Gas flow control in gas-assisted esu

IS 2 255 494 T3

DESCRIPTION

Gas flow control in gas-assisted electrosurgery.

The invention relates to a gas distribution apparatus as defined in the preamble of claim 1.

This invention relates to gas-assisted electrosurgery of the type that was pioneered as a result of the invention described in US-A-4,781,175 on which the preamble of claim 1 is based. More particularly, the present invention relates to a New and improved apparatus for controlling gas flow used in gas assisted electrosurgery in relation to gas flow conditions and back pressure. One consequence of the improvements of the present invention is a reduction in the circumstances in which gas embolism risks and inappropriate operating conditions may occur.

Gas-assisted electrosurgery is used to clot or stop blood flowing out of the tissue at the operation site. Gas-assisted electrocoagulation involves the transfer of arcs of electrical energy and ionized conductive paths in a gas stream that flows into tissue. The gas stream has the advantage of cleaning the blood from the tissue and allowing arcs of electrical energy to indirectly enter the tissue and create a lattice in the tissue. The reticulum forms a matrix-like structure in which blood naturally clots, thereby sealing the tissue preventing additional blood flow. Very substantial advantages result from this form of gas-assisted electrosurgery. Clotting occurs more quickly. Coagulation is possible under conditions in which coagulation was previously impossible or difficult to achieve. Less blood is lost during the operation and the surgical process is completed more quickly. The high integrity of the sealed surface of the tissue, known as gangrenous black scab, almost eliminates the possibility of subsequent bleeding after the process is complete. Healing occurs more quickly because the gangrenous black scab is thinner and more uniform compared to the gangrenous black scab that is achieved using normal gasless electrosurgery techniques.

Despite the numerous and significant advantages of gas-assisted electrocoagulation, concerns have been raised about its use. Perhaps the most significant concern is one regarding the risk of gas embolism in the patient. Gas embolism is the introduction of gas into the patient's blood system. If the amount of gas in the bloodstream is significant and accumulates in the heart, the heart is no longer able to pump blood. If used properly, gas-assisted electrocoagulation is safe in its ability to rapidly coagulate and seal tissue prior to the introduction of substantial amounts of gas. The ability of the surgeon to avoid circumstances in which gas embolism may occur and the quality of the equipment used in gas-assisted electrocoagulation may influence the risks of gas embolism.

A very effective technique of preventing gas embolism is to initiate the transfer of the arcs into the gas stream in a reliable manner and at a sufficiently separate distance from tissue that the impact of the gas on the tissue does not force excessive amounts of gas into of the tissue, but instead still causes the gas to clean the blood and other fluids accumulated on the surface or stroma of the tissue. US-A-4,781,175 and US-A-Re 34,432 describe techniques to ensure that electric arcs start at that distance.

Other types of gas-assisted electrocoagulation equipment use a normal gasless electrosurgical generator combined with a separate gas distribution device. These combination devices generally do not possess any additional arc initiation capabilities other than that available to initiate arcs in the still air environment in which the normal electrosurgical generator is normally used. A still air environment presents less difficulty in initiating arc transfer than a flowing gas environment, because flowing gas tends to disperse ionized species and makes it more difficult to initiate arc transfer to tissue. When a normal electrosurgical generator is combined with a separate gas distribution system, the gas flow can tend to "blow" the arcs and ionized species, making it very difficult or impossible to initiate transfer of the arc to tissue. To counteract this difficulty in initiating arc transfer, the natural reaction is to bring the gas distribution nozzle of the applicator device close to the tissue. This slows the gas flow as a result of the inherent back pressure that results from close placement. With reduced gas flow, it is easier for the normal electrosurgical generator to initiate the arc transfer. Once the arches have started, they are more easily maintained and the surgeon can remove the applicator to a working distance. However, a certain level of skill and recognition must be used by the surgeon to avoid the risk of gas embolism associated with initiating arch transfer at close working distances. Not all surgeons have this ability or even do not recognize the possibility of gas embolism from the incorrect use of gas-assisted electrosurgery.

The issue of applicator gas nozzle placement has recently become important due to the increasing use of gas-assisted electrosurgery in minimally invasive surgery, such as gastrointestinal surgery, endoscopy, and laparoscopy. In minimally invasive gas-assisted electrosurgery, a relatively long tube-shaped applicator is inserted into the patient without making an open incision. An ordinary miniature camera or optical lens is also placed inside the patient so that the surgeon can see the operation site. Once the electrosurgical applicator is located in the proper position, gas and electrical energy are delivered from the nozzle at the end of the tube-shaped applicator to achieve coagulation at the surgical site.

IS 2 255 494 T3

Gas-assisted electrosurgery is considered an advantage in minimally invasive surgery due to the very effective coagulation that can be achieved in a variety of difficult conditions and without the need for the degree of control or precision in placement required to achieve good coagulation. with electrosurgery without normal gas under similar conditions. Positioning is particularly important because it is very difficult to visualize the site of the operation and the position of the applicator in relation to the tissue with the monoscopic view available to the surgeon through the miniature camera or optical lenses. In other words, the surgeon does not have the advantage of depth perception when viewing the surgical site monoscopically, making placement very difficult. In fact, it is not uncommon for the surgeon to fail to make the applicator nozzle contact or enter the tissue. Such conditions are highly conducive to the risk of gas embolism because gas can enter tissue directly. Under conditions where the nozzle is adequately separated from tissue, the more uniform coagulation effects available from gas assisted electrosurgery compensate for the lack of position recognition available by the surgeon.

It is with respect to these and other considerations that the present invention has been developed.

It is the object of the invention to improve the gas distribution apparatus according to the preamble of claim 1 so that the gas flow rate is automatically controlled in such a way that a more reliable arc initiation is achieved without increasing the risk of embolism. Of gas.

Such an object is achieved by the gas distribution apparatus according to the preamble of independent claim 1 comprising the features of the characterizing part of claim 1. Further embodiments of the invention form the subject matter of the dependent claims .

In accordance with the invention, the relatively high gas flow rate selected by the surgeon for gas assisted electrosurgery is automatically and temporarily reduced to a relatively lower flow rate for the purpose of initiating arc transfer. Once the arc begins, the gas flow rate is automatically adjusted back to the desired higher flow rate so that normal gas assisted electrosurgery can progress to the desired gas flow rate. Automatic gas flow reduction for the purpose of arc initiation ensures that arc initiation conditions will be more reliable and consistent even when used in conjunction with electrical power control techniques used to improve arc initiation, such as such as those described in US-4,781,175 and US-A-Re 34,432. This improvement is particularly significant in those types of gas-assisted electrocoagulation in which a normal gasless electrosurgical generator is combined with a separate gas distribution apparatus. The improvement of initially reducing the gas flow rate allows the normal electrosurgical generator to more reliably initiate the arc transfer, because the lower gas flow rate is more conducive to the initiation of the arc transfer. Additionally, the lower gas flow rate during startup reduces the risk of gas embolism compared to the circumstance where a higher gas flow rate impacts tissue at a short distance.

Improved gas flow reduction during arc initiation is particularly beneficial in minimally invasive surgery. If the mouthpiece is positioned close to tissue or inserted into tissue, the reduced gas flow during arc initiation reduces the risk of gas embolism because less gas is initially delivered. The reduced flow rate during arc initiation allows checking if an occlusion occurs at a low risk rate of the gas flow. If an occlusion occurs, flow at the lower flow rate will be maintained or an alarm will be set which will also disable gas flow.

Improved gas flow reduction during arc initiation is also important in those gas assisted electrocoagulation systems which combine a normal gasless electrosurgical generator with a separate gas distribution apparatus. Most of these types of combination systems previously had no ability to improve arc initiation capabilities, because the normal gasless electrosurgical generator did not provide for adjustment of the power output to accommodate arc initiation. A further improvement available from the present invention relates to the detection of back pressure under all operating conditions and the disabling of the transfer of gas and electrical energy to the tissue when conditions of serious risk occur. By disabling the transfer of gas and electrical energy to the tissue, the surgeon is forced to take corrective action. The improvements of the present invention can be incorporated into the gas delivery apparatus such that when used in combination with an electrosurgical generator without normal gas, the combined system has an improved ability to initiate arc transfer to tissue and a risk reduced gas embolism.

