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Shunting Networks to Reduce Capacitive Coupling

IP.com Disclosure Number: IPCOM000222799D
Publication Date: 2012-Oct-23
Document File: 4 page(s) / 447K

Publishing Venue

The IP.com Prior Art Database

Abstract

Surgical instruments are being developed that advantageously combine monopolar and bipolar functions in the same device. Such devices include LigaSure Advance™ Pistol Grip sealer/divider by Covidien and the EnSeal PowerTip by Ethicon Endo-Surgery, Inc. Such instruments allow for the simultaneous sealing and transecting of vessels with advanced bipolar technology and creation of otomies and other dissection with the monopolar technology. While surgically advantageous, the presence of both monopolar and bipolar signals in a single instrument poses a number of technical challenges. One of the primary challenges is preventing “cross-talk” between the signals in the instrument and cable when one modality is used and the other is disabled, or when both modalities are in use at the same time. When the bipolar mode is selected, the monopolar mode is typically disabled, with the monopolar node disconnected from the other circuitry and “floating” with respect to the bipolar output. Since bipolar instruments typically have both conductors and poles of the electrosurgical output in close proximity in the cable, handle and end effector, the likelihood of cross talk to the monopolar nodes during operation of the bipolar mode is very low. When the monopolar mode is selected, the bipolar nodes are likewise disconnected and left “floating” with respect to the monopolar nodes. In the monopolar mode, the current path is through the cable and instrument into the tissue via the cutting tip then to the return pad, and back to the generator. The wires and current paths of the monopolar mode extend over a larger area than in the bipolar mode. In practice, the cable lay of the monopolar and bipolar circuits in surgical instruments is such that the monopolar signal can easily exhibit cross-talk and therefore couple capacitively to the “floating” metal of the bipolar electrodes. Therefore, the capacitive coupling between the monopolar signal and bipolar electrodes creates the potential for an unintended energy transfer between the bipolar end effector electrodes and the patient’s tissue. The transferred energy can be of such a magnitude that detrimental small tissue effects are observed.

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Shunting Networks to Reduce Capacitive Coupling

Surgical instruments are being developed that advantageously combine monopolar and bipolar functions in the same device.  Such devices include LigaSure Advance™ Pistol Grip sealer/divider by Covidien and the EnSeal PowerTip by Ethicon Endo-Surgery, Inc.  Such instruments allow for the simultaneous sealing and transecting of vessels with advanced bipolar technology and creation of otomies and other dissection with the monopolar technology.  While surgically advantageous, the presence of both monopolar and bipolar signals in a single instrument poses a number of technical challenges. One of the primary challenges is preventing “cross-talk” between the signals in the instrument and cable when one modality is used and the other is disabled, or when both modalities are in use at the same time. 

When the bipolar mode is selected, the monopolar mode is typically disabled, with the monopolar node disconnected from the other circuitry and “floating” with respect to the bipolar output.  Since bipolar instruments typically have both conductors and poles of the electrosurgical output in close proximity in the cable, handle and end effector, the likelihood of cross talk to the monopolar nodes during operation of the bipolar mode is very low. 

When the monopolar mode is selected, the bipolar nodes are likewise disconnected and left “floating” with respect to the monopolar nodes.  In the monopolar mode, the current path is through the cable and instrument into the tissue via the cutting tip then to the return pad, and back to the generator.  The wires and current paths of the monopolar mode extend over a larger area than in the bipolar mode.  In practice, the cable lay of the monopolar and bipolar circuits in surgical instruments is such that the monopolar signal can easily exhibit cross-talk and therefore couple capacitively to the “floating” metal of the bipolar electrodes.  Therefore, the capacitive coupling between the monopolar signal and bipolar electrodes creates the potential for an unintended energy transfer between the bipolar end effector electrodes and the patient’s tissue.  The transferred energy can be of such a magnitude that detrimental small tissue effects are observed.                                                                   

FIG. 1 is a parasitic model of a typical combined monopolar and bipolar instrument.  In this model, the instrument is shown in the power tip mode, in which the cutting, monopolar circuit is connected while the sealing, bipolar electrodes are disconnected.  In this model, C1 and C4 represent the capacitance that will be present between the bipolar wires, with C1> C4.  With the bipolar electrodes disconnected from the generator, the contribution of C1 and C4 to the reactive capacitance is negligible.  C3 and C6 represent the capacitance between the electrode node a...