Liquid Administration Apparatus

Abstract

An administration set includes a narrow bore valveless metering tube which leads from a liquid container to a vented drip chamber. From the drip chamber, the liquid discharges through one end of an infusion tube, the opposite end of which is adapted to infuse the reservoir liquid into an independent liquid system, e.g. the circulatory system of a patient. A container access cap having a tubular spout through which the container liquid flows and a vented sump into which the spout leads, maintains the effective elevation of the liquid drawn from the bottle at a substantially constant value. The drip chamber is mounted on a channel for vertical movement with respect to the access cap. One end of the metering tube drains the sump and the other forms the inner wall of a double walled nozzle in the drip chamber. A float is provided as a flow regulator in the chamber to automatically vary a constriction to the liquid access to the infusion tube in response to variations in system back pressure.

Parent Case Text

RELATED APPLICATION

This application is a continuation-in-part of my previous application Ser. No. 85,474 filed Oct. 30, 1970.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Administration sets with hydrostatic head variation means for flow rate regulation.

2. Brief Description of the Prior Art

Physiological fluids are normally infused into a patient with a parenteral administration set. The administration set is utilized to provide a fluid passage between a physiological fluid, e.g. a parenteral solution of sterile water or a saline or glucose water solution, etc., carried in a glass bottle for intravenous or arterial administration. Infusion of the parenteral solution has been achieved by suspending an inverted bottle above the patient and interconnecting a length of tubing forming part of the administration set to the bottle with a threaded bottle access cap or, if the bottle is stoppered, by piercing a membrane stopper at the mouth of the bottle with a vented penetrant. The tubing included a drip chamber connected in series therewith and through which the rate of solution flow could be observed. A constriction pinch valve was provided to restrict the fluid flow through the tubing to levels meeting the prescribed requirements of the patient. The free end of the tubing was connected to a hollow bore needle which was usually inserted into a blood vessel, e.g. a vein, of the patient.

A major disadvantage encountered with the presently used administration sets was the fact that the rate of solution flow has been known to vary. The rate of flow was observed through a drip chamber which included a nozzle constructed so that drops formed were of a predetermined size. The nurse or technician thereby determined the fluid flow rate in standard liquid measure and in accordance with the doctor's specifications by counting the number of drops during a given period of time. The flow rate was adjusted by constricting the tubing with various valve clamps.

Factors contributing to flow rate changes in actual hospital usage included the following: changes in the elevation of the infusion arm; changes in patient blood pressure; partial clotting at the infusion needle; a change in orientation of the infusion needle within the blood vessel; patient constriction of the infusion tubing, e.g. from lying on the tubing, and in some instances, actual tampering with the pinch valves by the patients.

Unfortunately, even under precisely controlled laboratory test conditions, with a constant restriction at the needle end of the tubing (the effect of which is a steady patient blood pressure and no change in the elevation level of the needle) the flow rate has been known to vary considerably over extended periods of time. In one such test, a flow rate had varied to the extent that after 14 hours the flow rate had decreased to one quarter of the original flow rate. In another test, the flow rate after 22 hours had decreased to one-seventh the original flow rate.

The gradual change in flow rate necessitated the constant checking and adjustment of intravenous feeding administration equipment during the administration. Thus, nurses usually were required to check the flow rate of all intravenous equipment as they made their usual rounds. Unfortunately, intravenous equipment has been known to remain unchecked for a considerable period of time, which often resulted in complications detrimental to the patient's health and recovery rate.

In addition to the previously mentioned factors contributing to flow rate changes under hosiptal conditions, there are the causes attributable to flow rate changes under laboratory conditions. Among the later causes are small variations in infusion liquid hydrostatic head at the needle and slight changes or "creeping" of the valves restricting the free fluid flow through the tubing (see U.S. Pat. No. 3,099,429). Dimensional changes in the tube itself may also be a factor.

It is believd that the purity of the physiological solutions contributes to flow rate changes and is such that the tubing will readily clog at the valve constrictions. This is because although the solutions are sterile, they still may have minute particles which will be deposited at the constriction in the tubing.

It is also believed that the variation in hydrostatic head, to which flow rate changes have been attributed was partially due to the inefficiency of the previous venting mechanisms utilized in the bottle access caps or stopper penetrants of previous administration sets. Previously, a relatively large vent opening e.g. 1/16th inch diameter was utilized. Unfortunately, the volumetric capacitance of the vents was such that they did not vent reliably and several bubbles at a time could be released. Furthermore, these bubbles would only be released when a fairly large partial vacuum was obtained above the vent level in the bottle. Thus, erratic venting was common and resulted in a pulsating flow rate. Because the vents did not reliably maintain an effective atmospheric pressure level at the outlet orifice, it was extremely difficult to achieve adequate flow control at slow flow rates, although the degrading effects were predominantly caused by the valving. Some bottle vents included a snorkel tube which led upward into the bottle to a level above the solution. This eliminated vent bubbles through the solution and kept atmospheric pressure above the solution. The drawback was that while solution was drawn from the bottle, the hydrostatic head forcing the solution into the patient continually decreased.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a liquid administration apparatus of the general character described which is so constructed that it is not subject to any of the foregoing disadvantages.

