This invention relates to a unique electrosurgery/cautery system.
In the following specification and claims, a distinction is made between the terms electrosurgery and cautery. In electrosurgery, radio frequency current flows into the tissue being treated from a first electrode usually termed the active electrode. The current usually exits at a second electrode termed the patient or indifferent electrode although, as will be brought out in more detail hereinafter, the patient electrode does not necessarily have to be employed in accordance with one aspect of the present invention. Electrical interaction between the active electrode and tissue at the treated site may either be ohmic (to thereby effect a desiccation mode of operation) or by electrical arc (to thereby effect a cut or fulguration mode of operation). In cautery an element such as a wire is electrically heated by passing a current therethrough, the cautery element typically being used to seal bleeding blood vessels in hospital surgical procedures and in minor surgery performed in doctors' offices. Hence, in summary, an important distinction between electrosurgery and cautery is that in the former current flows through the patient's tissue while in the latter current is restricted to the heating element.
In electrosurgery there are three effects which may be produced by passing radio frequency current through tissue--namely, desiccation, cutting and fulguration. In desiccation, the active electrode is held in firm contact with the tissue with the current passing directly into the tissue and the heating effect being brought about by I.sup.2 R heating. Thus, the mode of operation is ohmic.
In cutting, the active electrode is not in good contact with the tissue and electric sparks jump from the electrode to the tissue. The voltage waveform used is generally a sinewave and the sparks are short in length but heat the tissue intensely. The cells burst into steam and the steam maintains the layer of gas between the electrode and the tissue as the incision proceeds. In order to produce a cutting effect without desiccation, the generator must be current limited to less than about 200 milliamperes.
In fulguration, the coagulation occurs by means of a high voltage spark which jumps from the active electrode to the tissue. Thus, an arcing mode of operation occurs in both cuting and fulguration. The spark produces intense heating at every point it strikes, but a high crest factor voltage waveform, called a COAG waveform, makes long sparks and distributes the spark widely. This keeps the energy density down and minimizes the cutting effect.
Of the three electrosurgical modes, desiccation is the primary threat to the patient in the event that a grounded patient electrode loses contact with the patient's body. The patient's body invariably has some electrical contact with ground, either by capacitive coupling or by direct contact with a grounded object. Even with a child, his body is large enough to produce a significant capacitance between his body mass and the grounded operating table. As a result of this relatively low impedance to ground, it is difficult for large voltage differences to exist between the patient's body and ground. Therefore, when RF leakage currents leave the patient's body and go to ground via small, grounded contact points, they do so by direct ohmic connection. In order for electric sparks to jump from the patient's body to ground a voltage difference of over 1000 volts is needed. As a result, a patient electrode related burn is almost always in the desiccation mode.
It is possible that if a small grounded contact were the only electrical connection to ground, then a burn at this location could proceed from desiccation to fulguration after the burn site acquired a high impedance because of the electrosurgical action at that point. However, even in this case, it is clear that the fulguration burn could not have occurred if the desiccation had not taken place first.
Unfortunately, desiccation is usually needed at the site of surgery even though the intention is to cut or fulgurate. That is, in most electrosurgery, desiccation is combined with cutting or fulguration because the surgeon usually starts his cut or fulguration with the electrode in firm contact with the tissue. Since, by definition, the starting mode is desiccation, the desiccation must be complete before the tissue in contact with the electrode will acquire a high enough impedance so that sparking can begin and cutting or fulguration will occur. A typical prior art generator produces over an ampere of desiccation current to necrose and dry the tissue at the active electrode so that the tissue impedance will rise to the requisite amount.
In aforementioned related Application No. 1, a feedback system is described which limits the electrosurgical current to less than 200 ma so that only arcing (only cutting or fulguration) can take place. When used by itself, a system such as this is safer than an ordinary monopolar electrosurgical system and could even be used without a patient electrode with comparative safety. However, as indicated above, a current limited system cannot be used for most surgery because there is no way to get the electrode started. That is, since the current is limited to less than 200 ma and since at least an ampere is needed to desiccate the tissue so that arcing can commence, the current limited, arc only system cannot be used by itself for most surgery. In the abovementioned related Application No. 1, the necessary tissue desiccation is effected by providing a separate desiccation generator capable of delivering at least 1 ampere of electrical current through the tissue. Thus not only is a capability provided for initiating current limited fulguration or cutting but also the advantages inherent in desiccation vis-a-vis fulguration in certain applications are realized. For example, neural tissue is so fragile that if one attempts to fulgurate a bleeder, the hard surface eschar seals the bleeder but in doing so shrinks and pulls the surface or the tissue so that bleeding may start at the periphery of the eschar. Desiccation does not dry and shrink the tissue as much as fulguration and thus this mode more effectively seals neural bleeders. Hence, the use of the separate desiccation generator is advantageous in this application as well as others. However, it is desirable in some situations to effect necrosis of the tissue to thereby permit the establishment the spark needed for fulguration or cutting without employing a high amperage current to do so and thereby avoid the problems associated with such currents as discussed above.
It is thus an object of this invention to provide a system capable of providing (a) desiccation-type tissue necrosis and (b) cutting and/or fulguration where the "desiccation" is effected by cautery and the cutting and/or fulguration is effected by electrosurgery. Although the term "desiccation" is normally used in connection with electrosurgery, the term, in the following specification and claims, will also be used with respect to the tissue necrosis effected by cautery since, at low temperatures, the latter necrosis appears to be very similar if not identical to that caused by electrosurgical desiccation except that it appears to be more shallow. Since the cautery desiccates the tissue, no large currents pass through the patient to effect this function. Further, since the desiccation is not effected electrosurgically, the electrosurgical generator may be optimized for the high output voltage, high output impedance fulguration and cutting functions. That is, heretofore some electrosurgical generators have operated in modes which tend to be incompatible. Hence, it has been difficult to optimize all modes in a single generator. Aforementioned related Application No. 1 provides one solution to this problem and the subject invention another. That is, by implementing the desiccation mode with cautery, the electrosurgical arcing modes can be optimized without compromising the desiccation function in many applications.
It is a further object of this invention to provide in a current limited, cut only or fulgurate only electrosurgical generator, the capability of initiating the requisite arc without passing a large current through the patient's tissue.
It is a further object of this invention to effect the arc initiating function by employing cautery.
It is a further object of this invention to provide an electrosurgical generator of the above type in combination with a cautery power source where the electrosurgical generator and cautery power source both energize an electrode/heater element.
It is a further object of this invention to provide a combined electrosurgery/cautery system of the above type wherein the cautery is used for (a) tissue coagulation to effect shallow necrosis thereof and/or (b) cutting of the tissue.
It is a further object of this invention to provide a combined electrosurgery/cautery system of the above type wherein the electrosurgical function effects the fulgurate only mode when the cautery function is also employed to effect the cut mode of operation.
It is a further object of this invention to provide a combined electrosurgical/cautery system of the above type having a very small patient electrode or none at all.
It is a further object of this invention to provide different electrosurgical/cautery devices for use in combined systems of the above type.
Other objects and advantages of this invention will be apparent from a reading of the following specification and claims taken with the drawing.