GB2104387A - System for precisely controlling the flow of intravenous and enteric fluid to a patient - Google Patents

Abstract

A system for providing for the controlled introduction of an infusate from a reservoir (10) into a patient (14) in which the reservoir (10) is supported for gravity feeding and connected to the patient (14) through a fluid passage (16) which has a controller (18). The controller (18) includes a chamber (20) which has one wall in the form of a flexible diaphragm (48) an inflow passage (44) having an output port (50) facing the diaphragm (48) and an outflow passage (46) having an input port (52) facing the diaphragm (48). Flow control is provided by a piston (38) which moves the diaphragm (48) in relation to the input port (52) of the outflow passage (46) and which limits the maximum flow rate out of the chamber (20) to a value which is less than the maximum flow rate out of the chamber (20) when the chamber (20) is in the controller housing (36). When the chamber (20) separates from the controller housing 36 the flow automatically stops as the result of providing an outflow rate which is greater than the inflow rate. To prime the device, a latchable safety arm (54) is provided which, when removed, will change the flow control rate into the chamber (20) to a rate greater than out of the chamber (20). <IMAGE>

Description

SPECIFICATION System for precisely controlling the flow of intravenous and enteric fluid to a patient This invention relates to a system for precisely controlling the flow of fluid into a patient, and more particularly to a flow controller in the fluid passage of a fluid administration set which not only assures the delivery of a precisely measured flow of fluid, but which is safe in use.

It is well known that some medical patients, in and out of the hospital, require the continuous intravenous or enteric infusion of a fluid into their bodies. The devices for administering such fluids intravenously is commonly known as an IV set and comprises a fluid passage leading from a fluid container supported above the patient to an injection cannula which is inserted into the patient. The fluid passage is usually constructed of a plastic material and includes a transparent drip chamber to allow an attendant to count drops and thereby determine the flow rate of fluid delivered to the patient, as well as a control clamp which is utilized by the attendant to adjust the flow to provide a desired flow rate.

One of the requirements for infusing a fluid into a patient is that the flow rate not only be precise, but remain constant over long periods of time. Heretofore, it was the usual practice for the attendant to count the drops per unit time and to adjust the flow control clamp to provide a desired flow rate. One of the problems of controlling the flow rate in a plastic tube by means of a clamp is that all plastic tubing has hoop stress which resists any deformation and which requires a considerable amount of force to either close it to shut off flow or to nearly close it to provide a low flow rate. One clamp which is in use today and which provides the necessary force is the inclined plane roller clamp, but this clamp is not precise and does not lend itself to automatic operation like a pinch clamp.Another of the problems of controlling a plastic flow channel with a clamp is that the plastic has a tendency to creep and that, with the passage of time, the size of the opening controlled by the clamp becomes smaller resulting in a reduction of the flow rate. In fact, in a typical clamped controlled IV set, it is not uncommon that the flow rate decreases by 30% to 40% within one hour. This of course requires the attendant to take readings constantly and make the necessary clamp adjustments to assure a constant measured flow rate. This requires time and effort, and constant supervision by an attendant which is expensive and which still does not provide the desired assurances of a constant flow rate between times of attendant checks.

To over come this difficulty, a number of flow controllers have been devised which automatically and constantly adjust the flow rate by controlling a pinch clamp which lends itself better to automatic control that the inclined plane roller clamps. In these automatic systems, the drop rate is determined by photoelectric methods by which each drop falls through a beam of light and thereby interrupts the beam, with the interruptions being counted, and in which the count is compared with the desired count. Such a counter is disclosed in United States Patent Specification No. 4,014,010. When the actual and the desired drop counts are different, the controller generates an electrical control signal which is converted into a mechanical movement to make an appropriate adjustment to the clamp until the actual count is equal to the desired count.Such a system is fully described in United States Patent Specification No. 4,204,538 and United States Patent Specification No. 4,207,871, both assigned to IMED Corporation of San Diego, State of California, United States of America.

The flow system disclosed in the last three mentioned patent specifications provides a constant fluid flow but has the disadvantage of requiring a substantial amount of electrical energy for its operation to generate the necessary substantial forces to control a pinch clamp. Even though the required amount of electrical energy is readily available in hospitals, rest homes, and the like, it is not generally available, at least for any substantial length of time, to an ambulatory patient who must utilize a portable source of energy, such as batteries. Furthermore, the equipment for controlling the flow, as described in the above referenced patents, is fairly bulky, heavy, complex, expensive, and requires a high operating voltage which is potentially dangerous to the patient, which again detracts from its usefulness, particularly as applied to ambulatory patients.

