Device for monitoring an intravenous infusion system

Abstract: The device (1) for monitoring and controlling an intravenous infusion system comprises a sensor element (2) to be associated with the reservoir (13) of the intravenous infusion system and indirectly controlling both an optical or acoustic warning element (5) and a valving element (11). In this manner the nurse or patient no longer has to carefully monitor the delivery from the intravenous infusion system, which as is well known can be subject to operational problems.

Description: This invention relates to a device for monitoring an intravenous infusion system. Intravenous infusion systems that do not provide any means for terminating the flow of liquid through the delivery tube are known from WO 84/03632 and US 4,533,350. When the infusion is going to run out it is necessary to intervene immediately in order to stop the infusion. Otherwise the blood would begin to rise up the delivery tube because its pressure is no longer opposed by that of the drip liquid. Devices for monitoring an intravenous infusion system are known from FR-A-2 272 435, FR-A-2 331 088, US 4,509,943, US 5,078,683. In order to obviate the above drawback, said devices comprising valving elements for terminating the flow of the liquid through the delivery tube. A device for monitoring an intravenous infusion system is also known from US-A-3,655,095. It comprises a valve member operable in one condition to pass a drop of liquid and operable in another condition to arrest delivery of liquid drops through a tube. A solenoid is arranged whereby when it is energised, a valve member will be withdrawn against the urging spring. The tube is constructed of resilient material whereby upon withdrawal of member urging the spring, the passage within the tube will open to permit a drop to be formed in splash chamber. The valving element for terminating the flow of the liquid through the delivery tube constitutes a barren to the miniaturisation of the devices for monitoring an intravenous infusion system, because said valving element needs a supply of electric energy that is high for the known electric batteries or accumulators having low overall dimensions. The object of the present invention is to obviate the aforesaid drawbacks by providing a device for monitoring an intravenous infusion that can be easily miniaturised. This object is attained by a monitoring device for monitoring an intravenous infusion system in accordance with claim 1. Preferred embodiments of the invention are specified in the dependent claims. The invention is illustrated by way of non-limiting example in the figures of the accompanying drawings. Figure 1 is a schematic view of a device for monitoring an intravenous infusion system showing a first embodiment of the electronic circuit, represented as a block diagram, and a schematically represented valving element according to the invention; Figure 2 partially shows the device of Figure 1 applied to an intravenous infusion system; Figure 3 is a section on the line III-III of Figure 2; Figure 4 is a partial perspective view of a second embodiment of a device for monitoring an intravenous infusion system, which differs from that of Figures 1-3 by the structure of the gripper element and sensing means; Figure 5 is a section on the line V-V of Figure 4; Figure 6 is a section corresponding to that of Figure 5 Figure 7 is a front perspective view of the valving element according to the invention; Figure 8 is a rear perspective view of the valving element of Figure 7; Figure 9 is a view in the direction of the arrow IX of Figure 8; Figure 10 is a section on the line X-X of Figure 9; Figure 11 is a front view of the valving element of Figure 7 in the position in which it does not prevent flow; Figure 12 is a front view of the valving element of Figure 7 in the position in which it prevents flow; Figure 13 is a schematic view of another embodiment of a device for monitoring an intravenous infusion system showing a second embodiment of the electronic circuit and a schematically represented valving element. Figure 14 is a perspective view of another device for monitoring an intravenous infusion system of the type provided with the valving element shown in Figures 7-12; Figures 15 and 16 illustrate a perspective view of another device, comprising the sensor element, the electronic circuit and the valving element combined into a single element; With reference to the aforesaid figures and in particular to Figure 1, a monitoring device 1 for monitoring an intravenous infusion system comprises substantially a sensor element 2, an element 3 for measuring time intervals, a relay 4, a warning element 5 and a power unit 10. In the illustrated embodiment the sensor element 2 comprises a photosensor formed from a transmitting portion 6 and a receiving portion 7. The receiving portion 7 is operationally connected to the time interval measurement element 3 which is connected to the relay 4 operating the warning element 5. In the illustrated embodiment the warning element 5 is both an acoustic and lighting warning element 8 possibly incorporating a remote calling device 9 (for example for automatically calling the nurse via cable or radio). The power unit 10 powers all the elements of the circuit 1 at low voltage. According to the invention the device 1 comprises a valving element 11 for terminating the flow of liquid through a delivery tube 12 positioned downstream of a drip chamber or reservoir 13 of the intravenous infusion system. The embodiment of the valving element 11 is described hereinafter. For practical reasons the sensor element 2 is housed (see for example Figures 2 and 4) within the jaws 14 of a gripper element 15 to be applied to the outside of the drip chamber or reservoir 13. On that side which adheres to the drip chamber 13 the gripper jaws 14 have a curvature with a radius less than the radius of the drip chamber 13 of the smallest commercially available reservoirs. In this manner the gripper element or gripper 15 is always securely centered about