One of the embodiments of the present invention relates to an ability to automatically reduce the gas flow rate under circumstances where partial occlusion occurs. Generally, a partial occlusion will result from the applicator nozzle being too close or embedded in the tissue. Such partial occlusions can occur before or after arch transfer has been initiated during the course of the procedure, as a result of the surgeon moving the nozzle into or too close to the tissue. Such circumstances can also create a risk of gas embolism. According to this embodiment of the invention, the back pressure in the gas distribution tube is detected and when it exceeds a predetermined value, the normal operating gas flow rate is incrementally reduced until the reduction of the gas flow rate results in an acceptable level of back pressure that is not likely to increase the risk of gas embolism. If the occlusion dissipates and the back pressure decreases as a result, the gas flow rate will automatically adjust upward in increments until the user required operating gas flow rate is achieved or the maximum amount of flow rate consistent with acceptable back pressure. This improvement of continually evaluating the

ES 2 255 494 T3 back pressure and adjusting the gas flow up and down, further serves to reduce the risk of gas embolism while maintaining the ability to return to the desired operating conditions selected by the surgeon.

Another embodiment of the present invention relates to detecting the back pressure associated with a particular type of applicator and adjusting the gas flow rate to an acceptable value for this type of applicator. Adjusting the gas flow rate to an appropriate operating range for different types and categories of applicators results in further assurance that the flow conditions for that type of applicator are the most conducive to promoting arcing to tissue and reducing the risks of gas embolism, both during the initiation of the arc and during the continued use of the applicator.

A more complete appreciation of the present invention will be obtained by reference to the following detailed description of the presently preferred embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a generalized illustration of a gas-assisted electrosurgical unit embodying the present invention, illustrating a gas delivery apparatus, an electrosurgical generator, and an applicator employed in an exemplary surgical procedure on tissue;

Figure 2 is a block diagram of aspects of the gas distribution apparatus depicted in Figure 1;

Figure 3 is a flow chart of the functions performed by the gas distribution apparatus depicted in Figure 2 during start-up conditions when the arcs are initially transferred to tissue, in accordance with the present invention;

Figures 4A, 4B and 4C constitute a single flow chart of the functions carried out by the gas distribution apparatus shown in Figure 2 during an endoscopic mode operating condition, in accordance with the present invention;

Figure 5 is a flow chart of the functions carried out by the gas distribution apparatus shown in Figure 2 during an automatic mode operating condition, in accordance with the present invention; and Figure 6 is a flow chart of the functions carried out by the gas distribution apparatus shown in Figure 2 during a manual mode operating condition, in accordance with the present invention.

A gas-assisted electrosurgical unit (ESU) which embodies the present invention is globally illustrated in Figure 1 and is referenced as 40. Electrosurgical unit 40 includes three main components: an applicator 42, such as a pencil-type handpiece used in open surgery or a tube-shaped probe used in minimally invasive surgery; a gas distribution apparatus 44 and an electrosurgical generator (ESG) 46. Gas distribution apparatus 44 and electrosurgical generator 46 may be combined into a single unit as described in US-4 781 175, or each (44 and 46) may be separate but functionally interconnected as described. in US-A-5 041 110 and 5 330 469. A flexible cable 48 connects the gas distribution apparatus 44 to the applicator 42. Electrosurgical generator 46 is connected to distribute radio frequency (RF) electrical energy to gas distribution apparatus 44 and electrical energy from electrosurgical generator 46 is conducted through gas distribution apparatus 44 to a cable 48. In the case in Where applicator 42 is a minimally invasive surgical probe, flexible lead 48 may be an extension of a tube-shaped portion of the probe itself.

Gas distribution apparatus 44 distributes a predetermined flow of gas through conduit 50 within cable 48 to applicator 42. Gas exits a nozzle 52 positioned at the distal end of applicator 42 in a flow stream. or substantially laminar direct jet 54. Electrical energy supplied by electrosurgical generator 46 is conducted through gas distribution apparatus 44 and is conducted by conductor 56 positioned within conduit 50 of cable 48. Conductor 56 is electrically connected to an electrode in the form of needle 58 which is placed in nozzle 52. Electrical energy supplied by electrosurgical generator 46 ionizes gas flowing around electrode 58 and through nozzle 52 to create ionized conductive paths in jet 54. Gas distribution apparatus 44, cable 48, and nozzle 52 are an example of means for driving a predetermined gas in a jet 54. Electrosurgical generator 46, lead 48, and electrode 58 are an example of means for transferring electrical energy in ionized conductive paths in gas jet 54.

In an active mode of operation of the electrosurgical unit 40, electrical energy is transferred in the ionized conductive path in the jet 54 in the form of arcs 60. The arcs 60 travel within the jet 54 until they reach the tissue 62 of the patient. at the electrosurgical site. The flow of gas from jet 54 pushes accumulated blood from the surface or stroma of tissue 62 and allows electric arcs 60 to enter tissue 62 without being bypassed into the conductive blood. The electric arcs create a lattice 64 of holes created by the arc in the tissue 62. The natural blood clotting mechanism is activated by lattice 64, resulting in blood clotting, stopping further bleeding, and sealing the tissue. The sealed coagulated layer

ES 2 255 494 T3 on the surface or stroma of the tissue forms what is known as a "gangrenous black scab". Details of the characteristics of the type of gangrenous black scab created from gas assisted electrosurgery and the significant advantages of gas assisted electrosurgery are more particularly described in US-A-4 781 175.

Electrical energy from arcs 60 travels through gas jet 54 to tissue 62 and through tissue to return electrode or patient plate 70 which is in contact with tissue 62 of the patient. Patient plate 70 is connected by a return electrical conductor 72 to electrosurgical generator 46. Thus, a complete electrical circuit is established to conduct current from electrosurgical generator 46 to electrode 58 at nozzle 52, through jet 54 to and through tissue 62, to patient plate 70, through lead of return 72 and back to electrosurgical generator 46. This type of circuit connection in which electrical energy flows from the applicator through the patient's tissue to a return electrode which is positioned remotely from the operation site is typically referred to as "monopolar" electrosurgery.

When the surgeon activates or "keys" the electrosurgical unit 40 for the distribution of electrosurgical energy to the tissue, the ionized conductive paths are first established within the gas jet. The ionized state of the ionized conductive paths in the gas jet 54 creates a corona or glow discharge within the jet and the glow discharge or corona is capable of initiating arc conduction when the surgeon moves the nozzle 52 into operative proximity. with fabric 62. When nozzle 52 is placed in operative proximity to tissue, ionized conductive pathways to tissue 62 establish a sufficient closed circuit through tissue 62 to begin or initiate transfer of the arc in jet 54 to tissue 62. Without maintaining the gas in a sufficiently ionized state to create sufficient ionized species in the gas jet 54, it is impossible or extremely difficult to repeatedly and reliably initiate the transfer of arcs 60 in the gas jet 54 to the tissue. A relatively high flow rate of gas through nozzle 52 makes it difficult to maintain ionized conductive paths in the gas jet to reliably and consistently initiate arcing transfer to tissue, particularly with an electrosurgical generator 46 provided with a low power output and a decreased ability to transfer significant power at relatively high load impedances.

Electrosurgical generator 46 includes conventional control dials and selectors 74 for the surgeon to select the amount and conditions of electrical energy to be delivered. Conventional control dials and selectors 74 are also included when electrosurgical generator 46 and gas distribution apparatus 44 are enclosed in a single unit. Similarly, control dials and selectors 74 are a part of gas distribution apparatus 44 that allow the surgeon to select the amount of gas flow to be delivered to the surgical site. A display 76 displays the amount of gas flow as well as other information. The gas flow displayed at 76 may change during use of the electrosurgical unit 40 to reflect the different flow conditions of the nozzle 52. The control dial 74 is also intended to represent the conventional switches (foot and toe) which the surgeon presses to activate on the electrosurgical unit 40. Releasing the activation switches deactivates the electrosurgical unit, terminating the flow of gas and electric power.

