Infusion device constituted to detect an abnormal condition during bolus injection

Abstract

Infusion device constituted to detect an abnormal condition during bolus injection An infusion device (1) for administering a medical fluid to a patient (4) comprises a pumping mechanism (12) for pumping a medical fluid through an infusion line (3) towards a patient (4), a sensor device (120) for measuring a measurement value indicative of a pressure in the infusion line (3), and a control device (13) being constituted to control the pumping mechanism (12) for injecting a bolus of medical fluid into the infusion line (3). Herein, the control device (13) is constituted to determine, dependent on an injection of a bolus into the infusion line (3), a control parameter taking a change in pressure during injection of the bolus into account and to derive, from the control parameter, the presence of an abnormal condition during the injection of the bolus. In this way an infusion device is provided which in a reliable manner allows for the detection of an abnormal condition during the administration of a bolus.

Claims

1. An infusion device for administering a medical fluid to a patient, comprising: a pumping mechanism for pumping a medical fluid through an infusion line towards a patient, a sensor device for measuring a measurement value indicative of a pressure in the infusion line, and a control device configured to control the pumping mechanism for injecting a bolus of the medical fluid into the infusion line, the control device being configured to determine, dependent on an injection of the bolus into the infusion line, a control parameter taking a change in the pressure during the injection of the bolus into account and to derive, from the control parameter, a presence of an abnormal condition during the injection of the bolus, the abnormal condition being an occlusion in the infusion line, the sensor device being configured to measure a first measurement value at a first time at a start or prior to the injection of the bolus in order to derive the pressure in the infusion line at the first time, and to measure a second measurement value at a second time at an end of or after the injection of the bolus in order to derive the pressure in the infusion line at the second time, and the control device being configured to determine the control parameter according to an equation taking a difference in the pressure between the first time and the second time, a volume of the bolus, and an expected slope during a pressure rise in case of an occluded infusion line into account, wherein a quotient of the difference in the pressure and the volume of the bolus corresponds to an actual slope.

2. The infusion device according to claim 1, further comprising an input device configured to allow a user to request the bolus, the control device configured to control the pumping mechanism for injecting the bolus of the medical fluid into the infusion line upon a user's request input via the input device.

3. The infusion device according to claim 1, wherein the control device is configured to determine the control parameter according to the equation $C=\frac{P\left(t_2\right)\left[\mathrm{bar}\right]-P\left(t_1\right)\left[\mathrm{bar}\right]}{V_{\mathrm{Bolus}}\left[\mathrm{ml}\right].Math.\mathrm{Expected\_Slope}\left[\mathrm{bar}/\mathrm{ml}\right]}$ wherein C is the control parameter, P(t.sub.1) is the pressure in the infusion line at the first time and P(t.sub.2) is the pressure in the infusion line at the second time, V.sub.Bolus is the volume of the injected bolus, and Expected_Slope corresponds to the expected slope during a pressure rise in case of an occluded infusion line.

4. The infusion device according to claim 1, wherein the expected slope is determined taking a compliance of a syringe, a compliance of the infusion line, a stiffness of the pumping mechanism and/or a dimension of a cylindrical tube into account.

5. The infusion device according to claim 4, further comprising a storage device, wherein values for the compliance of the syringe, the compliance of the infusion line, the stiffness of the pumping mechanism and/or the dimension of the cylindrical tube are stored in the storage device of the infusion device for at least one syringe used on the infusion device.

6. The infusion device according to claim 1, wherein the control device is configured to conclude the presence of an abnormal condition during the injection of the bolus if the control parameter is larger than a first bound and/or is smaller than a second bound greater than the first bound.

7. The infusion device according to claim 6, wherein the first bound is 0.5, and/or the second bound is 1.5.

8. The infusion device according to claim 1, further comprising an output device for outputting an alarm message, wherein the control device is configured to trigger the output of an alarm message in case it is derived that an abnormal condition during the injection of the bolus is presented.

9. The infusion device according to claim 1, wherein the abnormal condition corresponds to a closed stopcock preventing flow through the infusion line.

