GB2031558A

GB2031558A - Apparatus for controlling the flow of intravenous fluid to a patient

Info

Publication number: GB2031558A
Application number: GB7930212A
Authority: GB
Original assignee: Imed Corp
Current assignee: Imed Corp
Priority date: 1978-09-01
Filing date: 1979-08-31
Publication date: 1980-04-23
Also published as: SE444995B; DE2926127A1; DE2926127C2; AU545751B2; NL183013B; NL7904958A; JPH0112834Y2; AU530314B2; FR2434626B1; IT7949663A0; GB2105495A; AU4719079A; CA1136507A; GB2031558B; FR2434626A1; GB2105495B; SE7904226L; IT1162340B; NL183013C; AU1480383A

Abstract

Flow from an input line 12 to an output line 16 is controlled by adjustment of a diaphragm 32 relative to a ring 30 which surrounds the end of an outlet passage 26 but has a notch for low flow rates. Manual setting is possible by screwing in a knob 40 which presses a plunger 36 against the diaphragm 32. Control may also be effected by a stepping motor coupled to the knob 40 and responsive to comparison of a desired flow rate with the rate measured by a drop sensor 62. <IMAGE>

Description

SPECIFICATION Apparatus for controlling the flow of intravenous fluid to a patient This invention relates to removable apparatus for controlling the flow of intravenous fluid from a source to a patient. The invention particularly relates to apparatus for providing for precise controls over the rate of fluid flow to a patient during the operation of the apparatus under normal circumstances such as in the room assigned to the patient and for controls over the rate of fluid flow in accordance with manual adjustments during such abnormal conditions as the transport of a patient from one room to another.More particularly, the invention relates to apparatus for providing for a manual control over the rate of fluid flow to a patient when removed from a system, for a setting of rate in a system upon insertion of the apparatus into the system and an overriding of the manual control by the system setting under such circumstances and for the reassertion of the manual control upon a removal of such apparatus from the system.

As the practice of medicine becomes increasingly complex and increasingly refined, the equipment and techniques used to provide care for a patient have become increasingly sensitive in order to assure that the patient receives optimum care. For example, after an operation has been performed on a patient and the patient is in the recuperative state, intravenous fluid often has to be introduced to the patient. The rate of introduction of fluid to the patient is dependent upon a number of different factors including the weight, age, sex and physical state of the patient. As the patient recovers from his illness, the rate of introduction of the intravenous fluid to the patient is preferably adjusted to assure that the patient receives an optimum benefit from the fluid.

A Aconsiderable effort has been devoted over a substantial period of time to provide a satisfactory system for controlling the rate at which fluid such as intravenous fluid is introduced to a patient. Considerable progress has been made in developing a satisfactory system for certain types of operations.

For example, a system providing for the pumping of fluid on a precise volumetric basis to a patient has been disclosed and claimed in patent 3,985,133 issued on October 1976, and assigned of record to the assignee of record of this application.

A number of fundamental problems have remained until fairly recently in systems providing for the flow of fluid on a gravitational basis to a patient.

Such problems have existed until recently even though a considerable effort has been devoted to the solution of such problems. For example, a satisfactory system has not existed until recently for providing for the introduction of fluid to a patient on a gravitational basis at a precise and predetermined rate. Furthermore, a system has not existed until recently which could be used on a sterile and hygienic basis for different patients such that any contamination from the use of the system for one patient would not affect the health or safety of subsequent patients.

U.K. Application Serial No. 7919859 for a "Cassette for Intravenous Controller" discloses and claims a cassette which is disposed in the system to provide for the flow of fluid on the controlled basis to the patient and which is easily removable from the system so that a sterile cassette can be replaced in the system for a previously used cassette every time that the system is to be used for a different patient.

Although the system and cassette disclosed and claimed in the application specified in the previous paragraph providefortheflowoffluid on a gravitational basis to a patient at precise rates under sterile conditions, improvements would be still desirable to enhance the scope of operation of the system. For example, it would be desirable to provide a system which could be coupled to a patient even during movement of the patient and which would provide for a flow of fluid to the patient at controlled rates during such movement. In this way, intravenous fluid could be introduced to the patient at such controlled rates even during the movement of the patient from an operating room to a recovery room or from the recovery room to a room of permanent assignment in a hospital.It would also be desirable to provide such a system with instantaneous capabilities of controlling precisely and automatically the flow of fluid on a gravitational basis to the patient after the movement of the patient to a room of permanent assignment. As will be seen, a system of such capabilities would have a considerable flexibility in operation since it would provide for a controlled flow of fluid to a patient under all conditions which may be encountered in a hospital.