One system which overcomes these difficulties is disclosed in co-pending British Patent Application No. 8133540, filed on 6th November 1981, for "Means and Method for Precisely Controlling the Flow of Intravenous and Enteric Fluid to a Patient" which is assigned to the same assignees as this application. That application discloses a manifold in the form of a chamber having an input and an output fluid passage which are inserted into the IV set fluid passage leading from the fluid container to the injection needle, either above or below the drop counting chamber. The output port of the chamber input fluid passage and the input port the chamber output fluid passages face a flexible, movable diaphragm which forms one wall of the chamber.

Fluid flow into the chamber is not controlled but fluid flow out of the chamber is controlled by moving the portion of the diaphragm across the input port of the chamber output fluid passage closer to the port to decrease fluid flow, and further away from the port to increase fluid flow. The position of the diaphragm portion across the input port is controlled by a piston which is connected to a stepping motor which, in turn is controlled by the output signal from the drop counter comparator. The manifold with the movable diaphragm wall facing the piston is locked into the controller housing, and a fail safe means is provided whereby, in case the manifold accidentally falls out of the controller housing, free flow of the fluid into the patient is prevented.While the system disclosed in the co-pending application overcomes most of the disadvantages or limitations of the prior art, it has been found that its fail safe system, which prevents free flow of fluid into the patient in case of accidental separation from the housing, has some limitation and a!so makes it extremely difficult and inconvenient to prime the system, i.e. to fill the fluid passages with the infusate.

The present invention provides a system for providing for the controlled introduction of fluid from a fluid reservoir into a tient, in which the fluid reservoir is supported for gravity feeding of the feeding of the fluid and has connected thereto, in the order stated, a first fluid passage, a device for determining fluid flow, a second fluid passage for introducing the fluid into the patient, and a fluid flow control meams associated either with said first or said second fluid passage. the fluid flow control means comprising: a chamber; first means for receiving the gravity fed fluid from said fluid reservoir and expelling said fluid into said chamber; second means associated with said first means to limit fluid flow into said chamber to a first maximum quantity; third means for receiving fluid from said chamber and for limiting maximum fluid flow out of said chamber to a second maximum quantity which is greater than said first maximum quantity, said third means including fluid flow adjustment means operative to control fluid flow out of said chamber and to the patient continuously between zero fluid flow and a fluid flow rate which does not exceed said first maximum quantity; and fourth means responsive to the difference between fluid flow into and out of said chamber and operative to decrease fluid flow into said chamber to substantially zero fluid flow when the outflow from said chamber exceeds the inflow into said chamber.

The present invention further provides a system for providing for the controlled introduction of fluid from a fluid reservoir into a patient, in which the fluid reservoir is supported for gravity feeding of the fluid and has connected thereto, in the order stated, a first fluid passage, a device for measuring fluid flow and for providing an electrical control signal commensurate with the difference between a desired and the measured fluid flow, a second fluid passage for introducing the fluid into the patient, and fluid flow control means responsive to said control signal and operative to control fluid flow through either said first or said second fluid passages, the fluid flow control means comprising: a chamber; first means for receiving the gravity fed fluid from said fluid reservoir and expelling said fluid into said chamber; second means associated with said first means to limit fluid flow into said chamber to a first maximum quantity; third means for receiving fluid from said chamber and for limiting maximum fluid flow out of said chamber to a second maximum quantity which is greater than said first maximum quantity, said third means including fluid flow adjustment means responsive to said control signal and operative to control fluid flow out of said chamber and to the patient continuously between zero fluid flow and a fluid flow rate which does not exceed said first maximum quantity; and fourth means responsive to the difference between fluid flow into and out of said chamber and operative to decrease fluid flow into said chamber to substantially zero fluid flow when the outflow from said chamber exceeds the inflow into said chamber.

