Cutting

• Fulguration (black coagulation)

• Desiccation (white coagulation)

Cutting

Cutting is usually achieved with a continuous waveform and a HF current flow. Applying the active electrode in the cutting mode creates a steady stream of arcs less than 10 |mm long with a temperature of about 4000-5000 K that rapidly increases temperature in the immediately adjacent tissue. Each arc strikes a cell along the leading edge of the incision, rapidly heating the intracellular fluid so that the membrane bursts and the intracellular fluid and its contents vaporize. Because the cell contents vaporize, as the electrode is moved, it "rides" smoothly in a steam envelope; thus, cutting is not a true contact mode and gives the surgeon no true tactile feedback.

With the cutting mode, tissue vaporizes so quickly that heat conduction is minimized, and the depth of tissue necrosis is lessened to 200 |mm or less.7 Cutting current confines damage to a very small area under the scalpel electrode. Only cells adjacent to the active electrode are vaporized, and cells a few layers deep essentially are undamaged. Therefore, electrical cutting can be very clean, but it is not generally accompanied by any hemostasis.

If the pure cutting electrical waveform is interrupted and the voltage increased to deliver the same wattage, then heat conduction is promoted, resulting in improved hemostasis because small vessels are coagulated. In this combination mode, the slightly interrupted waveform increases the thermal spread so that cutting is achieved with moderate hemostasis.

Fulguration

For fulguration, the active electrode is positioned usually 5-10 mm above the tissue, and a tree-like cluster of arcs is discharged onto the tissue surface. Fulguration is a high-impedance modality with relatively high voltage, low current, and a highly damped interrupted waveform. The peak-to-peak voltage is high enough to ignite and sustain longer than 1 mm. The arcs may have a temperature more than 5000 K, and they rapidly carbonize the superficial cell layers. Because the current density is relatively low in the target tissue, little desiccation occurs below the surface eschar.

Most of the energy delivered dissipates to heat the air around the active electrode. Because air is an insulator, a high-voltage current is necessary to ignite and sustain an effective arc. To reduce voltage and increase the arcing effect, an argon beam coagulator has been introduced to dry large oozing surfaces. Because the argon's arc ignition voltage is 20% less than that of air, the arcs scatter less, instead following in the laminar argon gas flow. Thus, they can be directed more precisely and over a greater distance than the random arc strikes associated with fulguration in air.

The disadvantages of fulguration are not only that the desiccation is superficial but also that the electrode tends to absorb heat, thus bonding with tissue it inadvertently touches. If the eschar is then pulled up, bleeding will start again.

Because electrofulguration is a noncontact mode, it produces hemo-stasis without the probe adhering to the coagulated tissue. It is most often used to seal broad areas of capillary oozing or ablate a rectal tumor.

Fulguration is used in sealing large areas of capillary bleeding. Because it requires much more voltage than electrosurgical cutting or desiccation, the surgeon must be especially cognizant of the risk imposed by capacitive or direct coupling during fulguration.

Desiccation

Desiccation is the only true contact mode of electrosurgery. The tissue temperature is increased to the point at which proteins denature and form a rigid coagulum. Although proteins start to denature at about 45°C, a temperature of at least 55°C is required to form a coagulum. The amount of tissue coagulated depends on the volume of tissue increased above the threshold temperature.

Because desiccation is accomplished without an arc, no energy dissipates into the air, and because the electrode is in contact with the tissue, less power is needed for desiccation than for fulguration or cutting. The impedance is low as desiccation begins, so desiccation can be achieved with low voltage and high current. As tissue dries and proteins denature, molecules with the potential to become ionized become immobilized in the coagulum matrix, and the tissue impedance increases.

Electrosurgery in Laparoscopic Surgery

Both monopolar and bipolar electrosurgery are currently widely used in laparoscopic surgery. Although bipolar electrosurgery is safer than monopolar, its application is limited to tissue desiccation, so most lapa-roscopic surgeons still prefer monopolar electrosurgery. The combination of bipolar electrosurgery with an endoscopic scissor is used by some surgeons. Monopolar electrosurgery for laparoscopic procedures is advantageous because: 1) it is a familiar dissecting method, 2) it provides excellent hemostasis, 3) it is universally available in operating suites, and 4) it is inexpensive. The disadvantages of monopolar elec-trosurgery are extensive smoke development and risk of thermal injury during dissection.

Smoke development can be extensive in laparoscopic colorectal surgery because of the unique need to dissect through the fatty mesentery. Because smoke evacuators and rapidly recirculating gas insufflators are not usually used, the smoke-filled gas is flushed out of the abdominal cavity through an open cannula site. Whether the smoke created represents an inhalation hazard for patients or operating room personnel is unknown but is of some concern.

