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 . An apparatus for detecting vascular access disconnection in a pumping apparatus that pulls blood from a vascular access through an arterial conduit and returns blood to the vascular access through a venous conduit, the vascular access disconnection apparatus comprising:
a detection circuit comprising:
a first terminal and first line connected to the first terminal;
a second terminal and second line connected to the second terminal;
a switching circuit configured to apply alternating voltages across the first and second terminals by alternating between:
a) a first switch configuration wherein a first reference voltage V+ is applied at the first terminal, and a lower second reference voltage V− is applied at the second terminal, and;
b) a second switch configuration wherein the first reference voltage V+ is applied at the second terminal, and the second reference voltage V− is applied at the first terminal; and
a voltage sensor for measuring a voltage signal at a midpoint of the first line;
a first and second connector, the first connector fluidly connecting the arterial conduit to an arterial needle, and the second connector fluidly connecting the venous conduit to a venous needle, the first connector including a first electrode in electrical contact with blood entering the arterial conduit and with the first line in the detection circuit, the second connector including a second electrode in electrical contact with blood exiting the venous conduit and with the second line in the detection circuit; and
a controller that detects a vascular access disconnect based on the voltage signal.
2 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the first line in the detection circuit further comprises a reference resistor between the first terminal and the midpoint.
3 . The apparatus for detecting vascular access disconnection of claim 2 , wherein the reference resistor has a resistance equal a mean value of resistance expected between the midpoint and the second terminal while a circuit is completed through the vascular access.
4 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the first line includes a first capacitor between the midpoint and the first electrode and the second line includes a second capacitor between the second terminal and the second electrode.
5 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the arterial and venous needles include a short tubing section, the short tubing section being less than half a length of the arterial and venous conduits.
6 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the arterial needle includes a short tubing section, the short tubing section being less than a third of a length of the arterial conduit.
7 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the arterial conduit and the vascular conduit are part of a hemodialysis blood flow circuit.
8 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the vascular access is a blood vessel or graft.
9 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the arterial conduit comprises a double lumen flexible tube having a first lumen for carrying blood, and a second lumen for carrying a wire connecting the first electrode to the first terminal.
10 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the controller is programmed to determine a resistance based on the voltage signal and trigger an alert signal when the resistance exceeds a pre-determined threshold.
11 . The apparatus for detecting vascular access disconnection of claim 1 , wherein the pumping apparatus includes a mechanical occluder that when closed can prevent flow through the arterial and venous conduits; and
wherein the controller is programmed to determine a resistance based on the voltage signal and close the occluder when the resistance exceeds a pre-determined value.
12 . An apparatus for detecting vascular access disconnection in a pumping apparatus that pulls blood from a vascular access through an arterial conduit and returns blood to the vascular access through a venous conduit, the vascular access disconnection apparatus comprising:
a detection circuit comprising:
a first terminal and first line connected to the first terminal;
a second terminal and second line connected to the second terminal;
a switching circuit configured to apply alternating voltages across the first and second terminals by alternating between:
a) a first switch configuration wherein a first reference voltage V+ is applied at the first terminal, and a lower second reference voltage V− is applied at the second terminal and;
b) a second switch configuration wherein the first reference voltage V+ is applied at the second terminal, and the second reference voltage V− is applied at the first terminal; and
a voltage sensor for measuring a voltage signal at a midpoint of the first line;
a first and second connector, the first connector including a first electrode and attached to the arterial conduit and detachably connected to an arterial needle, the second connector including a second electrode and attached to the venous conduit and detachably connected to a venous needle, the first electrode in electrical contact with blood entering the arterial conduit and with the first line in the detection circuit, the second electrode in electrical contact with blood exiting venous conduit and with the second line in the detection circuit; and
a controller configured to detect a vascular access disconnect based on the voltage signal.
13 . The apparatus for detecting vascular access disconnection of claim 12 , wherein the first line in the detecting circuit further comprises a reference resistor between the first terminal and the midpoint.
14 . The apparatus for detecting vascular access disconnection of claim 12 , wherein the first line includes a first capacitor between the midpoint and the first electrode and the second line includes a second capacitor between the second terminal and the second electrode.
15 . The apparatus for detecting vascular access disconnection of claim 12 , wherein the arterial needle includes a short tubing section, the short tubing section being less than a third of a length of the arterial conduit.
16 . The apparatus for detecting vascular access disconnection of claim 12 , wherein the arterial 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 first terminal.
17 . An apparatus for detecting vascular access disconnection in a pumping apparatus that pulls blood from a vascular access through an arterial conduit and returns blood to the vascular access through a venous conduit, the vascular access disconnection apparatus comprising:
a detection circuit comprising:
a first terminal and first line connected to the first terminal;
a second terminal and second line connected to the second terminal;
a switching circuit configured to apply alternating voltages across the first and second terminals by alternating between:
a) a first switch configuration wherein a first reference voltage V+ is applied at the first terminal, and a lower second reference voltage V− is applied at the second terminal and;
b) a second switch configuration wherein the first reference voltage V+ is applied at the second terminal, and the second reference voltage V− is applied at the first terminal; and
a voltage sensor for measuring a voltage signal at a midpoint of the first line;
a first electrode in contact with the blood in the arterial conduit, the first electrode electrically connected to the first line in the detection circuit via a first wire, the first wire in a second lumen of the arterial conduit;
a second electrode in fluid contact with blood in the venous conduit, the second electrode electrically connected to the second line in the detection circuit via a second wire, the second wire in a second lumen of the venous conduit; and
a controller configured to detect a vascular access disconnect based on the voltage signal.
18 . The apparatus for detecting vascular access disconnection of claim 17 , wherein the first line in the detecting circuit further comprises a reference resistor between the first terminal and the midpoint.
19 . The apparatus for detecting vascular access disconnection of claim 17 , wherein the first line includes a first capacitor between the midpoint and the first electrode, and the second line includes a second capacitor between the second terminal and the second electrode.
20 . The apparatus for detecting vascular access disconnection of claim 17 , wherein the arterial needle includes a short tubing section, the short tubing section being less than a third of a length of the arterial conduit.