The present invention further provides a system for providing for the controlled introduction of fluid from a fluid reservoir into a patient, in which the fluid reservoir is supported for gravity feeding of the fluid and has connected thereto, in the order stated, a first fluid passage, a device for measuring fluid flow and for providing an electrical control signal commensurate with the difference between a desired and the measured fluid flow, a second fluid passage for introducing the fluid into the patient, and fluid flow control means responsive to said control signal and operative to control fluid flow through either said first or said second fluid passages, the fluid flow control means comprising: a chamber; first means for receiving the gravity fed fluid from said fluid reservoir and expelling said fluid into said chamber; second means associated with said first means and movable between an operating position in which it limits fluid flow into said chamber to a first maximum quantity and a priming position in which it limits fluid flow to a second maximum quantity which is greater than said first maximum quantity; third means for receiving fluid from said chamber and for limiting maximum fluid flow out of said chamber to a third maximum quantity which is greater than said first maximum quantity and smaller than said second maximum quantity, said third means including fluid flow adjustment means responsive to said control signal and operative to control fluid flow out of said chamber and to the patient continously between zero fluid flow and a fluid flow rate which does not exceed said first maximum quantity, and fourth means responsive to the difference between fluid flow into and out of said chamber and operative to decrease fluid flow into said chamber to substantially zero fluid flow when the outflow from said chamber exceeds the inflow into said chamber while said second means is in said operating position.

The present invention further provides a system for providing for the controlled introduction of an infusate from a reservoir into a patient, in which the reservoir is supported for gravity feeding of the infusate and has connected thereto, in the order stated, a first fluid passage, a device for measuring fluid flow and for providing an electrical control signal commensurate with the difference between a desired and the measured fluid flow, a second fluid passage for introducing the fluid into the patient, and fluid flow control means responsive to said control signal and operative to control fluid flow through either said first or said second fluid passages, the fluid flow control means comprising: a chamber including a flexible diaphragm forming a wall thereof, a tubular inflow passage having an output port, and a tubular outflow passage having an input port, said output port and input port facing said diaphragm for fluid flow control; a safety arm removably latched across said diaphragm for spacing said diaphragm a first predetermined distance from said output port to limit fluid flow into said chamber to a first maximum quantity when latched and to a second maximum quantity larger than said first maximum quantity when unlatched; and fluid flow adjustment means for releasably holding said chamber, said adjustment means being responsive to said control signal and operative to move the portion of said diaphragm opposite said input port continuously between an inward position in which said output port is closed for zero fluid flow and an outward position in which said input port is opened for fluid flow not to exceed said first maximum quantity, said outflow passage being positioned with respect to said diaphragm and dimensioned for limiting maximum fluid flow out of said chamber when separated from said adjustment means to a third maximum quantity which is intermediate said first and second maximum quantity.

The present invention further provides apparatus for controlling the introduction of fluid from a fluid reservoir into a patient via a dispenser, the apparatus comprising a mani- fold having an inlet port for connection to the reservoir, an outlet port for connection to the dispenser, a member which defines, together with the manifold, a chamber and means associated with the member movable from a first position to a second position to vary the flow of fluid between the ports, such that in the first position the member is constrained against said means and in the second position the member is not constrained against said means, and means for moving said member so as to vary the volume of the chamber and thereby vary the flow between the ports.

Preferably said member comprises a flexible diaphragm, sealingly attached to the said manifold.

Preferably the means associated with the member comprises a second member, the arrangement being such that in the first position the second member causes the diaphragm to restrict the flow of fluid through the inlet port.

Preferably the diaphragm is disposed in a space between the manifold and the second member.

Preferably the manifold is in a bayonet fit within a housing, such that the housing retains the second member in the first position.

Preferably the second member may move from the first position to the second position by rotation about an axis, which axis is at an edge of the second member.

Preferably the chamber has a further inlet port arranged to be in communication with the said inlet port, the second member causes the diaphragm to cover the further inlet port when the second member is in the first position.

Preferably the said means for moving said member comprises a movable piston arranged to extend from the housing and movable to cause the member to cover the outlet port.

An embodiment of the present invention will now be described by way of example with reference to and as illustrated in the accompanying drawings, in which: Figure 1 is a schematic plan view of an embodiment of the invention in operative association with a fluid administration appara tus; Figure 2 is a cross-sectional view through the fluid flow controller of the preferred embodiment of the invention; Figure 3 is a section taken along line 3-3 of Fig. 2; Figure 4 is a cross-sectional view through the manifold with the safety bar shown in the unlatched (half open) position; Figure 5 is an end view of the manifold with the safety bar latched in the operating position; Figure 6 is a schematic diagram illustrating the fail safe principal employed in the flow control system of the present invention; and Figure 7 is a cross-sectional view through the manifold when removed from the controller housing and showing the diaphragm performing the fail safe function.