More specifically, it is an object of the present invention to provide a liquid administration apparatus of the general character described which includes a flow rate regulation system whereby changes in flow rate over periods of time are effectively eliminated.

A further object of the present invention is to provide a liquid administration apparatus of the general character described which includes a drain tube drawing liquid from a liquid container to an outlet substantially at atmospheric pressure and wherein the effective elevation of the outlet with respect to the effective elevation of the liquid drained from the container may be adjustably varied and maintained in any one of a number of positions to thereby adjust and maintain a steady flow rate of liquid from the container.

Another object of the present invention is to provide a liquid administration apparatus of the general character described which includes an improved liquid container venting system having a sump at atmospheric pressure and a tubular discharge spout leading from the container to the sump with the sump liquid permitting air to enter the container through the spout upon exposure of the spout opening by a slight lowering of the sump liquid level.

A further object of the present invention is to provide a self adjusting gravity flow liquid infusion device of the general character described which includes a hollow chamber into which a liquid is fed at a constant rate and a discharge tube leading from the chamber to an independent liquid system having a variable liquid back pressure and with the chamber including a float selectively restricting liquid communication between the chamber and the tube to equate the flow rate into the chamber with the flow rate out of the chamber.

A still further object of the present invention is to provide a liquid infusion device of the general character described which prevents the introduction of air into an infusion tube.

Further objects of the invention in part will be obvious and in part will be pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts which will be exemplified in the liquid administration apparatus hereinafter described and of which the scope of application will be indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings in which is shown one of the various possible embodiments of the invention,

FIG. 1 is an elevational view of a parenteral liquid administration set constructed in accordance with and embodying the invention, and showing the administration set positioned for use in feeding a physiological liquid;

FIG. 2 is an enlarged fragmentary elevational sectional view through a vented bottle access cap through which liquid is drawn from a reservoir bottle and from which portions of the administration apparatus are suspended ;

FIG. 2a is a sectional view taken substantially along the line 2a--2a of FIG. 2 and showing a restricting gasket which peripherally seals the mouth of the reservoir bottle;

FIG. 2b is a fragmentary elevational sectional view through a bottle having a stoppered opening and showing an adapter which is suitable for securing the vented access cap to the bottle;

FIG. 3 is an enlarged fragmentary perspective view of a drip chamber into which liquid flows from the sump through a metering tube, which chamber is slidably secured to a slotted channel depending from the access cap;

FIG. 4 is an enlarged sectional view taken substantially along the plane 4--4 of FIG. 3 and through the drip chamber and channel;

FIG. 5 is an enlarged longitudinal sectional view through the drip chamber and showing a float nested in the interior of the chamber with the float downwardly biased by a spring and with the chamber including an upper cover having a double walled drip nozzle;

FIG. 6 is a sectional view through the drip chamber, the same being taken substantially along the line 6--6 of FIG. 5 and showing the nozzle with both walls, and a vent through the cover;

FIG. 7 is a fragmentary sectional view taken sub-stantially along the line 7--7 of FIG. 6 and illustrating a nozzle vent hole between the nozzle and the chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in detail to the drawings, the reference numeral 10 denotes an administration apparatus constructed in accordance with and embodying the invention. The liquid administration apparatus 10 includes a physiological liquid administration bottle 12 conventionally constructed of glass and carrying a typical physiological fluid, e.g. a parenteral solution 14 of sterile water with or without medicinal solutes. The bottle 12 is adapted to be supported at an elevation above the patient, and for this purpose, a bail 16 is usually provided. It will be noted that bail 16 is pivotally connected to the bottle adjacent the bottom thereof and when suspended from a support 18, the bottle will lie in inverted position with its mouth downwardly directed.

In accordance with the invention, an administration set 20 is provided which permits constant and accurate metered control of the flow of liquid solution from the bottle into a separate independent liquid system. The administration set 20 includes a narrow bore, e.g. 0.04 inch diameter, flexible metering tube 22, the effective elevation of the discharge end of which may be varied with respect to the effective level of liquid drawn from the bottle 12 to thereby vary the hydrostatic head of liquid at the discharge end, thus the flow rate through the tube 22. The metering tube 22 discharges the parenteral solution 14 at a controlled flow rate determined solely by the hydrostatic head and the solution is subsequently infused into the patient through a conventional bore, e.g. 0.10 inch diam., infusion tube 24. If the administration set is utilized for inducing liquid into a patient's circulatory system through a blood vessel, a hollow bored needle 25 is positioned at the free end of the infusion tube.