This application provides a system with the capabilities discussed in the previous paragraph. The system includes apparatus which is free-standing and which is manually adjustable at such times to vary the rate at which intravenous fluid flows to a patient. Such manual adjustments may be operative to control the rate of fluid flow during the time that a patient is being moved from an operating room to a recovery room or from the recovery room to his assigned room.

The apparatus may also be inserted easily and conveniently into a system when the patient is recuperating in his assigned room. At such times, desired rates of fluid flow may be set in such system, which then overrides any previous manual adjustment of such apparatus and adjusts the rate of fluid flow in accordance with any such setting. This provides for a precise control of the flow of fluid in accordance with such settings during the time that the patient is in his assigned room.

In this way, the precise controls can become operative when the patient has been moved to his assigned room and the system is operative on a semipermanent basis in the assigned room. When a desired rate of fluid flow has been preset into the system, the system then operates in a servo loop to adjust the rate of fluid flow on an instantaneous basis so that the desired rate of fluid flow is precisely maintained.

The apparatus is removably disposed in the system for controlling the flow of fluid to the patient.

As a result, the manual adjustment may be provided when the apparatus is removed from the system and the system control of the rate of fluid flow may be provided when the apparatus has been coupled into the system. The removal of the apparatus from the system or the coupling of the apparatus into the system may be provided easily on an instantaneous basis.

The apparatus includes a plug member defining a passage which communicates at a first position with an input line and, at a displaced position in a particular direction, with an output line. A resilient member such as a diaphragm may be disposed in the particular direction in the passage and may be displaced in a transverse direction from the input and output lines. A rod may extend into the passage to stretch the diaphragm in the transverse direction.

A button may envelop one of the input and output lines to cooperate with the diaphragm in limiting the rate of flow of fluid through the passage in accordance with the stretching of the diaphragm in the transverse direction. The button may have a notch cooperating with the diaphragm in facilitating the flow of fluid through the passage at the desired rate.

A knob may be adjustably threaded on the plug memberto press the rod against the diaphragm.

The knob may be manually adjusted, during the movement of the patient from the operating room to the recovery room or from the recovery room to his assigned room, to control the rate at which fluid flows to the patient. The knob may be coupled to a driving member when the apparatus is inserted into the system. At such times, a motor drives the driving member through an angle dependent upon a rate which is preset into the system. In this way, the diaphragm is stretched in the transverse direction in accordance with the operation of the motor. The motor may be servo-controlled to adjust the stretching of the diaphragm at each instant in the transverse direction in accordance with the rate at which drops of the fluid are actually flowing to the patient.

This servo-control insures that the actual rate of flow of fluid to the patient corresponds to the rate preset into the system when the apparatus is inserted into the system.

The apparatus included in this invention is adapted to be included in the cassette disclosed and claimed in application No. 7919859, referred to above, orto be used as a separate item in the system without including the cassette in the system.

In the drawings: Figure 1 is a schematic diagram, partly in block form, of a system for controlling the flow of intravenous fluid to a patient on a gravitational basis; Figure 2 is a sectional view of control apparatus capable of being included in the system of Figure 1 and shows the positioning relative to such control apparatus of a drop sensor included in the system shown in Figure 1; Figure 3 is a sectional view of the apparatus shown in Figure 2 when the apparatus is removed from the system shown in Figure 1 and is in a position to provide for the flow of fluid at a very low rate; Figure 4 is an enlarged fragmentary sectional view of certain elements of the apparatus shown in Figures 2 and 3; Figure 5 is an exploded perspective view of the system shown in Figure 1 and of the apparatus of Figures 2 and 3 in a position removed from the system; and Figure 6 is a schematic view of a cassette which may be constructed to include the apparatus of Figures 2 and 3.

Figure 3 illustrates equipment which forms a part of this invention and which provides for flow of intravenous fluid to a patient at a rate dependent upon a manual adjustment of such apparatus. The equipment includes a source 10 of intravenous fluid and a conduit 12 extending from such source to apparatus generally indicated at 14 and forming a part of this invention. An output conduit 16 extends from the apparatus 14 to a patient schematically illustrated at 20.