Referring now to Fig. 1 of the drawings, there is shown a schematic plan view of an IV set comprising a fluid reservoir or container 10 which houses a fluid 12 which is to be fed into a patient 14, such as is illustrated by the artist's rendition of a hand-arm portion. Reservoir or container 10 is connected to the patient 14 through a flow passage or channel 16 which is divided into an upstream or upper portion 16a and a downstream or lower portion 16 b, and a fluid flow controller 18 in combination with a drop counting chamber 20. Drop counting chamber 20 has transparent side walls so that drops, such as is illustrated at 22, can be counted when, while falling, they interrupt a beam of light 24 from a light source (not shown) which passes through chamber 20 to a photodiode 26.The output lead 28 from photodiode 26 is connected to a comparator 30 which provides an electrical control signal on output lead 32 for controlling a stepping motor 31 whose lead screw 35, in combination with a piston, controls fluid flow controller 18 as will hereinafter be explained.

The means for counting drops, developing a signal commensurate with the actual drop count, comparing this signal with a signal commensurate with a desired drop count within comparator 30, and developing the control signal on lead 32, which is commensurate with the difference between the desired and the actual count, forms no part of this invention since there are numerous known devices which will provide a suitable control signal. The present invention can be used with any of the known counting devices which provide an actual count, compares the actual count with a desired count, and develop a control signal in case that the actual count does not accurately agree with the desired count.Further even though the invention will be explained in connection with an IV set, as illustrated in Fig. 1, it is also to be understood that fluid flow controller 18 of the present invention is applicable in exactly the same manner to an enteric feeding set in which a container, such as 10, is filled with an enteric fluid rather than an intravenous fluid 12, and fluid passage 16b is placed into a body cavity or a gastric duct rather than a vein.

Referring now to Figs. 2 and 3 of the drawings, there is shown a preferred embodiment of fluid flow controller 18 of the present invention comprising a manifold housing 40 defining an interior space or chamber 42 and including a chamber input passage 44 and a chamber output passage 46. Input passage 44 is connected to upper portion 16a of flow channel 16 and the output passage 46 is connected directly to drop counting chamber 20. One wall of chamber 42 is formed by a movable, flexible diaphragm 48, and output port 50 of input passage 44 as well as input port 52 of output passage 46 face diaphragm 48. Input passage 44 is also provided with a branch passage 45 which has an output port 51 normally closed as will be explained hereinafter. Finally, a safety bar or a latched bar 54 is provided to extend across the external side of diaphragm 48 as best seen in Figs. 4 and 5.Safety bar 54 is preferably made out of a flexible plastic material which is hinged to housing 40 at 55 and latched to housing 40 at 57 and includes a normally round boss 56 which, when bar 54 is in the latched or operating position as shown in Fig. 5, bears on the portion of diphragm 48 facing output port 51 to close branch passage 45.

Safety bar 54 is also provided with spacer means 58, which may take the form of two bosses of a predetermined height as shown in Fig. 5, which bear against the land or flat surface 60 surrounding output port 50 when the safety bar 54 is in the closed position to precisely space the overlying diaphragm portion from the output port 50. As will be explained in more detail hereinafter, such spacing causes surface portion 62 of safety bar 54 to position the underlying diaphragm portion of diaphragm 48 at a selected distance from output port 50 to thereby provide a constriction and to limit the maximum fluid flow from input passage 49 into chamber 42 to a first maximum quantity, also, to be called the operating maximum quantity.The position of safety bar 54 when unlatched or open, as shown in Fig. 4, will be referred to as the priming position, and the position of the safety bar 54 when latched or closed, as shown in Figs. 2 and 5 will be referred to as the operating position. The safety bar must be placed in the operating position before manifold housing 40 can be inserted into controller housing 36. Manifold housing 40 is provided with a locking means in the form of two locking lugs 64 and controller housing 36 is provided with a locking groove to form a bayonet joint.

Referring now particularly to Figs. 2 and 6, there is shown the portion of the fluid flow controller of the present invention which controls fluid flow out of chamber 42, where the fluid has accumulated after entering the chamber through input passage 44. Stepping motor 34, as best shown schematically in Fig.