Gas assisted electrosurgery can be performed in open surgical conditions where an open incision is made and the tissue is exposed to the open atmosphere. Under such circumstances, the surgeon typically holds a pencil-shaped applicator 42 and moves it relative to the tissue to effect coagulation. In many cases, the open procedure does not make it difficult to visualize the site of operation or the relative position of the nozzle 52 with respect to the tissue. However, in aggressive bleeding situations the surgeon may insert the nozzle 52 into rapidly accumulating blood and not be able to gauge the distance of the nozzle to tissue. Under circumstances where the patient has atypical physiology or where an unusual incision placement appears, the surgeon may require to position the mouthpiece relative to the tissue in a way that it cannot be seen, making it difficult to calibrate the placement. relative of the nozzle to the tissue. Under these circumstances, the mouthpiece can be positioned against the tissue and the tissue can partially occlude the mouthpiece, increasing the risk of gas embolism.

Visualization of the operative site is more difficult under minimally invasive surgical conditions, where a direct stereoscopic view is not possible. Figure 1 illustrates the minimally invasive surgical condition by illustrating the nozzle 52 of the applicator 42 inserted through the abdominal wall 78. Although not all the details of this conventional laparoscopic surgical situation are depicted, abdominal wall 78 is kept away from tissue 62 by insufflation of supplied gas pressure into abdominal cavity 80. A miniature chamber (not shown) is also inserted. into the abdominal cavity 80 through which the surgeon views the site of the operation. The insufflation of gas pressure also forms an impediment or resistance that must be overcome by the gas flow that is distributed from the nozzle 52. Therefore, in laparoscopic situations, the pressure of the insufflated gas limits or alters the flow characteristics. of the gas jet 54, particularly when pressure regulators rather than mass flow regulators control the gas flow. A mass flow regulator will distribute gas flow rates based on mass flow rate which is less influenced by back pressure. Accordingly, a mass flow regulator gas distribution apparatus 44 is more likely to continue to distribute gas flow in partially completed situations or in situations where nozzle 52 is positioned close relative to tissue 62. Pressure regulator systems tend to decrease the amount of gas flow delivered under back pressure conditions, but pressure regulator systems are not as accurate or reliable under other circumstances.

IS 2 255 494 T3

An endoscopic surgical situation is also depicted in Figure 1, in the sense that applicator 42 and nozzle 52 are inserted into the patient's body. In endoscopic applications, generally an optical lens system (not shown) is part of the probe applicator 42. Figure 1 also depicts a gastrointestinal surgical situation, except that the probe applicator 42 is generally inserted into a normal body conduit such as the esophagus and stomach. Endoscopic and gastrointestinal operating sites are not normally pressurized with insufflated gas.

The present invention focuses on an automatic ability of the gas distribution apparatus 44 to adjust the gas flow rate under various functional electrosurgical conditions and in response to the type of applicator 42 attached to the gas distribution apparatus 44. The characteristics of the flow adjustment The condition sensitive gas devices of the present invention are particularly useful in minimizing the risks of gas embolism, regardless of the skill level of the surgeon. The flow adjustment features of the present invention are also useful in establishing the best operating conditions for different types of applicators 42. The gas distribution apparatus 40 of the present invention will also terminate the transfer of gas and electrical energy under the conditions. of gas flow that are inappropriate for the continuity of the procedure. Under these conditions the gas distribution apparatus 44 activates an alarm 82 to notify the surgeon of these conditions. The gas flow adjustment features of the gas delivery apparatus are applicable for use with an electrosurgical generator 46 specifically used for gas-assisted electrocoagulation for use with an electrosurgical generator 46 of the type that is primarily intended for normal gas-free electrosurgery. When used with an electrosurgical generator without normal gas 46, an improved ability to control electrosurgical conditions that may give rise to gas embolism risks is achieved.

Details of gas distribution apparatus 44 are described with reference to FIG. 2. Gas distribution apparatus 44 produces a regulated gas mass flow rate from a gas flow path 98 which is supplied to conduit 50 of cable 48 and led to nozzle 52 (Figure 1). The regulation of the mass flow is carried out using a closed loop control system, in which the mass flow rate required by the user is compared to the measured mass flow rate, an error signal is developed regarding the difference and the flow of gas in the gas flow path 98 is adjusted until the control loop stabilizes.

The gas distribution apparatus 44 includes a gas source 100, a pressure regulator 102, a pneumatic manifold 104, a sensing port 106, and a filter 108. The gas source 100 may be a conventional initially pressurized argon gas reservoir. up to about 20.7 MPa (3000 pounds per square inch), to supply gas to pressure regulator 102. The present invention supplies argon gas, or any other inert gas that can be ionized with radio frequency energy for clinical applications in electrosurgery. A pressure gauge 110 is preferably interposed between the argon gas source 100 and the pressure regulator 102 to indicate the amount of gas remaining in the gas reservoir. The pressure regulator 102 reduces the pressure of the gas source 100 to a low pressure, preferably about 0.138 to 0.207 MPa (20 to 30 pounds per square inch) and provides this gas at low pressure to the pneumatic manifold 104. The secondary side Pressure regulator outlet or outlet 102 preferably has a pressure release valve 112 connected thereto as a safety mechanism in the event of failure. Pressure relief valve 112 opens at approximately 0.345 MPa (50 pounds per square inch) in the event that pressure regulator 102 fails to reduce pressure at its outlet.

Pneumatic manifold 104 includes electrically controlled valves 114 and 116 to control and regulate the mass flow of gas in flow path 98. Preferably, pneumatic manifold 104 includes a solenoid valve 114, which opens whenever the unit is activated. electrosurgical unit 40 (FIG. 1) for use and is closed whenever the electrosurgical unit 40 is deactivated. A proportional valve 116 regulates the mass flow rate of gas distributed in the flow path 98. The proportional valve 116 increases and decreases the gas flow as a result of a control signal (156) applied thereto. Optionally, a flow damper (not shown) may be positioned downstream of proportional valve 116 to damp any minor fluctuations or oscillations in gas flow that may occur as a result of variations in flow from proportional valve 116.

The sensing port 106 includes a calibrated flow limitation 118 that reduces the pressure from an inlet 120 of the sensing port 106 to an outlet 122 of the sensing port 106. The differential pressure across the sensing port 106 is the basis for the gas flow control information used in the mass flow control loop. Differential pressure across sensing orifice 106 between inlet 120 and outlet 122 is proportional to gas flow in flow path 98. An increase in flow causes an increase in differential pressure and a reduction in flow causes a reduction. in differential pressure measured across calibrated limitation 118. Hoses 124 and 126 connected to inlet 120 and outlet 122 on opposite sides of calibrated limitation 118 provide differential pressure information to a differential pressure transducer 132. A third hose 128 is connected at a downstream location of the calibrated limitation 118 to an absolute pressure transducer 134. The absolute pressure transducer 134 initially provides information regarding the atmospheric pressure in the flow path 98 downstream of the sensing orifice 106. Initially, before the gas flows through the flow path 98, the atmospheric air pressure The ambient environment corresponding to the altitude at sea level in which the electrosurgical unit 40 is used is detected by the transducer 134 through the third hose 128. Information on atmospheric pressure is used to compensate for the amount of gas distributed according to different altitudes. The altitude-related signal is later referred to as

ES 2 255 494 T3 the reference signal (or Ref). As gas flows in flow path 98, absolute pressure transducer 134 measures the back pressure of gas in flow path 98.

Filter 108 is included in the gas flow path 98 downstream of detection port 106 to ensure distribution of clean argon gas within cable 48, to nozzle 52, and tissue 62 (FIG. 1). A connector (not shown) couples the gas in the gas flow path 98 within the end of the cable 48. Electrical power from electrosurgical generator 46 is also preferably coupled through this same connector (not shown) to conductor 56 positioned in conduit 50 of cable 48 (FIG. 1).

