CA1127491A

CA1127491A - Medical infusion system

Info

Publication number: CA1127491A
Application number: CA306,306A
Authority: CA
Inventors: Jal S. Jassawalla
Original assignee: Andros Inc
Current assignee: Andros Inc
Priority date: 1977-07-05
Filing date: 1978-06-27
Publication date: 1982-07-13
Also published as: GB2065789B; AU3775178A; FR2396553A1; GB2065789A; IT7850154A0; ES471363A1; GB2000833B; US4199307A; JPS5445993A; FR2396553B1; MX146278A; DE2829215A1; GB2000833A; BR7804303A; AU532562B2; IT1107478B

Abstract

ABSTRACT
A medical infusion system is described employing a pump for conducting fluid or semi-solids from an upstream portion to a downstream portion of the system. The pump includes conduit means defining, in part, a removable cas-sette having a window therein and a diaphragm spanning the window. The casette has inlet and outlet openings valve-lessly communicating with the pumping chamber or cavity of an opening the conduit means at three different locations, one of which is before the casette and one of which is after the casette and the third of which is at the diaphragm of the casette.

Description

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This in~cntion relates to medical infusion systems and, more particularly, to an irnproved medical in~usion system and 6 to an improved pump and cassette for use therein.
Various medical infusion systems for the delivery of fluids or semi-solids into a patient are w~ll known in the prior art, and such systems are in wide-spread daily use in hospitals throughaut the world. These systems are commonly used for such things as the intra-venous or intra arterial delivery-of glucose solutions and blood plasma, for the delivery of drugs; and for enteral delivery of fluids and semi-solids. Typically, delivery is at controlled rates depending on the pati~nt-ls needs~
and in the case of drugs, the dru~-concentration-being delivered is con~rolled.
A commonly used form of infusion system for~-intravenous delivery of fluids is comprised of a fluid container, a drip chamber and an adjustable clamp in the tube leading from the drip chamber to the needle penetrating-m-the vein. The fluid container or bottle is supportea at an elevated position with respect to the-patient, with the drip _ chamber typically immediately thereunder. Transparent walls in the drip chamber coupled with a ~ixed volume of air there-in allows the visual determination of the drip rate, whichin turn is adjustable by the hose clamp. Thus, as 1uid being delivered seeps past the pinched area of the hos~, _ the air pressure in the drip chamber decreases, thereby encoura~ing the formation and dislodging of a drop from the tip of the small tube into the drip chamher coupled to the bottle. such systems may be used alone, or the drip chamber used in conjunction with some other type of metering or pumping mechanism so that the visually observed drip rate may be used as a cross-check to verify the proper operation of the pumping device.
Another form o~ medical infusion system is the common medical syringe. Such a device, as is well known in the art, employs a hollow barrel in which the fluid to be injected is held. The contents of the barrel are discharged through a needle or cathetex by a plunger which fits within the barrel and moves therein to reduce the internal volume of the barrel from its maximum to its minimum. Certain forms of automatic medical infusion appara~us employ the syringe type mode for displacing the fluid into the patient. Typically, however, such pumps are expensive, and are hard to control and refill.
Another type of system utilizes what is commonly referred to as a peristaltic pump. Such pumps are chaxac-terized by a length of flexible tubing which is disposed within an arc between a stator-like member and a rotor as-sembly. The rotor assembly is provided with a plurality of ~5 rollers which, upon rotation of th~ rotor assembly, success-ively pinch-off the tube and advance the location of the pinch-off so as to progressively advance the 1uid within the tube ~1 ~7~ ~

