Catheter insertion systems
Disclosed catheter insertion systems enable the user to identify the location of the needle based on the electrical properties of subcutaneous tissue relative the electrical properties of other fluids such as blood or air. Disclosed systems can include one or more of the following features: 1) the catheter assembly is modular (e.g., the catheter can be connected and disconnected from the detection unit at will); 2) the detection unit employs an electrical circuit that allows for the discernment between subcutaneous tissue and blood; 3) the system assists the end user with catheter advancement. Some embodiments can be used to insert catheters into a spaces where the needle passes first through subcutaneous fat and muscle before entering fluid or air.
1 . A catheter insertion system, comprising:
a disposable catheter unit comprising a needle, a guidewire passing through the needle, and a deployable catheter disposed over the needle; and
a detection unit coupled to the catheter unit, the detection unit comprising circuitry electrically coupled to a first electrode and a second electrode, wherein the needle acts as at least the first electrode, wherein the circuitry comprises a timer circuit and is configured to measure resistance between the first electrode and the second electrode while the catheter unit is inserted into a patient, and wherein the detection unit is configured to determine an anatomical space within which an end portion of the catheter unit is located within the patient based on the measured resistance.
2 . The catheter insertion system of claim 1 , wherein the second electrode comprises the guidewire.
3 . The catheter insertion system of claim 1 , wherein a portion of the guidewire within the needle is coated with an electrically insulating material, and an end of the guidewire is left bare.
4 . The catheter insertion system of claim 1 , wherein the timer circuit comprises a first comparator and a second comparator, and wherein a first output of the first comparator and a second output of the second comparator are connected to a flip flop configured to produce a signal based on a state of the first and second outputs.
5 . The catheter insertion system of claim 4 , wherein the circuitry comprises a capacitor configured to charge via a voltage provided across resistors, the resistors comprising a first resistor having a predetermine resistance and second resistor having an effective resistance corresponding to material between the first and second electrodes.
6 . The catheter insertion system of claim 5 , wherein the timer circuit further comprises a transistor connected to receive the signal from the flip flop, and wherein the transistor is configured to open to allow the capacitor to discharge when the signal from the flip flop is a first logical value.
7 . The catheter insertion system of claim 5 , wherein the signal from the flip flop is provided to an output stage of the timer circuit to produce an oscillating binary output.
8 . The catheter insertion system of claim 7 , wherein the oscillating binary output is sent to a microcontroller, and wherein a frequency of the oscillating binary output is dependent on relative values of the resistors and the capacitor and is used to determine the measured resistance.
9 . The catheter insertion system of claim 5 , wherein the first output is based on a comparison of a first input voltage to a first reference voltage, wherein the second output is based on a comparison of a second input voltage to a second reference voltage, and wherein the first and second reference voltages are respective percentages of the voltage provided across the resistors.
10 . The catheter insertion system of claim 9 , wherein the first reference voltage is a lower percentage of the voltage provided across the resistors than the second reference voltage.
11 . A catheter insertion system, comprising:
a disposable catheter unit comprising a needle, a guidewire passing through the needle, and a deployable catheter disposed over the needle; and
a detection unit coupled to the catheter unit, the detection unit comprising circuitry electrically coupled to a first electrode and a second electrode located in or on the needle, wherein the circuitry comprises a timer circuit configured to measure resistance between the first electrode and the second electrode while the catheter unit is inserted into a patient, and wherein the detection unit is configured to determine an anatomical space within which an end portion of the catheter unit is located within the patient based on the measured resistance.
12 . The catheter insertion system of claim 11 , wherein the guidewire comprises two staggered wires inside of the needle acting as the first electrode and the second electrode, respectively.
13 . The catheter insertion system of claim 12 , wherein each of the two staggered wires lie inside of the needle and are separated from one another by a distance.
14 . The catheter insertion system of claim 12 , wherein the two staggered wires are housed inside of a single insulated sheath.
15 . The catheter insertion system of claim 12 , wherein the two staggered wires are inter-wrapped with one another.
16 . The catheter insertion system of claim 12 , wherein the two staggered wires are insulated to prevent a short circuit between the two staggered wires.
17 . The catheter insertion system of claim 16 , wherein an inside of the needle is coated with an insulating material.
18 . The catheter insertion system of claim 11 , wherein the timer circuit comprises a first comparator and a second comparator, and wherein a first output of the first comparator and a second output of the second comparator are connected to a flip flop configured to produce a signal based on a state of the first and second outputs.
19 . The catheter insertion system of claim 18 , wherein the circuitry comprises a capacitor configured to charge via a voltage provided across resistors, the resistors comprising a first resistor having a predetermined resistance and second resistor having an effective resistance corresponding to material between the first and second electrodes.
20 . The catheter insertion system of claim 19 , wherein the signal from the flip flop is provided to an output stage of the timer circuit to produce an oscillating binary output, wherein the oscillating binary output is sent to a microcontroller, and wherein a frequency of the oscillating binary output is dependent on relative values of the resistors and the capacitor and is used to determine the measured resistance.