The apparatus 14 includes a plug member 22 formed from a suitable material such as a plastic material. The plug member 22 is provided with an input line 24 constructed to receive the input conduit 12 and with an output line 26 constructed to receive the output conduit 16. A cavity or passage 28 is disposed between, and in communication with, the input line 24 and the output line 26. Button 30 is disposed in the passage 28 in a closed loop around one of the lines such as the output line 26 and is preferably provided with an annular configuration.

The button 30 is preferably notched at one position as at 31 (Figure 4) to facilitate the flow of fluid on a controlled basis. The notch 31 may be V-shaped to provide a progressive control over the rate of fluid flow.

A Aresilient member such as a diaphragm 32 is disposed in the cavity or passage 28. The ends of the diaphragm 32 are provided with a bulbous construction and the bulbous ends are disposed in sockets 34 in the plug member 22 to maintain the diaphragm in a ataut relationship. The diaphragm 32 is disposed so that it extends in the same direction as the distance between the input line 24 and the output line 26 at the positions at which these lines communicate with the passage 22.

A Apusher rod 36 is disposed in a socket 38 in the plug member 22. The pusher rod 36 is disposed against the diaphragm 32 at a position intermediate the sockets 34 to stretch the diaphragm in a direction transverse to the disposition of the diaphragm in the passage 22. A knob 40 is internally threaded on a threaded protuberance 42 extending from the plug member 22. The knob 40 presses against the pusher rod 36. The knob 40 may be provided with a frusto-conical external surface which may be knurled or otherwise deformed to facilitate gripping.

The knob 40 may be rotatably adjusted on the protuberance 42 to adjust the pressure exerted against the pusher rod 36. This in turn provides for an adjustment of the force exerted by the pusher rod 36 against the diaphragm 32. In this way, the position of the diaphragm 32 adjacent the button 30 may be adjusted in accordance with adjustments in the positioning of the knob 40 so as to control the rate at which fluid flows through the passage 28 from the input line 24 to the output line 26. The manual adjustment of the knob 40 accordingly provides for a control of the rate at which fluid flows from the source 10 to the patient 20.

The notch 31 is provided in the button 30 to obtain a flow of fluid to the patient at low rates in accordance with the adjustment of the knob 40. This may be seen on a schematic basis in Figure 4. At such low rates, the diaphragm 32 tends to be drawn into the notch 31. The positioning of the diaphragm 32 in the notch 31 is dependent upon the adjustment of the knob 40. As a result, for low settings of the knob 40, fluid can flow through the passage to the output line only in the space between the diaphragm 32 and the bottom of the V-shaped notch 31.

The apparatus disclosed above is adapted to be used when the patient is being moved from an operating room to a recovery room or from a recovery room to an assigned room. Since the apparatus 14 is relatively small and can even be held in the palm of a hand, it can be held by a nurse or even can be disposed in the palm of a patient as the patient is being moved from one room to another.

During such movement, the rate of flow of fluid to the patient can be controlled by the adjustment of the knob 40 on the protuberance 42.

Figure 1 illustrates a system for providing an automatic control over the rate of flow of fluid on a gravitational basis to a patient. The system includes the apparatus 14 shown in Figures 2 and 3 and described in detail above. The apparatus 14 is adapted to be supported in fixed position relative to such system by a housing generally indicated at 50 in Figure 5. The holder includes a drive member 52 (Figure 5) which is provided with a socket 54. The socket 54 is knurled or otherwise deformed in a manner similar to the external surface of the knob 40 so as to engage the knob and rotate the knob as it rotates. The drive member 52 may be spring loaded to facilitate the driving relationship between it and the knob 40. The drive member 52 is adapted to be driven by a stepper motor 56.

The stepper motor 56 is included in an electrical system which is shown on a schematic basis in Figure 1. The system includes settings 58 (Figure 5) which are disposed on the front panel of the housing 50 and which are preferably provided with digital capabilities of a plurality of digits of progressive value. For example, three digits may be provided to register the values of units, tens and hundreds to provide capabilities of selecting rates of digital flow between values of "1" and "999".