In order to interconnect the metering tube 22 and parenteral solution 14 stored in the bottle 12, a vented access cap 26 is provided. The cap 26 is generally cylindrical and includes a threaded bore at the upper end which mates with the male threaded neck of the bottle 12. A tubular spout 30 extends downwardly from an annular shoulder stop 28 at the base of the threaded bore. The solution 14 flows through the spout 30 into an interior sump 29 of the access cap 26. The solution 14 is drawn from the sump 29 through the metering tube 22, one end of which is seated in a hollow drain socket extending from the base of the cap.

To provide an air vent for the bottle 14, a tapered Luer passageway 32 extends downwardly from the top of the cap adjacent the bore toward the sump 29. A suitable filtering material 34, e.g. synthetic sponge, etc. preferably having negligible resistance to air flow and hence a minimal air pressure drop, is seated in the passageway to remove airborne contaminants.

It will be appreciated that under normal operating conditions, a quantity of solution 14 will be collected in the sump 29 at the level L.sub.1 (see FIG. 2) and, as solution drains from the sump through the metering tube 22, the level of solution in the sump decreases to expose part of the open bottom of the spout 30. Upon exposure of the spout bottom, air enters the bottle through the spout and thus additional liquid is permitted to flow down the spout 30 bringing the liquid level L.sub.1 back to its normal position.

The cylindrical wall of the spout 30 is cut along an inclined plane to form the open bottom so that only a portion of the total cross-sectional area of the spout interior is exposed to atmospheric pressure. It has been found that if the spout opening were along a horizontal plane parallel to the liquid line at the level L.sub.1, the meniscus of the solution would prevent air from entering the spout until the level L.sub.1 was considerably below the open spout bottom. Such lowering of the liquid level L.sub.1 within the sump 29 (which level controls the effective head of water at the inlet end of the metering tube 22) would permit undesirable variation in metering tube flow rate. Cutting the cylindrical spout wall along an incline allows the meniscus to break easily such that minimal level change occurs in the sump between bubbles. Under actual operating conditions, the liquid level L.sub.1 oscillates about the highest elevation of the spout bottom a total distance of approximately 1/16th inch and the flow rate changes for such variation are inconsequential to the operation of the administration set even at very slow flow rates through the metering tube 22.

A membrane gasket 36 (see FIG. 2a) rests on the shoulder 28 and effects a water and air tight seal between the bottle 12 and the cap 26. Constrictions to free liquid flow from the bottle are provided by the gasket 36 which may include two openings. A minimal restriction to liquid flow from the bottle such as that presented by the membrane gasket is desirable to prevent flooding of the sump with a wetting of the filter 34 upon inversion of the bottle during initial set up.

It has been found that if a membrane gasket with two openings is utilized, upon bottle inversion, the solution usually flows slowly through one of the openings while air bubbles rise upwardly into the bottle through the other opening. Such controlled flow permits the level L.sub.1 to rise slowly and stop substantially at the highest elevation of the spout bottom. Satisfactory results have also been obtained using a single opening through the gasket.

The effective head of water drawn through the metering tube 22 from the sump is governed by the elevational distance between the sump level L.sub.1 (which remains substantially constant at the highest elevation of the spout opening) and the vented discharge of the metering tube 22.

Bottle venting through the cap 26 is highly reliable even at extremely slow flow rates through the metering tube 22 and since the spout opening (hence the normal level L.sub.1) is a substantial distance from the air filter 34, the filter 34 is seldom wetted. Even if the filter 34 becomes wet, e.g. upon drastic shaking of the bottle, accidental bottle inversion, mishandling, etc., normal venting resumes automatically as liquid is drawn from the sump 29. This is because a sufficient vacuum will form above the level L.sub.1 to remove any water blocking the filter 34. If the bottle is shaken or jolted, tending to force more liquid into the sump, the liquid level L.sub.1 in the sump will rise slightly resulting in a momentary increase in flow through the infusion tube until the level L.sub.1 reaches the highest elevation of the spout opening. The level L.sub.1 thus maintains its substantially constant value with only slight oscillations about the highest elevation of the spout opening.

Although the access cap 26 has been described for use in conjunction with a bottle 12 having a male threaded neck, it is also suitable for use with a stoppered bottle 112 (see FIG. 2b). For this purpose, an adapter having a hollow stopper penetrant tube 35 leading from the bottle to a hollow male threaded nipple 37 may be utilized. It will be appreciated that the inner upper wall of the nipple is downwardly outwardly flared from the tube 35 to prevent the entrapment of air bubbles. Optionally, a unitarily formed stopper penetrant and cap can be constructed with the stopper penetrant tube forming the sump spout at its lower end. In such instance, a flow constricting gasket need not be utilized since the penetrant tube will be of a diameter sufficient to constrict flow.

