Flow Regulating Device for Arterial Catheter Systems

1. Field

This invention pertains generally to intravenous catheter systems used in monitoring arterial functions and in the infusion of medical fluids to a patient. In particular, the invention relates to flow apparatus for controlling the flow of fluid at a desired continuous rate and to provide for intermittent, manually controlled larger flows of fluid to rapidly flush the catheter system.

2. State of the Art

Intravenous catheterization is a very useful procedure available for clinical monitoring of blood system and related parameters including arterial pulse waveform, stroke volume, heart rate, cardiac output, duration of systole, and systolic, diastolic and mean pressures. In addition, blood can be withdrawn for blood gas analysis.

To provide reliable operation over periods which may amount to several days, it has been found essential to flush the catheter continuously during its use with a regulated, continuous infusion of a relatively small flow of a liquid to prevent occlusion of the intravascular end of the catheter by blood coagulation. Continuous flushing systems have been proposed which utilize capillary tubes as flow resistors, with the flushing solution flowing therethrough under pressure. See, for example, U.S. Pat. No. 3,675,891 issued to Gordon S. Reynolds, et al. on Sept. 18, 1970, and an article appearing on pages 675-678 of the Journal of Thoracic and Cardiovascular Surgery, Volume 57, No. 5, May 1969.

Generally, the prior systems employed an objectionable large amount of apparatus including numerous stopcocks, with resulting loss of fidelity in the operation of the system. The device disclosed in U.S. Pat. No. 3,675,891 overcomes many of the deficiencies inherent in the earlier systems by providing a relatively small unitary piece of apparatus which was constructed so as to eliminate the use of all stopcocks. A resilient valve was provided to control a bypass around the capillary flow resistor, with the valve being operated by manually pulling a valve stem which extends longitudinally from the apparatus. The valve and stem system of such device, however, has certain drawbacks. For example, the protruding stem is subject of entanglement in tubing, bedding, or other paraphenalia resulting in possible undesired opening of the valve or breakage of the valve stem so as to preclude proper operation of the device. The valve stem can also be broken by pulling the stem to one side or the other rather than longitudinal, and the valve has also been found to occasionally fail in the open position. In addition, the valve and stem system is generally difficult to operate with one hand, and for all practical purposes, requires two-handed manipulation.

3. Objectives

The principal objective of the present invention is to provide an improved regulating device which is reliable and easy to operate, as well as being simple in construction. A particular objective of the invention is to provide a small, streamlined device for connection in the catheter system which can be operated easily with one hand and which does not include stopcocks or stem actuated valves as in the devices of the prior art.

The above objectives are achieved in accordance with the present invention by providing a small, unitary, flow regulating device comprising a control member having an inlet means adapted to be connected to a source of a medical fluid and an outlet means adapted to be connected to an intravenous catheter. The control member is provided with a first passage connecting the inlet and outlet means for fluid flow communication therebetween, with at least a part of the first passage comprising a section of flexible conduit having valve control means positioned therein. The valve means is adapted to open and permit a flushing flow of liquid to pass through the first passage when the conduit is squeezed and to close and thereby stop the flushing flow of fluid when the conduit is released.

A second passage is provided in the control member. The second passage by-passes the valve means and connects the inlet and outlet means for flow communication therebetween. A flow restriction means is provided in the second passage to restrict the flow of fluid therethrough to a limited, continuous flow under a given upstream pressure.

Additional objects and features of the invention will become apparent from the following detailed description of a preferred embodiment, taken together with the accompanying drawing.

In the drawing:

FIG. 1 is a diagrammatic illustration of a device in accordance with this invention in operative association with a catheter system which is inserted into the arm of a patient, the device itself being exaggerated for purposes of illustration;

FIG. 2 is a perspective view of a preferred embodiment of the device;

FIG. 3 is a central, vertical section through the device shown in FIG. 2; and

FIG. 4 is a vertical section of a modified version of the plug valve of FIG. 3.