The selections in the settings 58 are introduced to a comparator 60 (Figure 1) which compares such desired values with the actual values of flow provided by a drop sensor 62. The drop sensor may be of a conventional construction and is operative to sense the number of drops of fluid flowing through the output line 12 in a particular period of time such as one second. The comparator 60 compares the signals from the settings 58 and the drop sensor 62 and produces an error signal representing any differences between the characteristics of the signals being sensed. The error signal is then introduced to the stepper motor 56 to operate the stepper motor in a adirection for reducing the error signal. The stepper motor drives the drive member 52, which in turn drives the knob 50, in a direction to control the flow of fluid through the passage 28.In this way, the stepper motor 56 is controlled on an instantaneous basis to obtain a flow of fluid through the output line 16 at a rate directly related to the values provided in the settings 58.

As will be seen from Figure 5, the apparatus 14 is adapted to be removably disposed in the housing 50.

The housing 50 may include the drive member 52 and the stepper motor 56. In this way, the apparatus 14 may be easily coupled into the housing 50 when the system shown in Figure 5 is to be operative in an assigned room of a patient to provide a flow of fluid to the patient at a precise rate in a closed-loop.

The apparatus 14 may be easily decoupled from the housing 50 to operate independently of the system when the patient is being moved from an operating room to a recovery room or from a recovery room to an assigned room. Under such circumstances, the manual adjustment of the knob 40 is sufficient to regulate the flow of fluid at a desired rate with sufficient accuracy in an open-loop servo so that the patient is receiving good medical attention.

The apparatus 14 may also be included in a cassette which is generally indicated at 70 in Figure 6 and which is disclosed and claimed in application Serial No. 913,282. As disclosed in such application, the cassette 70 may be included in a system, such as that shown in Figure 1, for controlling the rate of flow of intravenous fluid to a patient on a gravitational basis. When the apparatus 14 is included in the cassette 70, it may be permanently disposed in the cassette rather than being removable as in the embodiment described above. However, even when the apparatus 14 is included in the cassette, it has the flexibility of being manually adjustable to control the rate of flow of intravenous fluid to a patient or of being controlled by the system in accordance with adjustments in the setting 58 shown in Figure 5.

When the apparatus 14 is included in the cassette 70, it may be disposed at any convenient position in the hydraulic circuit provided by the cassette. This hydraulic circuit is shown on a schematic basis in Figure 6. for example, the apparatus 14 may be disposed at a position 71 designated as "X" in an input line 72 in the cassette. The position "X" is provided in the input line 72 at a position in advance of any branching of the fluid into auxiliary lines in the cassette. In this way, all of the fluid flowing through the cassette passes through the apparatus 14.

The hydraulic circuit shown in Figure 6 includes a pair of auxiliary lines 74 and 76 extending from the input line 70 to opposite ends of a chamber generally indicated at 78. Valves 80 and 82 are respectively disposed in the auxiliary lines 74 and 76. A resilient member such as a diaphragm 84 is disposed in the chamber 78 to divide the chamber into a pair of compartments 86 and 88. Auxiliary lines 90 and 92 respectively extend from the compartments 86 and 88 to an output line 94. Valves 96 and 98 are respectively disposed in the auxiliary lines 90 and 92.

The apparatus 14 is preferably disposed in the output line 94 as illustrated in Figure 6.

The diaphragm 84 is stretchable in the chamber 78 to increase the volume of one of the compartments and correspondingly reduce the volume of the other compartment. A transducer generally indicated at 100 is movable with the movement of the diaphragm to indicate the disposition of the diaphragm at each instant. The transducer 100 produces at each instant a signal which controls the direction in which fluid flows into and out of the chamber. For example, the valves 80 and 98 may be initially open and the valves 82 and 96 may be initially closed. In this relationship, fluid flows into the compartment 86 and out of the compartment 88 and accordingly stretches the diaphragm 84 into the compartment 88. When the diaphragm has stretched to a particular limit, the transducer 100 produces a signal which causes the valves 80 and 98 to close and the valves 82 and 96 to open.In this relationship, fluid flows into the compartment 88 and out of the compartment 86 and accordingly causes the transducer 100 to stretch into compartment 86.

In this way, fluid flows at alternate times into the compartment 86 and out of the compartment 88 and at the other times into the compartment 88 and out of the compartment 86. The rate of fluid flow into and out of the compartments 86 and 88 is dependent upon the setting of the knob 40 in the apparatus 14.

The setting of the knob 40 may be manually adjusted or the knob 40 may be automatically set by the system of Figures 1 and 5 in accordance with values inserted into the settings 58.

