APPARATUS AND METHOD FOR DETECTING DISCONNECTION OF AN INTRAVASCULAR ACCESS DEVICE
An apparatus and method are disclosed for detecting the disconnection of a vascular access device such as a needle, cannula or catheter from a blood vessel or vascular graft segment. A pair of electrodes is placed in direct contact with fluid or blood in fluid communication with the vascular segment. In one embodiment, the electrodes are incorporated into a pair of connectors connecting arterial and venous catheters to arterial and venous tubes leading to and from an extracorporeal blood flow apparatus. Wires leading from the electrodes to a detecting circuit can be incorporated into a pair of double lumen arterial and venous tubes connecting the blood flow apparatus to the blood vessel or vascular graft. The detecting circuit is configured to provide a low-voltage alternating current signal to the electrodes to measure the electrical resistance between the electrodes, minimizing both the duration and amount of current being delivered. Detection of an increase in electrical resistance between the electrodes exceeding a pre-determined threshold value may be used to indicate a possible disconnection of the vascular access device.
1 . A system for detecting the disconnection of a vascular access device from a blood vessel or vascular graft, comprising:
a fluid delivery device for providing fluid through a first conduit into a first site of the blood vessel or graft;
a first electrode in contact with the lumen of the first conduit;
a second electrode in fluid communication with a second site of the blood vessel or graft;
an electronic circuit connected to the first and second electrodes, and configured to deliver a control signal to the first and second electrodes in order to measure the electrical resistance of a fluid between the first and second electrodes, wherein
at least one of the electrodes is located closer to the blood vessel or graft than to the fluid delivery device.
2 . The system of claim 1 , wherein the fluid delivery device comprises a pump.
3 . The system of claim 1 , wherein the fluid delivery device comprises a hemodialysis blood flow circuit.
4 . The system of claim 1 , wherein the second electrode is in contact with the lumen of a second conduit accessing the blood vessel or graft at the second site.
5 . The system of claim 4 , wherein the second conduit comprises part of a fluid flow path from the blood vessel or graft to the fluid delivery device.
6 . The system of claim 5 , wherein the first conduit comprises a first connector connecting a first vascular access catheter to a first tube segment, the second conduit comprises a second connector connecting a second vascular access catheter to a second tube segment, and the first and second vascular access catheters are shorter than the first and second tube segments.
7 . The system of claim 6 , wherein the first connector includes the first electrode and the second connector includes the second electrode.
8 . The system of claim 1 , wherein the first conduit comprises a double lumen flexible tube having a first lumen for carrying the fluid, and a second lumen for carrying a wire connecting the first electrode to the electronic circuit.
9 . The system of claim 1 , further comprising a controller configured to receive a signal from the electronic circuit, the signal representing the electrical resistance between the electrodes, wherein the controller is programmed to trigger an alert signal when the electrical resistance value exceeds a pre-determined threshold.
10 . The system of claim 9 , wherein the alert signal comprises an electrical command to a tubing occluder apparatus, wherein the tubing occluder apparatus includes a mechanical occluder arranged and configured to occlude the conduit.
11 . An apparatus for monitoring the continuity between a vascular access device and a blood vessel or vascular graft segment, comprising:
a first and second vascular connector, the first connector being attached on a proximal end to a distal end of a fluid-carrying lumen of a first double-lumen tube, and the second connector being attached on a proximal end to a distal end of a fluid-carrying lumen of a second double-lumen tube,
the first connector comprising a first electrode in contact with a lumen of the first connector and electrically connected to a wire within a wire-carrying lumen of the first double-lumen tube, and the second connector comprising a second electrode in contact with a lumen of the second connector and electrically connected to a wire within a wire-carrying lumen of the second double-lumen tube, wherein,
the wire within the first double-lumen tube and the wire within the second double-lumen tube are each connected to an electrical connector at a proximal end of the double-lumen tubes.
12 . The apparatus of claim 11 , wherein a distal end of each connector comprises a locking member for providing a reversible, air-tight connection between the connector and a mating connector of a vascular catheter.
13 . The apparatus of claim 12 , wherein a proximal end of the fluid-carrying lumen of the first double-lumen tube is connected to a blood pump, and a proximal end of the fluid-carrying lumen of the second double-lumen tube is connected to an air trap.
14 . The apparatus of claim 13 , wherein the air trap and the blood pump are configured for reversible connection to a dialyzer cartridge.
15 . A vascular connector comprising a proximal fluid connection end, a distal fluid connection end, and an electrode configured to electrically connect a fluid-carrying lumen of the connector with a wire external to the vascular connector.
16 . The vascular connector of claim 15 , wherein the proximal fluid connection end is configured to fluidly connect with an end of a flexible tube, and the distal fluid connection end is configured to reversibly connect with a mating connector of a vascular catheter.
17 . The vascular connector of claim 15 , wherein the electrode is installed in a conduit on the electrode connecting the lumen of the connector with an external surface of the connector.
18 . The vascular connector of claim 17 , wherein the electrode is lodged within the conduit, forming an air-tight seal between the lumen and the external surface of the connector.
19 . The vascular connector of claim 18 , wherein an elastomeric member is installed between the electrode and the conduit, contributing to the air-tight seal between the lumen and the external surface of the connector.
20 . An electrical circuit for measuring the resistance of a liquid between a first and second electrode, the first electrode connected to a first terminal of the electrical circuit, and the second electrode connected to a second terminal of the electrical circuit, comprising:
a capacitor C 1 connected on a first end to the first terminal and a capacitor C 2 connected on a first end to the second terminal;
a known reference resistance Rref connected on a first end to a second end of capacitor C 1 ;
switching means for connecting either;
a) a first reference voltage V+ to a second end of Rref, and a lower second reference voltage V− to a second end of C 2 to form a first switch configuration or;
b) the first reference voltage V+ to the second end of C 2 and the lower second reference voltage V− to the second end of Rref to form a second switch configuration; and measuring means for measuring a voltage Vsense at the connection between C 1 and Rref; wherein
the electrical circuit is configured to determine the value of the resistance of the liquid based on the known reference resistance Rref and the observed voltage Vsense for each of the first and second switch configurations.
21 . The electrical circuit of claim 20 , wherein the resistance-Rref is chosen to permit conductivity measurement of an electrolyte solution suitable for intravascular infusion.
22 . The electrical circuit of claim 21 , wherein the electrolyte solution comprises dialysate solution.
23 . The electrical circuit of claim 20 , wherein the resistance Rref is chosen to permit measurement of the resistance of a volume of blood between the first and second electrodes.