The device of the present invention is adapted to be incorporated in various catheter systems. As used throughout the specification and claims, the term "catheter systems" is meant to include systems using catheters, cannulas, or other tubes inserted into the arterial system of a patient and used to monitor arterial functions and parameters as well as withdrawing blood from or infusing medical fluids into the arterial system.

By way of example, the flow control device is shown in the drawing and will be described herein as incorporated into a catheter system for monitoring arterial pressure and recording of arterial pulse waveforms. The catheter used in such a system is very thin, having an inside diameter of about one-half millimeter. The catheter must be maintained in open and operable condition for transmitting pressure pulses. The tendency for a blood clot or other occlusion to form at the end of the catheter positioned within the arterial system is greatly reduced by continuously infusing a sterile solution into the arterial system through the catheter in an amount which will not harm the patient but will retard the formation of occlusions in the catheter. Generally, depending on the size of the patient, from about 2 cc to about 7 cc of solution per hour has been found to be safe and beneficial.

In accordance with the present invention, means are also provided for manually flushing the catheter system from time to time with a momentary increase in the flow of solution through the catheter. The increased flow of fluid clears the catheter of any clots or occlusions which have formed or are being formed. In addition, the increased flow of fluid permits rapid clearing of all air from the system during the installation of the catheter into the arterial system of the patient, as will be discussed more fully hereinafter.

A preferred embodiment of the flow control device is shown in the four figures of the drawing, wherein similar components of the device are identified with the same reference numeral. The device comprises a control member 10, which as shown in FIG. 1 is adapted to be connected by tube 11 to a supply of a medical fluid in container 12. The control member 10 is also connected by tube 13 to a catheter which has been positioned within the arm of a patient 14. Means are provided for connecting the control member 10, in fluid flow communication through tube 15, to diagnostic apparatus (not shown in the drawing) which is capable of monitoring various arterial functions such as those mentioned previously. A variety of diagnostic apparatus is well known to the medical art and does not, per se, constitute part of the present invention. As will be more fully described hereinafter, the means which are provided for connecting tube 15 to control member 10 can also be used for hypodermic injections to and for withdrawing of blood samples from the patient.

The construction of the control member 10 is best shown in FIGS. 2-4, and will be described with reference thereto. As illustrated, the control member 10 consists of a body member 16 having upstanding end caps 16a and 16b, respectively, such that in side elevation, the body member 16 has a broad, generally U-shaped profile. The end cap 16a is provided with inlet means for connecting the control member 10 to the tube 11 which, in turn, is connected to a supply of medical fluid, such as the container 12 shown in FIG. 1. The inlet means as shown in FIGS. 2 and 3 comprises a short piece of tubing 17 which is securely affixed to the end cap 16a at one of its ends and has a male fitting 18 attached to its other end. The fitting 18 is adapted to releasably engage a female fitting 19 on the end of tube 11. Various types of fittings, some being, as illustrated, adapted for interlocking engagement between lugs on the male fitting and internal thread-like receptacles on the female fitting, and some being adapted for simple sliding engagement, are commercially available for use in the present invention.

The other end cap 16b is provided with outlet means which is adapted to be connected to an intravenous catheter by way of an appropriate tube, such as tube 13 shown in FIG. 1. As illustrated in FIGS. 2 and 3, the outlet means comprises a fitting 20 which is adapted for connection to a mutually corresponding fitting on a fluid conveying tube leading to the catheter. The fitting 20 can be any of various type fittings conventionally used for connecting medical tubing together or to other medical apparatus. As shown, the fitting 20 is of the type having an internally threaded receptacle 20a (FIG. 3) adapted to receive a male fitting having lugs thereon for engagement with the threads of the receptable.

