Infusion device and method allowing for detecting a drift in a sensor signal

Abstract

An infusion device (1) for administering a medical fluid to a patient (P) comprises a pumping mechanism (11) for exerting a force onto a delivery set (2, 3) for delivering a medical fluid from the delivery set towards a patient (P), a sensor device (14) for measuring the force exerted on the delivery set (2, 3) by the pumping mechanism (11), the sensor device (14) being constituted to output a sensor signal indicative of the force exerted onto the delivery set (2, 3), and a processor device (15) for controlling operation of the infusion device (1). Herein, the processor device (15) is constituted to perform a diagnosis routine during which a sensor signal of the sensor device (14) is obtained and compared to an expected sensor signal, to allow for detecting a drift in the sensor signal of the sensor device (14).

Claims

1. An infusion device for administering a medical fluid to a patient, comprising: a pump configured to exert a force onto a delivery set for delivering a medical fluid from the delivery set towards a patient, a sensor configured to measure the force exerted on the delivery set by the pump, the sensor being configured to output a sensor signal indicative of the force exerted onto the delivery set, and a processor configured to control operation of the infusion device, wherein the processor is configured to perform a diagnosis routine during which a sensor signal of the sensor is obtained and compared to an expected sensor signal, to allow for detecting a drift in the sensor signal of the sensor, the sensor signal is obtained while the pump is not in operative connection with the delivery set, and the sensor comprises a zero reference corresponding to the expected sensor signal when the pump is not in operative connection with the delivery set, wherein, if the comparison during the diagnosis routine yields that a difference of the sensor signal obtained and the expected sensor signal is larger than a first predefined threshold, the zero reference of the sensor is corrected.

2. The infusion device according to claim 1, wherein the delivery set comprises a syringe having a tube containing a medical fluid and a piston movable with respect to the tube, the infusion device comprising a receptacle for receiving the syringe and a pusher device for acting onto the piston for pumping the medical fluid from the tube towards a patient.

3. The infusion device according to claim 2, wherein the sensor is arranged on the pusher device, wherein the pusher device comprises an anti-siphon arm configured to fix the piston with respect to the pusher device.

4. The infusion device according to claim 3, wherein the processor is configured to perform a second diagnosis routine while the anti-siphon arm fixes the piston with respect to the pusher device.

5. The infusion device according to claim 4, wherein, dependent on the comparison during the second diagnosis routine, a mismatch between the obtained sensor signal and the expected sensor signal is recorded, a message is generated indicating that maintenance of the infusion device is advisable, and/or operation of the infusion device is terminated.

6. The infusion device according to claim 3, wherein the anti-siphon arm is configured to press the piston towards the sensor to bring the piston into abutment with the sensor or with a pressure transmitting element configured to act onto the sensor.

7. The infusion device according to claim 3, wherein the anti-siphon arm is displaceably mounted on a sensor support of the sensor received in or on the pusher device.

8. The infusion device according to claim 1, wherein the sensor comprises at least one sensor element configured as a strain gauge or an extension gauge.

9. The infusion device according to claim 1, wherein the sensor comprises a multiplicity of sensor elements electrically connected to each other to form a bridge circuit having nodes in between which the sensor signal is obtained.

10. A method for operating an infusion device for administering a medical fluid to a patient, the method comprising: exerting by a pump a force onto a delivery set for delivering a medical fluid from the delivery set towards a patient, measuring by a sensor the force exerted on the delivery set by the pump, the sensor being configured to output a sensor signal indicative of the force exerted onto the delivery set, and controlling by a processor operation of the infusion device, wherein during a diagnosis routine a sensor signal of the sensor is obtained and compared to an expected sensor signal, to allow for detecting a drift in the sensor signal of the sensor, the sensor signal being obtained while the pump is not in operative connection with the delivery set, and the sensor provides a zero reference corresponding to the expected sensor signal when the pump is not in operative connection with the delivery set, and, if the comparison during the diagnosis routine yields that a difference of the sensor signal obtained and the expected sensor signal is larger than a first predefined threshold, the zero reference of the sensor is corrected.