The smoke may have biologic as well as chemical effects. Heating biologic tissue results in the formation of molecules with aromatic ring structures and unsaturated radicals that may be harmful when inhaled. Electrosurgery smoke has been shown to be mutagenic in vitro to the TA98 strain of Salmonella8 and to negatively affect the lungs in rats (muscular hypertrophy of vessel walls, alveolar congestion, and emphysematous changes).9 These effects have also been seen in smoke generated by CO2 laser application.9,10

Human immunodeficiency virus (HIV) proviral DNA with a median aerodynamic diameter of 0.31 |mm (range 0.1-0.8 |mm) has been reported in the laser plume of vaporized HIV-containing tissue.11 Matchette et al.12 found viable bacteriophages in CO2 laser plume, but the events were rare in their study. Because most of the viable particles were large (at least 7.5 |mm in aerodynamic diameter), these particles should be easily filtered with a recirculating insufflator. The significance of these scientific reports remains to be determined. No epidemiologic evidence exists that operating room personnel or patients have been harmed when exposed to electrosurgery smoke or laser plume. Nonetheless, we recommend taking simple measures to reduce the exposure to smoke, such as using an insufflator with a filter larger than 0.2 | m to recirculate CO2 gas or one that is equipped with a smoke evacuation line connected to a suction circuit (Olympus). These measures will not only reduce the risk of any harmful effects of smoke but also improve visibility during use of electrosurgery in laparoscopic surgery.

Extent of Tissue Damage

The tissue temperature many centimeters from the operative area may increase substantially when using proper electrosurgical techniques. If tissue is desiccated and the current has to pass through a duct-like structure on its way to the dispersive electrode (Figure 3.3), the cross-sectional area of its pathway is reduced, so the current density will increase at this point. Thus, the tissue desiccation may occur far from the primary active electrode. This concept is quite important when duct-like structures, such as the appendix, pieces of the greater omentum, or adhesions are cut or desiccated.

Although bipolar instruments may help confine the effects of elec-trosurgery to the structures grasped, extensive coagulation may also damage surrounding tissue. For instance, ureter injuries have been reported after using bipolar electrocoagulation near the ureters in gynecologic surgery.13

In laparoscopic surgery, closely monitoring the effect of electrical current on tissue is mandatory because the laparoscope provides only a limited view during dissection. Inadvertent injuries using monopolar electrosurgery occur primarily at the active electrode and the return electrode.

Near the active electrode, injuries can occur in any part of the instrument: the handle, the insulated shaft, or at the uninsulated tip. These inadvertent injuries occur for three primary reasons: 1) insulation failure, 2) direct coupling, or 3) capacitive coupling (Figure 3.6A and B).14

Insulation failure occurs most often at the distal shaft as a result of repeated heating of the instrument or because of damage to insulation when the instrument is inserted in the cannula. Insulation failures near the instrument tip can be recognized immediately if the tip is in view during the application of electrical current. Also, all exposed metal at the tip of the instrument being used must be visible in the laparoscopic field. The insulation on the shaft of the instrument rarely fails, but is potentially dangerous because it is usually not recognized during lapa-roscopic procedures.

Capacitive Coupling Laparoscopic Surgery

Figure 3.6. Insulation failure can occur by two major means when performing electrosurgery. A Direct coupling between two instruments. B Capacitive coupling when the charged instrument is being used with a metal cannula that is insulated from the abdominal wall by a nonconducting anchoring device.

Figure 3.6. Insulation failure can occur by two major means when performing electrosurgery. A Direct coupling between two instruments. B Capacitive coupling when the charged instrument is being used with a metal cannula that is insulated from the abdominal wall by a nonconducting anchoring device.

Direct coupling describes any inadvertent contact between the active instrument and other metal instruments or cannulae in the abdomen. Whereas the metal instrument tip is free and ready to be used for coagulation or cutting, the more proximal metal parts can touch other instruments; this contact may lead to accidental coagulation or cutting without insulation failure. Thus, during the application of cutting or coagulating current, the entire instrument blade must be visible in the laparoscopic field.

The third important mechanism of inadvertent tissue damage during monopolar electrosurgery is capacitive coupling. Capacitance is the ability of an electric nonconductor to store energy. A capacitor consists of two conductors separated by an insulator. Capacitive coupling can occur if an instrument with insulation failure along the shaft is used in a metal cannula with a plastic abdominal wall anchoring device; the plastic anchoring device prevents the current from flowing through the metal cannula into the abdominal wall and onto the dispersive electrode.14,15 In general, 10%-40% of the power of the electrosurgical unit may be coupled, or transferred, from the isolated shaft to the active electrode to the cannula. As long as the current can pass through a low power-density pathway and return to the dispersive electrode, it will not harm the patient. If the path to the dispersive electrode is blocked through a high-resistance, nonconductive anchoring device, however, capacitive coupling can occur.