along the tube at a rate determined by the rate of rotation of the rotor. Typically such system~ are driven in rotation by some form of motor-gear assembly so as to provide the gener-ally desired low pumping rate by the low speed xotation of the rotor. Such pumps have the advantage of having a disposable element in the fluid flow path, in that the length of tubing in the pump may be replaced ater each use. In principle, the pumps also have the further advantage of providing low and variable flow rates by way of positive displacement of fluid. In practice, however, these systems characteristically exhibit poor accuracy and poor reproducibility. They also have the disadvantages of ~eing mechanically complex, and require a substantial amount of power, thereby making them relatively expensive and difficult to use on battery operation~
Another form of pump utilizes a limited positive displacement by rapidly varying the volume of a pump chamber and employing inlet and outlet check valves. Such pumps have some advantages in that they may be specifically arranaed so as to not pump air, thereby providing for automatic shu~-off of the pump in the event of exhaustion of~thè supply of fluid --being injected. Also such pumps may utilize a form of electro-magnetic device allowing a pulse source to provide a variable pulse rate to thereby vary the pump rate. More importantly, however, such pumps may employ a replaceable cassette which forms the pump chamber or cavity and which may be replaced for each patient and type of fluid. Thus, sterility can be easily assured and cross contamination easily avoided~

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Such pumps also have a number of disadvantages/
however. In particular, the replaceable cassettes for such pumps are often relatively expensive and must be fabricated from a relatively large number of close tolerance parts.
Aside from such elements as coil springs and close fitting moving parts for check valves, sueh pumps sometimes employ metal parts whieh must be proteeted against corrosion, etehing, and other adverse effects thereon which may result in dissolved materials being infused.
10~ Still another form of pump, somewhat akin to a peristaltic pump, is the type of pump wherein a conduit is restrieted and opened in a sequence whieh produees the desired pumping action. Sueh a pump is shown and deseribed in U.S.
Patent No. 2,105,200. Pumps of this type, however, have frequently not provided suffieient accuracy for many purposes, and are hard to control, clean and refill.
It is an object of the present invention to provide an improved medical infusion system.
Another object of the invention is to provide an improved pump for use in a medical infusion system.
A further object of the invention is to provide an improved eassette for use in a medieal infusion system whieh is low in eost, relatively simple of operation, and of high reliability.
The present invention resides in a pump for use in a medieal infusion system for pumping fluids or semi-solids from an upstream portion of the infusion system to a downstream portion thereof and wherein a reeiproeable member movable inerementally is provided for varying the volume of the pump ehamber with a replaeeable pump eassette being provided for defining the pump ehamber. The cassette ineludes a rigid enclosure defining a cavity having inlet and outlet openings valvelessly communicating with the cavity, the tm/~ L~ - 5-rigicl enclosur~ hav.ing a window therein/ the inle-t and outlet openincJs each havinc3 a cross~sectional area of the ratio of which to -the are~ o:E the window is not greater than about 0.3 to 1. ~ flexible diaphragm extends across the window and is irnpermeable to the paSsacJe of fluid or semi-solids -therethrough, the diaphragm being engageable with the reciprocable member when the cassette is positioned in an operat.ing position in the pump. The diaphragm is of a size such that the area of the diaphragm not engaged with the reciprocable member is less than about three quarters of the total area oE the diaphragm so that the movement of the reciprocable member varies the volume of the cavity.
Other objects and features of the inventlon will bccome apparent to those skilled in the art from the following description takin in connection with the accompanying drawings wherein:

tm/~ -5a-.~.i FIGURE 1 is a schematic view of a medical infusion system constructed in accord~nce with th~ invention~
FIGURE 2 is a schematic perspective view of a cassette and portions of the pump of the system of FIGURE l;
S FIGURES 3 and 4 are schematic sectional views illustrating the operation of the pump portions of FIGURE 2;
FIGURE 5 is a graph illustrating the operation of the cam driving means illustrated in FI&U~E 3;
FIGURE 6 is a top plan view of an alternate configuration of a cassette and poxtions of the pump o the system of FIGURE l; and FIGURE 7 is a side view of the pump portion of FI GURE 6 .
Very generally, the medical infusion system of the ~1~ invention includes (FIGURE 1) an upstream portion ll, which may be in fluid communication with a source 12 of fluid. A
downstream portion 13 is secured suitably for delivering the fluid or semi-solid to a patient 14D A pump 15 pumps fluid from the upstream portion ll to the downstream portion 13.
The pump includes (EIGURE 3) means 16 for supporting a conduit means 17 extending between the upstream and downstream portions.
Means 21 are provided for selectively restricting and opening the conduit means 17 at locations spaced therealong in a sequence such as to pump fluid in the conduit means. The conduit means include a replaceable cassette ox rigid section 18 forming a rigid enclosure with a window 19 therein. ~
flexible diaphragm 20 extends across the window and is imper-meable to the passage of fluids or semi-solids. Part of the restricting means engage the diaphragm and is driven increment-~0 ally to control pumping.