10. The infusion device according to claim 1, wherein the infusion device is a syringe pump.

11. A method of operating an infusion device for administering a medical fluid to a patient, the method comprising: injecting a bolus of a medical fluid into an infusion line, measuring a measurement value indicative of a pressure in the infusion line, and determining, dependent on an injection of the bolus into the infusion line, a control parameter taking a change in the pressure during the injection of the bolus into account and deriving, from the control parameter, a presence of an abnormal condition during the injection of the bolus, the abnormal condition being an occlusion in the infusion line, the step of measuring a measurement value comprising measuring a first measurement value at a first time at a start or prior to the injection of the bolus in order to derive the pressure in the infusion line at the first time, and measuring a second measurement value at a second time at an end of or after the injection of the bolus in order to derive the pressure in the infusion line at the second time, and the step of determining the control parameter comprising determining the control parameter according to an equation taking a difference in pressure between the first time and the second time, a volume of the bolus, and an expected slope during a pressure rise in case of an occluded infusion line into account, wherein a quotient of the difference in the pressure and the volume of the bolus corresponds to an actual slope.

12. An infusion device for administering a medical fluid to a patient, comprising: a pumping mechanism for pumping a medical fluid through an infusion line towards a patient, a sensor device for measuring a measurement value indicative of a pressure in the infusion line, and a control device configured to control the pumping mechanism for injecting a bolus of the medical fluid into the infusion line, the control device being configured to determine, dependent on an injection of the bolus into the infusion line, a control parameter taking a change in the pressure during the injection of the bolus into account and to derive, from the control parameter, a presence of an abnormal condition during the injection of the bolus, the sensor device being configured to measure a first measurement value at a first time at a start or prior to the injection of the bolus in order to derive the pressure in the infusion line at the first time, and to measure a second measurement value at a second time at an end of or after the injection of the bolus in order to derive the pressure in the infusion line at the second time, the control device being configured to determine the control parameter according to an equation taking the difference in pressure between the first time and the second time, a volume of the bolus, and an expected slope during a pressure rise in case of an occluded infusion line into account, and the control device being configured to determine the control parameter according to the equation $C=\frac{P\left(t_2\right)\left[\mathrm{bar}\right]-P\left(t_1\right)\left[\mathrm{bar}\right]}{V_{\mathrm{Bolus}}\left[\mathrm{ml}\right].Math.\mathrm{Expected\_Slope}\left[\mathrm{bar}/\mathrm{ml}\right]}$ wherein C is the control parameter, P(t.sub.1) is the pressure in the infusion line at the first time and P(t.sub.2) is the pressure in the infusion line at the second time, V.sub.Bolus is the volume of the injected bolus, and Expected_Slope corresponds to the expected slope during a pressure rise in case of an occluded infusion line.

13. The infusion device according to claim 12, further comprising an input device configured to allow a user to request the bolus, the control device configured to control the pumping mechanism for injecting the bolus of the medical fluid into the infusion line upon a user's request input via the input device.

14. The infusion device according to claim 12, wherein the expected slope is determined taking a compliance of a syringe, a compliance of the infusion line, a stiffness of the pumping mechanism and/or a dimension of a cylindrical tube into account.

15. The infusion device according to claim 14, further comprising a storage device, wherein values for the compliance of the syringe, the compliance of the infusion line, the stiffness of the pumping mechanism and/or the dimension of the cylindrical tube are stored in the storage device of the infusion device for at least one syringe used on the infusion device.

16. The infusion device according to claim 12, wherein the control device is configured to conclude the presence of an abnormal condition during the injection of the bolus if the control parameter is larger than a first bound and/or is smaller than a second bound greater than the first bound.

17. The infusion device according to claim 16, wherein the first bound is 0.5, and/or the second bound is 1.5.

18. The infusion device according to claim 12, further comprising an output device for outputting an alarm message, wherein the control device is configured to trigger the output of an alarm message in case it is derived that an abnormal condition during the injection of the bolus is presented.