2, has a lead screw 35 and a piston 38 affixed to the lead screw which passes through an opening in controller housing 36 to contact the outside of the portion of diaphragm 48 facing input port 52. In response to a control signal on line 32, which indicates to the controller whether the actual fluid flow out of outflow passage 46 should be greater or smaller, piston 38 either moves to the left to move the diaphragm closer to input port 52 to thereby cut down on the flow out of chamber 42, or moves to the right to thereby move the diaphragm farther away from input port 52 to thereby increase fluid flow out of the chamber. It is an important feature of the present invention that piston 38, while manifold housing 42 is locked into controller housing 36 is limited in its movement to the right such that the maximum fluid flow rate through output passage 46 is never greater than the operating maximum fluid flow quan tity through output port 50. Of course, the same effect can be achieved by utilizing a stationary piston skirt to limit maximum travel of the diaphragm within the allowable flow rate limits in controller housing 36 which is positioned to limit the maximum flow rate through output passage 46 as specified above.

The reason for limiting fluid flow out of output passage 46 to a quantity which does not exceed the maximum fluid flow through input port 50, when manifold housing 40 is locked into controller housing 36, will now be explained with the assitance of Fig. 6. Fig. 6 shows a fluid reservoir 100 filled with a fluid 102 which passes through an upper fluid passage 104 and into a chamber 106 which has a flexible diaphragm 108 forming one wall thereof. Chamber 106 is connected to a lower fluid passage 110 for removing fluid from the chamber. Further, an adjustable flow restrictor 105 is provided in upper fluid passage 104 and an adjustable flow restrictor 111 is provided in lower fluid passage 112.

The flow restrictors may be in the form of an inclined plane roller clamp or a pinch clamp, but the type of flow control which is used is not important in connection with explaining the following principal.

When fluid flow into chamber 106, as controlled by restrictor 105, is greater than the fluid flow out of chamber 106, as controlled by restrictor 111, diaphragm 108 will bulge outwardly to assume the position shown as 108'. The reverse is likewise true, namely, when fluid flow out of chamber 106 exceeds fluid flow into chamber 106, diaphragm 108 will move inwardly and assume the position shown at 108".

Referring now to Fig. 7, there is once more shown manifold housing 40 with safety arm 54 in the operating position. As indicated previously, the maximum fluid flow into chamber 42 through input passage 44 is limited to a first maximum quantity, the operating maximum quantity, by the spacers 58 and surface 62. This operating maximum quantity is greater than the maximum outflow quantity through passage 46 when manifold housing 40 is locked into controller housing 36 as shown in Fig. 2. As long as the inflow into chamber 42 is greater than the outflow from chamber 42, as illustrated in Fig. 2, diaphragm 54 will assume a position similar to that of 108' shown in Fig. 6 to allow fluid flow into chamber 42 and a precisely controlled fluid flow out of chamber 42, this flow being controlled by piston 38.

If, however, manifold housing 40 falls out of controller housing 36, such as is possible accidentally or even when it is purposely removed, the diaphragm portion overlying input port 52 is no longer restricted by piston 38, which limits fluid flow out of the chamber 42 to a quantity less than the operating inflow quantity, and diaphragm 42 will have the tendency to assume a position similar to that of 108" shown in Fig. 6. This situation is shown in Fig. 7 which causes the diaphragm portion overlying output port 50 to cover the same and thereby close it to prevent any further fluid from entering chamber 42. If no fluid enters chamber 42, there can be no outflow from chamber 42 and, accordingly, the flow of fluid stops which is the fail safe mechanism that is desirable in case of accidental or nonaccidental removal of the disposable manifold housing 40 from controller housing 36.It should also be noted that for best control of the fail safe feature, it is desirable to have output port 50 positioned to face the center of diaphragm 48 because this is the most flexible and movable portion of the diaphragm and therefore will be least subject to stresses from the rim portion and most effective in closing output port 50 to prevent any further fluid from entering chamber 42. As far as input port 52 is concerned, its position under the diaphragm is not critical since piston 38 can provide sufficient mechanical force to move any diaphragm portion it faces without being overly sensitive to possible rim forces exerted by the diaphragm.