Referring now more particularly to FICURE 1, the invention is shown in the form of an intravenous delivery system for deliverin~ fluid from a fluid reservoir or stor-age means 12 to a patient 14. The flllid is introduced intra-venously through a suitable catheter 23 attached to thedownstream portion 13 of the delivery system. The catheter is held in place by adhesive tape 25 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 27. A drip char~er 29 is attached to the lower portion of the bottle 12 ana may be of conventional.
construction. An empty bottle alarm 31 of suitable design may be employed beneath or attached to the drip chamber to s.ignal when-the contents of the bottle 12 have been drainedO- The contents of the-bottle 12 pass through.the upstream portion- -.
ll of the--delivery system, the upstream portion constitu~ing, in the illustrated embodiment, a flexible--hose.-..
Although the bottle 12 is shown-positioned.on the:-:
support 27 in an elevated condition with respect to the patient.
14, as is typical-of many-in~ravenous delivery systems,-it i~
not critical in the--system-of the invention that the bottle--be so elevated inasmuch as the fluid is conveyed to the patient by the positive pumping action of the pump 15 r The pump 15, shown in FIGURE 1, may be s~-itably contained in a housing 33 having control knobs including a knob 35 thereon and a vent 37 fox cooling the internal con~ents. The pump 15 may-be supported on a bedside table 39 or other suitable structure and i~

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located between the upstream portion 11 and the downstream portion 13 of the de]ivery system. Grommets ~1 orm the entrance and the exit to -the houslng 33 for the upstream and downstream portions 11 ~nd 13, respectively.
S Referring now more particularly to FIGURE 2, the internal construction of a portion o~ the pump 15 is shown in a schematic perspective drawing. A rigid section 18 of tubing or conduit forms a rigid enclosure or cassette for the pump which is easily replaceable. The rigid section 18 is supported inside the housing 33 of the pump 15 by suit-able supporting means, not shown. The upstream portion 11 (FIGURE 1) of the system is coupled to the rigid section 18 which is made from a rigid (plastic) material by a suitable sleeve coupling 105.- Similarly,-the-downstream portion 13 --(FIGURE 1) of the system is coupled to the tube--section lB ~~
by a suitable sleeve coupling 107.:-A windo~ 19 is cut-ou~
of the tube section 18 and-is of-a--size such-as to permit~;
passage-into the tube section l8 through the window of restricting means described below. An outer sleeve 111 of flexible resilient-material is fitted over the outside of the-tube section 18 covering the window-1-9. The sleeve 111 is of material which-is impermeable to passage_of-th~---fluid being infused and thereby provides, over the window 19, a flexible diaphragm 20 through which the restricting means descriked below can change the volume of the interior of the rigid section 18. The sleeves--105 and 107 are also of flexible material and are-positioned~in alignment with the restricting means described below.