Differential pressure transducer 132 supplies an output voltage signal on line 130 that is proportional to differential pressure across flow limitation 118 at sensing port 106. The voltage signal at 130 from the Differential pressure transducer 132 is provided with an amplifier 138 which amplifies the voltage signal at 130 to provide an output voltage called dP (delta pressure) on line 140. The dP signal at 140 is proportional to the gas flow through the detection port 106.

The absolute pressure transducer 134 supplies an output voltage signal on line 136 that is proportional to the absolute pressure sensed downstream of the calibrated limitation 118. The signal at 136 is proportional to the back pressure caused by the applicator, caused by the position of the applicator relative to tissue or caused by an occlusion, while gas is flowing in the flow path 98. The voltage signal at 136 from the absolute pressure transducer 134 is provided to an amplifier 142 which amplifies the voltage signal and provides an output voltage called P_TObs (absolute pressure) on line 144. Signal P_TObs on line 144 is proportional to the absolute pressure sensed by transducer 134.

The output voltage signals dP and P_Abs on lines 140 and 144, respectively, they are supplied to an analog multiplier 146 that multiplies the two signals 140 and 144. The output signal of the resulting product at 148 from multiplier 146 is linearly proportional to the measured mass flow rate of gas conducted to through the flow path 98. The ratio of that represented by signal 140 and the absolute pressure represented by signal 144 to the measured flow represented by signal 148 is well known. The output signal at 148 therefore represents the measured mass flow rate of gas flowing through the flow path 98.

The voltage signal P_Abs is also supplied as an intake signal to an amplifier 147. An output signal from amplifier 147 is supplied at 149 as the voltage signal (PMEA) relative to the measured back pressure of the gas flow through the flow path 98, or ambient atmospheric pressure when no gas is flowing through flow path 98. The PMEA signal at 149 is applied as an intake signal to a control loop microcontroller 150. An analog-to-digital converter (not shown, but included within the microcontrol 150) converts the PMEA voltage signal into a digital signal for use by the microcontrol 150.

Microcontrol 150 is connected to flow control selector 74 to receive various input signals from user requirements including activation requirements by the surgeon. The signal at 153 is related to the user required gas flow rate selected by the surgeon.

The microcontrol 150 establishes a flow output signal (VGAS) at 151 which is initially set by the user request admission signal at 153. The VGAS signal at 151 is referred to as the displayed flow rate and this signal is presented to the user on display 76. In cases of safe and normal operation, the displayed flow rate signal (VGAS) will essentially correspond to the value represented by the user request signal at 153. However, under some circumstances as described below, the displayed flow rate signal VGAS at 151 may be modified by the action of the microcontroller 150 in response to the value of the measured back pressure signal PMEA at 149. Under such circumstances, the amount VGAS displayed on display 76 will differ from the amount represented by user request signal 153. The VGAS signal is an analog signal created by a digital-to-analog (D / A) converter (not shown) included within the microcontroller 150.

The voltage signal of the mass flow rate measured at 148 from the analog multiplier 146 is amplified by an amplifier 152 and the resulting signal at 155 is compared to the VGAS signal at 151 by a differential amplifier 154. Therefore, the displayed flow rate represented by the VGAS signal is compared with the signal of the gas mass flow measured at 155. Any difference between the measured gas mass flow signal and the displayed flow signal is represented by a control signal at 156 supplied by the differential amplifier 154. The control signal at 156 will cause an adjustment to the flow set by the proportional valve 116 , thereby increasing or decreasing the gas flow rate through the proportional valve 116. When the measured flow rate (signal 155) exceeds the displayed flow rate (signal 151), the control signal 156 distributed to the proportional valve 116 will reduce the gas flow. Conversely, when the measured flow rate is less than the displayed flow rate, the control signal 156 causes the proportional valve 116 to increase the gas flow through the flow path 98. As the gas mass flow rate changes with different flow conditions at the site of operation, the described control loop will alter the control signal at 156 until a steady state gas flow rate corresponding to the flow rate of the gas is obtained. gas required by the user or allowed. A conventional emitter follower circuit (not shown) receives control signal 156 and directs current to proportional valve 116 relative to the value of control signal 156.

IS 2 255 494 T3

When the measured back pressure (PMEA) exceeds the defined limit conditions, operational disablement and corrective actions are taken, according to the operating mode of the electrosurgical unit and its gas flow setting. The back pressure signal PMEA 149 is monitored by the microcontrol to achieve these functions. If the back pressure exceeds a predetermined limit, the operation of the gas distribution apparatus 44 is turned off and the solenoid valve 114 and proportional valve 116 are turned off to terminate the gas distribution. When a dangerous occlusion condition occurs, it is preferable to terminate the gas flow through the gas flow path 98 and terminate the distribution of radio frequency electrical energy from the electrosurgical generator 46 (Figure 1), provide an audible alarm (such as a beep or tone) to the surgeon from alarm 82 (Figure 1) and provide a visual indication (such as an error code or message) on display 76 about the condition that caused the disconnection. Less dangerous partial occlusions, transient minor occlusions and certain other control conditions cause a reduction in the flow of gas distributed in the flow path 98.

Since the gas flow rate is controlled by the closed loop regulation of the mass flow, the gas flow will attempt to be maintained even when an occlusion blocks the gas flow from the nozzle 52. Under such circumstances, without the characteristics of the flow adjustment described here, a stroke or other dangerous condition may occur. Therefore, the back pressure itself within the gas flow path 98 is used to anticipate an occlusion or other restriction in the gas flow lines and to control the mass flow rate of the gas when the back pressure exceeds previously established limits. determined. The previously determined limits of back pressure are specific to different modes of operation of the gas distribution apparatus and are related to the various gas flow settings required by the user, all of which are selected by the surgeon.

When the gas distribution apparatus 44 is first turned on, the PMEA voltage signal at 149 is read and stored in the memory of the microcontroller 150. This initial value is used as a reference voltage or signal (Ref) for the duration of the procedure. and for other purposes associated with the functional mode of the electrosurgical unit, as described below. In addition, for each setting or flow rate within a permitted functional range of gas flow rates from the electrosurgical unit, the PMEA voltage is anticipated to be a specific incremental value above the set reference voltage. The anticipated incremental value of the PMEA signal at each flow rate is empirically determined and is related to the characteristics of the components used in the gas distribution apparatus 44. The anticipated incremental values ​​for each flow rate are stored in a memory associated with the microcontrol 150 for use during the operations described below.

One of the improvements available from the present invention relates to facilitating a more reliable initiation of arc transfer energy in gas jet 54 to tissue, even under conditions where electrosurgical generator 46 does not have the ability to specifically modify the energy distribution for improved arc initiation. This improvement is particularly useful to avoid the risk of gas embolism in those circumstances where it is necessary to bring the mouthpiece 52 (Figure 1) close to the tissue to initiate the transfer of the arch. Under such circumstances, the proximity of the nozzle to the tissue with the relatively high gas flow rate selected for continuous electrocoagulation can increase the risks of gas embolism.

Generally speaking, the gas flow rate is temporarily reduced in order to improve arc initiation after the electrosurgical unit is activated and allows any occlusion to be detected under the less hazardous conditions of reduced gas flow. After the arc transfer has started and no occlusion is detected, the relatively high gas flow rate required by the user is then automatically delivered. This particular functionality is described with reference to Figure 3 and is referred to herein as "soft start".

The "soft start" procedure represented in Figure 3 is executed by the instruction code contained within the microcontrol 150 (Figure 2). The soft start functional flow begins in step 180 and is applied for an initial period of time beginning with activation of the electrosurgical unit. Microcontrol 150 receives a signal indicative of the activation request from the surgeon as one of the signals from control selector 74 (FIG. 2). In response to the activation request, a start time clock is initially started (not shown). Immediately thereafter, a determination is made at step 182 as to whether this is the start, that is, time zero, or if it is not, of the soft start procedure. If so, a determination is made in step 184 whether the displayed flow (which is initially the same as the flow required by the user) is greater than 2 standard liters per minute. If so, the measured gas flow rate is reduced to 2 standard liters per minute, as depicted in step 188.