Valveless flow rate regulation of parenteral solution discharge from the sump 29 through the metering tube 22 is principled upon liquid flow in a gravity flow system which may be regulated by changing the head or elevation between the atmospheric pressure level at the fluid reservoir and the discharge port of a siphon tube. For viscous flow in a small bored tube (not considering kinetic energy of the fluid) it has been found that the flow rate in a siphon system is proportional to the effective head height, i.e. the head between the atmospheric level in the reservoir and the atmospherically vented discharge end of the siphon tube. It should be noted that the effective atmospheric level in the bottle reservoir, i.e. the liquid level L.sub.1 in the sump of the present system, remains substantially constant near the opening of the spout.

In order to maintain and adjustably vary the effective elevation of the discharge end of the metering tube 22 with respect to the sump liquid level L.sub.1, a movable drip chamber 38 is provided. The drip chamber 38 includes a metering tube receiving nozzle cover 40 which engages a hollow body formed of a transparent cylindrical viewing segment 42. The cover 40 includes a cylindrical side wall at the lower end of which an annular groove is formed and within which the upper end of the segment 42 is seated.

A passage fixture 44 which receives and guides the metering tube 22 is formed in the cover 40. The fixture 44 includes a passageway which accommodates the metering tube 22 without constricting its bore (to eliminate calibration problems). A portion of the metering tube 22 adjacent the free end extends vertically downward from the cover 40 as a hollow protuberance into a downwardly projecting hollow cylindrical shell 46 having a downwardly outwardly flared discharge opening 47 at the bottom, thereby forming a double walled discharge nozzle 48. The inner wall of the nozzle 48 is, in actuality, one wall of the metering hollow protuberance, i.e. the tube 22, while the shell 46 forms the outer wall.

The purpose and function of the double walled nozzle 48 is to reduce the hydrostatic head variation normally encountered in forming a drop of solution 14. If a single walled nozzle is used, which is, in effect, the discharge end of the metering tube 22, the radius of the meniscus at the open end of the bore will be initially quite small. This is because the tube bore is of a relatively small diameter. Since surface tension fluid pressure formed by the meniscus is inversely proportional to the radius, a relatively high hydrostatic head is required to break through the meniscus and allow a drop to be formed.

Presently used drip chamber nozzles would be disadvantageous in particular applications of the flow control system of this invention because the system would not operate with maximum reliability at extremely slow flow rates where minimal hydrostatic head at the nozzle is utilized. If the administration set is not for use at extremely low infusion flow rates, a conventional nozzle will suffice.

The double walled nozzle 48 is ideal for producing a stabilized system wherein very little drop formation pressure variation is required at the metering tube. This is because a column of solution 14 will collect within the shell 46 which acts as a pressure bias. It should be noted that the shell 46 includes a vent passage 54 (see FIGS. 5 and 7) above the collected liquid and communicating with the interior of the drip chamber (which is at atmospheric pressure). The passage 54 is at an elevation well above the discharge end of the metering tube 22. It will now be seen that the upper level L.sub.2 of the column of liquid collected in the shell 46 is at atmospheric pressure because the vent passage 54 is above the column. Thus, the surface tension of the meniscus formed at the discharge opening 47 of the shell 46 is just sufficient to keep the collected column of solution within the shell 46.

The slightest addition of liquid to the column within the shell 46 will increase the elevation of the solution level L.sub.2 and hence the head of pressure at the shell discharge opening. As soon as the head of liquid collected within the drop is sufficient to expand the meniscus, the drop will grow. Thus, only a minimal head increase of solution at the nozzle is necessary to cause a drop to fall.

The internal diameter of the shell 46 can be optimized to minimize fluctuations of the level L.sub.2, hence head fluctuations in the nozzle column for a given drop size. For drops having a volume of about 1/15th cc., an internal shell diameter of about 1/4 inch has been found satisfactory. For drops of a smaller size, a reduced diameter may be used. Good results with only small fluctuations of the level L.sub.2 have been obtained with a liquid meniscus having a volume approximately 1/3 the drop size suspended below the nozzle discharge opening at the commencement of each drop formation cycle.

It was previously mentioned that the drip chamber 38 is at atmospheric pressure. This is accomplished by a passage 56 through the cover 40. A suitable filter 58 of construction similar to the filter 34 is seated and recessed in the passage 56 to prevent the entrance of airborne contaminants.

