CA1148431A - Medical infusion system - Google Patents

Abstract

MEDICAL INFUSION SYSTEM

ABSTRACT

A medical infusion system is described employing a pump and cassette combination for conducting fluid or semisolids from an upstream portion to a downstream portion of the system. The cassette includes a rigid enclosure defining a pumping chamber and has a window with a diaphragm spanning the window. The diaphragm is engaged by means on the pump for varying the volume of the pumping chamber. The configuration of the cassette is such that the outlet for the pumping chamber is located at the top of the pumping cavity and the internal configuration of the cavity causes gas bubbles to migrate to the outlet opening. A passage communicates between the outlet opening and a location proximate to the lower portion of the cassette.

Description

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This invention relates to a medical lnfusion systems and, m~re particularly, to an improved pump and cassette for use therein.
A medical infusion system which operates to pump fluid or semisolids from an upstream portion to a downstream portion is known. The pump includes upstream and downstream conduit means and a removable cassette communicates between the two. The cassette has a window therein and a diaphragm spans the window~
~ Means on the pump engage the diaphragm for varying the volume of 10 the pumping cavity formed by the cassette. The cassette has inlet and outlet openings valvelessly communicating with the cavity.
Fluid in the conduit is pumped by restricting and opening the conduit means at upstream and downstream locations and displacing the contents of the cassette pumping chamber or cavity i appropriately.

The medical infusion system described hereinabove provides significant advantages over many prior art constructions.
There are no valves employed in the cassette, thus significantly improving the reliability and reducing the complexity of manufacture and therefore the cost. Ir.creased accuracy over ; prior cassette designs is also achieved. By properly controlling the pinch off of the tubes at the inlet and the outlet of the ~` cassette, good constant flow rates may be achieved, even to very low rates.
It has been observed that, in the infusion system described above, the presence of air in the cassette pumping cavity can detrimentally effect the operation of the device. These eEfects result from three phenomena. First, at high back pressures, the fluid level in the drip chamber feeding ~he system csm/~f . , '` ~
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rises, due to expansion of the compressed air as the inflow valve opens prlor to filling, which may trigger an empty bo~tle alarm. 5econdly, flow output decreases as the back pressure and volume of air increases, S affecting pumping accuracy. Thirdly, at low back `~ pressures, which may be caiused by low needle level ~minus 12" to minus 36" belo~7 the casse~te), the delivered flow rate is higher, due to the expansion of : the air upon opening of the outflow valve, also a~fecting accuracy.
The effects of air in the casse~te can be substantially reduced or eliminated by, in effect, inverting the cassette so the outlet from the pump chamber is on the top and the inlet is on the bottom.
In such a position, air bubbles migrate to the outlet and are pumped out with the expelled fluid or semisolid. Such a principle is em~loyed in the cassette described in U.S. Patent No. 4,140,118 issued February 20, 1979. Although successful, such an arrangement may result in confusion on the part of hospital personnel as ; to which is the inlet. This is because most conventional and prior art drug infusion systems are arranged so ~hat the flow is continuously downward from the bottle to the inlet, which is at the top of the pump.
It is an object of the present invention to provide an improved cassette and an improved combination of a pump and cassette for a drug infusion system.
Another, more specific object of the invention is to provide a drug ~nfusion system utilizing the combination of a pump and cassette wherein the effect on accuracy of air in the casiette is substantially eliminated and wherein the cassette is easy to ins~all in the pump and is not con~using in setting the system up for operation.
A further vbject o the invention is to provide , .,~ ~ . .

