Patent Application
20140148802
This invention concerns a system and method for protecting patients and patient monitoring equipment during a medical procedure utilizing radio frequency energy such as electrosurgery.
During a radio frequency procedure such as an electrosurgical procedure, a high-frequency electric current (AC current) is applied to biological tissue in order to directly heat the biological tissue to treat a patient for a particular condition. Electrosurgical devices beneficially enable a practitioner to treat a subject area with precision while reducing an amount of blood loss from the patient undergoing treatment. The electrosurgical instrument may include an electrosurgical generator that generates a voltage which is applied through an electrosurgical tool to the patient. The patient's body is contacted by a return plate which receives the current flowing through the patient enabling the return to ground. The return plate may be a relatively large metal plate or a flexible metalized plastic pad which is connected to the return electrode of the AC source. During the procedure, the electric current flows from the active electrode on the electrosurgical tool, through the body to the return electrode, and then back to the electrosurgical generator.
As this is a surgical procedure, there is a recognized need to monitor a plurality of patient parameters during the surgery to insure that the patient vitals are stable. For example, conventional monitoring may include an electrocardiogram (ECG) monitor that is connected to the patient by a plurality of leads that monitor the electrical impulses of the patient's heart. However, a problem exists whereby a patient burn may be caused by the increased current present during an electrosurgical procedure. Moreover, in order to prevent a burn, the insertion of a high impedance block significantly degrades the quality of the signal being monitored by the ECG. An exemplary block diagram showing the conventional method of protecting a patient from being burned is shown in
While conventional burn prevention systems are able to provide the necessary impedances to prevent burning a patient, these systems result in degraded monitoring. A system according to invention principles addresses deficiencies of known systems.
In one embodiment, an apparatus is provided for protecting a patient during a radio frequency medical procedure. A detector includes an input receiving electrical impulses representing at least one patient parameter to be monitored from at least one shielded sensor connected to the patient. The detector detects at least one of (a) a voltage associated with parasitic current generated during a radio frequency medical procedure and (b) a current generated during a radio frequency medical procedure. A control circuit is coupled to the detector and compares at least one of (a) the detected voltage with a threshold voltage value and (b) the detected current with a threshold current value. A switch is coupled between the detector and the control circuit. In response to a control signal generated by the control circuit, the switch selectively switches between a conductive state and a non conductive state. The conductive state maintains a low impedance at the at least one shielded sensor and maintains the shield of the at least one shielded sensor in an effective state when at least one of (a) the detected voltage is below the threshold voltage value and (b) the detected current is below the threshold current value. The non-conductive state provides a high impedance at the at least one shielded sensor and causes the shield of the at least one shielded sensor to become ineffective when at least one of (a) the detected voltage is equal to or greater than the threshold voltage value and (b) the detected current is equal to or greater than the threshold current.
In another embodiment, a method is provided for protecting a patient during a radio frequency medical procedure. The method of protecting a patient includes detecting at least one of (a) voltage associated with a parasitic current generated during an radio frequency medical procedure and (b) a current generated during a radio frequency medical procedure, at an input that receives electrical impulses representing at least one patient parameter to be monitored from at least one shielded sensor connected to the patient. A control circuit compares at least one of (a) the voltage detected by the detector with a threshold voltage value and (b) the current detected by the detector with a threshold current value. In response to a control signal generated by the control circuit, a switch switches between a conductive state and a non-conductive state. The conductive state maintains a low impedance at the at least one shielded sensor and maintaining the shield in an effective state when at least one of (a) the detected voltage is below the threshold voltage value and (b) the detected current is below the threshold current value. The non-conductive state provides a high impedance at the at least one shielded sensor and causes the shield of the sensor to become ineffective when at least one of (a) the detected voltage is equal to or greater than the threshold voltage value and (b) the detected current is equal to or greater than the threshold current value.