However, a position near the rim of the diaphragm is selected to be near input port 52 to prevent the diaphragm from occluding the port of the output passage by vacuum. The same criteria are applied for locating the output port of branch passage 45.

It will also now be readily understood that an IV set, with the fluid flow controller of the invention described hereinbefore having safety bar 54 in the operating position, will be difficult to prime because the fail safe feature closes the controller. Normally, priming is accomplished by compressing the flexible wall of drop counting chamber 20 to create a vacuum and suck fluid into chamber 42 and then down through the rest of the IV set. As explained heretofore, as long as the maximum inflow rate to chamber 42 is restricted to be less than the maximum outflow rate from chamber 42, port 50 is covered by diaphram 48. Accordingly, priming in this position is unsatisfactory.

To prime the IV set of the present invention, safety bar 54 is swung into the open or priming position, as shown in Fig. 4, which accomplishes two results: firstly, it allows fluid from reservoir 10 to flow through branch inflow passage 45 into chamber 42 and, further, it removes the diaphragm portion overlying output port 50 to thereby increase the maximum output flow out of that port.

This causes the maximum flow into chamber 42 to increase to a point where it is greater than the maximum outflow from the chamber and thereby causes the condition shown by diaphragm 108' in Fig. 6. The device is now free flowing which will greatly facilitate prim ing.

By way of summary, it should be understood that for proper working of the invention, a number of conditions have to be satisfied.

Firstly, as long as manifold housing 40 is securely locked to controller housing 36, which requires safety arm 54 to be in the operating position, the inflow of fluid to chamber 42 from reservoir 10 must be greater than the outflow of fluid from the chamber so that the diaphragm has a tendency to bulge out and not obstruct any passages. Another way of stating this is that the maximum inflow rate to the chamber must exceed the maximum outflow rate from the chamber under any conditions of operation. Secondly, for a proper working of the fail safe mechanism in the event that manifold housing 40 is removed from or falls out of controller housing 36, it becomes necessary for the flow to stop so that there be not free flow.This is accomplished by the present invention by providing that the maximum outflow rate from chamber 42 increases to a value which is greater that the maximum inflow rate into the chamber, without changing the inflow rate to the chamber.

This condition is satisfied if the manifold is constructed in such a manner that if piston 38 no longer provides a maximum spacing of the diaphragm portion overlying input port 52 the same has a capacity of providing a greater outflow rate than the inflow rate. Thirdly, to allow priming, it is necessary that the inflow rate to chamber 42 becomes greater than the greatest possible outflow rate from chamber 42 so that the condition of a free flow exists.

This is accomplished by providing for a safety bar which opens up a branch passage and removes the diaphragm portion facing output port 50 to increase the flow rate.

There has been described a system for precisely controlling the flow of intravenous and enteric fluid to a patient which includes a fail safe system by which accidental free flow is prevented through the inherent design of the manifold and which can be primed by moving a safety bar which causes a free flow condition.

An embodiment of the present invention provides a system for precisely controlling the flow of fluid in an IV set, or the like, which is capable of being primed and which has a fail safe system which does not interfere with priming.

An embodiment of the present invention further provides a new and improved controller for precisely controlling the flow of fluid in a disposable IV set, or the like, while maintaining sterile integrity, in which a part of the controller is disposable along with the remainder of the IV set, and which has an improved fail safe system which effectively prevents free flow when the disposable portion of the controller accidentally separates from the permanent portion (housing) of the controller.

An embodiment of the present invention further provides a system for precisely controlling the flow of fluid in an IV set, or the like, which includes a fail safe system guarding against free flow when the disposable portion of the IV set falls out of the controller housing, and which allows priming to start initial fluid flow.

Claims (25)

1. A system for providing for the controlled introduction of fluid from a fluid reservoir into a patient, in which the fluid reservoir is supported for gravity feeding of the fluid and has connected thereto, in the order stated, a first fluid passage, a device for determining fluid flow, a second fluid passage for introducing the fluid into the patient, and a fluid flow control means associated either with said first or said second fluid passage, the fluid flow control means comprising: a chamber; first means for receiving the gravity fed fluid from said fluid reservoir and expelling said fluid into said chamber; second means associated with said first means to limit fluid flow into said chamber to a first maximum quantity; third means for receiving fluid from said chamber and for limiting maximum fluid flow out of said chamber to a second maximum quantity which is greater than said first maximum quantity, said third means including fluid flow adjustment means operative to control fluid flow out of said chamber and to the patient continuously between zero fluid flow and a fluid flow rate which does not exceed said first maximum quantity; and fourth means responsive to the difference between fluid flow into and out of said chamber and operative to decrease fluid flow into said chamber to substantially zero fluid flow when the outflow from said chamber exceeds the inflow into said chamber.

