Infusion device with impedance measurement

1. An ambulatory infusion device for the infusion of a liquid drug into a patient's body over an extended time period, comprising:

a) an infusion cannula designed to be placed in the patient's subcutaneous tissue;

b) at least two subcutaneous electrodes, the at least two subcutaneous electrodes being comprised by the infusion cannula and being placeable in the subcutaneous tissue;

c) an impedance measuring unit, the impedance measuring unit being operatively coupled to the at least two electrodes and configured to measure at least one impedance value between the at least two electrodes, a variation of the at least one impedance value reflecting a displacement of interstitial fluid by drug upon drug administration;

d) an event trigger unit operatively coupled to the impedance measuring unit and being configured to evaluate the at least one impedance value and to generate an event trigger if evaluation of the at least one impedance value indicates the occurrence of an administration anomaly.

2. The ambulatory infusion device according to claim 1 , wherein the infusion device is configured to administer consecutive drug pulses, the impedance measuring unit is configured to measure consecutive impedance values, and wherein the event trigger unit is configured to generate an event trigger if evaluation of the consecutive impedance values indicates that a predefined number of consecutive drug pulses have not been administered.

3. The ambulatory infusion device according to claim 1 , wherein the impedance measuring unit is configured to monitor the at least one impedance value as a function of time and/or position and wherein the event trigger unit is configured to generate an event trigger if the at least one impedance value as a function of time and/or position indicates the occurrence of an administration anomaly.

4. The ambulatory infusion device according to claim 3 , wherein the event trigger unit is configured to detect the presence or absence of a characteristic temporary impedance value variation upon drug administration and to generate an event trigger in case of the absence of the temporary impedance value variation.

5. The ambulatory infusion device according to claim 1 further comprising a subcutaneous center electrode and a subcutaneous counter electrode, the subcutaneous center electrode being arranged in the center of an administration aperture of the infusion cannula and the subcutaneous counter electrode being arranged at the infusion cannula in a distance from the subcutaneous center electrode.

6. The ambulatory infusion device according to claim 1 further comprising a set of at least three subcutaneous electrodes.

7. The ambulatory infusion device according to claim 6 , wherein the at least three subcutaneous electrodes are comprised by the infusion cannula at different axial positions along the cannula axis.

8. The ambulatory infusion device according to claim 6 , wherein the impedance measuring unit is configured to measure at least two impedance values between the at least three subcutaneous electrodes.

9. The ambulatory infusion device according to claim 8 , wherein the event trigger unit is configured to detect if the at least two impedance values indicate the presence of a characteristic non-uniform impedance distribution along the cannula axis resulting from drug administration and to generate an event trigger if the at least two impedance values indicate the absence of the characteristic non-uniform impedance distribution.

10. The ambulatory infusion device according to claim 1 further comprising an upstream electrode arranged upstream from the infusion cannula.

11. Use of an infusion cannula in an ambulatory infusion device according to claim 1 , for subcutaneous drug infusion over an extended time period, wherein the infusion cannula comprises the at least two subcutaneous electrodes.

12. A method for administration supervision in an ambulatory infusion device for subcutaneous drug infusion over an extended time period, comprising the steps of:

a) measuring by an impedance measuring unit at least one impedance value between at least two subcutaneous electrodes, the at least two subcutaneous electrodes being comprised by an infusion cannula, a variation of the at least one impedance value reflecting a displacement of interstitial fluid by drug upon drug administration;

b) generating by an event trigger unit an event trigger if an evaluation of the at least one impedance value indicates the occurrence of an administration anomaly.

13. The method for administration supervision according to claim 12 further comprising generating an event trigger if the impedance value evaluation indicates that a predefined number of consecutive drug pulses has not been administered.

14. The method for administration supervision according to claim 12 further comprising detecting the presence of a characteristic temporary impedance value variation upon drug administration and generating an event trigger in case of the absence of the temporary impedance value variation.

15. The method for administration supervision according to claim 12 further comprising detecting the presence of a characteristic non-uniform impedance distribution along the cannula axis resulting from drug administration and generating an event trigger in case of the absence of the characteristic non-uniform impedance distribution.