Description

(1) The idea of the invention shall subsequently be described in more detail with reference to the embodiments shown in the figures. Herein:

(2) FIG. 1 shows a view of an infusion device constituted as a syringe pump;

(3) FIG. 2 shows a schematic drawing of a pumping mechanism of the infusion device;

(4) FIG. 3 shows a sensor device in the shape of a load cell; and

(5) FIG. 4 shows an electric circuit schematic of the sensor arrangement.

(6) FIG. 1 shows an embodiment of an infusion device 1 in the shape of a syringe pump. The infusion device 1 comprises a housing 10 having a front face 100 and a display device 13 arranged thereon. The display device 13 may for example be a touch-sensitive display allowing a user to enter commands for operation of the infusion device 1 and displaying operational information regarding the process of an actual infusion operation.

(7) The infusion device 1 comprises a receptacle 12 in which a syringe 2 having a cylindrical tube 20 is arranged. A piston 21 is movable within the cylindrical tube 20 and is in engagement with a pusher device 11 of a pumping mechanism of the infusion device 1. At an end of the cylindrical tube 20 opposite the piston 21 a delivery line 3 extends from the cylindrical tube 20 towards a patient B, the delivery line 3 being connected to the cylindrical tube 20 at a first end 30 and to the patient B at a second end 31.

(8) The piston 21 comprises a head 210 facing away from the cylindrical tube 20 and being in abutment with the pusher device 11 of the infusion device 1. During operation of the infusion device 1, the pusher device 11 is electromotorically driven in an actuation direction A such that the piston 21 is moved into the cylindrical tube 20 and a medical fluid contained in the cylindrical tube 20 is delivered via the delivery line 3 towards the patient B.

(9) The infusion device 1 comprises a processor device 15 and a storage device 16. Via the processor device 15 the infusion operation of the infusion device 1 is controlled. In the storage device 16 operational parameters, such as mechanical characteristics of the syringe 2 used on the infusion device 1 as well as operational data, may be stored.

(10) During an infusion process a medical fluid, for example a medication or a nutritional fluid for the parenteral feeding of a patient or the like, is delivered from the cylindrical tube 20 via the delivery line 3 towards the patient B. For this, the piston 21 is continuously pushed into the cylindrical tube 20 in the actuation direction A such that a desired flow rate is obtained, which is programmed by a user prior to the start of the infusion operation.

(11) The delivery line 3 generally is made of a flexible tubing made for example from a PVC material. The delivery line 3 extends from the cylindrical tube 20 to the patient B and is, at its first end 30, in fluid connection with the cylindrical tube 20 and, at its second end 31, for example connected to a needle for providing an intravenous access to the patient B. During an infusion process an occlusion O in the delivery line 3 must be avoided and, if it nevertheless occurs, must be detected such that appropriate countermeasures to overcome the occlusion O can be taken. For this, a force sensor 14 is placed on the pusher device 11 facing the head 210 of the piston 214 measuring a force exerted on the piston 21 during an infusion process. From a force measured by means of the force sensor 14 an estimate of the pressure within the syringe 2 can be obtained, such that the pressure within the syringe 2 and the delivery line 3 can be monitored. If it is found that the pressure within the syringe 2 and the delivery line 3 rises beyond a permissible threshold value, an alarm is triggered indicating that an occlusion O may be present in the system.

(12) Generally, the pressure in the delivery line 3 is very small (almost 0) during normal infusion operation in case no occlusion O is present. If an occlusion O occurs, the pressure will start to rise and will continue to rise (if the occlusion O does not disappear) until a threshold value is exceeded, at which moment an alarm is triggered by the processor device 15 such that a user is warned of the occlusion O.