2. A system for providing for the controlled introduction of fluid from a fluid reservoir into a patient, in which the fluid reservoir is supported for gravity feeding of the fluid and has connected thereto, in the order stated, a first fluid passage, a device for measuring fluid flow and for providing an electrical control signal commensurate with the difference between a desired and the measured fluid flow, a second fluid passage for introducing the fluid into the patient, and fluid flow control means responsive to said control signal and operative to control fluid flow through either said first or said second fluid passages, the fluid flow control means comprising: a chamber; first means for receiving the gravity fed fluid from said fluid reservoir and expelling said fluid into said chamber; second means associated with said first means to limit fluid flow into said chamber to a first maximum quantity; third means for receiving fluid from said chamber and for limiting maximum fluid flow out of said cham ber to a second maximum quantity which is greater than said first maximum quantity, said third means including fluid flow adjustment means responsive to said control signal and operative to control fluid flow out of said chamber and to the patient continuously between zero fluid flow and a fluid flow rate which does not exceed said first maximum quantity; and fourth means responsive to the difference between fluid flow into and out of said chamber and operative to decrease to fluid flow into said chamber to substantially zero fluid flow when the outflow from said chamber exceeds the inflow into said chamber.

3. A system in accordance with Claim 2 in which said fourth means comprises a flexible diaphragm covering one wall of said chamber.

4. A system in accordance with Claim 3 in which said third means includes a tubular outflow passage out of said chamber having an input port facing said diaphragm and in which said flow adjustment means moves the portion of the diaphragm disposed opposite said input port between an inward position in which said output port is closed for zero fluid flow and an outward position in which said input port is opened for fluid flow not to exceed said first maximum quantity.

5. A system in accordance with Claim 3 in which said first means comprises a tubular inflow passage into said chamber having an output port facing said diaphragm.

6. A system in accordance with Claim 5 in which said second means comprises a support means for supporting at least the portion of said diaphragm opposite said output port at a predetermined distance from said output port to thereby limit the fluid flow rate into said chamber to said first maximum quantity.

7. A system for providing for the controlled introduction of fluid from a fluid reservoir into a patient, in which the fluid reservoir is supported for gravity feeding of the fluid and has connected thereto, in the order stated, a first fluid passage, a device for measuring fluid flow and for providing an electrical control signal commensurate with the difference between a desired and the measured fluid flow, a second fluid passage for introducing the fluid into the patient, and fluid flow control means responsive to said control signal and operative to control fluid flow through either said first or said second fluid passages, the fluid flow control means comprising: a chamber; first means for receiving the gravity fed fluid from said fluid reservoir and expelling said fluid into said chamber: second means associated with said first means and movable between an operating position in which it limits fluid flow into said chamber to a first maximum quantity and a priming position in which it limits fluid flow to a second maximum quantity which is greater than said first maximum quantity: third means for receiving fluid from said chamber and for limiting maximum fluid flow out of said chamber to a third maximum quantity which is greater than said first maximum quantity and smaller than said second maximum quantity, said third means including fluid flow adjustment means responsive to said control signal and operative to control fluid flow out of said chamber and to the patient continuously between zero fluid flow and a fluid flow rate which does not exceed said first maximum quantity, and fourth means responsive to the difference between fluid flow into and out of said chamber and operative to decrease fluid flow into said chamber to substantially zero fluid flow when the outflow from said chamber exceeds the inflow into said chamber while said second means is in said operating position.

8. A system in accordance with Claim 7 in which said fourth means comprises a flexible diaphragm covering one wall of said chamber.

9. A system in accordance with Claim 8 in which said third means includes: tubular outflow passage out of said chamber having an input port facing said diaphragm and in which said flow adjustment means moves the portion of the diaphragm disposed opposite said input port between an inward position in which said output port is closed for zero fluid flow and an outward position in which said input port is opened for fluid flow not to exceed said first maximum quantity.