A further disadvantage of conventional nozzles is the fact that the drop formation pressure was not consistent. It is believed that various naturally occurring vibration frequencies enable a meniscus to vibrate and the meniscus ruptures easier at the natural frequencies with the released drop starting successive oscillation cycles. If the frequency of drop formation matches one of these natural frequencies, the flow rate no longer remains a linear function of head height. In order to retard such oscillations in the column of solution within the shell, the metering tube 22 extends to an elevation only slightly above the discharge end of the shell and thus provides a friction drag to dampen the oscillations. Alternatively, baffles (not shown) may be positioned between the metering tube and the shell.

As has been previously mentioned, flow rate through the metering tube 22 is regulated by varying the liquid level L.sub.2 at the effective discharge end of the metering tube 22. Since there are no valve constrictions in the metering tube 22, the flow will remain constant for any set elevation of the drip chamber 38. A slotted support channel 60 extends vertically downwardly from the access cap 26, and may be unitarily molded therewith. The channel 60 provides a support for the drip chamber 38 and permits the adjustment of the elevation of the drip chamber with respect to the level L.sub.1.

In order to adjustably mount the drip chamber 38 to the channel 60, a threaded shank 62 (see FIG. 5) extends radially outwardly from the wall of the cylindrical segment 42 into a longitudinal slot 64 formed in the channel 60. It should be noted that the slot is closed ended at its top and bottom to provide sufficient strength for the channel and to prevent the drip chamber from inadvertent disengagement from the channel. A hand tightened thumb screw or nut 66 engages the threaded shank 62 and it utilized to tighten the drip chamber against the channel once a desired flow rate has been set. It will be appreciated that when the nut 66 is loosened, the drip chamber 38 may slide with respect to the channel with the shank riding in the slot 64.

Although the particular configuration of the channel 60 is not of major consequence, it has been found that a channel having a cylindrical inner wall of concave transverse cross section conforming to that of the drip chamber has been quite suitable because it guides the drip chamber for up and down movement yet permits the drip chamber to be locked at a selected elevation by the nut 66.

The channel 60 includes numerical indicia vertically positioned along a generally planar vertical face 68 which is readily viewable by an operator adjusting or setting the flow rate of the administration set. The indicia are consecutively numbered and uniformly spaced and are provided in convenient readily used flow measuring terms, e.g. cc/hour. An indicator reference such as an arrow 70 is positioned on the drip chamber 38. More than one scale of indicia may be provided for calibration of liquids of widely differing viscosities.

On a production basis, the scale indicia positions are chosen, and by coordinating the diameter and length of the metering tube 22, accurate calibration is achieved. Each unit is subsequently calibrated by using the proper length of tubing 22, once the bore diameter is fixed. This calibration method utilizes the phenomenon that flow rate is directly proportional to the fourth power of the bore diameter and inversely proportional to the tube length.

It will be appreciated that if the nut 66 is loosened and the drip chamber 28 slid upwardly along the channel so that a lower number appears at the arrow 70, the effective head between the liquid level L.sub.1 of the sump and the liquid level L.sub.2 of the nozzle 48 will be reduced, resulting in a reduction in flow rate. Additionally, the channel zero indicium is coordinated so that when the arrow 70 is in alignment therewith, the sump liquid level L.sub.1 and the nozzle column liquid level L.sub.2 are at substantially the same elevation effecting a null head at the discharge end of the metering tube thereby stopping flow. Flow is also reliably stopped if the level L.sub.2 is above L.sub.1. Since the sole flow rate control of this administration set is by moving the drip chamber in the channel, (which is positioned remotely from the patient) the opportunity for a patient to change the flow rate by tampering is greatly reduced.

In order to regulate flow through the infusion tube such that the flow rate into the patient is the same as the flow rate into the drip chamber through the metering tube, a generally cylindrical float 72 is provided within the cylindrical segment 42 of the drip chamber. The float 72 is preferably hollow and constructed of plastic or may be formed of a buoyant material, e.g. closed celled synthetic foam. The float 72 includes a valve stem 74 extending downwardly along the longitudinal axis of the float and terminating at a pointed tip. The stem 74 extends into a hollow tail 75 of the funnel shaped bottom of the cylindrical segment 42 with a conical pointed tip of the valve stem 74 engaging an annular valve seat 76. The seat 76 is constructed of a relatively soft material, e.g. silicone rubber, and is nested within the tail 75. The base of the seat 76 abuts an annular inwardly extending flange stop 78 while the wall of the seat 76 is upwardly inwardly tapering at its top. The tapered upper wall facilitates flexing of the seat 76 to accommodate and effectively seal against the conical tip of the valve stem 74. It provides an extremely reliable seal even if foreign particles are present in the solution 14. Furthermore, the seal is reliable in the presence of slight molding defects in the valve stem or seat 76. The tail 75 provides a guide for the valve stem 74 because the clearance between the valve stem 74 and the tail 75 is less than the inner radius of the valve seat. Thus, the tip of the valve stem will always be aligned with the valve seat bore.

