electrosurgery electrosurgery electrosurgery is the application of a high-frequency (radio frequency) alternating polarity, electrical current to biological tissue as a means to cut, coagulate, desiccate, or fulgurate tissue. (these terms are used in specific ways for this methodology—see below). its benefits include the ability to make precise cuts with limited blood loss. electrosurgical devices are frequently used during surgical operations helping to prevent blood loss in hospital operating rooms or in outpatient procedures. electrosurgerya surgeon using a monopolar rf electrosurgical instrument to coagulate (and desiccate) tissue in the excision of a lipomameshd004598 in electrosurgical procedures, the tissue is heated by an electric current. although electrical devices that create a heated probe may be used for the cauterization of tissue in some applications, electrosurgery refers to a different method than electrocautery. electrocautery uses heat conduction from a probe heated to a high temperature by a direct electrical current (much in the manner of a soldering iron). this may be accomplished by direct current from dry-cells in a penlight-type device. electrosurgery, by contrast, uses radio frequency (rf) alternating current to heat the tissue by rf induced intracellular oscillation of ionized molecules that result in an elevation of intracellular temperature. when the intracellular temperature reaches 60 degrees c, instantaneous cell death occurs. if tissue is heated to 60–99 degrees c, the simultaneous processes of tissue desiccation (dehydration) and protein coagulation occur. if the intracellular temperature rapidly reaches 100 degrees c, the intracellular contents undergo a liquid to gas conversion, massive volumetric expansion, and resulting explosive vaporization. appropriately applied with electrosurgical forceps, desiccation and coagulation result in the occlusion of blood vessels and halting of bleeding. while the process is technically a process of electrocoagulation, the term "electrocautery" is sometimes loosely, nontechnically and incorrectly used to describe it. the process of vaporization can be used to ablate tissue targets, or, by linear extension, used to transect or cut tissue. while the processes of vaporization/ cutting and desiccation/coagulation are best accomplished with relatively low voltage, continuous or near continuous waveforms, the process of fulguration is performed with relatively high voltage modulated waveforms. fulguration is a superficial type of coagulation, typically created by arcing modulated high voltage current to tissue that is rapidly desiccated and coagulated. the continued application of current to this high impedance tissue results in resistive heating and the achievement of very high temperatures—enough to cause breakdown of the organic molecules to sugars and even carbon, thus the dark textures from carbonization of tissue. diathermy is used by some as a synonym for electrosurgery but in other contexts diathermy means dielectric heating, produced by rotation of molecular dipoles in a high frequency electromagnetic field. this effect is most widely used in microwave ovens or some tissue ablative devices which operate at gigahertz frequencies. lower frequencies, allowing for deeper penetration, are used in industrial processes. rf electrosurgery is commonly used in virtually all surgical disciplines including dermatological, gynecological, cardiac, plastic, ocular, spine, ent, maxillofacial, orthopedic, urological, neuro- and general surgical procedures as well as certain dental procedures. rf electrosurgery is performed using a rf electrosurgical generator (also referred to as an electrosurgical unit or esu) and a handpiece including one or two electrodes—a monopolar or bipolar instrument. all rf electrosurgery is bipolar so the difference between monopolar and bipolar instruments is that monopolar instruments comprise only one electrode while bipolar instruments include both electrodes in their design. the monopolar instrument called an "active electrode" when energized, requires the application of another monopolar instrument called a "dispersive electrode" elsewhere on the patient's body that functions to 'defocus' or disperse the rf current thereby preventing thermal injury to the underlying tissue. this dispersive electrode is frequently and mistakenly called a "ground pad" or "neutral electrode". however virtually all currently available rf electrosurgical systems are designed to function with isolated circuits—the dispersive electrode is directly attached to the esu, not to "ground". the same electrical current is transmitted across both the dispersive electrode and the active electrode, so it is not "neutral". the term "return electrode" is also technically incorrect since alternating electrical currents refer to alternating polarity, a circumstance that results in bidirectional flow across both electrodes in the circuit. bipolar instruments generally are designed with two "active" electrodes, such as a forceps for sealing blood vessels. however, the bipolar instrument can be designed such that one electrode is dispersive. the main advantage of bipolar instruments is that the only part of the patient included in the circuit is that which is between the two electrodes, a circumstance that eliminates the risk of current diversion and related adverse events. however, except for those devices designed to function in fluid, it is difficult to vaporize or cut tissue with bipolar instruments. electrical stimulation of neural and muscle cells neural and muscle cells are electrically-excitable, i.e. they can be stimulated by electric current. in human patients such stimulation may cause acute pain, muscle spasms, and even cardiac arrest. sensitivity of the nerve and muscle cells to electric field is due to the voltage-gated ion channels present in their cell membranes. stimulation threshold does not vary much at low frequencies (so called rheobase-constant level). however, the threshold starts increasing with decreasing duration of a pulse (or a cycle) when it drops below a characteristic minimum (so called chronaxie). typically, chronaxie of neural cells is in the range of 0.1–10 ms, so the sensitivity to electrical stimulation (inverse of the stimulation threshold) decreases with increasing frequency in the khz range and above. (note that frequency of the alternating electric current is an inverse of the duration of a single cycle). to minimize the effects of muscle and neural stimulation, electrosurgical equipment typically operates in the radio frequency (rf) range of 100 khz to 5 mhz. operation at higher frequencies also helps minimizing the amount of hydrogen and oxygen generated by electrolysis of water. this is especially important consideration for