the drip chamber 13 independently of its size. The photosensor or sensor 2 can be of barrier type, reflection type, reflex type, infrared or modulated infrared type according to requirements. The sensor 2 need not, however, be of optical type, i.e. need not be a photosensor, but instead can be a capacitive proximity sensor. All the aforementioned sensing means can be housed in or associated with the gripper element 15 to allow it to be rapidly applied to the drip chamber 13. Depending on requirements or the operational characteristics of the sensor elements 2 the monitoring device 1, on application, can be made to detect the passage of the droplet 16 along its vertical trajectory or the presence or absence of the portion of liquid 17 in the reservoir 13 or the level of the surface 18 of said portion of liquid 17 within the chamber 13. In the first case (see the device shown in Figures 2 and 3), each time the droplet 16 crosses the axis 19 the time interval measuring element 3 begins to count time intervals from zero. If, after a total time interval of an extent predetermined on the basis of the type of medicament to be administered, there is no further passage of droplets 16 with corresponding zeroing of the measured time intervals, the time interval measuring element 3 operates the warning elements 5, 8 and/or 9 via the relay 4, depending on how it is programmed. In the second and third case the time interval measuring element 3 immediately operates the relay 4 on disappearance of the portion of liquid 17 or the surface 18 respectively. In these cases no delay need be incorporated as it is obvious that the liquid is about to finish. For constructional and applicational reasons the time interval measuring element 3, the relay 4, the warning element 5 and the power unit 10 can all be housed within the same housing 20 from which plug pins 21 emerge for plugging into a conventional electric socket. The devices provided with optical sensors shown in Figures 2 and 3 operate regularly provided that an axis 22 of the droplet trajectory encounters the axis 19 , i.e. that the droplet 16 passes through the beam 19. If this is not so, then the passage of the droplet 16 is not detected. This situation can occur for example if, due to an error in its application to the bottle 25, the axis of symmetry of the drip chamber 13 does not coincide with but instead cuts the axis 22. This occurs in practice if the bottle 25 and/or reservoir 13 are very inclined instead of upright. Under such conditions when the total time interval counted by the time interval measuring element 3 exceeds the predetermined, this activates the warning elements 8, 9 even though the intravenous infusion system is operating regularly. Since the monitoring device 1 is of the type which also comprises the valving element 11 there is an unjustified interruption in delivery because of the compressing of the tube 12. This drawback can be overcome by the embodiments shown in Figures 4, 5 and 6. The sensing means of the device shown in Figures 4 and 5 comprise the transmitting portion 6, the receiving portion 7, a first reflex reflector 23 and a second reflex reflector 24. The transmitting portion 6, the receiving portion 7 and the first reflex reflector 23 are all positioned on the same side of the axis 22 of the droplet trajectory, whereas the second reflex reflector 24 is positioned on the other side, on an appendix 30A (Fig. 4) fixed to the first jaw 14 of the gripper element 15. The reflex reflector 24 is positioned to form a constant reflection angle for the received ray, independently of the amount by which the two jaws 14 of the gripper 15 are opened. The axis 19 becomes a broken polygonal line between the said elements, giving it maximum probability of encountering the droplet 16, independently of the axis of the trajectory 22 followed by the droplet. This embodiment therefore operates regularly even if the axis of symmetry of the drip chamber 13 cuts the axis 22. In the illustrated embodiment the broken axis or polygonal line 19 comprises four parts because it undergoes three reflections. By choosing suitable reflex reflectors 23 and 24 it is however possible to increase or decrease the number of reflections and hence the number of component parts of the broken line 19, so that droplets of a particularly small diameter can also be detected. The embodiment shown in Figure 6 uses photosensors and differs by comprising a transmitting portion 6 positioned between two side-by-side receiving portions 7 all opposing a first reflex reflector 23. A valving element according to the invention is shown in Figures 7-12. From the operational viewpoint the valving element 11 is able to maintain the tube 12 closed without absorbing electrical energy. This is a great advantage in terms of practical use and construction because the device 1 can be made independent of the mains supply and more easily miniaturized. In this respect, conventional valving elements can compress the tube 12 only if the electromagnet is energized and hence only if electrical power is present, with a corresponding current consumption. This means that if the power supply is from an electric battery the shut-off state can be maintained only for a limited time period, which is further reduced because of the presence of further electricity-consuming components in the device. Contrary to this, in the valving element 11, according to the invention the electromagnet acts only in the sense of releasing a locking element which is able to compress the tube 12 by the effect of the action of elastic means which are preloaded on applying the monitoring device 1 to the intravenous infusion system. More specifically the valving element according to the invention comprises a multiple gripper element of the normally closed type, indicated overall by 11 and comprising a first jaw 26, a second jaw 27 and a third jaw 28, a first spring 29, a second spring 30 and a locking device 35. The first jaw 26 operates against the second jaw 27 and the third jaw 28 by the action of the first spring 29 