The apparatus and system described above has certain important advantages. It provides for the introduction of fluid on a gravitational basis to a patient at preset rates even when the patient is being moved from an operating room to a recovery room or from a recovery room to an assigned room. This rate of fluid flow may be manually preset to any desired value.

The apparatus and the system including the apparatus also provide for the flow of intravenous fluid on a gravitational basis to a patient at precisely controlled rates when the patient has been moved to his assigned room. Such precisely controlled rates may be inserted by a physician or nurse into the system by the operation of the setting 58. The system then operates in a closed-loop servo to insure at each instant that the rate of fluid flow to the patient is precisely regulated at the desired rate inserted by the physician or nurse.

The apparatus and system are also advantageous because they can be easily converted between manual control of the rate of fluid flow or system control of the rate of fluid flow. The apparatus and system are further advantageous because the apparatus 14 is relatively small and light and can be easily moved with the patient as the patient is transported from the operating room to the recovery room or from the recovery room to the assigned room.

Although this application has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Claims

1. In combination for controlling the flow of intravenous fluid to a patient, means for providing a source of fluid, means defining an inlet line from the source and an outlet line to the patient, means disposed between the inlet line and the outlet line for defining a passage communicating with the inlet and outlet lines, resilient means disposed in the passage for controlling the size of the passage in accordance with the positioning of the resilient means in the passage, and means operatively coupled to the resilient means for adjustably positioning the resilient means in the passage to control the rate at which fluid flows through the inlet lines to the outlet line.

2. The combination set forth in Claim 1 wherein the resilient means constitutes a diaphragm disposed in the passage and the diaphragm is pressed into the passage by the adjustably positioned means to control the size of the passage in accordance with such pressure.

3. The combination set forth in Claim 2 wherein the adjustably positioned means are manually adjustable and means are adjustably provided for setting the flow of fluid to any value desired and means are responsive to the adjustable setting of the desired flow of fluid for adjusting the positioning of the adjustably positioned means in accordance with such setting.

4. The combination set forth in Claim 3 wherein the means responsive to the setting of the desired flow of fluid include means for engaging the manually operated adjustably positioned means and motor means responsive to such engagement of the adjustably positioned means for driving the adjustably positioned means to a position corresponding to the desired setting of the fluid flow.

5. The combination set forth in Claim 2 wherein the diaphragm extends across the passage at a position adjacent to at least one of the inlet and outlet lines and the adjustably positioned means stretches the diaphragm into the passage in accordance with adjustments in the position of the adjustably positioned means and the stretching of the diaphragm moves the diaphragm toward a button surrounding at least one of the input and output lines to control the rate at which fluid flows through the lines.

6. The combination set forth in Claim 5 wherein the annular button is provided with a cut in at least one position and wherein the diaphragm is positioned to be seated in the cut in accordance with the positioning of the adjustably positioned means to facilitate the flow of fluid through the passage and the input and output lines at the controlled rate.

7. In combination for controlling the flow of intravenous fluid to a patient, first means defining an input line, second means spaced from the first means and defining an output line, the first and second means being spaced by a cavity, and third means removably disposed in the cavity and defining an adjustable passage for the flow of fluid from the first means into the second means, the third means including resilient means disposed in the passage for inhibiting the flow of fluid through the passage in accordance with the constraint of the resilient means and further including means disposed against the resilient means and adjustable to adjust the constraint of the resilient means.

8. The combination set forth in Claim 7 wherein the passage includes an annular button disposed around a particular one of the first and second means and the resilient means includes a resilient diaphragm and the adjustably positioned means includes a pusher rod disposed against the diaphragm at a position within the area encompassed by the annular button and further includes a knob pressing the pusher rod against the diaphragm and rotatable to adjust the force exerted by the pusher rod against the diaphragm.

9. The combination set forth in Claim 8 wherein a cut is provided in the annular button and the diaphragm is adjustably positioned in the cut in accordance with the force exerted by the pusher rod to facilitate the flow of fluid through the passage and the first and second means at the controlled rate.

10. The combination set forth in Claim 8 wherein the first and second means are spaced from each other in a particular direction in the passage and the diaphragm extends in the passage in the particular direction and is spaced in a transverse direction from the first and second means and is constructed to be stretched in the transverse direction in accordance with the force exerted by the pusher rod.