applications in liquid medium in closed compartments, where generation of gas bubbles may interfere with the procedure. for example, bubbles produced during an operation inside an eye may obscure a field of view. common electrode configurations for devices with isolated circuits there are several commonly used electrode configurations or circuit topologies: with "bipolar" instruments the current is applied to the patient using a pair of similarly-sized electrodes. for example, special forceps, with one tine connected to one pole of the rf generator and the other tine connected to the other pole of the generator. when a piece of tissue is held by the forceps, the rf alternating polarity electrical current oscillates between the two forceps tines, heating the intervening tissue by the previously described synchronous oscillation of intracellular ions. in monopolar configuration the patient is attached to the dispersive electrode, a relatively large metal plate or a flexible metalized plastic pad which is connected to the rf generator or electrosurgical unit (esu). the surgeon uses a pointed or blade shaped electrode called the "active electrode" to make contact with the tissue and exert a tissue effect - vaporization, and its linear propagation called electrosurgical cutting, or the combination of desiccation and protein coagulation used to seal blood vessels for the purpose of hemostasis. the electric current oscillates between the active electrode and the dispersive electrode with the entire patient interposed between the two. since the concentration of the rf current reduces with distance from the active electrode the current density rapidly (quadratically) decreases. since the rate of tissue heating is proportional to the square of current density, the heating occurs in a very localized region, only near the portion of the electrode, usually the tip, near to or in contact with the target tissue. on an extremity such as a finger, there is limited cross-sectional area to disperse the current, a circumstance which might result in higher current density and some heating throughout the volume of the extremity. another bipolar instrument is characterized with both electrodes on the same design, but the dispersive electrode is much larger than the active one. since current density is higher in front of the smaller electrode, the heating and associated tissue effects take place only (or primarily) in front of the active electrode, and exact position of the dispersive electrode on tissue is not critical. sometimes such configuration is called sesquipolar, even though the origin of this term in latin (sesqui) means a ratio of 1.5. dedicated non-grounded machines without a dispersive electrode relatively low-powered high frequency electrosurgery can be performed on conscious outpatients with no grounded machines without a dispersive electrode . operating at low currents with no dispersive electrode is possible because, at the medium rf frequencies (usually 100 – 500 khz) that the machines generate, the self-capacitance of the patient's body (which is between the patient's body and the machine's ground) is large enough to allow the resulting displacement current to act as a virtual "circuit completion path." one example of such a machine is called a hyfrecator. this term began in 1940 as a birtcher corporation brand name hyfrecator for "high frequency eradicator", but now serves generically to describe a general class of single-electrode, non-isolated (earth-referenced) low-powered electrosurgical machines intended mainly for office use. an accidental circuit completion path through an earth-ground creates the danger of a burn at a site far away from the probe electrode, and for this reason single-electrode devices are used only on conscious patients who would be aware of such complications, and only on carefully insulated tables. in such a setting, hyfrecators are not used to cut tissue, but to destroy relatively small lesions, and also to stop bleeding in surgical incisions made by blade instruments under local anesthesia. electrosurgical modalities in cutting mode electrode touches the tissue, and sufficiently high power density is applied to vaporize its water content. since water vapor is not conductive under normal circumstances, electric current cannot flow through the vapor layer. energy delivery beyond the vaporization threshold can continue if sufficiently high voltage is applied (> +/-200 v) to ionize vapor and convert it into a conductive plasma. vapor and fragments of the overheated tissue are ejected, forming a crater. electrode surfaces intended to be used for cutting often feature a finer wire or wire loop, as opposed to a more flat blade with a rounded surface. coagulation is performed using waveforms with lower average power, generating heat insufficient for explosive vaporization, but producing a thermal coagulum instead. electrosurgical desiccation occurs when the electrode touches the tissue open to air, and the amount of generated heat is lower than that required for cutting. the tissue surface and some of the tissue more deep to the probe dries out and forms a coagulum (a dry patch of dead tissue). this technique may be used for treating nodules under the skin where minimal damage to the skin surface is desired. in fulguration mode, the electrode is held away from the tissue, so that when the air gap between the electrode and the tissue is ionized, an electric arc discharge develops. in this approach, the burning to the tissue is more superficial, because the current is spread over the tissue area larger than the tip of electrode. under these conditions, superficial skin charring or carbonization is seen over a wider area than when operating in contact with the probe, and this technique is therefore used for very superficial or protrusive lesions such as skin tags. ionization of an air gap requires voltage in the kv range. besides the thermal effects in tissue, the electric field can produce pores in the cellular membranes – a phenomenon called electroporation. this effect may affect cells beyond the range of thermal damage. wet field electrosurgery there are wet and dry field electrosurgical devices. wet field devices operate in a saline solution, or in an open wound. heating is as a result of an alternating current that passes between two electrodes. heating is usually greatest where the current density is highest. therefore, it is usually the smallest or sharpest electrode that generates the most heat. cut/coag most wet field electrosurgical systems operate in two modes: "cut" causes a small area of tissue to be vaporized, and "coag" causes the tissue to "dry" (in the sense of bleeding being stopped). "dried" tissues are killed (and will later slough or be replaced by fibrotic tissue) but they are