The apex angle of the conically pointed tip of the valve stem is selected so that cooperation between the valve stem 74 and the seat 76 results in a fast response. Furthermore, angle selection will prevent the valve stem 74 from sticking in the valve seat 76. To prevent the valve stem 74 from pushing into the seat 76 to the extent that the seat would receive a set degrading deformation, a stem penetration limit stop is provided. The limit stop is effected by dimensioning the drip chamber and float such that the float bottoms at the base of the cylindrical segment 42 only after a predetermined penetration of the valve stem 74 into the seat 76. The limit stop thus assures an indefinite shelf life for the administration set.

The float 72 is generally positioned so that its longitudinal axis and the longitudinal axis of the drip chamber 38 are coincident. At the upper end of the float, an annular horizontal shoulder 80 is provided. Projecting upwardly from the area circumscribed by the shoulder is a domed head 82. It will be noted that the head 82 is positioned beneath the nozzle 48 so that drops of solution 14 discharged from the nozzle will impinge upon the head 82 then flow down the sides of the float 72 as a curtain to be collected between the side walls of the float 72 and the inner wall of the cylindrical segment 42. It has been previously mentioned that the wall of the cylindrical segment 42 is transparent. This is to facilitate viewing the drops of solution 14 as they fall.

The nozzle 48 may be offset slightly from the center of the dome 82 so that the liquid tends to flow down one side of the float and air may raise up the opposite side. Furthermore, longitudinal grooves may be provided along the wall of the float or the inner wall of the drip chamber to act as flow channels for the liquid to thus insure rapid filling of the drip chamber to operative levels.

If the clearance between the float and the segment 42 is too small, viscous drag on the float results while too large a clearance is not advantageous since it retards alignment of the float in the drip chamber.

It will be appreciated that slight clearance is provided between the walls of the float and the walls of the cylindrical segment 42 so that a minimal amount of dead volume is present and very few drops are required to bring a collected solution level within the drip chamber to a sufficient height to raise the float 72 and hence the valve stem 74 thereby permitting the flow of liquid through the infusion tube.

Once the infusion tube is filled with liquid and with the needle 25 end of the infusion tube positioned for infusion into the patient's circulatory system, the float provides a variable pressure flow regulator which maintains the flow rate through the infusion tube coincident with the flow rate into the drip chamber. Hence, the actual infusion rate into the independent liquid system will be solely dependent upon the head height between the levels L.sub.1 and L.sub.2. If the patient's blood pressure increases, the flow rate through the infusion tube 24 momentarily decreases due to the increased back pressure. Since the flow into the drip chamber remains constant, the drip chamber liquid level i.e. the liquid collected in the clearance between the float 72 and the walls of the cylindrical segment 42 rises, thereby lifting the float upwardly.

When the float lifts, the valve stem rises and increases the dimensions of the access passageway through the valve seat 76. Flow through the infusion tube remains constant since the infusion pressure at the needle has increased primarily due to the enlarged access passageway. Thus, the effective pressure of solution entering the patient increases automatically. Similarly, the increase in circulatory system back pressure due to other variables, e.g. the patient raising the elevation of an infusion arm, partial needle clotting, etc. will be automatically compensated in response to increased back pressure.

If the circulatory system back pressure decreases due to a lowering of the patient's blood pressure or the lowering of an infusion arm, an initial momentary increase in draw or flow through the infusion tube will cause the collected level within the drip chamber to decrease (since the in flow through the nozzle into the drip chamber remains constant while the draw through the infusion tube momentarily increases) thereby causing the float to lower and the valve stem 74 to constrict the access passageway through the seat. The head of liquid pressure at the infusion needle will now decrease primarily because the valve seat is constricted. Thus, the float valve equates the flow rate through the infusion tube with the flow rate into the drip chamber by automatically compensating for external factors which might affect flow.

Should a nurse or attendant decide to completely stop flow for a short period of time, she need merely adjust the elevation of the drip chamber so that the levels L.sub.1 and L.sub.2 are coincident,thus terminating flow through the nozzle 48. As soon as flow through the nozzle 48 is terminated, the liquid level within the drip chamber decreases (since the liquid is still being infused) until such point as the float lowers to completely seal against the valve seat 76 so that air will not enter and a column of trapped liquid is effectively sealed within the infusion tube. Upon resumption of flow through the metering tube, the float rises to resume infusion.