11. In combination for controlling the flow of intravenous fluid from a source to a patient, a plug member, means defining a passage in the plug member, means defining in the plug member an input line communicating with the passage in the plug member, means defining in the plug member an output line communicating with the plug member, resilient means included in the plug member and adjustably disposed in the passage for controlling the flow of fluid through the passage between the input and output lines in the plug member in accordance with the adjustable disposition of the resilient means in the passage, means included in the plug member and adjustably positioned against the resilient means for adjusting the disposition of the resilient means in the passage, and means supporting the plug member in a removable reiationship and providing for a flow of fluid from the source into the input line of the plug member and from the output line of the plug member to the patient.

12. ' The combination set forth in Claim 11 wherein the plug member has a threaded protuberance and the adjustable positioning means includes a pusher rod disposed against the resilient means and further includes a knob adjustably threaded on the protuberance on the plug member and pressing the pusher rod against the resilient means in accordance with such adjustable positioning.

13. The combination set forth in Claim 11 wherein the resilient means is a diaphragm disposed in the passage and wherein means are disposed in the passage and are cooperative with the diaphragm to block the flow of fluid through one of the input and output lines and wherein the diaphragm is pressed by the adjustable positioning means toward the blocking means to control the rate at which fluid flows through the passage from the input line to the output line.

14. The combination set forth in Claim 13 wherein the input and output lines respectively communicate with the passage at positions spaced in a particular direction and the diaphragm is spaced from the input and output lines in a direction transverse to the particular direction and is stretched in the particular direction and is pushed by the adjustably positioned means toward the input and output lines.

15. The combination set forth in Claim 14 wherein the adjustably positioned means includes a pusher rod disposed against the diaphragm to force the diaphragm in the transverse direction in accordance with adjustments in the positioning of the adjustably positioned means and the adjustably positioned means further includes a knob threadedly disposed on the plug member and positioned against the pusher rod to press the pusher rod against the diaphragm and wherein a button is disposed around one of the input and output lines at a position adjacent to the diaphragm to cooperate with the diaphragm in controlling the flow of fluid.

16. The combination set forth in Claim 15 wherein the button is disposed in a closed loop around one of the input and output lines and a cut is provided in the button in at least one position and the diaphragm is disposed relative to the cut to be disposed in the cut in accordance with the force exerted on the diaphragm by the pusher rod to facilitate the flow of fluid through the passage at a controlled rate.

17. In combination for controlling the flow of intravenous fluid to a patient, means defining a passage for the flow of fluid, resilient means disposed in the passage for controlling the rate of flow of fluid through the passage and constructed to limit the flow of fluid through the passage in accordance with the variations in force exerted against the resilient means, manually operable control means for producing an adjustable force against the resilient means in a direction to limit the rate of flow of fluid through the passage in accordance with such manual operation, means settable to any desired rate of fluid flow, and means operatively coupled to the control means and to the settable means and responsive to any setting of the settable means for overriding any manual positioning of the control means to position the control means in accordance with such setting.

18. The combination set forth in Claim 17 wherein the means defining the passage are disposed in a member in removable relationship to the member and are effective, upon removal from the member, to limit the rate of fluid flow in accordance with the positioning of the manually adjustable means.

19. The combination set forth in Claim 18 wherein the passage-defining means include a plug member and wherein the manually adjustable means include a knob threadedly disposed on the plug member and the settable means and the overriding means are disposed in a system for providing a controlled flow of the intravenous fluid to the patient on a continuous basis at a rate dependent upon the setting of the settable means and wherein the passage defining means and the control means are removable from the system to provide for the flow of fluid through the passage in accordance with manual adjustment of the control means.

20. The combination set forth in Claim 19 wherein the resilient means are disposed in the passage in the direction of fluid flow and are constructed to be stretched in a direction transverse to the direction of fluid flow to limit the rate at which fluid flows in the passage.

21. The combination setforth in Claim 19 wherein the overriding means include a drive member disposed to become coupled to the control means and the control means are constructed to be driven by the drive member and the overriding means include a motor for driving the drive member and means for controlling the operation of the motor to obtain a drive of the drive member to a position dependent upon the setting of the settable means.

22. in combination in a system for controlling the flow of fluid to a patient where the system receives fluid from a source and passes the fluid through a conduit at a controlled rate to the patient, a plug member removably disposed in the conduit, means defining a passage in the plug, means defining an input line in the plug member for communication between the conduit and the passage at the input end of the conduit, means defining an output line in the plug for communication with the passage at the output end of the passage, resilient means disposed in the passage to control the flow of fluid through the passage in accordance with the constraint imposed upon the resilient means, and means adjustably positioned on the plug member and disposed against the resilient means to constrain the resilient means in accordance with such adjustable positioning.