and the second spring 30 respectively, which operate as first and second biasing means respectively side by side on a single pin 31. The first jaw 26 and second jaw 27 encounter each other to form a tubular groove 32 the diameter of which is such that it adheres to the tube 12 without compressing it or reducing its internal diameter, but such as to be able to keep the valving element 11 retained on the tube 12. In contrast the first jaw 26 and third jaw 28 encounter each other with a profile such as to compress the tube 12. In the illustrated embodiment both the first jaw 26 and third jaw 28 are provided with tube compressing projections 33 able to generate a high localized pressure on the tube 12, which being traditionally of flexible material is easily compressed by the elastic force of the second spring 30. As can be seen in particular in Figure 10, the third jaw 28 comprises a stem 34 which extends parallel to, and inwards of, the corresponding stem of the second jaw 27. In this manner when acting on the first jaw 26 and in particular on the second jaw 27 in order to open them, the third jaw 28 is also urged into its open position. The third jaw 28 is then locked in its open position by the automatic action of the locking device 35, which acts as disabling means comprising an electromagnet 36, a floating pin 37 and a third spring 38. The third spring 38 is preloaded such as to urge the pin 37, which is nothing other than the core of the electromagnet 36 (arrow F) between the first jaw 26 and the third jaw 28 so as to maintain them mutually open when the first jaw 26 and second jaw 27 are operated to open. The movement of the pin 37 between the first jaw 26 and third jaw 28 is preferably facilitated by two friction reducing rollers 39 when the electromagnet 36 acts in the sense of causing the pin 37 to move in the direction of the arrow G to release the third jaw 28. The operation of the multiple gripper element 11 is as follows. To apply the multiple gripper element 11 to the tube 12, the first jaw 26 and second jaw 27 are operated so as to open all three jaws 26-28, the third jaw 28 being simultaneously dragged into its open state by its engagement with the second jaw 27. The floating pin 37 becomes wedged between the first jaw 26 and third jaw 28 to maintain them mutually open. The multiple gripper element 11 is positioned so that the tube 12 lies between the jaws, and it is then left. The first jaw 26 and second jaw 27 adhere to the tube 12 at the tubular groove 32 without the tube being compressed, but such that the valving element 11 is retained. When the electromagnet 36 is energized the floating pin 37 moves in the direction of the arrow G, to hence close the third jaw 28 onto the first jaw 26, consequently compressing the tube 12 by the action of the second spring 30. With particular reference to Figure 13, the device shown therein represents another embodiment of the monitoring device, which differs from the first embodiment mainly by the structure of the electronic circuit, which comprises the following units: an oscillator 43, a first droplet counter 44, a droplet frequency memory 45, a second droplet counter 46, a set frequency comparator 47, a first logic gate 48 and a second logic gate 49, a first threshold unit 50 and a second threshold unit 51, an acoustic/optical warning unit 8 and a luminous display 52. The units 43-45 form a self-setting unit 53. The units 43-51 can be physically combined into a single microprocessor 54, which can be housed in the gripper element 15. Figure 14 shows the luminous displays 52 and a warning light 8. The gripper element 15 comprises a recess 55 on which to press in order to open the element during its application to the drip chamber 13. Within the recess 55 there is the pushbutton 56 for switching on/switching off the monitoring device 1. In this manner, switching on and/or off are automatic on application and/or removal of the monitoring device 1 to or from the drip chamber 13 of the intravenous infusion system. The operation of the monitoring device 1 is as follows. The device 1 must be applied to the intravenous infusion system when this has passed beyond its initial transient state and hence operates under normal working conditions with the correct delivery frequency. The electronic memory circuit initially memorizes said droplet delivery frequency and assumes it as the reference frequency. The delivery frequency should be the optimum as it has been chosen by specialized personnel operating the intravenous infusion system. The monitoring device 1 continuously compares the reference delivery frequency with the instantaneous frequency. If this latter is within a scheduled tolerance, which can be set during the setting-up of the system, the monitoring device 1 does not act. If not, then it indicates the abnormality by emitting light and/or acoustic signals, and finally possibly shutting off delivery by operating the valving element 11. However, as will be apparent, in order for the described device to ensure proper administration, it is essential that the reference frequency is correctly established during the initial stages of administration by the person operating the intravenous infusion system. It is therefore apparent that even if an error arises in estimating the correct delivery frequency, this is assumed to be correct by the monitoring device 1 when this is applied to the chamber 13. The monitoring device 1 is therefore only able to check that the frequency is maintained within the prescribed frequency limits which have been assumed to be correct. The embodiment of the monitoring device 1 shown in Figures 15 and 16 differs from the previous one in that the sensor element 2, the electronic circuit 54, 5 and the valving element 11 are combined into a single element 70 in which the upper part of the first jaw 26 and the second jaw 27 adhere to the drip chamber 13 instead of adhering to the tube 12. The lower part of the first jaw 26 and the third jaw 28 are shaped so as to adhere to the tube 12 and to be able to compress it.