Thereafter in step 188 an occlusion test is started in the flow path. The PMEA back pressure signal (149, FIG. 2) is checked in step 190 to terminate if it exceeds a previously determined alarm limit (LIM_AL). The previously determined alarm limit LIM_AL referred to in figure 3 represents an empirically defined maximum back pressure limit which can be accepted for a flow rate of 2 standard liters per minute which is established in step 186. If the back pressure exceeds this limit of previously determined alarm and an unacceptable back pressure condition exists, an alarm condition is initiated as depicted in step 192. In conjunction with the alarm condition initiated in step 192, the electrical energy (RF) from the electrosurgical generator 46 (Figure 1) and the gas flow rate from the gas distribution apparatus 44 (Figure 1 and 2) is terminated as shown in step 192, thereby deactivating the electrosurgical unit. Once the unit is deactivated

ES 2 255 494 T3 electrosurgical in step 192 it is necessary to initiate again another activation request for continued use of the electrosurgical unit, after the cause of the occlusion has been determined and corrected.

If the determination in step 190 is no, indicating that the measured back pressure (PMEA) is less than the previously determined alarm limit (LIM_AL), the procedure flow advances to step 194 and then returns from step 190 to the start step 180. of the procedure. Additionally, if the determination that the displayed flow rate is less than 2 standard liters per minute in step 184, the flow is low enough to initiate good arc-to-tissue transfer so that the program flow advances to step 194. A loop or execution of the soft start procedure flow occurs every 100 milliseconds.

With the second and subsequent loops through the soft start procedure flow, the activation time clock (not shown) has advanced to the point where the determination made in step 182 causes the program flow to advance to the determination in step 196. In step 196 the determination is made as to whether the time clock has exceeded 600 milliseconds, which occurs in approximately the sixth loop through the procedure depicted in FIG. 3. If the determination in step 196 is no, begin an occlusion test in step 188, followed by execution of the subsequent functionality represented by steps 190 and 192. If the determination in step 196 is yes, the user-required flow rate value (153, FIG. 2) is displayed, as shown in step 198. After that, the program flow advances to step 194.

With each subsequent step beyond the first step through the soft start control procedure depicted in Figure 3 and if a back pressure alarm and trip condition does not exist and until the elapsed time of this soft start procedure exceeds 600 seconds, the program flow advances from step 196 to steps 188, 190 and 194, thereby returning for another execution of the soft start procedure at 100 millisecond intervals. When transitions have occurred through a sufficient number of loops in the program flow depicted in Figure 3 and the determination at step 196 is yes, the gas flow rate is then set at step 198 to display on display 76 (Figures 1 and 2) the gas flow rate required by the user. Therefore, with the execution of step 198, the temporarily reduced gas flow rate set during the soft start procedure is thereafter set to the gas flow rate that has been required by the user, unless other factors intervene thereafter. described later.

The initially lower gas flow rate established in step 184 promotes arc transfer starting. The arc transfer immediately begins to create a gangrenous black crust that positions the tissue against gas ingress and the sealing effect continues as the relatively higher gas flow rate is distributed. The amount of time over which the reduced start gas flow rate is delivered is limited, thereby only momentarily and almost imperceptibly limiting the electrocoagulation effect of that full effect desired by the surgeon. Even if the low start gas flow does not momentarily clean the blood from the tissue, the higher gas flow that occurs very quickly will. If for some reason the arc initiation has not started at the end of the soft start sequence, the full flow distribution will be recognized by the surgeon as representative of a problem, at which point the surgeon must deactivate the electrosurgical unit and start another activation sequence after corrective action has been taken.

The soft start enhancement is of particular use and benefit in those gas assisted unit combinations utilizing a normal gasless electrosurgical generator in combination with a gas distribution apparatus. The improved starting capability available from gas flow control is comparable to that improved utility that was previously available only by modifying the electrical and power output characteristics of the electrosurgical generator to start the arc transfer. Since a typical normal gasless electrosurgical generator does not offer the ability to modify its electrical output characteristics for gas-assisted electrosurgical arc initiation, most, if not all, of its gas-assisted electrosurgical unit combinations type do not possess enhanced arc initiation characteristics. This improvement of the present invention provides such improved arc initiation characteristics without modifying the output characteristics of the electrosurgical generator.

This initial low flow rate that is established during the soft start procedure (step 184, Figure 3) is sufficient to determine if an occlusion initially exists and allows any occlusion to be removed before the gas flows at the actual required flow rate. A gas embolism condition may occur almost immediately after the gas distribution apparatus is activated and the soft start procedure will allow detection of such conditions. PMEA tension sampling (149, Figure 2) is performed for an occlusion during this time period. Two effects can cause detection and response delays before gas flow can terminate in response to an occlusion. The first delay effect is the amount of time required to build back pressure in the gas flow path 98 (FIG. 2). The first delay may depend on the type of applicator attached and the required flow rate. The second delay may be intentionally selected to anticipate some minimum but safe period of time for an occlusion to exist before action is taken in response. This second delay allows slight intermittent or transient flow limitations to be ignored.

The period of time chosen for the soft start may not be sufficient to detect an occlusion in all cases; however, the soft start can still provide advantages that can minimize the risks of embolism caused by the distribution of relatively high gas flows to the patient. Low flow pre-pressurizes the gas flow path before a higher gas flow begins, thereby reducing

ES 2 255 494 T3 mode the amount of time the highest gas flow rate will provide before an occlusion can be detected at the highest gas flow rate. In this manner, the inadvertent flow will be distributed to the patient at the lowest starting flow rate for part of the time and the electrosurgical unit 40 can then be turned off before too much gas flows. Pre-pressurization also provides pressure to transducers 132 and 134 (FIG. 2) so that the required higher gas flow can be regulated and stabilized with minimal or no excess when the soft start time period ends.

The soft start procedure is preferably incorporated into all functional mode flow verification procedures described below. Since the soft start procedure must occur before the gas flow adjustment procedures described below, it is preferable to place the soft start procedure at the beginning of the flow check procedures described later. The manual mode flow verification procedure described below in conjunction with Figure 6 is so short, however, that it may also be acceptable to place the soft start procedure after the flow verification procedure depicted in Figure 6.

One of the improvements of the present invention involves detection of back pressure to determine the type of applicator connected to the gas distribution apparatus. This improvement is particularly beneficial in the determination when minimally invasive applicators (endoscopic or gastrointestinal) are attached. The functionality of this particular aspect of the invention is referred to below as the "endo" mode and is more fully described in Figures 4A, 4B and 4C. The endo mode limits the maximum allowable flow to 4 standard liters per minute. The flow rate for endo mode is therefore 0.1 to 4 standard liters per minute and is set by user-selected minimum and maximum flow limits based on user-selected power settings.

Gastrointestinal (GI) electrosurgical probes are examples of types of applicators used in the endo mode and are characterized by an outer diameter that is in the range of from about 1.5mm to about 3.4mm. The inner diameter can be 25% to 35% smaller. These applicators can produce back pressure in excess of 6.89 kPa (one pound per square inch) even at very low flow rates and can even produce as much as 41.4 kPa (6 pounds per square inch) back pressure at 4 standard liters per minute, thereby mimicking the behavior of an occlusion. Such high back pressures cause the flow velocity in the nozzle orifice 52 (FIG. 1) to increase, which can cause arc start failures or short arc transfer and working distances.

When operating in endo mode, the control microcontrol 150 will set a maximum limit for the PMEA signal (149, Figure 2) and, when this limit is exceeded, the flow rate will be reduced to no more than 2 standard liters per minute. The microcontroller 150 reduces the flow rate by varying the control signal 156 (FIG. 2). By reducing the flow rate, the back pressure will be reduced and the velocity of the gas in the nozzle orifice 52 will be reduced allowing for easier ionization and transfer of the arc. Exemplary limits established for flow reduction and occlusion alarm actions are listed in Table 1 below.