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As previously mentioned, restrictiny means 21 are employed to sequentially restrict and open the conduit means 17 in a sequence such as to pump flu.id in the conduit means from the upstream portion 11 to the downstream portion 13 of 5 the delivery system. Although any suitable means for con-stricting the conduit:means 17 in the manner described below may be employed, in the apparatus illustrated in FIGURES 3 and 4, the restxicting means 21 include first, second and third movable members 63, 65, and 67, respectively. The movable member 63 comprises an elongated bar which i5 slidably supported by suitable means not shown. Similarly, the second movable member 65 comprises an elongated bar slidably mounted by suitable means, not shown. The movable members63 and 65 - have rounded ends ~or engaging.the respective sleeves 105 and~
107, and are-shaped and-sized to conform with a rounded recess-.-in the.support-means.16, thus:ensuring-that_the sleeYes.can.be completely pinched-off-at--the-two locations-where-they .are engaged by the movable members-63 and-65.- .
The third movable member 67 comprises an elongated 20 bar slidably mounted in-a suitable.support,- not shown.-The~
member 67 engages the diaphragm 20 over the window 19 in the rigid section or cassette 18.- As the member 67 moves ~orward,- -the membrane is distended inwardly as shown in ~IGURE 4, thereby reducing the volume defined by the rigid section 18.
For moving the movable members 63, 65, and 67.in.
the desired sequence, the ends of the movable members opposite the tube section 19 carry suitable cam followers, not shown, ~ ~7~ 9~

bi~sed resiliently against the surface of x~spective cams ~1, 93, and 95. The cams 91, 93, and 95 are mounted on a cam shaft 97 which is rotated by a driving mo-tor 103. The driving motor is a stepping motor to provide incremental rotation of the shaft and therefore incremental movemen-t and control over the members 63, 65 and 67.
In FIGUR~ 3, the second movable member 65 .is in a position such as to restrict or pinch-off the sleeve 107.
Du~ to the natural 10w or pressure head of the fluid in the upstream portion,or to the suction (negative pressure) cxeated by the retraction of the member-67, the-rigid section -1-8 fills as far as the movable member 65. The pumping stroke is illus-trated in FIGUR~ 4 wherein the movable member 65 is retracted to fully open the sleeve 107 and the-first movable member_63. --15 . has closed to restrict or occlude the-sleeve 105-upstream from.
the movable member 67. Movement-of the-movable member 67 in-wardly reduces the volume of the rigid section 18 causing~at~ ..
least some of the contents to be expelled toward-the-downstream-poxtion of the delivery system. The distance-wh.ich-the movable member 67 moves inwardly determines the displacement volume during the pumping stroke.---The filling-and pumping strokes-are conducted in sequence and repeated according to the rota-tion of the cam shaft 97 and the configuration of the cams 91, 93 and 95.
Referring to FIGU~B 5, a plot is provided illus- -trating the motion versus degrees of shaft rotation for the three movable members 63, 65 and 67, respectively. At the left-hand edge position or 0 position ~hown in the plot, .t 9~L

t11e upstream movable member 63 is closed whereas the members 65 and 67 are open. ~lovement of the member 67 from the fully open position to the occl~lded position di,splaces at leas-t some of the contents of the xigid section 1~ between the members 63 and 65. Following this movement, the member 65 moves to the occluded position to close the downstream sec-tion of the rigid section 18. O.nce this occurs, the member 63 moves to the open position as does the member h7, allowing filling of the tube section once again. Between 180 and 270~, the upstream movable membex 63 moves from the open position to the closed-position,-and between 270 and 360 the down-stream movable member 65 moves to the open position. This places the sys~em in readiness for the next displacement stroke beginning with 0~
Referring now to FIGU~ES 6~and 7, an alternate--configuration for the rigid section or cassette of the pum~
is shown. The rigid section or rigid enclosure.l8 is of.a:. _ 1attened configuration defining a pancaXe shaped cavity or enclosure. The window 19 is circular and the diaphragm 20' is formed by a membrane.spanning the windowO ;The~membxane may bè formed integrally with the rigid enclosure or part thereof during molding, or may be formed separately,.,and-suitably attached. Inlet and outlet orifices 113 and 115 are formed integrally with the rigid section 18l, and the flexible sleeves 105' and 107' are attached ~hereto.
Typical applications of the invention would involve maximum pressures of about 20 psi. Accoxdingly, ~lZ~

