Method and device for sensing the detachment of the venous needle from a patient during dialysis

• US 20030176829A1
• Filed: 02/14/2003
• Published: 09/18/2003
• Est. Priority Date: 06/15/2001
• Status: Active Grant

• Current Assignee: Gambro Lundia AB (Baxter International Inc.)
• Original Assignee: Gambro Lundia AB (Baxter International Inc.)
• Inventors: Lodi, Carlo Alberto, Canini, Enrico, Francesco, Paolini
• Granted Patent: US 7,060,047 B2
• Time in Patent Office: Days
• US Class Current: 604/4.01
• CPC Class Codes: A61M 1/3653 Interfaces between patient blood circulation and extra-corporal blood circuit
• CPC Class Codes: A61M 1/3655 Arterio-venous shunts or fistulae
• CPC Class Codes: A61M 1/3656 Monitoring patency or flow at connection sites; Detecting disconnections
• CPC Class Codes: A61M 1/3669 Electrical impedance measurement of body fluids; transducers specially adapted therefor
• CPC Class Codes: A61M 1/367 Circuit parts not covered by the preceding subgroups of group A61M1/3621
• CPC Class Codes: A61M 2039/1005 Detection of disconnection
• CPC Class Codes: A61M 2205/12 with interchangeable cassettes forming partially or totally the fluid circuit
• CPC Class Codes: A61M 5/16831 Monitoring, detecting, signalling or eliminating infusion flow anomalies low-level float-valves causing cut-off A61M5/40; indicating or recording presence, absence or direction of flow in general G01P13/0066

Abstract

A method of sensing the detachment of the venous needle (13) from a patient (P) during an extracorporeal blood treatment in a dialysis machine (1) having an extracorporeal blood circuit (2), in which an electric current is made to flow along a closed-loop path (P1) of an electrical circuit (37) formed by an electrical line (21, 22, 23) external to the extracorporeal circuit (2), a portion of extracorporeal circuit (2) directly connected to the venous needle (13), and the patient (P); a signal correlated with the electric current along the electrical line (21, 22, 23) is detected; and the signal is compared with a threshold value by means of a control unit (15).

Claims

1. Method for sensing the access to the cardiovascular system of a patient (P) during an extracorporeal blood treatment in a dialysis machine (1) comprising an extracorporeal blood circuit (2) provided with a venous branch (10) comprising a venous needle (13) for accessing the cardiovascular system of the patient (P), the said method being characterized in that it comprises the steps of:

making an electric current flow along an annular path (P1) of an electrical circuit (37) formed by an electrical line (21, 22, 23) external to the extracorporeal circuit (2), a portion of the venous branch (10), and the patient (P);

sensing a signal correlated with the electric current along the said electrical line (21, 22, 23); and

comparing the said signal with a threshold value to detect the opening of the said electrical circuit (37) by the use of signal processing means (15).

2. Method according to claim 1, characterized in that the venous branch (10) extends between a filter (4) and the venous needle (13);

the extracorporeal circuit (2) comprising a dropper (11) located in the said venous branch (10);

the said portion of the venous branch (10) lying between the said dropper (11) and the venous needle (13).

3. Method according to claim 1 or 2, characterized in that the said patient (P) and one end of the said electrical line (21, 22, 23) are connected to earth.

4. Method according to claim 1 or 2, characterized in that an alternating current is made to flow at a relatively high frequency in such a way that the patient (P) and the earth are equivalent to the opposing plates of a capacitor, and in that one end of the said electrical line (21, 22, 23) is earthed.

5. Method according to claim 3, characterized in that the said frequency is greater than 10 kHz.

6. Method according to any one of the preceding claims, characterized in that the said electrical line (21, 22, 23) comprises a first and a second branch (22, 23) and a voltage source (21) located between the first and the second branch (22, 23), the method providing for the detection of the said signal in the second branch (23).

7. Method according to claim 6, characterized in that the said signal is a voltage signal measured across the terminals of an impedance (Z3) located in the second branch (23).

8. Method according to any one of the preceding claims, characterized in that slow variations of the said signal, particularly those with a frequency of less than one per second, are filtered out.

9. Method according to any one of the preceding claims, characterized in that the efficiency of the electrical line (21, 22, 23) and of the signal processing means (15) is tested.