19. The infusion device according to claim 12, wherein the abnormal condition corresponds to a closed stopcock preventing flow through the infusion line.

20. The infusion device according to claim 12, wherein the infusion device is a syringe pump.

Description

(1) The idea underlying the invention shall subsequently be described in more detail with respect to the embodiments shown in the FIGURES. Herein:

(2) FIG. 1 shows a view of an embodiment of an infusion device in the shape of a syringe pump.

(3) FIG. 1 shows an embodiment of an infusion device 1 in the shape of a syringe pump having a housing 10 and a receptacle 11 arranged on the housing 10 to receive a syringe 2 therein.

(4) The syringe 2 comprises a cylindrical tube 20 which, when installing the syringe 2 on the infusion device 1, contains a medical liquid, for example a medication, to be infused to a patient 4. The cylindrical tube 20 is connected, via a connector 200, to an infusion line 3 which may extend from the syringe 2 towards a patient 4 for infusing the medical liquid to the patient 4.

(5) For installing the syringe 2 on the receptacle 11 of the infusion device 1, the cylindrical tube 20 of the syringe 2 is placed in the receptacle 11 and is mechanically connected to the housing 10 by means of a fixation device 110. By means of the fixation device 110, for example constituted by a releasable clamp element, the cylindrical tube 20 is secured within the receptacle 11 such that the cylindrical tube 20 is held in position on the receptacle 11.

(6) The syringe 2 comprises a piston 21 which, for delivering medical fluid contained in the cylindrical tube 20, can be pushed into the cylindrical tube 20 in a pushing direction X. For this, the infusion device 1 comprises a pumping mechanism in the shape of a pusher device 12 movably arranged within a guide device 120 and connected to a suitable drive mechanism via a connecting rod 121.

(7) For operating the infusion device 1, the syringe 2 is installed on the infusion device 1 and, for performing an infusion process, the pusher device 12 is electrically moved, controlled by a control device 13 of the infusion device 1, in the pushing direction X to move the piston 21 into the cylindrical tube 20 for delivering the medical fluid contained in the cylindrical tube 20 via the infusion line 3 towards the patient 4.

(8) Generally, if during an infusion process an occlusion occurs on the infusion line 3 connected to the cylindrical tube 20 of the syringe 2, the pressure in the infusion line will rise. To detect an occlusion, hence, the pressure in the infusion line 3 can be observed, and when an abnormal rise in pressure is found it can be concluded that an occlusion is present.

(9) To observe the pressure in the infusion line 3, the force applied to the piston head 210 of the piston 21 by means of the pusher device 12 is measured by a sensor device 14 in the shape of a force sensor placed on the pusher device 12 facing the piston head 210. 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 infusion line 3.

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

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

(12) 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. 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 may vary in dependence on the specific syringe 2 used on the system and may additionally depend on the position of the piston 21 within the cylindrical tube 20 and on the velocity by which the piston 21 is moved relative to the cylindrical tube 20 during an infusion process. For the frictional force component F.sub.0 for example a constant may be assumed, or a mathematical model may be used to determine the frictional force component F.sub.0 for a particular syringe 2.

(13) By determining the pressure P in this way and for example by comparing the determined pressure P to a predefined threshold it can be concluded whether an occlusion is present in the infusion line 3 or not. If it for example is found that the pressure P rises above the threshold, it is concluded that an occlusion is present.

(14) An occlusion or another flow interruption (due for example to a closed stopcock 30 placed on the infusion line 3) in a particular system will generally cause a rise of the measured force according to a rather well-defined slope, which can be determined when mechanical characteristics of the system such as the compliance of the infusion line 3, the compliance of the syringe 2 and the stiffness of the mechanical system of the pusher device 12 are known.

(15) The expected slope is the theoretical slope that the pressure should follow in case the line is occluded at the catheter level. It depends on: the flowrate, the syringe mechanical properties (especially the syringe stopper stiffness), the syringe pump mechanical properties (especially the pusher stiffness), the infusion line mechanical properties (the tube compliance). the fluid properties (which can be neglected if it is assumed that the fluid to be pumped is an incompressible liquid).