The outlet means at end cap 16b preferably also includes a second fitting 21, which, as shown, is a male fitting having side lugs 21a which are adapted to releasably engage the threads of a mutually corresponding fitting on a tube, such as tube 15 shown in FIG. 1, for connecting the control member 10 to diagnostic apparatus capable of monitoring various functions such as blood pressure, etc., as mentioned previously. The fitting 21 could be of the female type such as fitting 20; however, inasmuch as the fitting on the diagnostic apparatus is likely to be of the female type, and connecting tubing conventionally has a male fitting at one end and a female fitting at the other end, it is advantageous to make the fitting 21 of the male type, as shown.

A fluid flow passage connects the inlet and outlet means in the end caps 16a and 16b of body member 10. As illustrated in FIGS. 2 and 3, the flow passage comprises bores 16c and 16d through the respective end caps 16a and 16b which are in flow communication with the tube 17 and fitting 20, respectively. The end caps 16a and 16b have inwardly facing hubs 16e and 16f, which are adapted to receive the respective ends of a flexible conduit 22, so that the conduit 22 connects the bores 16c and 16d for fluid flow communication therebetween. The flow passage thus comprises the bores 16c and 16d of the end caps 16a and 16b together with the flexible conduit 22.

A valve means is positioned within the flexible conduit 22 and is adapted to open and permit the intermittent, larger, flushing flow of fluid to pass through the flexible conduit 22 when the conduit 22 is squeezed, and to close when the squeezing action on the conduit 22 is terminated. Preferably, the valve means comprises a substantially cylindrical plug member 23 (FIG. 3) positioned coaxially within the flexible conduit 22. The plug member 23 has a raised band 23a thereabout intermediate its ends, with the band 23a having a sufficient diameter that its exposed surface forms a substantially flow tight seal with the interior wall of the flexible conduit 22, so that when the flexible conduit is not being squeezed, fluid is substantially completely prevented from flowing around the plug between the raised band 23a and the interior wall of flexible conduit 22. The portion of the plug member on either side of the raised band 23a is of a reduced diameter and thus an open flow space 24 is formed between the flexible conduit 22 and the portions of the plug member 23 on either side of the raised band 23a.

When the flexible conduit 22 is subjected to a squeezing action in the vicinity of the raised band 23a, the seal between the raised band 23a and the interior wall of the flexible conduit 22 is broken, due to deformation of the flexible conduit 22 which creates flow channels extending across the raised band 23a. Fluid can then flow around the plug member 23 and through the flexible conduit 22. Upon termination of the squeezing action on the flexible conduit 22, the seal between the raised band 23a and the interior wall of the flexible conduit 22 is automatically re-established, thereby terminating the flow of fluid around the plug member 23. Advantageously, the base portion of the body member 16 has concave depressions 16g (FIG. 2) in the side thereof facing the flexible conduit 22 and the two sides thereof extending from the flexible conduit, respectively. The concave depressions form finger guides on each side of the control member 10 which aid in positioning one's fingers for squeezing the flexible conduit 22.

A second passage is provided in the control member 10 for by-passing the valve means in the flexible conduit 22 and connecting the inlet and outlet means of body member 16. Such a by-pass passage could be routed through the body member 16 from the inlet means in end cap 16a to the outlet means in end cap 16b. Preferably, however, the second passage is combined in the valve means itself as shown in FIGS. 3 and 4. In the preferred mode, the plug member 23 is positioned concentrically in the flexible conduit 22 and is provided with a bore extending longitudinally through the plug member 23 which by-passes the valve means in the flexible conduit 22.

Flow restriction means is provided in the second passage for limiting the amount of fluid passing through the second passage to a desired relatively small rate.

As illustrated in FIG. 3, the flow restriction is advantageously provided by forming at least a portion of the bore 25 into a capillary section 25a having a very small diameter in the order of several hundredths of a millimeter. The capillary section 25a of bore 25 is shown in FIG. 3 in greatly exaggerated proportions for purposes of clarity, since the portion 25a in reality is so small in diameter as to be practically invisible without the use of some type magnification. By incorporating capillary sections 25a of different diameters and lengths, a broad series of apparatus can be readily produced from which individually sized units can be chosen which will deliver the desired amount of fluid under the given upstream pressure which is to be utilized in the particular application.