the "rigidity" of the rigid section 18 is selected approp-riately~ It is preferred that the movable member 67 engage the diaphragm 20 throughout its stroke, and that khere always be a slight inward loading on the diaphraym. For satis~ac-tory accuracy, it is preferred that the unsupported or unen-gaged area of the diaphragm not exceed 75% o the total diaphragm (window) area.
Rather than the cam drive illustrated~ other means for operating the restrictin~ means may be utilized, such as a lead screw drive. However, incremental contxol over the aiaphragm movement is significant in achieving proper accuracy and control. By suitable aesign, a desired displacement volume may be selected for each step. Digital control is then readily possible-with commercially available and relatively inexpensi~e micro-computer chips. Functions such as flow~rate, total volume deli~ered and flow error-monitoring may -easily-be handled by --known-digital techniques~
It is usually preferable to design the system to -operate such that the return strokes, i~e. filling strokes, be of the same duration regardless of the delivery--rate-and-=
volume. Thus, the flow~may be more even where-the-member-67 is retracted at a relatively quick fixed rate as opposed to the varying inward (delivery) rate. Digital capability makes such operation easily achievable. , The size of the outlet and inlet openings relative to the diaphragm or window--size is of significance. With inlet and outlet openings which are too large, regurgitation becomes a large enough factor to deleteriously affect accuracy~

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Thus, it is yreferred th~t ~ach of the inlet and outlet openings have a cross-sectional area having a ratio to the diaphra~m or window area of not greater than about 0.3.
The medical infusion system of the inventiOn provides some significan-t advantages over many prior art constructions. There are no valves employed in the system for the pumping operation and ~herefore none in the cassette, thus significantly improving the reliability and reducing the complexity of manufacture and therefore the cost. Any reason-ably strong type of fle~ible tubing will operate as thesleeves 105 and 107 in the system of the invention, and the tubing may be easily replaced since it is inexpensive. By properly designing the cams and the size of the movable res-tricting elements, good constant flow rates may be achieved, even-to very lo~ rates~
Various modifications_of the invention in addition to those shown and described herein.will become..apparent to -those skilled in the art from the_foregoing description-and accompanying drawings. Such modif~cations are intended to 20 _. fall within the scope of the appended claims.