(16) The pressure slope can either be expressed referring to time or referring to volume. Expressing the expected slope with reference to volume, the expected slope at a position i during movement of the piston 21 of the comes out to be:

(17) $\mathrm{Expected\_slope}\left(i\right)\left[\mathrm{bar}/\mathrm{ml}\right]=\frac{\mathrm{dP}\left(i\right)\left[\mathrm{bar}\right]}{\mathrm{dVolume}\left(i\right)\left[\mathrm{ml}\right]}$

(18) The expected slope is equivalent to a volumetric stiffness, which is the inverse of the system compliance. One can therefore write

(19) $\frac{1}{\mathrm{Volumetric\_Stiffness}\left[\mathrm{bar}/\mathrm{ml}\right]}=\underset{k=1}{\overset{3}{.Math.}}\frac{1}{\mathrm{Volumetric\_Stiffness}\left(k\right)\left[\mathrm{bar}/\mathrm{ml}\right]}$$\mathrm{Where}\{\begin{array}{c}\mathrm{Volumetric\_Stiffness}\left(1\right)\left[\mathrm{bar}/\mathrm{ml}\right]=\frac{1}{\mathrm{Syringe\_Compliance}\left[\mathrm{ml}/\mathrm{bar}\right]}\\ \mathrm{Volumetric\_Stiffness}\left(2\right)\left[\mathrm{bar}/\mathrm{ml}\right]=\frac{1}{\mathrm{Line\_Compliance}\left[\mathrm{ml}/\mathrm{bar}\right]}\\ \mathrm{Volumetric\_Stiffness}\left(3\right)\left[\mathrm{bar}/\mathrm{ml}\right]=\frac{100.Math.\mathrm{Pusher\_Stiffness}\left[\mathrm{gf}/\mathrm{mm}\right]}{{\mathrm{Syringe\_Surface}\left[{\mathrm{mm}}^2\right]}^2}\end{array}$
and the expected slope comes out to be:

(20) $\mathrm{Expected\_slope}\left[\mathrm{bar}/\mathrm{ml}\right]=\frac{1}{\begin{array}{c}\mathrm{Syringe\_Compliance}\left[\mathrm{ml}/\mathrm{bar}\right]+\\ \mathrm{Line\_Complince}\left[\mathrm{ml}/\mathrm{bar}\right]+\\ \frac{{\mathrm{Syringe\_Surface}\left[{\mathrm{mm}}^2\right]}^2}{100.Math.\mathrm{Pusher\_Stiffness}\left[\mathrm{gf}/\mathrm{mm}\right]}\end{array}}$

(21) This can be converted to a slope by millimeter, assuming that for a different syringe 1 mm is equivalent to (syringe_Surface S [mm.sup.2]/1000) ml:

(22) $\mathrm{Expected\_slope}\left[\mathrm{bar}/\mathrm{mm}\right]=\frac{\mathrm{Synringe\_Surface}\left[{\mathrm{mm}}^2\right]}{\begin{array}{c}1000.Math.(\mathrm{Syringe\_Compliance}\left[\mathrm{ml}/\mathrm{bar}\right]+\\ \mathrm{Line\_Compliance}\left[\mathrm{ml}/\mathrm{bar}\right])+10.Math.\\ \frac{{\mathrm{Syringe\_Surface}\left[{\mathrm{mm}}^2\right]}^2}{\mathrm{Pusher\_Stiffness}\left[\mathrm{gf}/\mathrm{mm}\right]}\end{array}}$

(23) This also can be converted to gf/mm. Assuming that for a given syringe F [gf]=10.2*P [bar]*S [mm.sup.2], the slope in bar/mm can be converted into a slope in gf/mm:

(24) $\mathrm{Expected\_slope}\left[\mathrm{gf}/\mathrm{mm}\right]=\frac{0.0102.Math.{\mathrm{Syringe\_Surface}\left[{\mathrm{mm}}^2\right]}^2}{\begin{array}{c}(\mathrm{Syringe\_Compliance}\left[\mathrm{ml}/\mathrm{bar}\right]+\\ \mathrm{Line\_Compliance}\left[\mathrm{ml}/\mathrm{bar}\right])+\\ \frac{{\mathrm{Syringe\_Surface}\left[{\mathrm{mm}}^2\right]}^2}{\mathrm{Pusher\_Stiffness}\left[\mathrm{gf}/\mathrm{mm}\right]}\end{array}}$

(25) Example parameter values for a 5 cc syringe of a particular brand and a particular infusion device are summarized in Table 3:

(26) TABLE-US-00001 TABLE 3 Parameter Value Syringe_Compliance 0.0566 ml/bar Line_Compliance 0.145 ml/bar Pusher_Stiffness 9279 gf/mm Syringe inner diameter 11.87 mm Syringe surface S 110.66 mm.sup.2

(27) Using these parameters, the following values for the expected slope are obtained: Expected_Slope [bar/ml]=4.65 [bar/ml] Expected_Slope [bar/mm]=0.514 [bar/mm] Expected_Slope [gf/mm]=568.8 [gf/mm]

(28) This expected slope is independent of the flow rate.

(29) Thus, it can be assumed that, in the above case, the expected slope in case of an occlusion will be close to 0.5 bar/mm for the particular syringe and the particular infusion device for which the parameters are valid.

(30) The expected slope may for example be computed for the particular parameters of the infusion line 3, the syringe 2 and the device 1 in use upon installation of a particular syringe 2 in connection with an infusion line 3 on the infusion device 1. In test measurements it was found that the expected slope in case of an occlusion is well distinguished from any slope that usually arises during a normal infusion process when no occlusion is present.

(31) In order to allow the computation of the expected slope, the infusion device 1 comprises a storage device 130, for example in the shape of a database, in which relevant parameters of different syringes 2 and infusion lines 3 which potentially may be used on the infusion device 1 are stored. In the storage device 130 in particular a syringe compliance for one or multiple syringes 2, a line compliance for one or multiple infusion lines 3, a pusher stiffness of the pusher device 12 (including its driving mechanism), and geometric data of one or multiple syringes 2, in particular an inner diameter of the cylindrical tube 20, may be stored. Hence, upon identification of a particular syringe 2 and a particular infusion line 3 by a user, for example by inputting suitable control data into the infusion device 1 upon installation of the syringe 2 and the infusion line 3 on the infusion device 1, the expected slope can be computed and can be used as it shall be described subsequently.

(32) Knowing the expected slope, generally an occlusion can be detected by comparing the actual slope of a pressure rise in the infusion line 3 to the expected slope. In addition and independent of the occlusion detection during an infusion process using the expected slope it can be detected whether during the injection of a bolus an abnormal condition, in particular an occlusion in the infusion line 3 or a closed stopcock 30, exist.

(33) Boluses may be injected into the infusion line 3 independent of an ongoing infusion operation. The injection of boluses may for example be triggered by the patient 4 him- or herself, for example by pressing a suitable button 100 on the infusion device 1, causing the control device 13 to initiate injection of a bolus (i.e., the administration of a discrete amount of the medical fluid contained in the cylindrical tube 20 to the patient 4) by correspondingly moving the pusher device 12 by a predefined distance.

(34) Herein, the following scenario may occur:

(35) A patient 4 may, overnight, request multiple boluses by pressing the button 100 on the infusion device 1. If a nurse erroneously has left the stopcock 30 closed on the infusion line 3, the pusher device 12 may upon the repeated requests of boluses be moved, but the medical fluid may not flow from the cylindrical tube 20 through the infusion line 3 due to the closed stopcock 30. If the overall volume of the multiple boluses does not cause the pressure within the infusion line 3 to exceed the predefined occlusion threshold, no occlusion alarm may be triggered. If then a nurse in the morning detects that the stopcock 30 is closed and opens the stopcock 30, this may cause the administration of the overall volume of the repeated boluses to the patient 4 at once, which may be hazardous.