In an alternate embodiment of the plug member 23 shown in FIG. 4, the flow restriction is provided by positioning a resistance element 26 in the bore 24 of the plug member 23. The resistance element 26 comprises a marine-bore capillary tube, with the diameter of the bore in the element 26 being very small, in the order of hundredths of a millimeter. The bore in the element 26 of FIG. 4 is shown in greatly exaggerated proportions for purposes of illustration. To aid in positioning the marine-bore resistance element 26 in the bore 24 of plug member 23, the bore 24 has a downstream section having a reduced diameter as shown in FIG. 4. The capillary tube 26 is then forced into bore 24 from the upstream end thereof until it abuts the edges of the reduced diameter section of bore 24. The outside diameter of the resistance element 26 is sufficient so that a tight, non-leaking seal is made between the external surface of the element 26 and the bore 24.

Preferably, the second passage extending through the plug member 23, i.e., the bore 24 is coaxial with the longitudinal axis of the plug member 23. Also, the downstream end of the plug member 23 is advantageously tapered as shown in FIGS. 3 and 4. The tapered end of the plug member 23 is received in a flared receptacle in the end of hub 16f. The flared receptacle is formed symmetrically about the axis of the first passage, and, thus, when the tapered end of the plug member 23 is received therein, the bore 24 of plug member 23 is maintained in axial alignment with the bore 16d in end cap 16b.

In use, the flow device of this invention is efficient, reliable, and easy to manipulate. Prior to the insertion of the catheter into an artery or vein of the patient, the flow device of this invention is connected between the catheter and a source of medical fluid. The medical fluid can be contained in a pressurized vessel, or a container which is elevated sufficiently above the patient so as to provide for the working upstream pressure necessary for proper flow of fluid through the bore 24 of the device.

All air bubbles are eliminated from the catheter system by squeezing the flexible tube 22, thereby flushing the system with a relatively large flow of fluid which flows past the valve plug 23. When all air bubbles have been eliminated, the squeezing action on tube 22 is terminated and the relative large flow of fluid stops, with only the limited, small flow of fluid through the second passage or bore 24 continuing. The catheter is then inserted into the patient's body, with the small flow of fluid passing through the catheter into the vein or artery of the patient. This continuous flow of fluid through the catheter reduces the occurrence of blood clotting or other occlusions occuring in the end of the catheter positioned within the patient's body.

The fitting 21 on the end cap 16b of the flow control device is, of course, connected to whatever indicating or recording means is desired, or to a pressure transducer for oscilloscopic observations. To assure quality of the information obtained from the catheter system, the system is manually flushed from time to time with a relatively rapid flushing flow of fluid by simply squeezing the flexible tube 22 of the flow control apparatus to permit fluid to flow around the valve plug 23. When the squeezing action is terminated the relatively rapid flow of fluid through the catheter stops, and the smaller flow of fluid from the bore 24 continues in its normal course. The periodic flushing of the catheter system is accomplished quickly and easily, using only one hand of the person handling the apparatus.

The device of this invention can also be advantageously used in combination with a stopcock downstream of the unit 10 to obtain blood samples from the patient or to infuse a desired amount of medication or blood samples to the patient without requiring a second catheterization, cannulation or hypodermic injection of the patient.

Although the apparatus has been shown and described in connection with a catheter system wherein the catheter is placed in the arm of a patient, it is to be understood that the catheter may be entered into various veins or arteries of the body as the general medical situation requires. It is further to be understood that the present disclosure, including the detailed description of a preferred embodiment of the invention, is made by way of example and that various other embodiments are possible without departing from the subject matter coming within the scope of the following claims, which subject matter is regarded as the invention.