Claims

Claim 1. A pump for use in a medical infusion system for pumping fluid or semi-solids from an upstream portion of the infusion system to a downstream portion thereof, said pump comprising, conduit means, means for supporting said conduit means for extending between the upstream and downstream portions of the system, first constricting means for selectively restricting and opening said conduit means at a first location thereof, second restricting means for selectively restricting and opening said conduit means at a second location thereof spaced from said first location, actuator means for selectively restrict-ing and opening said conduit means at a third location thereof between said first and second restricting means to displace a predetermined volume in said conduit means, and means for operating said first and second restricting means and said actuator means in a sequence such as to pump fluids or semi-solids in said conduit means, said conduit means including a rigid section positioned between said first and second locations and defining a pumping cavity, said rigid section having a window therein, a flexible diaphragm extending across said window and being impermeable to the passage of fluid or semi-solids therethrough, said rigid section of said conduit means having inlet and outlet openings the cross-section of each of which has a ratio to the area of said window not greater than about 0.3 to 1, said actuator means being engaged with said diaphragm and being of a size such that the area of said diaphragm not engaged with said actuator means is less than about three quarters of the total area of said diaphragm, said operating means including drive means for providing incremental movement of said actuator means to control incrementally the pumping of fluids or semi-solids.
Claim 2. A pump according to Claim 1 wherein said rigid section of said conduit means is of substantially tubular configuration.
Claim 3. A pump according to Claim 1 wherein said rigid section of said conduit means is of generally flattened configuration defining a pancake shaped pump cavity.
Claim 4. A pump according to Claim 1 wherein said supporting means include means defining an elongated groove for receiving the flexible conduit.
Claim 5. A pump according to Claim 1 wherein said drive means include a rotary shaft, first, second, and third cams mounted thereon in coupled relation to said first and second restricting means and said actuator means, respec-tively, and a stepping motor for rotating said shaft.
Claim 6. A system according to Claim 2 wherein said diaphragm is formed in part by a relatively flexible sleeve positioned coaxially of said rigid section and extending over said window therein whereby said diaphragm comprises the portion of said flexible sleeve extending over said window.
Claim 7. A pump according to Claim 1 wherein said first and second locations on said conduit means each includes a flexible tube connected to said rigid section of said conduit means.
Claim 8. A medical infusion system for delivering fluid from a source of supply to a patient, said system com-prising, an upstream portion and a downstream portion, conduit means extending between said upstream portion and said down-stream portion, and a pump for pumping fluid through said conduit means from said upstream portion to said downstream portion, said pump including means supporting said conduit means, first restricting means for selectively restricting and opening said conduit means at a first location thereon, second restricting means for selectively restricting and opening said conduit means at a second location thereon spaced from said first location, actuator means for selectively restricting and opening said conduit means at a third location between said first and second restricting means to displace a predetermined volume therein, and means for operating said first and second restricting means and said actuator means in a sequence such as to pump fluids or semi-solids in said conduit means, said conduit means including a rigid section positioned between said first and second locations and defining a pumping cavity, said rigid section having a window therein, a flexible diaphragm extending across said window and being impermeable to the passage of fluid or semi-solids therethrough, said rigid section of said conduit means having inlet and outlet openings the cross-section of each of which has a ratio to the area of said window not greater than about 0.3 to l, said actuator means being engaged with said diaphragm and being of a size such that the area of said diaphragm not engaged with said actuator means is less than about three quarters of the total area of said diaphragm, said drive means including means for providing incre-mental movement of said actuator means to pump fluids or semi-solids incrementally.
Claim 9. In a pump for use in a medical infusion system for pumping fluids or semi-solids from an upstream portion of the infusion system to a downstream portion thereof, and wherein a reciprocable member movable incrementally is provided for varying the volume of a pump chamber, a replaceable pump cassette for defining the pump chamber, said cassette comprising, a rigid enclosure defining a cavity having inlet and outlet openings valvelessly communicating with said cavity, said rigid enclosure having a window therein, said inlet and outlet openings each having a cross-sectional area the ratio of which to the area of said window is not greater than about 0.3 to 1, a flexible diaphragm extending across said window and being impermeable to the passage of fluid or semi-solids there-through, said diaphragm being engageable with said reciprocable member when said cassette is positioned in an operating position in said pump, said diaphragm being of a size such that the area of said diaphragm not engaged with said reciprocable member is less than about three quarters of the total area of said diaphragm, whereby movement of said reciprocable member varies the volume of said cavity.
Claim 10. A cassette according to Claim 9 wherein said rigid enclosure is of substantially tubular configuration.
Claim 11. A cassette according to Claim 10 wherein said rigid enclosure is of generally flat configuration defining a pancake shaped cavity.
Claim 12. A replaceable pump cassette for use 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 and wherein a reciprocable member movable incrementally is provided for varying the volume of a pump chamber defined by the cassette, said cassette comprising, a rigid enclosure defining a pumping cavity, an inlet opening valvelessly communicating with said cavity and an outlet opening valvelessly communicating with said cavity, said inlet and outlet openings having means for connecting same to the upstream and downstream portions, respectively, of the medical infusion system, said rigid enclosure having a window therein, a flexible diaphragm extending across said window and being impermeable to the passage of fluid or semi-solids therethrough, said inlet opening and said outlet opening each having a cross-sectional area having a ratio to the area of said window of less than about 0.3, said diaphragm being engageable with said reciprocable member when said cassette is positioned in an operating position in said pump, said diaphragm being of a size such that the area of said diaphragm not engaged with said reciprocable member is less than about three quarters of the total area of said diaphragm, whereby movement of said reciprocable member varies the volume of said cavity.
Claim 13. A cassette according to Claim 12 wherein said rigid enclosure is of substantially tubular configuration.
Claim 14. A cassette according to Claim 12 wherein said rigid enclosure is of generally flat configuration defining a pancake shaped pump cavity.