery tube 96 and associating with the nose 100 of a valve stem 102, defines a valve 103. At the upper portion of valve stem 102 is a float 106. Valve stem 102 is movably supported by a support bracket 108 which maintains the valve stem 102 centered within the chamber 26, but which allows the passage of parenteral solution. Just beneath the valve seat 98 is a reduced-area secondary delivery aperture 110.

In operation, when the chamber 26 of the flow regulator 10"' is filled with fluid, float 106 rides high in the reservoir chamber 26, with the nose 100 of valve stem 102 consequently being maintained out of association with the valve seat 98. When the liquid level drops (due to an empty IV bottle), nose 100 becomes seated on valve seat 98, and the primary flow path through the valve 103 is closed. All further flow of the parenteral solution therefore takes place through secondary delivery aperture 110, at the preset reduced rate of approximately 25 cc/hour.

Referring now to Figures 1 la and 1 lb, an alternate configuration of the valve 40 is shown. This valve configuration is indicated at 40" and is supported at the top of the primary delivery tube 30. The valve 40" includes a cage 112 which is apertured at spaced locations 114 around the periphery thereof. The top of cage 112 is closed, at 116, to maintain a float ball 118 therein.

When the level of the parenteral solution is above the top of valve 40" in the reservoir chamber (not shown), the ball 118 floats to the top of the cage 112, abutting the top 116.

Openings 114 therefore communicate with the interior of the primary delivery tube 30, and parenteral solution follows the path indicated in Figure 1 la by arrows 120. When the level of arenteral solution falls, on the other hand, the ball 118 drops down and seats against valve seat 122, interrupting communication between openings 114 and the interior of delivery tube 30.

Figure 12 illustrates yet another arrangement for delivering parenteral solution to the infusion tube from the secondary delivery mechanism. In this figure, the primary delivery tube 30 is centered in the reservoir chamber 26 and includes a lower inlet 124, outside the confines of chamber 26. A metering secondary delivery tube 126, the inlet of which is elevated from the bottom of reservoir chamber 26, is fitted in an elbow 128 which, in turn, feeds into the lower inlet 124 of primary delivery tube 30. This embodiment has the advantage that the secondary delivery tube 126 can be more easily mounted between the reservoir chamber 26 and the primary delivery tube 30. In all other respects, operation is identical.

Finally, with reference to Figures 13 and 14, a combined support and drop-former will be described. Here, the reservoir chamber is indicated at 130 and supports a primary delivery tube 30 such as that already described. The base of the reservoir chamber 130 is continuous with and molded into a drip chamber, shown at 132. A metering membrane 134, like that described above at 68 and 78, when reference was made to Figures 4 and 6, is positioned at the base of the reservoir chamber 130, and serves as the secondary delivery source which meters the parenteral solution to drip chamber 132 from reservoir chamber 130 at a rate approximating 25 cc/hour. Membrane 134 is supported by a spider 136 comprising an inner ring 138 which associates with the primary delivery tube 30, and an outer ring 140 adapted to rest on and seal to a sloped ledge 141 of drip chamber 132. Spider 136 also includes four (for example) spokes 142 connecting the inner and outer rings. The respective inner and outer rings 138 and 140 are dimensioned to support the membrane 134, and so that all of the parenteral solution which enters the drip chamber 132 directly from the reservoir chamber 130 passes through metering membrane 134. The bottom surfaces of spokes 142 are angled, as shown at 144, so that the parenteral solution flowing through the secondary delivery mechanism flows along surfaces 144, to form drops such as that shown at 146. At the same time, the parenteral solution flowing in the primary flow path, for example through membrane 78, is also formed into drops at the drop former 148 of the delivery tube 30.

Above, specific embodiments of the present invention have been described. It should be appreciated, however, that these embodiments were described for purposes of illustration only, without any intention of limiting the scope of the present invention claimed.

For example, the invention may be incorporated in a complete administration set for delivering parenteral solution from a source directly to a patient; the invention may also take the form of an add-on unit to be used in combination with an administration set presently on the market.