(13) To observe the pressure in the delivery line 3, the force applied to the piston head 210 of the piston 21 by means of the pusher device 11 is measured by the sensor 14. The force measured in this way allows for an indirect measurement of the pressure within the cylindrical tube 20, which generally equals the pressure in the delivery line 3.

(14) In particular, the pressure in the cylindrical tube 20 depends on the measured force according to the following relation:

(15) $P=\frac{F-F_0}{S}.$

(16) Herein, P denotes the pressure, F denotes the measured force, F.sub.0 denotes a frictional force component and S denotes the effective surface by which the piston 21 acts onto the liquid contained in the cylindrical tube 20. The effective surface S is substantially determined by the inner diameter of the cylindrical tube 20.

(17) By determining the pressure in this way and by comparing the determined pressure P to a predefined threshold it can then be concluded whether an occlusion O is present in the delivery line 3 or not. In particular, if it is found that the pressure rises above the threshold, it is concluded that an occlusion O is present.

(18) Whereas F is measured and S is known from the geometrical dimensions of the cylindrical tube 20 of the syringe 2, the frictional force component F.sub.0 can for example be obtained from a calibration on a particular syringe or doing a statistical analysis of multiple syringes of the same or different kinds, brands and volumes.

(19) FIG. 2 shows, in a schematic drawing, the mechanics of an embodiment of a pusher device 11 of the infusion device 1. The pusher device 11 comprises a housing 110 and is movable along the actuation direction A during an infusion operation to push the piston 21 at a constant speed into the cylindrical tube 20 of the syringe 2 in order to deliver a medical fluid from the cylindrical tube 20 at a constant dose rate towards the patient B. The pusher device 11 herein is driven by a suitable driving mechanism comprising an electric drive (not shown) controlled by the processor device 15.

(20) For pushing the piston 21 into the cylindrical tube 20, the piston 21 via its piston head 210 is operatively connected to the pusher device 11 via an anti-siphon arm 17 mounted on the pusher device 11. The anti-siphon arm 17 is pivotably mounted via a shaft 170 on a sensor support 18 of the sensor device 14. The shaft 170, for this, is mounted on a support member 181 integrally connected with the sensor support 18 such that the shaft 170 is pivotable with respect to the support member 181, and in addition is axially displaceable along its pivoting axis (by at least a small margin).

(21) The shaft 170 is pretensioned with respect to the support member 181 via a spring element 171 providing a spring elastic force axially on the shaft 170. The anti-siphon arm 17 herein is pivotable from a non-activated, released position in which the anti-siphon arm 17 does not act onto the piston head 210 for connecting it to the pusher device 11 into an activated position in which the anti-siphon arm 17 is pivoted in the pivoting direction P to act onto the piston head 210. In the activated position the anti-siphon arm 17 exerts a force axially onto the piston head 210 along the pivoting axis, caused by the spring element 171, in order to press the piston head 210 into abutment with a pressure transmitting element 19 which is elastically supported, via a spring element 190, on a front face 180 of the sensor support 18 of the sensor device 14 and acts onto the sensor device 14 to transmit a pressure towards the sensor device 14.

(22) The pressure transmitting element 19 is sealed with respect to the housing 110 of the pusher device 11 by means of a sealing membrane 112 extending from the pressure transmitting element 19 and surrounding the pressure transmitting element 19. The inside of the housing 110 of the pusher device 11 hence is closed towards the outside to prevent entrance of moisture and dirt.

(23) The piston 21 is, via the pressure transmitting element 19, in operative abutment on the sensor device 14 such that the sensor device 14 may measure a force exerted on the piston head 210 of the piston 21 by means of the pusher device 11. The sensor support 18 is mounted within the housing 110 a means of a mounting element 111 such that the sensor support 18 is fixedly connected to the housing 110 of the pusher device 11.

(24) As described above, via the force sensor 14 the force acting onto the piston 21 is measured, thus allowing for estimating the pressure within the cylindrical tube 20 and within the delivery line 3, such that an occlusion in the delivery line 3 can be detected by observing the pressure.