23. The combination set forth in Claim 22 wherein the resilient means includes a diaphragm and a button is disposed in the passage around one of the input and output lines in the plug member and is disposed relative to the resilient means to cooperate with the resilient means in progressively blocking the flow of fluid through the passage in accordance with progressive constraints of the resilient means.

24. The combination set forth in Claim 23 wherein a notch is provided in the button to facilitate the controlled flow of fluid through the passage with progressive constraints of the resilient means.

25. The combination set forth in Claim 24 wherein the adjustable positioning means includes a knob threadedly disposed on the plug member and manually adjustable in position.

26. The combination set forth in Claim 24 wherein the plug member is included in a system to control the rate of flow of fluid and the knob is provided with an external configuration for receiving a drive member in the system in locking engagement with the knob to be driven by the drive member to an adjustable position in accordance with adjustments in the adjustable settings.

27. In combination for controlling the flow of fluid from a source to a patient, means providing settings of desired rates of fluid flow, means for providing for the flow of the fluid from the source to the patient, means for sensing the rate at which the fluid flows from the source to the patient, means responsive to the settings of the desired rate of fluid flow and to the sensings of the actual rate of flow fluid for producing error signals having characteristics representing any differences in the desired and actual rates, means including an adjustably positioned member for controlling the rate of flow of the fluid through the control means in accordance with the adjustable positioning of the member, the member being manually adjustable to control the rate of fluid flow, means for removably receiving the control means, and means responsive to the error signal, with the control means disposed in the receiving means, for overriding the manual adjustment of the adjustably positioned means to adjust the positioning of the member to minimize the error signal.

28. The combination set forth in Claim 27 wherein the control means includes a drive member for engaging the adjustably positioned member with the control means disposed in the receiving means and further includes a motor responsive to the error signal for driving the drive member in a direction to minimize the error signal.

29. The combination set forth in Claim 28 wherein the control means define a passage for the flow of fluid and a resilient member is disposed in the passage for controlling the size of the passage in accordance with the constraint of the resilient member and the adjustably positioned means adjustably constrains the resilient member in accordance with adjustments in its positioning.

30. The combination set forth in Claim 29 wherein the resilient means extends along the passage and is constrained in a transverse direction to control the size of the passage.

31. In combination for controlling the flow of fluid from a source to a patient, means providing settings of desired rates of fluid flow, means for providing for the flow of the fluid from the source to the patient, means for sensing the rate at which the fluid flows from the source to the patient, means responsive to the settings of the desired rate of fluid flow and to the sensings of the actual rate of fluid flow for producing error signals having characteristics representing any differences in the desired and actual rates, housing means, the flow means including a cassette removably disposed in the housing means for controlling the flow of fluid from the source, means including an adjustably positioned member included in the cassette for controlling the rate of flow of the fluid through the control means and the cassette in accordance with the adjustable positioning of the member, and means responsive to the error signal for adjusting the positioning of the adjustably positioned member in a direction to minimize the error signal.

32. The combination set forth in Claim 31 wherein the control means includes a plug member defining a passage and further includes resilient means disposed in the passage to control the size of the passage in accordance with the constraint of the resilient means and operatively coupled to the adjustably positioned member to become constrained in accordance with adjustments in the positioning of the member.

33. The combination set forth in Claim 32 wherein the adjusting means includes a drive member coupled to the adjustably positioned means and further includes a motor operatively coupled to the drive member and responsive to the error signal for driving the drive member in a direction to minimize the error signal.

34. The combination set forth in Claim 1 wherein the means defining the inlet and outlet lines and the passage and the adjustably positioned means are disposed in a cassette and the cassette includes a chamber for receiving fluid from the inlet line and passing fluid to the outlet line and further includes transducer means disposed in the chamber for sensing the rate of flow of fluid through the chamber.

35. The combination set forth in Claim 34 wherein resilient means are disposed in the chamber to divide the chamber into first and second compartments and wherein means are included in the cassette and are responsive to the signals from the transducer means for providing at first alternate times for the flow of fluid from the inlet line to the first compartment and from the second compartment to the outlet line and for providing at the other alternate times for the flow of fluid from the inlet line to the second compartment and from the first compartment to the outlet line.