(36) Hence, there is a desire to detect an abnormal condition during the administration of a bolus, independent of an occlusion detection during a regular infusion process.

(37) For this, a pressure rise during the injection of a bolus is monitored. For example, the pressure at the beginning or (immediately) prior to the beginning of the injection of the bolus may be obtained by a reading of the force sensor 14 in order to determine a first pressure value, and the pressure in the infusion line 3 at the end or (immediately) after the administration of the bolus may be determined by another reading of the force sensor 14 an order to obtain a second pressure value. From the difference of the second pressure value and the first pressure value a value for the rise in pressure during the injection of the bolus is obtained. By dividing the pressure difference by the defined volume of the injected bolus, an actual slope (pressure per volume) is obtained, which may be compared to the expected slope computed as described above in order to conclude whether an abnormal condition is present during the injection of the bolus.

(38) If it is found that the actual slope of the pressure rise is at or at least close to the expected slope, it can be concluded that likely an occlusion on the infusion line 3, for example due to a closed stopcock 30, is present, such that an alarm message or at least a warning message may be triggered and for example output as a text message via a display device 101 of the infusion device 1.

(39) In particular, the following equation may be used to compute a control parameter:

(40) $C=\frac{P\left(t_2\right)\left[\mathrm{bar}\right]-P\left(t_1\right)\left[\mathrm{bar}\right]}{V_{\mathrm{Bolus}}\left[\mathrm{ml}\right].Math.\mathrm{Expected\_Slope}\left[\mathrm{bar}/\mathrm{ml}\right]}$

(41) Herein, C is the control parameter, P(t.sub.1) is the pressure in the infusion line 3 at a first time at the beginning or prior to the administration of the bolus and P(t.sub.2) is the pressure in the infusion line 3 at a second time at the end or after the administration of the bolus. V.sub.Bolus is the volume of the injected bolus, and Expected_Slope corresponds to the expected slope during a pressure rise in case of an occluded infusion line computed as described above.

(42) If the actual slope is close to the expected slope, the control parameter will assume a value close to 1. Hence, by monitoring whether the control parameter falls into a range around 1 it can be concluded whether an abnormal condition similar to an occlusion is present during the injection of the bolus.

(43) The lower bound for the range may for example be 0.5, whereas the upper bound of the range may for example be a 1.5. Hence, if the control parameter falls into a range bounded by 0.5 and 1.5, it is concluded that an abnormal condition similar to an occlusion is present during the injection of the bolus.

(44) It is to be understood that the bounds given are merely examples. The bounds may be suitably adjusted. For example, the lower bound may be in a range between 0.4 and 0.9, for example at 0.8, whereas the upper bound may be in a range between 1.1 and 1.6, for example at 1.2.

(45) If it is found that the control parameter falls into the noted range, a suitable message may be output for example via the display device 101. In this way for example a nurse may be informed that during the request of a bolus the infusion line 3 has been interrupted, for example due to a closed stopcock 30, which the nurse may then take into account in the decision whether to open the stopcock 30 or not.

(46) The invention is not limited to the embodiments described above, but may be implemented also in an entirely different fashion.

(47) For example, a similar procedure as described above in order to detect an abnormal condition during the injection of a bolus may also be applied on an infusion device in the shape of a volumetric (peristaltic) infusion pump.

(48) The expected slope may be determined in a different way, for example in a calibration measurement on a particular syringe and a particular infusion line. The described procedure hence only serves as an example.

LIST OF REFERENCE NUMERALS

(49) 1 Infusion device 10 Housing 100 Input device 101 Output device (display device) 11 Receptacle 110 Fixation device 12 Pumping mechanism (pusher device) 120 Guide device 121 Connecting rod 13 Control device 130 Storage device 14 Sensor device 2 syringe 20 Cylinder tube 200 Connector 21 Piston 210 Piston head 3 Infusion line 30 Stopcock 4 Patient X Movement direction