Enhanced signal detection for access disconnection systems

1. An access disconnection system comprising: an extracorporeal circuit; a dialysate circuit; a first sensing apparatus configured to sense a first signal indicative of a first electrical impedance produced by fluid flowing through the extracorporeal circuit; and a second sensing apparatus configured to sense, in a parallel ground path, a second signal indicative of a second electrical impedance produced by a respective fluid flowing through the dialysate circuit and a portion of the extracorporeal circuit.

2. The access disconnection system of claim 1 , which includes first and second contacts provided in the extracorporeal circuit and a signal source communicating with at least one of the first and second contacts and configured to generate a signal within fluid flowing through the extracorporeal circuit.

3. The access disconnection system of claim 2 , wherein the signal generated by the signal source is split into the first and second signals.

4. The access disconnection system of claim 3 , wherein the second signal has at least one characteristic selected from the group consisting of: (i) being in parallel with the first signal; and (ii) being indicative of a patient's electrical potential relative to ground.

5. The access disconnection system of claim 1 , which includes a controller in communication with the first and second sensing apparatuses, the controller configured to monitor the first signal only for an access disconnection if the second signal is below a threshold.

6. The access disconnection system of claim 1 , which includes a controller in communication with the first and second sensing apparatuses, the controller configured to monitor the second signal only for an access disconnection if the second signal is above a threshold.

7. The access disconnection system of claim 1 , which includes a controller in communication with the first and second sensing apparatuses, the controller configured to monitor the first and second signals for an access disconnection.

8. The access disconnection system of claim 1 , wherein at least one of the first and second electrical impedances is a lumped electrical impedance.

9. The access disconnection system of claim 1 , wherein the fluid flowing through the extracorporeal circuit is at least substantially blood and the fluid flowing through the dialysis circuit is at least substantially dialysate.

10. An access disconnection system comprising:

an extracorporeal circuit;

a dialysate circuit;

an electrical path extending from the dialysate circuit to the extracorporeal circuit;

a signal source configured to induce a signal into the electrical path from the signal source;

a sensing apparatus configured to sense the signal, the signal indicative of an electrical impedance of the electrical path, including sensing the electrical impedance (i) in a parallel ground path or (ii) in the extracorporeal circuit and in the parallel ground path; and

an apparatus positioned at multiple points along the electrical path, and configured to create a virtual open circuit that prevents the signal induced into the electrical path by the signal source from flowing between the multiple points.

11. The access disconnection system of claim 10 , which includes a grounding device configured to bring a patient to ground, such that when the patient is connected to the extracorporeal circuit and to the grounding device, the electrical path extends from the extracorporeal circuit to ground.

12. The access disconnection system of claim 10 , which includes electronics configured to cause an alarm when the sensing apparatus senses an increase of electrical impedance due to a disconnection of a patient from the extracorporeal circuit.

13. The access disconnection system of claim 12 , wherein the increase of electrical impedance is due to the signal being shunted through a larger electrical impedance path of the extracorporeal circuit upon the access disconnection.

14. The access disconnection system of claim 10 , wherein the virtual open circuit is in the dialysate circuit.

15. The access disconnection system of claim 14 , wherein at least one of the signal source and sensing apparatus communicates with the electrical path at the dialysate circuit between the multiple points and the extracorporeal circuit.

16. An access disconnection system comprising: an extracorporeal circuit; a dialysate circuit; a signal source configured to initiate, at the dialysate circuit, a signal into the dialysate circuit; and a single sensing apparatus configured to sense the signal, the signal indicative of at least one electrical impedance in the extracorporeal circuit, at least one electrical impedance in a ground path between the extracorporeal circuit and the dialysate circuit, and at least one electrical impedance in the dialysate circuit.

17. The access disconnection system of claim 16 , which includes an apparatus positioned to apply a potential at multiple points along the dialysate circuit, the applied potential creating a virtual open circuit between the multiple points.

18. The access disconnection system of claim 17 , which includes an electrical path extending from the signal source located at one side of the multiple points, through the extracorporeal circuit, through a path to earth ground, through the dialysate circuit located at a second side of the multiple points, to isolated ground.