From an observation of FIG. 5 it will be seen that a spring 84 is employed between the chamber 40 and the float 72 to downwardly bias the float. One end of the spring 84 is seated against the shoulder 80 of the float while the other end of the spring abuts an annular flange 86 which extends inwardly from the side wall of the cover 40 adjacent the grooved shoulder interlock between the cover 40 and the cylindrical segment 42. As shown in FIG. 5, the spring employed is a helical coil spring, but it has been found that any conventional spring, e.g.a leaf spring, might optionally be employed. The spring is utilized to provide a force to positively seat the valve stem 74 in the seat 76. Furthermore, the spring keeps the float valve closed under severe shock loads, and will provide an additional margin of safety precluding the entrance of air into the infusion tube should the drip chamber be inverted during infusion because it exerts a seating force on the float greater than the float weight.

This particular drip chamber permits the use of the same administration set with successive solution bottles. When a bottle is emptied, the liquid level in the drip chamber lowers to the point wherein the valve stem seats, the nurse may then unscrew the bottom from the cap 26, turn the administration set upside down and secure the cap to a new bottle. Then the bottle and administration set are inverted to resume infusion at the previously determined rate. During this entire reloading procedure, the spring 84 has positively sealed the infusion tube against the entrance of air. The response time of flow regulating systems embodying this invention has been approximately one second. The response time is a function of float diameter, float clearance, float specific gravity, seat bore diameter and the spring constant.

Quite successful operation has been found utilizing a drip chamber wherein the float weight was approximately 3 grams and with the spring force on the order of three to five times the float weight with a spring constant of about 1/4 lb./inch. Additionally, it has been found that utilizing a float of approximately one inch diameter and 1.5 inches in length, a float clearance, i.e. distance between the float and the inner wall of the cylindrical segment 42 of about 0.01 inches has been found quite satisfactory in minimizing dead volume and assuring rapid filling of the drip chamber and fast response to fluid system back pressure changes.

The float volume is preferably large so that the float specific gravity provides a buoyant force sufficient to overcome the suction force of the liquid draining through the valve seat. A relatively small valve seat bore diameter (approximately 0.04 inches) helps to minimize the suction force without sacrificing system response time. It has been found that most of the float buoyant force is used to overcome the spring force. Because the actual float movement is extremely small, the spring force exerted on the float is practically constant, enabling near optimum operation at all rates of flow and back pressure combinations.

Float vibration problems are effectively eliminated if the float mass is kept relatively small. This is because the resonant frequency of the system would be high (about 100 cycles/sec.).

In actual operation, the administration set 20 is set up under a procedure substantially as follows: the cap 26 is secured to the neck of the bottle 12 and the bottle is inverted. The drip chamber is lowered along the channel 60 and solution 14 rapidly flows through the metering tube, discharging through the nozzle 48 and filling the space between the float and the cylindrical segment 42. The float rises a total travel of about 1/64 inch and allows the solution to fill the infusion tube 24, purging the air contained therein. Once the infusion tube is completely filled with liquid, the drip chamber is moved along the channel 60 to the position indicating zero flow, at which point flow through the metering tube terminates. The float 72 then seals the valve seat 76 preventing the entrance of air and further preventing the discharge of liquid through the needle. The needle may now be inserted into the proper blood vessel of the patient after which the desired flow rate may be set by moving the drip chamber downwardly along the channel 60 and the nut 66 is thereafter tightened to lock the precalibrated flow rate.

Although the administration apparatus embodying the present invention has been described in an exemplary fashion as a device for the metered infusion of liquid into the circulatory system of a patient, it will be appreciated that this invention may be equally utilized for controlled infusion of any liquid into a suitable liquid system thereby replacing costly liquid chemical feeders.

Thus, it will be seen that there is provided an administration apparatus which achieves the various objects of the invention and which is well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the present invention and as various changes might be made in the embodiment above set forth, it is to be understood that all matter herein described or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Claims

Having thus described the invention, there is claimed as new and desired to be secured by Letters Patent:

1. A calibrated administration set for the variable control of the infusion flow of a liquid carried in a container over a range of flow rates, including particularly low flow rates, into a separate liquid system having a variable liquid back pressure, the administration set comprising means adapted to form an access for liquid flow from the container, the access means including means maintaining a substantially constant effective elevational level of container supply liquid at atmospheric pressure while liquid is flowing from the container and actual liquid level in the container decreases, flexible flow metering conduit means for transmitting the liquid from the access means, one end of the flow metering conduit means being in liquid communication with the access means, means providing a discharge nozzle at the other end of the flow metering conduit means, means atmospherically venting the nozzle, the flow metering conduit means, the access means and the nozzle forming an unconstricted valveless passageway for gravity liquid flow from the substantially constant level of supply liquid located in the access means, the primary factor of flow resistance in the valveless passageway being provided solely by the flow metering conduit means, flow regulating means for adjustably controlling the rate of flow of liquid through the valveless passageway and maintaining such flow at a predetermined valve without sub-stantial fluctuations, the flow regulating means consisting of means adjustably fixing the nozzle end of the flow metering conduit means at a specific elevation with respect to the elevational level of supply liquid at atmospheric pressure to thereby maintain the effective head of liquid at the nozzle at a fixed desired value, the means adjustably fixing the nozzle end including means receiving the nozzle end of the flow metering conduit means, support means, means maintaining the support means fixed with respect to the elevational level of supply liquid at atmospheric pressure and means selectively permitting and preventing relative movement between the support means and the receiving means, the liquid flowing through the conduit means at a rate adjustably controlled solely by the effective head of liquid at the nozzle, and infusion means for infusing the liquid discharged from the nozzle into the system at the same flow rate as the liquid is flowing through the conduit means regardless of changes in system back pressure whereby the desired liquid flow rate may be adjustably set and accurately maintained over extended time durations.