TABLE 1

<td>Action</td><td>PMEA (standard liters per minute)</td><td>PMEA V</td><td>Comments</td>

<td>Occlusion alarm</td><td> &lt;1,0</td><td>Ref + 0.5 V</td><td>RF &amp; flow disabled</td>

<td>Occlusion alarm</td><td>&gt; 1.0 and &lt;1.5</td><td>Ref + 1.2 V</td><td>RF &amp; flow disabled</td>

<td>Occlusion alarm</td><td> &gt;1,5</td><td>Ref + 1.3 V</td><td>RF &amp; flow disabled</td>

<td>Flow reduced by 0.5</td><td>&gt; 1.0 and &lt;1.5</td><td>Ref + 0.6 V</td><td>Reduced flow</td>

<td>Flow reduced by 0.5</td><td> &gt;1,5</td><td>Ref + 0.7 V</td><td>Reduced flow</td>

<td>Reduced by 0.5 but not less than 0.1</td><td> &lt;1,0</td><td>Ref + 0.3 V</td><td>Reduced flow</td>

When the PMEA signal is greater than the set reference voltage (Ref) plus an appropriate reference range GI, such as approximately 0.3 V (an empirically derived value that depends on the ac10

In characteristics of the equipment used in the gas flow apparatus 44), the attached applicator is assumed to be a GI probe. The GI reference range distinguishes the back pressure of a GI probe from an endoscopic probe, which is less restrictive. With the desired flow rate set greater than 2 standard liters per minute for a GI probe, the flow is automatically reduced to 2 standard liters per minute or 1.5 standard liters per minute with each activation of the electrosurgical unit. Care must be taken, however, not to damage the electrode with the high electrical energy if the power is set too high. When the activation requirement is finished, then the flow rate is returned to the original setting, but no gas flows until the electrosurgical unit is deactivated.

Table 1 shows an example of the action to take for typical flow ranges. The flow rate will be reduced as represented in the action column if the PMEA signal exceeds the specified limits. The set reference voltage (Ref) is typically in the range of 2 V to 2.6 V. For each displayed flow rate range set by microcontrol 150 (DIAL), a maximum PMEA signal is represented, above which both an occlusion alarm action and a gas flow reduction action will occur. For a flow reducing action, the gas flow rate is reduced in appropriate steps, such as 0.5 standard liters per minute. In a preferred embodiment, the gas flow rate is reduced only one step for the activation of the current radio frequency. For an occlusion alarm action, not only is gas flow disabled, but electrical power is also terminated and the electrosurgical unit is disabled.

In this example, for a desired flow rate in a low range, such as less than about 1.0 standard liter per minute, if the PMEA signal is more than the set reference voltage plus an appropriate default margin, such as about 0.3 V, then a flow reducing action is carried out in which the displayed flow rate is reduced by an appropriate amount, such as for example about 0.5 standard liters per minute, as long as the resulting flow rate is not less than the appropriate minimum, such as for example about 0.1 standard liters per minute. If, however, the PMEA signal is greater than the set reference voltage plus an appropriate occlusion margin, such as for example about 0.5 V, then an occlusion alarm action is taken. For a desired flow rate in a medium range, such as for example between about 1.0 and about 1.5 standard liters per minute, if the PMEA signal is more than the set reference voltage plus an appropriate default margin, such as for example about 0.6 V, then a flux reducing action is carried out; but if the PMEA signal is greater than the set reference voltage plus an appropriate occlusion margin, such as for example 1.2 V, then an occlusion alarm action is performed. For a desired flow rate in an appropriate high range, such as for example above about 1.5 standard liters per minute, if the PMEA signal is more than the set reference voltage plus an appropriate default margin, such as for example about 0 , 7 V, then a flux reducing action is carried out; but if the PMEA signal is greater than the set reference voltage plus an appropriate occlusion margin, such as for example about 1.3 V, then an occlusion alarm action is performed.

Figures 4A, 4B and 4C constitute a flow chart for an exemplary gas flow adjustment procedure in the endo mode. This flow verification procedure is performed at appropriate intervals, such as approximately every 10 milliseconds. Microcontroller 150 (FIG. 2) initiates the procedure in step 200 and proceeds to step 201 in which it determines if the displayed flow rate is less than the setting required by the user. This step 201 prevents the procedure from performing the following flow reduction steps more than once, so that if the answer to step 201 is yes, the procedure branches to step 220 depicted in FIG. 4B. if the answer to step 201 is no, then it is determined whether the PMEA signal exceeds the allowed reference range GI (GI_REF) in step 202. If not, the procedure then branches to step 210. But if so, then in step 204, a GI probe indication signal (GI PROBE) is connected, to indicate that the procedure assumes the presence of a GI probe; and a timer is started at zero, so that the occlusion detection procedure can be done after an appropriate interval of time. Then in step 206, the procedure determines if the displayed flow rate is set greater than a maximum value, such as about 2.0 standard liters per minute, above which it will be inappropriate to drive a GI probe. If so, then in step 208, the displayed flow rate is set back to the maximum allowable gas flow rate for a GI probe (such as for example 2 standard liters per minute). Then in step 207 it is determined if the power selected by the user is greater than a previously determined maximum (such as for example approximately 80 W), above which the applicator electrode will be damaged if the gas flow rate is set too high. under. If so, then the control flow branches to passage 220 depicted in FIG. 4B. In a preferred embodiment, the endo mode will only reduce the gas flow rate once and then keep the flow rate at the value until conditions are appropriate to return the flow rate to the original setting required by the user (see step 232, Figure 4C). . If the determination in step 206 or 207 is no, the control flow proceeds directly to step 210 without changing the actual flow rate in step 208.

Beginning at step 210, steps are taken to reduce the gas flow rate if the back pressure is too high, but not high enough to turn off the electrosurgical unit. In step 210, the displayed flow rate range is determined. If the displayed flow rate is in an appropriate low range, such as less than about 1.0 standard liters per minute, then the procedure determines in step 212 if the PMEA signal is greater than a supplemental low reference voltage (REF_SUP LOW ), which is the established reference voltage plus an appropriate low fallback margin, such as approximately 0.3 V. If the displayed flow rate is in the mid range, such as greater than or equal to about 1.0 standard liters per minute and less than about 1.5 standard liters per minute, then the procedure determines in step 214 whether the PMEA signal is greater than a supplementary mean reference voltage (REF_SUP MED), which is the set reference voltage plus an appropriate mean supplementary margin, such as 0.6 V. If the displayed flow rate is in the range

ES 2 255 494 T3 high, such as for example greater than or equal to approximately 1.5 standard liters per minute, then the procedure determines in step 216 if the PMEA signal is greater than a supplementary high reference voltage (REF_SUP HIGH), which is the set reference voltage plus an appropriate high fallback margin, such as 0.7 V. If the condition verified in steps 212, 214 or 216 is determined to be true, then this condition indicates too great a back pressure, such that the displayed flow rate provided by the microcontroller 150 to control the proportional valve 116 is reduced by an appropriate amount, such as for example about 0.5 standard liters per minute (step 218) and control proceeds to step 220 depicted in Figure 4B. If the condition verified in steps 212, 214 or 216 is determined not to be true, then the back pressure is acceptable, therefore no set actual flow adjustment is made and control proceeds directly to step 220 depicted in FIG. 4B.