Claims: A device (1) for monitoring an intravenous infusion system, said infusion system comprising at least one drip chamber (13) for receiving droplets (16) of a liquid (17) for intravenous infusion, a delivery tube (12) connected to said drip chamber (13), wherein said device for monitoring an intravenous infusion comprises sensing means (2, 6, 7, 23, 24) operatively associated with said drip chamber (13) for sensing dripping droplets, an electronic unit (2-10, 53, 54) including means (45) for memorising a droplet frequency, a droplet counter (46) for counting the droplets (16) sensed by said sensing means (2, 6, 7, 23, 24), a comparator means for comparing the frequency of droplets (16) counted by said droplet counter (46) with said memorised droplet frequency, relay means (4) operable by said comparator means when said comparator means detects a difference between the frequency of droplets counted by said counter and said memorised droplet frequency, a valving element (11) operable by said relay means (4) for terminating the flow of liquid through said delivery tube (12), characterised in that said valving element (11) includes a first (26) and a third (28) relatively movable jaw for selectively clamping closed an associated delivery tube (12), a second jaw (27) movable relative to said first jaw (26) for clamping engagement to an associated delivery tube (12) or drip chamber (13), for keeping the valving element retained on the tube (12) or on the drip chamber (13), a second spring (30) for normally biasing said first jaw (26) and third jaw (28) towards a clamping closure position relative to said delivery tube (12), said second spring (30) being preloaded on applying to the monitoring device (1) to the infusion system, a first spring (29) for normally biasing said first jaw (26) and second jaw (27) towards a clamping engagement position relative to said delivery tube (12) or drip chamber (13), and a locking device (35) comprising a floating pin (37), a third spring (38) operatively associated to said floating pin (37) for urging the floating pin (37) between said first jaw (26) and said third jaw (28) to maintain them mutually open, and an electromagnet (36) which, when briefly energised, acts on said floating pin (37) against said third spring (38) for effecting relative movement of said first jaw (26) and said third jaw (28) through the bias of said second spring (30). A device according to claim 1, characterised in that said sensing means (2, 6, 7, 23, 24) includes photosensing means for sensing dripping droplets (16) dripping downwardly along a vertical axis (22). A device according to claim 1, characterised in that said photosensing means (2, 6, 7, 23, 24) includes a portion for transmitting (6) a beam (19) through an area through which droplets (16) drip downwardly along said vertical axis, said photosensing means further includes a portion for receiving (7) said beam (19). A device according to claim 3, characterised in that said photosensing means includes reflecting means (23, 24) for reflecting said beam (19) at least once to effect the passage of said beam (19) through said area at least twice before being received by said receiving portion (7) thereby increasing the probability of droplet sensing particularly when offset from said generally vertical axis (22). A device according to claim 4, characterised in that said vertical axis (22) corresponds to the axis of said at least one drip chamber (13). A device according to claim 4, characterised in that said beam transmitting portion (6) and said beam receiving portion (7) are generally positioned at one side of said area and said reflecting means (23, 24) is substantially positioned opposite to the side of said area. A device according to claim 3, characterised in that said beam transmitting portion (6) and said beam receiving portion (7) are generally positioned at opposite sides of said area. A device according to claim 4, characterised in that said reflecting means (23, 24) are positioned generally at opposite sides of said area. A device according to claim 1, characterised in that it comprises a device for optically reading a bar code. A device according to claim 1, characterised in that said sensing means comprise a capacitive proximity sensor.

Inventors: BELLIFEMINE FRANCESCO, BELLIFEMINE, FRANCESCO
Applicants: BELLIFEMINE FRANCESCO, BELLIFEMINE, FRANCESCO
Application year: 1993
Main classification: A61M5
IPC codes: A61M5