(25) The sensor device 14, in the illustrated embodiment, has the shape of a load cell, the sensor support 18 being formed by an integral metal body made for example from aluminum and having a front face 180 on which an arrangement of sensor elements 140 is placed, as depicted in FIGS. 3 and 4. The sensor elements 140 in the shape of strain gauges or extension gauges may be electrically connected, as shown in FIG. 4, to form a Wheatstone bridge having nodes C1, C2 in between which an electric voltage signal can be obtained, the voltage signal being proportional to the force exerted on the sensor device 14.

(26) When a force is exerted on the sensor device 14, the sensor support 18 will be elastically deformed, which will lead to a stretching of some of the sensor elements 140 and to a contracting of the other sensor elements 140. Such stretching/contracting causes a voltage signal in between the nodes C1, C2, which can be picked up and can be used to derive a force measurement.

(27) Within such load cells, a drift may occur, caused by a varying temperature or by aging effects over the lifetime of the sensor device 14. Such drift may have an effect on the accuracy of a force measurement, such that a drift should be detected and potentially be corrected.

(28) Herein, two different kinds of drifts may occur, namely a zero drift and a span drift. The zero drift occurs when no force is exerted on the sensor device 14. The span drift, in contrast, occurs when a force is exerted on the sensor device 14.

(29) To be able to detect a drift of the sensor signal, it is proposed to perform a diagnosis routine which enables the infusion device 1 to detect a drift and potentially correct a drift.

(30) Herein, different diagnosis routines may be carried out, the different diagnosis routines allowing to detect a zero drift on the one hand and a span drift on the other hand.

(31) In a first diagnosis routine, a sensor signal of the sensor device 14 is obtained when no syringe 2 is arranged on the infusion device 1 such that the pusher device 11 is not in operative connection with a piston 21 of a syringe 2. In this case the sensor device 14 is not loaded, such that the sensor signal of the sensor device 14 should be at or at least close to a stored zero reference, namely the reference sensor signal of the sensor device 14 while the sensor device 14 is not subjected to force. If it is found that the sensor signal obtained during the first diagnosis routine deviates from the stored zero reference by more than an allowable margin, the zero reference can be corrected making use of the obtained sensor signal, wherein in a first variant the stored zero reference may simply be replaced by the actually obtained sensor signal or in a second variant the stored zero reference may be updated making use for example of an infinite impulse response (IIR) filter.

(32) During the first diagnosis routine, the obtained sensor signal is compared to the stored zero reference. Herein it can be checked whether the obtained sensor signal lies outside of a range around the stored zero reference. If this is the case, the zero reference is updated.

(33) The first diagnosis routine is carried out controlled by the control device 15, which is programmed by software to perform the first diagnosis routine. The first diagnosis routine herein is carried out while no infusion operation is performed and, beneficially, while no syringe 2 is placed on the infusion device 1.

(34) The infusion device 1 can automatically detect if a syringe 2 is placed on the infusion device 1 or not, for example by sensing the position of the anti-siphon arm 17. The first diagnosis routine may for example be carried out only if the anti-siphon arm 17 is in the non-activated, released position.

(35) Alternatively or in addition, the control device 15 may be programmed to carry out a second diagnosis routine to detect a span drift of the sensor device 14. This second diagnosis routine is carried out when a syringe 2 is placed on the infusion device 1 and when the piston 21 of the syringe 2 is in operative connection with the pusher device 11 by fixing the piston 21 to the pusher device 11 via the anti-siphon arm 17.

(36) For fixing the piston 21 to the pusher device 11, the anti-siphon arm 17 is pivoted in the pivoting direction P around its pivoting axis such that the anti-siphon arm 17 acts onto the piston head 21 and presses it axially towards the pusher device 11. In the fully activated position, herein, the anti-siphon arm 17 will press the piston head 210 with a defined force towards the pressure transmitting element 19 and hence towards the sensor device 14, the defined force being determined by the elastic tensioning force of the spring element 171 which elastically tensions the shaft 170 axially with respect to the sensor support 18.