The patient protection apparatus automatically increases an impedance of patient connected ECG leads. This advantageously provides a shield during a medical procedure employing RF energy. A medical procedure employing RF energy generates an electromagnetic frequency and/or RF current that is applied to tissue of a patient. Examples of medical proceduces using RF energry to treat a patient includes but is not limited to (a) electrosurgery; (b) RF ablation; (c) RF lesioning; (d) any other RF engery application to tissue. The patient protection apparatus advantageously provides a shield during electrosurgery to reduce energy conduction and thus prevent patient burns by automatically detecting an increased amount of current generated by an active electrosurgical tool. An electrosurgical procedure is one type of medical procedure employing RF energy and is described for purposes of example only. One skilled in the art would recognize the ability to employ the patient protection apparatus during any RF procedure thereby increasing the impedance of a patient connected to a monitoring device. A current burn to a patient may be considered a function of electrode surface area and the current density flowing through the electrode. Thus, the apparatus may be able to effectively provide a high impedance and prevent burns at the site of the electrode on a patient's body. The apparatus also advantageously returns the impedance and the ECG shields to a low impedance level when an amount of current flowing through the body of the patient is below a threshold value indicating that there is no electrosurgical procedure currently underway. Thus, the automatic reversion to a low impedance condition advantageously provides a high level of shielding and consequently high signal integrity. Therefore, the patient protection apparatus advantageously provides instantaneous and automatic mode changes between good patient protection on the one hand and high performance ECG monitoring (low noise, good bandwidth) on the other.
During electrosurgery, the patient 200 is connected to an ECG monitor in the conventional manner as discussed above. An electrosurgical apparatus includes an electrosurgical generator 220 electrically connected between an electrosurgical tool 225 and a return plate 230. The electrosurgical tool may be any type of electrosurgical tool that is medically appropriate for the surgery being performed and to treat the patient 200. In one embodiment, the electrosurgical tool 225 is an electric scalpel which applies high energy RF power that is generated by the generator 220. The high energy RF power is applied to a precise point on the patient and the current flowing to the tool 225 typically returns to the generator 220 through the return plate 230 thereby completing the electrosurgical circuit.
Depending on the type of electrosurgical procedure being performed and the location at which the electrosurgical tool 225 is operating on the patient's body 200, placement of the electrical leads 215a-215c may result in a low impedance unintended pathway for current flowing through the electrosurgical tool 225. For example, in the instance where the patient parameter monitor 210 is an ECG monitor and the electrical leads 215a-215c are ECG leads connected to the patient 200, the placement of the ECG electrodes in relation to the electrosurgical site (e.g. the point at which the tool contacts the patient's body) results in a low impedance pathway for the current. Should this low impedance pathway be formed, the current applied by the electrosurgical tool 225 gets shunted away from the patient's body 200 and instead flows through the ECG leads resulting in current density being present at the ECG electrode that increases the temperature, causing a burn to the skin of the patient 200 at the point where the ECG electrodes are attached. This increased current density occurs because the individual electrodes cover a small area on the patient 200.
A patient protection apparatus 235, which will be described in greater detail below with respect to
The patient protection apparatus 235 includes a control circuit 315 that senses parasitic current in the shield and determines that a patient burn potential exists. At that time, the apparatus 235 switches from the first mode of operation to the second mode in the manner discussed below. The patient protection apparatus 235 includes at least one resistor 325 connected between a pick-off diode 320 and a switch 330. In one embodiment, the switch 330 is a MOSFET switch. In another embodiment, the switch 330 is a MOSFET switch that has an inherent internal resistance such that there need not be a discrete resistor present in the apparatus. The control circuit 315 is also connected between the pick-off diode 325 and the switch 330 thereby forming a complete circuit when the switch 330 is a first “on” position. When the switch 330 is in the first “on” position, the switch 330 is conducting, providing a low impedance shield for the particular electrode enabling high quality monitoring of an input signal by the monitoring circuit 305.
In the event that parasitic current is conducted along the lead 215, a voltage is created across the at least one resistor 325 and the control circuit 315 automatically senses this voltage via the pick-off diode 320. Upon sensing of this voltage across the resistor 325, the control circuit causes the switch to move from the first “on” position to the second “off” position. In the second “off” position, the switch 330 is not conducting and the shield is allowed to float and move along in voltage with the signal conductor of the input cable (e.g. the center lead of a coaxial cable). This prevents the parasitic current from flowing through the shield and burning the patient at the point which the electrode is connected to the patient. When the switch 330 is in the second “off” position, the quality of the signal being monitored by the monitoring circuit 305 is reduced but the patient is protected which is a necessary trade-off that must be made during an electrosurgical procedure. However, the patient protection apparatus 235 advantageously reduces an amount of time that the quality is reduced because the protection is enabled in response to the voltage sensed at resistor 325.