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a casette design of improved construction which ~acilitates use with a minimum amount of confusion.
The invention comprises a replaceable pump casse.tte, either alone or in combination with a pump, for a medical infusion system which pumps fluid or semi-solids from an upstream portion of the infusion system to a downstream portion thereof. The cassette includes a rigid enclosure defining a pumpinq cavi-ty and having inlet and outlet openings and further having a window therein.
' A flexible diaphragm extends across the window and is impermeable to the passage of fluids or semi-solids therethrough. The diaphragm is engageable by means on the pump for varying the volume of the pumping cavity. The cassette is of configuration such that it is oriented with the inlet and outlet openings both positioned proximate at the top of the pumping cavity with the cassette in an operative position in the pump. The pumping cavity has an internal configuration including interior walls curved to direct all gas bubbles within the pumping cavity to the outlet opening with the cassette in the operative position. Either the pump or the cassette includes means defining a passage communicating between the outlet opening and a location displaced from the outlet opening which may be located proximate the lower portion of the cassette with the cassette in the operative position.
Other objects of the invention will become apparent to those skilled in the art from the following description taken in connection with the accompanying drawings wherein-:
FI~URE 1 is a schematic view of a medical infusion .
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-` system in which the invention ls lncorporated;
FIGURE 2 is a front view of a cassette constructed in accordance wi~h the invention;
FIGURE 3 is a full section view of the cassette of FIGURE 2 taken along the line 2-2 of FIGURE 2 with the invention;
FIGURE 4 is a full section view of the cassette and a portion of a pump therefor constructed in accordance with the invention; and PIGURES 5 and 6 are, respectively, front plan schematic views of two further embodiments of the invention.
Very generally, the cassette and pump combination of the invention (FIGURES 1 and 4) operates to pump fluids or semisolids from an upstream portion 11-12 to a downstream portion 13 of a medical infusion system for a patient 14. The pump 15 supports a cassette 16 (FIGURES 2-3, 5 or 6) comprising a rigid enclosure 17 defining a pump cavity 18. The rigid enclosure has an inlet opening 21 located to be proximate the top of the cassette when the cassette is in an operative position in the ` 20 pump. An outlet opening 23 is also provided in the rigid enclosure, and the enclosure further has a window 25 therein. A flexible diaphragm 27 extends across the window and is impermeable to the passage of fluids or semisolids therethrough. Actuator means 28 ; engage the diaphragm to vary the contents of the cavity 18. The casse~te is of .3a -.
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, ., a configuration ~or orienting the casset~e with respect ` to the pump such t~at the outlet opening is positioned ; at the top of the pumping cavity when the cassette is in an operati~e position with respect to the pump~ The pumping cavity has an internal configuration to cause gas bubbles to migrate to the outlet opening with the cassette in the oper~tive position. An outlet passage 29 communicates between the outlet opening and a location displaced from the outlet opening which loction is positioned for convenience in settinq up the cassette and pump for operation. The passage may be located in the cassette or may be located in a portion of the pump itself adjacent to the cassette.
Reerring now more particularly to FIGURE 1, the invention is shown in the 40rm of an intr~venous delivery system for delivering fluid from a fluid reservoir or storage means 12 to a patient 14. The fluid is introduced intravenously through a suitable catheter 30 attached to the downstream portion 13 of the delivery system. The catheter is held in place by adhesive tape 31 on the arm of the patient 14 as is well-known in the art. The fluid reservoir 12 may be a conventional intravenous delivery system bottle suspended on a stand 32. A drip chamber 33 is attached to the lower portion of the bottle 12 and may be of conventional construction. An empty bottle alarm, not shown, of suitble design may be employed beneath or attached to the drip chamber to signal when the contents of the bottle 12 have been drained. The contents of the bottle 12 pass through the upstream conduit portion ll of the delivery system, the upstream conduit portion constituting, in the illustrated embodiment, a flexible hose.
Although the bottle 12 i8 ~hown positioned on the support 32 ln an elevated condition wlth respe~t to .
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the patient 14, as is typical of many intravenous delivery systems it is not critical in the system of the invention that the bottle be so elevated inasmuch as the Pluid is conveyed to the patient by the positive pumping action of the pump 15. ~he pump 15, shown in FIGURE 1, may be suitably contained in a housing 34 having control knobs including a knob 35 thereon. The pump 15 may be supported on a bedside table 39 or other suitable structure and is located between the upstream portion 11 and the downstream portion 13 of the delivery system~
Grommets 41 form the entrance and the exit to the housing 33 for the upstream and downs~ream portions 11 and 13, respectively.
The sys4em of the invention employs a replaceable cassette 16 in the pump 15. The cassette utilized in the system of the present invention does not require any valve~s, vastly simplifying the system and drasticlly lowering the cost o~ the replaceable portion thereof. In addition, the system of the present invention employs a cassette in which a substantial displacement occurs during each pumping stroke. This s~roke dIsplacement in the system of the present invention i5 preferably about at least 0.25 ml and less than about one ml. In this range, the most acceptable performance results. Typical volume of the pumping chamber with the diaphragm in position for maximum volume is about l.9 ml.
; The cassette is specifically illustrated in FIGURES 2 and 3. Basically, the cassette is in ony ` 30 three pieces. The main piece is a molded housing 17 of a suitable medical grade plas~ic. The outline of the housing is generally circular with an asymetric Plange 40 in the shape of a rectangle plus a contiguous semicircle. This asymetric shape enables a corresponding configurat~uon in the pump to permit ` .