(37) Since the force of the anti-siphon arm 17 is defined and will be (approximately) constant, the sensor device 14 should, when the piston head 210 is fixed to the pusher device 11, pick up a constant force measurement (at least as long as no infusion operation is being performed and the force hence is due solely to the connection force caused by the anti-siphon arm 17). If it is found that this force measurement varies, it therefore can be concluded that a span drift in the sensor device 14 is present.

(38) Hence, during the second diagnosis routine, with the piston head 210 fixed to the pusher device 11 via the anti-siphon arm 17, a sensor signal is obtained and compared to an expected sensor signal, the expected sensor signal corresponding to the predefined force by which the anti-siphon arm 17 presses the piston head 210 towards the sensor device 14. If it is found that the obtained sensor signal substantially deviates from the expected sensor signal, it can be concluded that a span drift is present.

(39) Herein, dependent on the amount of the deviation, different measures can be taken.

(40) If the deviation is small, the deviation can simply be recorded and logged in a log file.

(41) If the deviation is substantial, but not excessive, a message may be generated advising a user that maintenance should be carried out. Such message can for example be electronically sent (via the Internet) to a maintenance service outside of the healthcare institution, for example of a manufacturer of the infusion device 1, such that the maintenance service may be ordered to perform a maintenance.

(42) If the deviation is large, as the most severe countermeasure a further operation of the infusion device 1 may be prohibited, because a force measurement may no longer be reliable and hence an occlusion may not reliably be detected. In this case also a high priority alarm may be triggered.

(43) The expected sensor signal for the second diagnosis routine may for example be known from calibration. In particular, by calibration the force by which the antis anti-siphon arm 17 presses the piston head 210 towards the sensor device 14 can be measured and a corresponding expected sensor signal can be stored.

(44) It can be provided that the second diagnosis routine is carried out only when the anti-siphon arm 17 is fully activated and hence, in a defined fashion, presses the piston head 210 towards the sensor device 14.

(45) To increase reliability of the second diagnosis routine, the measurements can be repeated multiple times, wherein a countermeasure is initiated only if consecutive diagnosis measurements yield a mismatch of the obtained sensor signal from the expected sensor signal.

(46) The second diagnosis routine can also be used to detect a failure of the sensor device 14 due to other effects than a drift. If for example the sensor device 14 with its sensor elements 140 arranged to form a Wheatstone bridge comprises a shortcut or an open circuit, this would be detected during the second diagnosis routine.

(47) The idea underlying the invention is not limited to the embodiments described above, but may be carried out in an entirely different fashion.

(48) In particular, diagnosis routines as proposed above are not limited to infusion devices in the shape of syringe pumps, but may be carried out also on other infusion devices such as volumetric (peristaltic) infusion pumps.

(49) Also, the pumping mechanism of a syringe pump may have a different shape than described above. Similar diagnosis routines may be applied also in this case.

LIST OF REFERENCE NUMERALS

(50) 1 Infusion device

(51) 10 Housing

(52) 100 Front face

(53) 11 Pusher device

(54) 110 Housing

(55) 111 Mounting element

(56) 112 Membrane

(57) 12 Receptacle

(58) 13 Display device

(59) 14 Force sensor

(60) 140 Sensor element

(61) 15 Processor device

(62) 16 Storage device

(63) 17 Anti-siphon arm

(64) 170 Shaft

(65) 171 Spring element

(66) 18 Sensor support

(67) 180 Front face

(68) 181 Support member

(69) 19 Pressure transmitting element

(70) 190 Spring element

(71) 2 Pumping device (syringe)

(72) 20 Cylindrical tube

(73) 21 Piston

(74) 3 Delivery line

(75) 30, 31 End

(76) A Actuation direction

(77) B Patient

(78) C1, C2 Nodes

(79) O Occlusion

(80) P Pivoting direction