10. A system in accordance with Claim 8 in which said first means comprises a tubular inflow passage into said chamber having an output port facing said diaphragm.

11. A system in accordance with Claim 10 in which said second means comprises a support means movable between an operating position in which it supports at least the portion of said diaphragm opposite said output port at a predetermined first distance from said output port to thereby limit the fluid flow rate into said chamber to said first flow quantity and a priming position in which at least the portion of the diaphragm opposite said output port is at a predetermined second distance to allow the flow rate into said chamber to increase to said second quantity.

12. A system in accordance with Claim 11 in which said output port faces the center portion of said diaphragm for greatest sensititivity to decrease fluid flow into said chamber when fluid flow out of said chamber exceeds fluid flow into said chamber.

13. A system for providing for the controlled introduction of an infusate from a reservoir into a patient, in which the reservoir is supported for gravity feeding of the infusate and has connected thereto, in the order stated, a first fluid passage, a device for measuring fluid flow and for providing an electrical control signal commensurate with the difference between a desired and the measured fluid flow, a second fluid passage for introducing the fluid into the patient, and fluid flow control means responsive to said control signal and operative to control fluid flow through either said first or said second fluid passages, the fluid flow control means comprising: a chamber including, a flexible diaphragm forming a wall thereof, a tubular inflow passage having an output port, and a tubular outflow passage having an input port, said output port and input port facing said diaphragm for fluid flow control: a safety arm removably latched across said diaphragm for spacing said diaphragm 3 first predetermined distance from said output port to limit fluid flow into said chamber to 2 first maximum quantity when latched and to a second maximum quantity larger than said first maximum quantity when unlatched; and fluid flow adjustment means for releasably holding said chamber, said adjustment means being responsive to said control signai and operative to move the portion of said diaphragm opposite said input port continuously between an inward position in which said output port is closed for zero fluid flow and an outward position in which said input port is opened for fluid flow not to exceed said first maximum quantity, said outflow passage being positioned with respect to said diaphragm and dimensioned for limiting maximum fluid flow out of said chamber when separated from said adjustment means to a third maximum quantity which is intermediate said first and second maximum quantity.

14. A system in accordance with Claim 13 in which said tubular inflow passage includes a further output port which forces said diaphragm and in which said safety arm closes said further output port when latched.

15. A system in accordance with Claim 14 in which said further output port is positioned under said diaphragm such that normal flexure of said diphragm will not obstruct said port when said safety bar is unlatched.

16. Apparatus for controlling the introduction of fluid from a fluid reservoir into a patient via a dispenser. the apparatus comprising a manifold having an inlet port for connection to the reservoir, an outlet port for connection to the dispenser, a member which defines, together with the manifold, a chamber and means associated with the member movable from a first position to a second position to vary the flow of fluid between the ports, such that in the first position the member is constrained against said means and in the second position the member is not constrained against said means, and means for moving said member so as to vary the volume of the chamber and thereby vary the flow between the ports.

17. Apparatus as claimed in Claim 16 in which said member comprises a flexible diaphragm, sealingly attached to the said manifold.

18. Apparatus as claimed in Claim 17 in which the means associated with the member comprises a second member, the arrangement being such that in the first position the second member causes the diaphragm to restrict the flow of fluid through the inlet port.

19. Apparatus as claimed in Claim 18 in which the diaphragm is disposed in a space between the manifold and the second member.

20. Apparatus as claimed in Claim 19 in which the manifold is in a bayonet fit within a housing. such that the housing retains the second member in the first position.

21. Apparatus as claimed in Claim 20 in which the second member may move from the first position to the second position by rotation about an axis, which axis is at an edge of the second member.

22. Apparatus as claimed in Claim 21 in which the chamber has a further inlet port arranged to be in communication with the said inlet port, the second member causing the diaphragm to cover the further inlet port when the second member is in the first position.

23. Apparatus as claimed in any one of Claims 16 to 22 in which the said means for moving said member comprises a movable piston arranged to extend from the housing and movable to cause the member to cover the outlet port.

24. Apparatus for controlling the introduction of fluid from a fluid reservoir into a patient via a dispenser substantially as hereinbefore described with reference to Figs. 1 to 5 and Fig. 7.

25. A system for providing the controlled introduction of fluid from a fluid reservoir into a patient substantially as hereinbefore described with reference to Figs. 1 to 5 and Fig.