2. An administration set constructed in accordance with claim 1 wherein the means selectively permitting and preventing relative movement between the support means and the receiving means includes means slidably interconnecting the receiving means and the support means.

3. An administration set constructed in accordance with claim 2 wherein the support means includes a slotted channel extending downwardly from the access means, the receiving means being movable along a fixed path registered with the slot.

4. An administration set constructed in accordance with claim 1 wherein the unconstricted valveless passageway includes a flow path of transverse cross sectional area at least as great as the transverse cross sectional area of the flow metering conduit means.

5. An administration set constructed in accordance with claim 1 wherein the means maintaining the effective level of liquid includes means forming a liquid spout for liquid communication with the liquid in the container, means forming a sump beneath the spout, the spout extending into the sump, means atmospherically venting the sump, the flow metering conduit means being in liquid communication with the sump for drawing from the liquid collected in the sump, the spout having a discharge opening positioned within the sump, at least a portion of said discharge opening extending in a plane angularly oriented with respect to the plane of the liquid level within the sump, the liquid meniscus easily breaking at the highest elevation of the spout opening to permit the entrance of air into the container and the discharge of additional liquid through the spout to replenish the sump, whereby the effective atmospheric level of liquid drawn from the container is substantially maintained at the highest elevation of the spout discharge opening.

6. An administration set constructed in accordance with claim 1 wherein the infusion means includes a cylindrical drip chamber, the means atmospherically venting the nozzle including means venting the chamber, means forming an outlet orifice in the chamber, said outlet orifice being positioned at the bottom of the chamber, a flow regulating valve positioned within the chamber, the valve including a cylindrical body of smaller diameter than the chamber and a dependent valve stem, the valve having a specific gravity such that it is buoyant in the supply liquid, the valve stem being generally aligned with the outlet orifice, and a quantity of supply liquid collecting in the chamber and lifting the valve body to permit liquid flow through the outlet orifice and into the separate liquid system, the valve body lowering to constrict the outlet orifice upon a decrease in the back pressure of the separate liquid system and rising from the outlet orifice upon an increase in said system back pressure to thereby maintain a constant infusion of flow.

7. An administration set constructed in accordance with claim 1 wherein the nozzle includes a downwardly extending hollow protuberance having an open bottom, a substantially cylindrical shell positioned about the protuberance, the shell having inner dimensions larger than the outer dimensions of the protuberance and thereby providing a span between the shell and the protuberance, the shell extending downwrdly to an open bottom, the shell open bottom being at an elevation lower than the bottom of the protuberance, the means venting the nozzle including means forming a vent passage through the shell, the span carrying a column of liquid having a meniscus at the bottom of the shell, the surface tension of the meniscus supporting and maintaining the column, the flow of liquid through the conduit means causing the column to enlarge and causing a drop to form and be released, the infusion means including a drip chamber means in the chamber for collecting drops issuing from the nozzle, the collecting means being spaced from the shell bottom a distance sufficient to permit successive drops to freely fall, and means providing an atmospherically vented free fall space between the shell bottom and the collecting means.

8. A drip chamber for use with a physiological liquid administration set, the chamber comprising a nozzle having a downwardly extending hollow probuberance, the protuberance having an open bottom, and a substantially cylindrical shell positioned about the protuberance, the shell having inner dimensions larger than the outer dimensions of the protuberance and thereby providing a span between the shell and the protuberance, the shell extending downwardly to an open bottom lower than that of the protuberance, means forming a vent passage through the shell, the span carrying a column of liquid having its meniscus at the bottom of the shell, the surface tension of the meniscus supporting and maintaining the column, the flow of liquid through the protuberance causing the column to rise and a drop to form and be released, the chamber further including means for collecting drops issuing from the nozzle, the collecting means being spaced from the shell bottom a distance sufficient to permit successive drops to freely fall, and means providing an atmospherically vented free fall space between the shell bottom and the collecting means.