Starting at step 220 depicted in Figure 4B, the procedure performs the steps to disconnect the electrosurgical unit 40 when the back pressure is so high that a high risk condition has occurred, such as an occlusion. In step 220, the procedure determines if an appropriate time interval (TIMER) has elapsed, such as approximately 220 milliseconds, so that a complete shutdown of the electrosurgical unit 40 has not occurred too quickly, thereby providing time to that a transient occlusion problem be corrected prior to disconnection. If so, then it is appropriate to reset the timer again. If not, the occlusion may be transient and the procedure branches off at the end of the occlusion detection portion of the procedure depicted in FIG. 4B. If the appropriate time interval set in step 220 has passed, then the procedure determines the range of flow rate displayed in step 222. If the displayed flow rate is in a low range, such as less than about 1.0 standard liters per minute, then the procedure determines in step 224 if the PMEA signal is greater than a low alarm trigger reference voltage. (LOW_TRIP_POINT), which is the set reference voltage plus an appropriate low occlusion margin, such as about 0.5V for example. If the displayed flow rate is in the mid-range, such as greater than or equal to about 1.0 standard liters per minute and less than about 1.5 standard liters per minute, then the procedure determines in step 226 whether the PMEA signal is greater than a mean alarm trigger reference voltage (MEAS_TRIP POINT), which is the set reference voltage plus an appropriate mean occlusion margin, such as about 1.2 V. If the displayed flow rate is in the high range, such as greater than or equal to approximately 1.5 standard liters per minute, then the procedure determines in step 228 whether the PMEA signal is greater than a trigger reference voltage of the high alarm (HIGH POINT_TRIP), which is the set reference voltage plus an appropriate high occlusion margin, such as 1.3 V. The alarm trigger reference voltages are the trip point above which an occlusion alarm needs to be set, so if the condition verified in steps 224, 226, or 228 is determined to be true, then this condition indicates that the back pressure is so high that an occlusion may interfere with the safe performance of the electrosurgical unit 40, therefore the procedure disables the electrosurgical unit 40 and establishes a flow limit error (step 230), which indicates an occlusion alarm condition and provides an alarm and displays prompts to the user on display 76 and alarm 78 (figure 1). Thereafter the flow of control proceeds to step 232 depicted in FIG. 4C. If the condition verified in steps 234, 236, or 228 is determined not to be true, then it is assumed that no occlusion condition exists, so control proceeds directly to step 232 depicted in FIG. 4C.

In step 232 depicted in FIG. 4C, the procedure determines whether it is appropriate to return the displayed flow rate to the original setting required by the user. In step 232, it is determined whether the PMEA signal is less than a V_REQ_USER signal, which is the set reference voltage plus the anticipated incremental rise that would result from the user-required adjustment minus an appropriate margin, such as about 19 mV, an experimentally established safety value. Also in step 232 it is determined whether the displayed flow rate is greater than the current anticipated flow rate equivalent to that of the PMEA signal. If the answer to step 232 is yes, the displayed flow rate is set to the user-required setting and the GI probe signal is turned off (step 234) and the procedure terminated (step 236). Otherwise, as determined in step 232, the procedure ends without returning the settings to their original values.

It will be understood that the maximum limits for measured back pressure (PMEA) depicted in Figures 4A, 4B and 4C are only exemplary and that experience or experimentation may indicate that different limits might be more appropriate in different applications. Additionally, different responses to different back pressure conditions may be found to be appropriate for different applications.

The automatic mode of operation of the electrosurgical unit is mainly selected for open surgical procedures, in which gas flow rates of up to 10 standard liters per minute are commonly used. The automatic mode, referred to herein as the "auto" mode, operates on essentially the same principle as the endo mode to reduce or completely disable gas flow or operation of the electrosurgical unit 40. In the auto mode, the gas flow rate is adjusted relative to the power setting of the electrosurgical unit 40, although it will be understood that the auto mode may include any situation in which the surgeon does not manually control the flow rate, but merely establishes a desired power level and allow electrosurgical unit 40 to automatically adjust flow rate as appropriate.

In auto mode, it is preferred that the gas flow be reduced, or "supplemented", in single liter increments, in an attempt to keep the measured back pressure within defined and appropriate limits. Steps of different sizes or even a continuous adjustment of the gas flow can be used in other embodiments or in other

ES 2 255 494 T3 applications. It is also preferred that the flow rate is reduced to not less than 4 standard liters per minute or some other appropriate minimum value. Therefore, if the desired flow setting is 10 standard liters per minute, then the flow can only be reduced by as much as 6 standard liters per minute. If the minimum flow rate is reached and the maximum pressure limit occurs, then an alarm will be set and the electrosurgical unit will be disabled.

For each adjustment required by the user, the limit to which the flow rate will be supplemented preferably occurs at essentially the same point, such as for example when the PMEA signal exceeds the set reference voltage plus an anticipated incremental rise indicated by the adjustment required by the user plus an experimentally determined appropriate default margin. Such an appropriate range may be about three analog-to-digital (A / D) conversion counts of microcontroller 150 (FIG. 2), which is three times the A / D resolution. An occlusion alarm will result when the PMEA signal exceeds an absolute maximum at any flow rate, such as approximately 3.3 V, or when the PMEA signal exceeds the set reference voltage plus the anticipated incremental rise due to the adjustment required by the user plus an appropriate occlusion margin, such as for example about ten A / D counts. It is preferred that the occlusion alarm effectively disconnects the electrosurgical unit 40 by disabling the transfer of radio frequency energy and gas flow. The occlusion alarm condition will need to be maintained for an appropriate time before the alarm will actually occur.

For example, the resolution of the analog-to-digital converter (not shown) of the microcontroller 150 (FIG. 2) may be approximately 0.02 V for each A / D count, or bit. For example, Table 2 illustrates typical anticipated and default limits for each user-required setting from 4 to 10 standard liters per minute. This example assumes that the displayed flow rate has a lower limit of 4 standard liters per minute. The default voltage is three counts, or approximately 0.06 V, above Ref plus the anticipated voltage for each user-required setting. After the displayed flow rate has been supplemented, the procedure will check to see if the PMEA signal exceeds the new default limit. It is also preferred that, after a fallout, the PMEA signal is compared to the fallout limit in the original setting required by the user. In other words, in this example, if the original setting required by the user was 10 standard liters per minute, then after each supplement occurs, the next PMEA signal check will compare the actual PMEA signal with 2.45V, the default limit for a user-required setting of 10 standard liters per minute. The maximum voltage for PMEA at which an occlusion alarm is set is approximately 10 counts, or approximately 0.2 V, above the reference plus the anticipated voltage for each user-required setting.

TABLE 2

<td>DIAL (standard liters per minute)</td><td>PMEA (anticipated)</td><td>PMEA (supplementary)</td><td>PMEA (occlusion)</td>

<td> 10</td><td>2.39 V</td><td>2.45V</td><td>2.59 V</td>

<td> 9</td><td>2.35 V</td><td>2.41V</td><td>2.55V</td>

<td> 8</td><td>2.31 V</td><td>2.37 V</td><td>2.51 V</td>

<td> 7</td><td>2.27 V</td><td>2.33 V</td><td>2.47V</td>

<td> 6</td><td>2.24 V</td><td>2.30 V</td><td>2.44V</td>

<td> 5</td><td>2.20 V</td><td>2.26 V</td><td>2.40 V</td>

<td> 4</td><td> -</td><td> -</td><td> -</td>

The auto mode flow verification procedure is illustrated by the flow chart depicted in Figure 5. This flow verification procedure is performed at appropriate intervals, such as approximately every 100 milliseconds. The microcontroller 150 enters the procedure in step 250 and proceeds to determine if the displayed flow rate is greater than a previously determined minimum value, such as about 4 standard liters per minute in this example (step 252). In this example, the minimum flow rate for an auto mode procedure is assumed to be 4 standard liters per minute. If the answer is no at step 252, then control branches to step 262 where it begins checking to determine if an occlusion condition exists. Otherwise, the procedure will verify whether the displayed flow needs to be reduced (step 254) by determining whether the PMEA signal is greater than an appropriate default limit (SUP_LIM), which is the set reference voltage (Ref) plus the anticipated incremental increase over Ref voltage indicated by user required setting plus appropriate offset. In this example, the deviation is approximately 59 mV, or three counts from the analog-to-digital converter that distributes the PMEA signal to microcontrol 150. The procedure will also check to ensure that an appropriate time interval (DELTA TIME) has passed since it was performed. the last flow check so that a sufficient amount of time has passed to allow

ES 2 255 494 T3 that any previous flow changes stabilize in the gas flow path. In this example, the time interval is represented as 0.25 seconds, but it can be any appropriate value. The clock that counts this time interval is reset each time the flow rate is changed. If the answer in step 254 is yes, then the procedure reduces the displayed flow rate by a predetermined appropriate amount, such as about 1 standard liter per minute (step 256). As indicated, this step will not allow you to reduce the gas flow below the established minimum, approximately 4 standard liters per minute in this example. If, however, the answer in step 254 is no, then the procedure will check (step 258) if the conditions are correct for the gas flow rate to be increased to return the gas flow rate closer to its original value. .