10. Method according to claim 9, characterized in that the electrical line (21, 22, 23) is disconnected from the venous branch (10) and the said electrical line (21, 22, 23) is connected, selectively, to a first test impedance (Z4) equivalent to the total impedance of the portion of the venous branch (10) and the patient (P) with the venous needle (13) connected, and to a second test impedance (Z5) equivalent to the total impedance of the portion of the venous branch (10) and the patient (P) with the venous needle (13) disconnected, in such a way as to simulate the detachment of the venous needle (13).

11. Method according to any one of the preceding claims, characterized in that the said electrical line (21, 22, 23) is connected to the venous branch (10) by a capacitive coupling.

12. Method according to claim 11, characterized in that the said capacitive coupling comprises an electrode (35) provided with a ring (36) placed around the said venous branch (10), the ring (36) and the blood corresponding to the plates of a capacitor.

13. Device for sensing the detachment of the venous needle (13) from a patient (P) during an extracorporeal blood treatment in a dialysis machine (1) comprising an extracorporeal blood circuit (2) provided with a venous branch (10) connected to the venous needle (13) for accessing the cardiovascular system of the patient (P) , the said device (14) being characterized in that it comprises:

an electrical line (21, 22, 23) external to the extracorporeal circuit (2), to form, in combination with a portion of the venous branch (10) and the patient (P), an electrical circuit (37) extending along a closed-loop path (P1);

a sensor (17) interacting with the electrical line (21, 22, 23) to detect a signal correlated with the current flowing in the said electrical circuit (37); and

means (15) of processing the said signal for sensing the opening of the said electrical circuit (37).

14. Device according to claim 13, characterized in that the venous branch (10) extends between a filter (4) and the venous needle (13), the extracorporeal circuit (2) comprising a dropper (11) located in the said venous branch (10), the said line (21, 22, 23) being connected at a single point to the said extracorporeal circuit (2), and the said point being located in the venous branch (10) between the said dropper (11) and the venous needle (13).

15. Device according to claim 13 or 14, characterized in that the said electrical line (21, 22, 23) is connected to earth, the said patient (P) also being connected to earth.

16. Device according to claim 13 or 14, characterized in that it comprises an alternating voltage generator (16) to supply an alternating current to the said circuit (37), the voltage having a relatively high frequency in such a way that the patient (P) and the earth are equivalent to the opposing plates of a capacitor, the said electrical line (21, 22, 23) being connected to earth.

17. Device according to claim 16, characterized in that the said voltage has a frequency of more than 10 kHz.

18. Device according to claims 13 to 17, characterized in that the said electrical line (21, 22, 23) comprises a first and a second branch (22, 23) and a voltage source (21) located between the first and the second branch (22, 23), the said sensor (17) being located in the second branch (23).

19. Device according to claim 18, characterized in that the said sensor (17) is a sensor of the voltage across the terminals of an impedance (Z3) located in the second branch (23), the said signal being a voltage signal.

20. Device according to any one of claims 13 to 19, characterized in that the said signal processing means (15) comprise a filter (30) for filtering the slow variations of the said signal, particularly the variations with a frequency of less than one per second.

21. Device according to any one of claims 13 to 20, characterized in that it comprises means (24, 25, 26) for testing the efficiency of the electrical line (21, 22, 23) and of the signal processing means (15).

22. Device according to claim 21, characterized in that the electrical line (21, 22, 23) comprises a selector (24) for disconnecting the electrical line (21, 22, 23) from the venous branch (10) and for selectively connecting the said electrical line (21, 22, 23) to a first test impedance (Z4) equivalent to the total impedance of the portion of the venous branch (10) and the patient (P) with the venous needle (13) connected, and to a second test impedance (Z5) equivalent to the total impedance of the portion of the venous branch (10) and the patient (P) with the venous needle (13) disconnected, in such a way as to simulate the detachment of the venous needle (13).

23. Device according to any one of claims 13 to 22, characterized in that it comprises a capacitive coupling for connecting the said electrical line (21, 22, 23) to the venous branch (10).

24. Device according to claim 23, characterized in that the said capacitive coupling comprises an electrode (35) provided with at least a ring (36) placed around the said venous branch (10), the ring (36) and the blood corresponding to the plates of a capacitor.

25. Device according to claim 24, characterized in that the capacitive coupling comprises a number of rings placed around the venous branch.

26. Device according to claim 23, characterized in that the venous branch includes a rigid box, made of transparent plastic material, the capacitive coupling comprising an electrode (35) defined by a plate conductive element placed in contact with said rigid box.