WHAT I CLAIM IS: 1. An automatic flow regulator for delivering a liquid, such as a parenteral solution, from a source to a patient, the flow regulator comprising: a reservoir chamber for receiving liquid from the source; inlet means at one end of said reservoir chamber for associating with said source, and for delivering liquid from said source to said reservoir chamber; primary delivery means within said reservoir chamber for delivering liquid from said reservoir chamber to an outlet at a first flow

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figure 10 illustrates still another embodiment of the inventive flow regulator, at 10". In this embodiment,the regulator is equipped with a primary delivery tube 96. A valve seat 98, within the confines of delivery tube 96 and associating with the nose 100 of a valve stem 102, defines a valve 103. At the upper portion of valve stem 102 is a float 106. Valve stem 102 is movably supported by a support bracket 108 which maintains the valve stem 102 centered within the chamber 26, but which allows the passage of parenteral solution. Just beneath the valve seat 98 is a reduced-area secondary delivery aperture 110. In operation, when the chamber 26 of the flow regulator 10"' is filled with fluid, float 106 rides high in the reservoir chamber 26, with the nose 100 of valve stem 102 consequently being maintained out of association with the valve seat 98. When the liquid level drops (due to an empty IV bottle), nose 100 becomes seated on valve seat 98, and the primary flow path through the valve 103 is closed. All further flow of the parenteral solution therefore takes place through secondary delivery aperture 110, at the preset reduced rate of approximately 25 cc/hour. Referring now to Figures 1 la and 1 lb, an alternate configuration of the valve 40 is shown. This valve configuration is indicated at 40" and is supported at the top of the primary delivery tube 30. The valve 40" includes a cage 112 which is apertured at spaced locations 114 around the periphery thereof. The top of cage 112 is closed, at 116, to maintain a float ball 118 therein. When the level of the parenteral solution is above the top of valve 40" in the reservoir chamber (not shown), the ball 118 floats to the top of the cage 112, abutting the top 116. Openings 114 therefore communicate with the interior of the primary delivery tube 30, and parenteral solution follows the path indicated in Figure 1 la by arrows 120. When the level of arenteral solution falls, on the other hand, the ball 118 drops down and seats against valve seat 122, interrupting communication between openings 114 and the interior of delivery tube 30. Figure 12 illustrates yet another arrangement for delivering parenteral solution to the infusion tube from the secondary delivery mechanism. In this figure, the primary delivery tube 30 is centered in the reservoir chamber 26 and includes a lower inlet 124, outside the confines of chamber 26. A metering secondary delivery tube 126, the inlet of which is elevated from the bottom of reservoir chamber 26, is fitted in an elbow 128 which, in turn, feeds into the lower inlet 124 of primary delivery tube 30. This embodiment has the advantage that the secondary delivery tube 126 can be more easily mounted between the reservoir chamber 26 and the primary delivery tube 30. In all other respects, operation is identical. Finally, with reference to Figures 13 and 14, a combined support and drop-former will be described. Here, the reservoir chamber is indicated at 130 and supports a primary delivery tube 30 such as that already described. The base of the reservoir chamber 130 is continuous with and molded into a drip chamber, shown at 132. A metering membrane 134, like that described above at 68 and 78, when reference was made to Figures 4 and 6, is positioned at the base of the reservoir chamber 130, and serves as the secondary delivery source which meters the parenteral solution to drip chamber 132 from reservoir chamber 130 at a rate approximating 25 cc/hour. Membrane 134 is supported by a spider 136 comprising an inner ring 138 which associates with the primary delivery tube 30, and an outer ring 140 adapted to rest on and seal to a sloped ledge 141 of drip chamber 132. Spider 136 also includes four (for example) spokes 142 connecting the inner and outer rings. The respective inner and outer rings 138 and 140 are dimensioned to support the membrane 134, and so that all of the parenteral solution which enters the drip chamber 132 directly from the reservoir chamber 130 passes through metering membrane 134. The bottom surfaces of spokes 142 are angled, as shown at 144, so that the parenteral solution flowing through the secondary delivery mechanism flows along surfaces 144, to form drops such as that shown at 146. At the same time, the parenteral solution flowing in the primary flow path, for example through membrane 78, is also formed into drops at the drop former 148 of the delivery tube 30. Above, specific embodiments of the present invention have been described. It should be appreciated, however, that these embodiments were described for purposes of illustration only, without any intention of limiting the scope of the present invention claimed. For example, the invention may be incorporated in a complete administration set for delivering parenteral solution from a source directly to a patient; the invention may also take the form of an add-on unit to be used in combination with an administration set presently on the market. WHAT I CLAIM IS:

1. An automatic flow regulator for delivering a liquid, such as a parenteral solution, from a source to a patient, the flow regulator comprising: a reservoir chamber for receiving liquid from the source; inlet means at one end of said reservoir chamber for associating with said source, and for delivering liquid from said source to said reservoir chamber; primary delivery means within said reservoir chamber for delivering liquid from said reservoir chamber to an outlet at a first flow

rate, said primary delivery means including means for discontinuing the conveyance of liquid from said reservoir chamber to the outlet when the level of liquid in said reservoir chamber drops, by continued infusion, below a predetermined threshold level; and secondary delivery means for continually conveying liquid from said reservoir chamber to the outlet at a second flow rate less than said first flow rate.

2. The flow regulator recited in claim 1, wherein the means for discontinuing the conveyance of liquid from the reservoir chamber to the outlet is a valve which closes to the passage of air when said level of liquid drops below said threshold level.

3. The flow regulator recited in claim 2, wherein said valve is a filter membrane designed to pass liquid, but to block the flow of air.

4. The flow regulator recited in claim 1, wherein the means for discontinuing the conveyance of liquid from the reservoir chamber to the outlet is a filter membrane positioned in said reservoir chamber for passing liquid and for blocking the flow of air therethrough; and wherein said secondary delivery means is a membrane for determining said second flow rate by the area and pore size thereof and which permits the passage of liquid but blocks the passage of air.

5. The flow regulator recited in claim 1,2 or 3, wherein said primary delivery means is a tube mounted in said reservoir chamber, having an entry at one end and a discharge at the other end, said discharge communicating with the outlet.

6. The flow regulator recited in claim 5, wherein said secondary delivery means is a tube in liquid communication with said reservoir chamber at one end thereof and with said primary delivery means at the other end thereof.

7. The flow regulator of claim 5 when appendant to claim 2, wherein said valve is affixed to said entry of said tube.

8. The flow regulator recited in claim 1, wherein said secondary delivery means is an aperture through the wall of said primary delivery means, in liquid communication with said reservoir chamber at one end thereof and with said primary delivery means at the other end thereof.

9. The flow regulator recited in claim 1, wherein said secondary delivery means is a membrane designed to pass liquid but to block the flow of air; and further comprising a drop-forming support for mounting said membrane.

10. The flow regulator recited in claim 2, wherein said reservoir chamber is collapsible; and wherein said valve is closed by the collapse of said reservoir chamber.

11. The flow regulator recited in claim 2, wherein said valve is a float valve.

12. The flow regulator recited in claim 2, wherein said valve is a filter membrane designed to pass liquid, but to block the flow of air, said filter member having a preselected surface area and a pore size for determining said first flow rate.

13. The flow regulator recited in claim 1, wherein said reservoir chamber is elongated and designed to operate in a vertical orientation; and wherein said means for discontinuing the conveyance of liquid from the reservoir chamber to the outlet is a valve mounted in said reservoir chamber, and positioned in the region of said threshold level.

14. The flow regulator recited in claim 1, wherein the volume of said reservoir chamber below the threshold level and said second flow rate are such that flow at said second flow rate occurs for approximately 2 hours.

15. The flow regulator recited in claim 1, and further comprising coupling means connected to said primary delivery means and said secondary delivery means for associating with flexible infusion tubing communicating with the patient.

16. A flow regulator according to claim 1, wherein the outlet is provided at the opposite end of the reservoir chamber; the primary delivery means mounted in the reservoir chamber has an inlet end and a discharge end, and includes a membrane filter valve at its inlet end for blocking the flow of air through the primary delivery means when the level of liquid in the reservoir chamber drops below a predetermined threshold level at the level of the membrane valve; and the secondary delivery means comprises a membrane filter for continuously conveying liquid from said reservoir chamber to said outlet means at a second flow rate less than said first flow rate and for blocking the passage of air when the level of liquid drops below said membrane.

17. A flow regulator according to claim 1 or 16, wherein the secondary delivery means is provided within said reservoir and comprises a filter membrane of preselected surface area and pore size for defining said second flow rate and for blocking the passage of air when the fluid in said reservoir falls below said filter membrane of the secondary delivery means.

18. An automatic flow regulator constructed and arranged to operate substantially as hereinbefore described with reference to and as shown by the accompanying drawings.