Supplementation can occur with certain applicators, particularly those that do not have a standard nozzle, a small nozzle, or an applicator that has limited flow due to its length. These types of applicators will cause the flow to supplement from the original setting required by the user. The number of increments in which the flow rate is reduced will generally depend on the initial setting required by the user. For example, the flow can be reduced by just one interval, or about 1 standard liter per minute, to a relatively low user-required initial setting, but the flow can be reduced by a larger amount, such as for example 4 standard liters. per minute (4 standard 1 liter intervals per minute), at a relatively high user-required initial setting. In other cases, an applicator can be used at moderate or low initial flow rates, but a higher flow rate will cause flow or occlusion alarms, in which case the manual mode of operation should be selected for use.

In step 258, the flow procedure again ensures that an appropriate time interval (DELTA TIME) has passed, such as about 0.5 seconds in this example. For example, the procedure will take about a second and a half to return the flow rate to the original setting in the case where the gas flow rate has been reduced by three steps, or about 3 standard liters per second in this example. Also, the equivalent voltage of the displayed flow rate must be less than the set reference voltage plus the anticipated incremental rise due to the adjustment required by the user minus an appropriate margin, such as for example approximately 39 mV (or two counts of the A / D converter ). If the answer in step 258 is yes, then the back pressure conditions are acceptable for the displayed flow rate to be increased one turn interval toward the user-required setting, so the procedure in this example increases the displayed flow rate by 1. standard liter per minute at step 260 and proceeds to step 262. Otherwise, the procedure continues directly to step 262 to begin checking for an occlusion condition.

In step 262, the procedure determines whether the PMEA signal is greater than an occlusion alarm trigger limit (TRIP_AL), which is the set reference voltage plus the anticipated incremental rise due to user required adjustment plus a appropriate occlusion margin, above which occlusion can be expected to occur. In this example, the margin is represented as approximately 0.2 V, or ten counts from the A / D converter. If the answer is yes, then the procedure increments one count (occlusion count) in step 266 and then checks if the occlusion count is greater than 3 (step 268). Thus, since this exemplary flow verification procedure is performed approximately once every 100 milliseconds, the occlusion condition that triggers the response yes in step 262 will have to exist for approximately 300 milliseconds before it is actually established. an occlusion alarm. This delay prevents the electrosurgical unit 40 from deactivating too quickly due to an occlusion and provides time to clear the occlusion. Once the occlusion count passes above 3, the procedure deactivates the electrosurgical unit 40 by disabling the radio frequency signal and gas flow and displays a flow alarm (step 270). If the conditions do not indicate a possible occlusion in step 262, then the procedure resets the occlusion count to zero (step 264). The procedure ends at step 272.

It will be understood that other applications of the gas flow regulating technique and apparatus depicted herein may preferably require verification of different parameters to determine whether the gas flow rate needs to be reduced or increased or whether it is necessary to disable the unit's apparatus. electrosurgical. The parameters depicted in the above example are depicted for illustrative purposes only and are not intended to limit the scope of the invention.

In the manual mode of operation of the electrosurgical unit, the user or surgeon directly controls the actual flow rate, so that gas flow rates are not automatically reduced in the case of too high a back pressure condition, as is the case in automatic mode. . Instead, the manual mode will only detect an occlusion, set an alarm, and deactivate the electrosurgical unit 40 to avoid potentially serious conditions. Table 3 illustrates an example of the manual mode in which an alarm is set when the PMEA signal exceeds the maximum PMEA limit displayed for a particular setting required by the user. The typical line pressure at the maximum limit of the gas flow path is also plotted. It is also preferred that the manual mode has an appropriate maximum limit of the PMEA signal (such as for example about 3.3 V) that is applied regardless of the required flow rate setting.

IS 2 255 494 T3

TABLE 3

<td>Required flow (standard liters per minute)</td><td>Maximum PMEA</td><td>Pressure in line (mmHg / pounds per square inch)</td>

<td> 10</td><td>3.17V</td><td> 344/6,6</td>

<td> 9</td><td>3.13 V</td><td> 332/6,4</td>

<td> 8</td><td>3.09V</td><td> 321/6,2</td>

<td> 7</td><td>3.05V</td><td> 309/6,0</td>

<td> 6</td><td>3.02 V</td><td> 298/5,8</td>

<td> 5</td><td>2.97V</td><td> 286/5,5</td>

<td> 4</td><td>2.94V</td><td> 275/5,3</td>

Figure 6 illustrates an example manual mode flow verification procedure. Preferably, this procedure is carried out at appropriate intervals, such as for example every 100 milliseconds. The microcontroller 150 begins the procedure in step 300 and proceeds to verify in step 302 if the PMEA signal is greater than the maximum allowable limit, which includes two conditions for a possible occlusion condition: if the PMEA signal is greater than the maximum allowable limit (approximately 3.3V in this example) for all required flow settings, and if the PMEA signal is greater than the set reference voltage plus the anticipated incremental rise due to flow displayed plus an appropriate occlusion margin (approximately 0.78 V in this example). If either condition is true, then the procedure deactivates the electrosurgical unit 40 by disabling the radio frequency signal and gas flow and displays a flow alarm (step 304) before branching at the end (step 312). If the answer in step 302 is no, then in a preferred embodiment, the procedure checks in step 306 to determine if the soft start procedure is still in effect (FIG. 3). If so, then it is preferred to ensure that there is no occlusion at this point before allowing the soft start to increase the displayed flow rate to the setting required by the user. This verification provides the surgeon with more opportunities to correct the occlusion condition before a higher flow rate of gas is delivered. Therefore, in step 308, it is determined whether the PMEA signal is greater than an appropriate test limit, such as for example the set reference voltage plus the anticipated incremental rise due to the displayed flow rate plus an appropriate margin, such as by example about three A / D converter counts. If the answer in step 308 is yes, the displayed flow rate is set to 2 to standard liters per minute in step 310, such that the soft start procedure cannot reset the displayed flow rate to a higher value. If any of the answers to steps 306 or 308 is no, then the procedure will end at step 312.

It will be understood that other functional parameters that are preferable in different applications of the technique and gas flow adjusting apparatus described herein can be determined for a manual mode of operation of an electrosurgical unit 40. It will be further understood that other modes of operation, in addition to the endo, automatic, and manual described herein, they can be defined for use with the gas flow adjustment technique and apparatus described herein. Therefore, the examples provided above are intended to be illustrative only and are not intended to limit the scope of the invention.

The exemplary modes of operation described above illustrate advantages of the gas flow adjustment apparatus and method especially with respect to safety during a surgical procedure. Gas flow reduction steps in endo and auto modes significantly reduce the risk of embolism during a surgical procedure. Additionally, the reduced flow rates provide an opportunity to clear transient occlusion conditions before sudden overpressurization occurs or before the electrosurgical unit is deactivated, so the enhancements not only help offset the surgeon's skills, but also help to maintain a convenient working condition for the surgeon without unwanted discomfort due to equipment deactivation. The back pressure sensing characteristics allow operations with many different applicators with unusual flow path diameters and lengths or curvatures. The reduced flow rates also help maintain consistent and appropriate arch transfer for the uniform creation of a gangrenous black crust on the tissue. Many other advantages and improvements will become apparent to those skilled in the art after acquiring a full understanding and understanding of the present invention.

Currently preferred embodiments of the invention and their improvements have been described herein with a degree of particularity. This description has been made by way of a preferred example. It will be understood that the scope of the present invention is defined by the following claims and will not be unnecessarily limited by the detailed description of the preferred embodiment set forth above.