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mounting of the cassette only in the proper orientation as explained below. A socke~ 43 is provided for connection to the upstream conduit portion o the infusion system, and a socket 44 (on the lower side of the housing 17) is provided for connection to the downstream conduit portion o~ the infusion system.
Unlike many prior art cassettes, the inlet and ou~let cor.tain no valves. The housing 17 de~ines the pumping chamber 18 which is generally in the shape of a cylinder havinq one open side or window 25. An annular recess 45 surrounds the open side of the pumping chamber and receives the annular lip 47 of the flexible diaphragm 27. The diaphragm 27 is comprised of a suitahle medical grade flexible material which is impervious to the fluids or semisolids being pumped ~nd which is capable of flexing as described below sufficien~ly so as to enab_e the de~ired displacement, also described in detail below. ~or the purpose. of holding the flexible diaphragm in place, a mounting ring 49 seats in and mates with a projectinq annular lip 51 on the housing 17 and is suitably sealed to the housing, such as by ultrasonic welding, to form a seal and to hold the diaphra~m 27 in place spanning ~he open side o~ the pumping chamber 18.
: 25 Referring ko FIGURE 4, means are employed to sequentially restrict and open the upstream and downstream conduit portions 11 and 13, respectively, in a sequence such as to provide a valve type action to enable fluid to be pumped from the upstream conduit portion 11 to the downstream conduit portion of 13 of the delivery system. Although any suitable means ~or constricting the conduit portions in the manner described below may be employed, in the apparatus illustrated in FI~URE 4, the restricting means are khe tapered ends of movable rods or bars 63 and 65, . ~.

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respectively. The bars are movably supported, by suitable means not shown, insidP the housing 34 of the pump lS. The rounded tips of the tapered ends of the bars 63 and 65 engage the respective upstream conduit portion 11 and downstream conduit portion 13. The conduit portions are supported in mating grooves or channels in a chassis 66 inside the housing 34 of the pump 15. A boot 53 e~tends across the chassis 66 as shown to provide a seal between the region of the cassette 18 and the drive means described below.
For the purpose o expelling the contents of the pumping chamber 18, ~he rounded end o an elonga'ed bar 67 is movably mounted in a suitable support, no~
shown, to the chassis 66. The rounded tip of the bar 67 engages the diaphragm 27 over the open side of the pumping chamber 1~ of the cassette 16. ~hen t~le cassette is properly mounted~ the ~ctuator means 28 distend the diaphragm 27 sligh~ly inward even at maximum retraction; thus constantly being in engaqement with the diaphragm throughout the pumping s~roke. The volume of the pumping cavity in this maximum retracted position of ~ the bar 67 is at its maximum operating volume. As the ; bar 67 moves inwardly the membrane is distended . inwardly, thereby reducing the volume of the pumping chamber 18.
The pump lS includes a hinged door 60 which opens to allow insertion and removal o the cassette 16 and the regions of the upstream and downstream portions 11 and 13 which are inside the`pump housing 34. As may be seen in FIGURE 4, when the door 60 is closed, a coil . spring 55 held in a recess 57 o~ ~he door, the latter being covered by a plate 59, presses a biasing cup 61 against the cassette hou~ing 17, thus holding tha housing in position against the chassi~ 66. Pressure blocks 62 and 64 are provided attached to the door 27 by `: :

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adjusting screws 68. ~he block 62 is positioned on the - opposite side of the ups~ream conduit portion 11 from the rod 63. Similarly, the block 64 is positioned on the opposite side of the downstream conduit portion 13 from the rod 65. By suitably adjusting the position of the blocks 62 and 64 using the screws 68, the pressure exerted by the restricting means during ~he operation described below may be adjusted during manufacture to insure complete seal off of the tube and thus total closure, as described.
For moving the bars 63, 65 and 67 in the desired sequence, the ends of the movable bars 63, 65 and 67 opposite the cassette and conduit portions carry suitable cam followers 71 biased tby springs, not shown) against the surface of cams 91, 93 and 95. The cams ~l, 93 and 95 are mounted on a cam shaft 97 which is rotated by a driving motor 103. The driving motor is a stepping motor to provide incremental rotation of the shaft and . therefore incremental movement and control over the movable bars.
In FIGURE 4, the lower restricting means 65 is in a position such as to restrict or pinch-off the downstream flexible conduit portion 13. Dué to the natural ~low or pressure head of the fluid in the upstream portion, or to the suction (negative pressure~
created by the retraction of the member 67, the pumping chamber 13 of the cassette 16 fills. The pumping stroke occurs when the second restricting means 65 are retracted to fully open the conduit portion 13 and the first restricting means 63 have closed to restrict or occlude the upstream conduit portlon 11. Movement of the actuator means 67 inwardly reduces the volume o the ~ pumping chamber 18 causing at lea~t ~ome of the contents `~ to be expelled to the downstream portion of the delivery system. The distance which the actuator means 67 move .