The patient protection apparatus 235 includes the at least one resistor 320, the pick-off diode 325 and the switch 330 (see
The control circuit 315 automatically changes the position of the switch 330 in response to introduction of parasitic current at any one of the electrodes 410, 420, 430 and/or 440. Parasitic current may result during an electrosurgical procedure which may cause a voltage to be generated across the resistor 320 and sensed by the pickoff diode 325. If the sensed voltage is above a threshold value (greater than a reference voltage in the order of 1 Volt), the control circuit causes the switch to move from the first “on” position to the second “off” position. When this occurs, the control circuit 315 turns “off” the switch 330, releasing the shields and reducing the current dramatically. Because the switch 330 is no longer sinking significant current, the voltage on the shield sensed by the control circuit 315 now follows the voltage on the patient electrode thereby maintaining the position of the switch 330 in the second “off” position. When the electrosurgical procedure ends or, in the event that the medical professional pauses the procedure by deactivating the electrosurgical tool, the voltage drops across the resistor 320, the pickoff diode 325 senses the voltage change and the control circuit 315, and the switch 330 returns to the first “on” position rendering the shields on the respective electrodes effective and enabling high quality patient parameter monitoring.
Under conditions of high current induced in the shields, current enters through the most positive electrode, passes through resistor 320 to “ground”, while at the corresponding most negative electrode, the said current passes through the parasitic diode in the MOSFET switch, through the resistor 320 for that second electrode, and back through that shield to the patient. Simultaneously, the most positive electrode drives the corresponding pickoff diode 325 into conduction, charging an input capacitor 506 (peak detector) in the control circuit 315. A voltage detector 504 of the control circuit is coupled to the switch 330 and directs the operation of the switch between the first “on” position and the second “off” position. In one embodiment, the voltage detector 504 may be a comparator which compares the voltage sensed by the peak detector 506 to a threshold value and, if the sensed voltage is equal to or greater than the threshold, the switch is caused to move from the first “on” position to the second “off” position. When the switch is in the “off” position, the impedance level is increased, thereby disabling any shield on the electrode and substantially reducing the current from flowing through the electrode and thus preventing a patient burn. The time constant of the circuit determines the reset time of the circuit (typically milliseconds). This time constant is effectively the “recovery” time of the circuit, and corresponds to the time when the shields are again effective.
During electrosurgery, current flows through the patient and further through the leads connecting the patient monitor to the patient. During this procedure, one lead has more current flowing therethrough and is hotter than the other leads. Current flows down this lead which is provided to the at least one resistor and the switch (e.g. MOSFET). The current on the shield flows through the resistor resulting in a voltage being sensed by the pickoff diode associated therewith thereby resulting in the opening of the switch to the “off position”. The peak detector 506 is charged and the voltage detector 504 recognizes the voltage resulting from the current in the shield reached the threshold value and automatically switches switch from the “on” position into the “off” position. In the “off” position, the shields are able to float thereby increasing the impedance on the lead and preventing the current density at the respective electrodes from increasing and causing a burn on the skin of the patient. When the voltage detector determines that the voltage is below the threshold value, the control circuit 315 causes the switch to return to the “on” position and begin conducting again thereby lowering the impedance and improving the signal quality being monitored by the patient monitoring device.
Referring now to
An advantageous feature of the patient protection apparatus is that the circuit switches abruptly from the first “on” position to the second “off” position as a result of sensing the shield current as the ESU procedure begins, and subsequently switching from the second “off” position the first “on” position as a result of sensing the shield voltage during the ESU procedure through the time when the ESU procedure ends. This helps prevent the circuit from oscillating on and off at the edge of operation.
The electrosurgical procedure continues during the time represented by reference numeral 706. During this time period, there is an increase in voltage sensed by the voltage detector due to the floating shield. The voltage detector continuously compares the sensed voltage to the threshold and MOSFET switch operation is controlled thereby. During the electrosurgical procedure the current flowing through the resistor is substantially decreased (approximately 3 mA) and remains substantially constant through the procedure.
Referring now to
The operation of the patient protection apparatus is now described with respect to the flowchart of
The patient protection apparatus described above with respect to
Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly to include other variants and embodiments of the invention which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention. This disclosure is intended to cover any adaptations or variations of the embodiments discussed herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2011/045660 | 7/28/2011 | WO | 00 | 1/16/2014 |
