Sensing cannula systems
Described herein are sensing cannula systems that include a surgical instrument, a detection unit, and a conductive pad having a reference electrode and configured to be placed on the patient at a location outside the patient's body. The surgical instrument can include a cannula (such as a fat grafting cannula) having an electrically conductive distal tip and electrical insulation covering the cannula proximally from the distal tip, wherein the distal tip comprises a first electrode. The detection unit can include electrical circuitry that is electrically coupled to the surgical instrument and the conductive pad and operable to measure an electrical impedance between the first electrode and the reference electrode to determine what type of tissue the distal tip is in.
1 . A sensing cannula system, comprising:
a surgical instrument comprising a cannula having an electrically conductive distal tip and electrical insulation covering the cannula proximally from the distal tip, wherein the distal tip comprises a first electrode, and wherein the surgical instrument is configured such that at least the distal tip of the cannula is insertable into a patient's body;
a conductive pad comprising a reference electrode and configured to be placed on the patient at a location outside the patient's body; and
a detection unit comprising electrical circuitry, the detection unit electrically coupled to the surgical instrument and the conductive pad and operable to measure an electrical impedance between the first electrode and the reference electrode;
wherein the detection unit is configured to determine what type of tissue is adjacent to the distal tip based on the measured electrical impedance, such that the system can detect if the distal tip is adjacent a selected tissue type and alert a user of the system, and wherein the detection unit is further configured to record absolute impedance values and changes in impedance values as the cannula is moved within the patient's body; and
wherein the detection unit comprises an oscillator circuit configured to generate a square wave, and the oscillator circuit is further configured such that a frequency of the square wave generated by the oscillator circuit changes as a result of the impedance of tissue between the first electrode and the reference electrode; and
the detection unit is further configured to determine what type of tissue is adjacent the distal tip of the cannula by measuring the frequency of the generated square wave.
2 . The system of claim 1 , wherein the cannula comprises an inner passageway that is operable to conduct fat to or from the patient's body such that the surgical instrument is configured for fat grafting.
3 . The system of claim 1 , wherein the reference electrode is configured to be placed on the patient's skin.
4 . The system of claim 1 , wherein the detection unit is attached to a distal portion of the surgical instrument.
5 . The system of claim 1 , further comprising a signal that alerts the user when the measured impedance changes or reaches a predetermined threshold value.
6 . The system of claim 1 , wherein the first electrode is an exposed metal portion of the distal tip of the cannula.
7 . The system of claim 1 , wherein the first electrode is an electrode that is attached to the distal tip of the cannula.
8 . The system of claim 1 , wherein the detection unit is configured to record changes in impedance values and changes in the cannula tip location as the cannula is moved within the patient's body.
9 . The system of claim 1 , further comprising a valve or clamp configured to stop flow of material through the cannula based on detection of a specified impedance value.
10 . The system of claim 9 , wherein the system comprises the valve, and the valve is actuatable to shut off flow of material through the cannula based on detection of the specified impedance value.
11 . The system of claim 9 , wherein the system comprises the clamp;
the system further comprises a syringe coupled to the cannula; and
the clamp is operable to impede motion of a plunger of the syringe based on detection of the specified impedance value.
12 . The system of claim 1 , wherein the cannula comprises an inner passageway that is operable to conduct material to or from the patient's body.
13 . The system of claim 1 , wherein the oscillator circuit is further configured such that the frequency of the generated square wave is inversely proportional to the measured impedance, and the detection unit is further configured to determine what type of tissue is adjacent the distal tip by comparing the frequency of the square wave with a specified threshold frequency.
14 . The system of claim 13 , wherein the detection unit is configured to alert the user of the system to contact of the cannula with muscle or blood when the frequency of the square wave is greater than the specified threshold frequency.
15 . The system of claim 14 , wherein the specified threshold frequency is 100 Hz, and the detection unit is configured to alert the user of the system to contact with muscle or blood when the frequency of the square wave is greater than 100 Hz.
16 . The system of claim 13 , wherein the detection unit is configured to alert the user of the system when the frequency of the square wave crosses the specified threshold frequency.
17 . A method of sensing a type of tissue that is adjacent to a tip of a surgical instrument by an electronic sensing unit coupled to the surgical instrument, the method comprising:
by the electronic sensing unit, creating an electrical circuit that includes a first electrode adjacent the tip of the surgical instrument, a reference electrode positioned on a patient at a location outside of the patient's body, and a portion of patient tissue interposed between the first electrode and the reference electrode;
by the electronic sensing unit, determining an impedance in the circuit derived from the patient tissue;
by the electronic sensing unit, determining what type of tissue is adjacent the tip of the surgical instrument based on the determined impedance; and
by the electronic sensing unit, recording absolute impedance values and changes in impedance values as the tip of the surgical instrument is moved within the patient's body;
wherein the electronic sensing unit comprises an oscillator circuit, and the method further comprises generating, with the oscillator circuit, a square wave, and a frequency of the square wave generated with the oscillator circuit varies as a function of the impedance of the portion of patient tissue interposed between the first electrode and the reference electrode, and determining what type of tissue is adjacent the tip of the surgical instrument further comprises measuring the frequency of the generated square wave.
18 . The method of claim 17 , wherein determining what type of tissue is adjacent the tip of the surgical instrument comprises determining if the tip of the surgical instrument is adjacent to muscle.
19 . The method of claim 17 , further comprising generating an alert signal based on the determined impedance.
20 . The method of claim 17 , wherein the reference electrode is positioned on the patient's skin.
21 . The method of claim 17 , wherein determining what type of tissue is adjacent the tip of the surgical instrument is also based on a distance between the reference electrode and the first electrode.
22 . The method of claim 17 , wherein the reference electrode remains stationary on the patient while the first electrode moves within the patient along with the surgical instrument.
23 . An electronic sensing unit configured to perform the method of claim 17 .
24 . The method of claim 17 , wherein the surgical instrument is a cannula.
25 . The method of claim 24 , further comprising determining that a tip of the cannula is in contact with a selected tissue type and shutting off flow of material through the cannula.
26 . The method of claim 17 , further comprising recording the changes in impedance values and changes in the location of the tip of the surgical instrument as the surgical instrument is moved within the patient's body.