inwardly determines the displacement volume during the pumplng strokeO The filling and pumping strokes are conducted in sequence and repeated according to the rotation of the cam shaf~ 97 and the co~figuration of the cams 91, 93 and 95.
: In the embodiment of the cassette of FIGURES 2 and 3, the back wall of the cassette has a vertical passage 29 bored therein which extends upwardly and terminates at the upper end of the pump cavity. A
horizontal opening or a hole 23, forming the outlet opening, extends from the pump cavity 18 adjacent the periphery thereof to the vertical passage. The curvature of the interior surface of the pump~ng cavity assists bubbles of gas in migrating toward the upper end o~ the pumping cavity. Accordingly, such bubbles readily pass through the hole 23 and into the upper end - of ~le passage to be forced out with the flow of fluid `~ or semisolids during pumping. Accordingly, any air enterinq the pumping cavity will be forced out and will ` 20 not accumulate therein. ~ecuase air is unable to build ` up in the pumping cavity, the accuracy of the system is preserved.
Referring now to FIGURE 5, an arrangement is shown wherein the passage 29 which connects the outlet " 25 opening 23 to a location proximate to the lower portion ~ of the cassette 16 is formed in the mounting block or - chassis 66 of the pump itself. The outlet opening, which is of generally circular cross section, has an axis which is substantially vertical with the cassette mounted for operation. The passage 29 provides a loop which the cassette 16 to a position below the cassette.
; The flexible tubin~ normally connected to the cassette ; and forming the downstream portion of the drug delivery d' system is pl~ced in this passage by the operator lnstalling the cassette. The door 60 i5 then closed and .

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3~-the dev~ce is ready for operation. An air in line detector 105 may be provided for warning purposes. The flexible tubing is occluded by the bars 63 and 65 at 63' and 65', respectively.
In FIGURE 6, an embodiment is shown in which the outlet opening 23, which is of generally circular cross section is on a substantially horizontal axis when the cassette is positioned or opertion. The flexible tubing then extends, for at least part of its ; 10 length, horizontally from the outlet opening to exit the side of the pump.
It may be seen~ therefore, that the invention provides a replaceable pump and cassette comb nation for a medical infusion system which is easy to use and which avoids problems resul~ing from the accumulation of air in the pumping cavity of the cassette. The device is easy to instal and maintains the typical configuration wherein the inlet or upstream portion of the infusion ~; system extends from the top of ~he pump and the downstream portion extends from ~he bottom.
Various modifications of the invention in addition to those shown and described herein will become apparant to those skilled in the art ~rom the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the apended claims.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a pump for a medical infusion system which pumps fluid or semi-solids from an upstream portion of the infusion system to a downstream portion thereof, a replaceable pump cassette comprising, a rigid enclosure defining a pumping cavity, said rigid enclosure having inlet and outlet openings therein and further having a window therein, a flexible diaphragm extending across said window and being impermeable to the passage of fluids or semi-solids therethrough, said diaphragm being engageable by means on said pump for varying the volume of said pumping cavity, said cassette being of a configuration for orienting said cassette in said pump such that said inlet and outlet openings are both positioned proximate the top of said pumping cavity when said cassette is in an operative position in said pump, said pumping cavity having an internal configuration including interior walls curved to direct all gas bubbles within said pumping cavity to said outlet opening with said cassette in the operative position, said pump including means defining a passage communicating between said outlet opening and a location displaced from said outlet opening with said cassette in the operative position.

2. The combination of claim 1 wherein said passage defining means are located on said cassette.

3. The combination of claim 2 wherein said passage is defined by said rigid enclosure.

4. A replaceable pump cassette for use in a pump for a medical infusion system which pumps fluids or semi-solids from an upstream portion of the infusion system to a downstream portion thereof, said cassette comprising, a rigid enclosure defining a pumping cavity, said rigid enclosure having inlet and outlet openings therein and further having a window therein, a flexible diaphragm extending across said window and being impermeable to the passage of fluids or semisolids therethrough, said cassette being of a configuration for orienting said cassette in the pump such that said inlet and outlet openings are both positioned proximate the top of said pumping cavity when said cassette is in an operative position in the pump, said pumping cavity having an internal configuration including interior walls curved to direct all gas bubbles within said pumping cavity to said outlet opening with said cassette in the operative position, said cassette further including means defining a passage communicating between said outlet opening and a location proximate to the lower portion of said cassette with said cassette in the operative position.

5. A cassette according to Claim 4 wherein said passage comprises a conduit extending through the wall of said rigid enclosure.

6. A cassette according to Claim 4 wherein said passage defining means comprises a wall coextensive with said rigid enclosure in said pumping cavity.