Stray currents produced during capacitive coupling may produce inadvertent burns on intraabdominal structures. When a metal cannula (or instrument with insulation failure) touches any organ or intraabdominal structure when stray current is stored in the cannula, this electrical energy may be discharged from the metal cannula to any structure touching it, including those outside the field of vision of the surgeon. Capacitive coupling can occasionally be recognized by neuro-muscular stimulation of the abdominal wall.

Direct coupling and capacitive coupling rarely cause electrical injury. Unfortunately, they are seldom recognized during a procedure because they usually occur outside the view of the laparoscope14,15; however, such injuries can be prevented. Capacitive coupling can be prevented if the anchoring device and the cannula are both made of plastic or metal.

Although alternating current has the potential to cause an effect at both the active and the return electrodes, the effect usually occurs at the active electrode because the current density is much higher at the active electrode because it is smaller, and tissue temperature is directly proportional to the square of the current density. The alternating current delivered at the active electrode is identical to that at the return electrode; therefore, if the current density is the same at the return electrode as at the active electrode, the same thermal effect will occur at both. Monopolar electrosurgery is frequently used with a return grounding electrode, which allows any current flow through the body to safely disperse. The maximum temperature attained under a dispersive electrode depends on the maximum current density, the duration of activation, and the relative cooling from tissue perfusion.

The distribution of the current under the dispersive electrode depends on the design of the electrode and the anatomic distribution of tissue under it.

Resistive and capacitive contact electrodes can be used as dispersive electrodes with a low risk of inadvertent thermal injury if the electrode is applied correctly and not accidentally dislodged. Resistive electrodes usually are gel pads or a conductive adhesive and are in resistive contact with the tissue. Capacitive electrodes have a nonconductive film between a metallic plate and the skin surface, so that a capacitor is formed and a type of capacitive coupling is used to prevent injury. Although resistive dispersive electrodes, in contrast to capacitive electrodes, have a nonuniform heating pattern because the current is more concentrated at the electrode edges, both types of dispersive electrodes appear to be equally safe in surgery.

To prevent burns at the return electrode, manufacturers have incorporated electronic sensors with circuit breakers (contact-quality monitoring electrodes) in the electrosurgical unit that monitor the quality of the connection between the dispersive electrode and the patient as well as between the cable and connector when no surgical current is in use. The change in contact impedance during the procedure is determined by a microprocessor, and if impedance increases, the electrosurgical unit will shut down. These safety features, together with the proper use of dispersive electrodes, have substantially reduced the number of burns at the return electrode.

Bipolar Electrosurgery

A closed circuit is necessary for all electrical energy to be used in surgery. If both electrodes are used as active electrodes, the application is bipolar.

Bipolar electrosurgery has been used for decades in both open and laparoscopic surgery. Earliest uses were in tubal ligation procedures using such devices as the Kleppinger machine. Because the electrodes are in close proximity, tissue effects are localized. Total power required to affect the tissue is small compared with that required for monopolar electrosurgery, where current must flow through the body to the ground electrodes.

Recently, important adaptions have been made in bipolar electrosur-gery technology, resulting in the LigaSureTM Vessel Sealing System (Valleylab, Boulder, CO), which is a bipolar electrothermal device using a high-amperage, low-voltage current. Developed for both open and laparoscopic procedures, it is capable of sealing vessels up to 7 mm in diameter. By grasping the tissue with the device and activating the energy source, both physical pressure and electrothermal energy are delivered to the vessels. The elastin and collagen of the wall of the vessel are partially denatured, and then allowed to cool briefly as a seal intrinsic to the vessel wall forms. The newly sealed tissue, which is often transparent, can then be divided using a cutting knife built into the LigaSure™ device (Figure 3.7). In our experience, this device has helped make laparoscopic surgery immensely easier, especially in the handling of mesentery and omentum.

The LigaSure™ device has a similar appearance to other energy devices. There is a generator box that houses the energy source for the tissue sealing as well as the hardware responsible for sensing the changes in tissue density that indicate a seal. A cord connects either the 5-mm (LigaSure VTM) or the 10-mm device (LigaSure AtlasTM) to the generator. A major advantage of the new instruments is the ability to cut the tissue at the same time after sealing it. After tissue sealing has taken place, a trigger can be depressed, deploying a cutting mechanism that bisects the sealed area of tissue.

A tissue-response feedback mechanism on the device measures the density of the tissue and calculates the appropriate amount of electrothermal energy to be delivered. The generator then provides an audible tone when the sealing process is complete. Depending on the thickness of the tissue, we find that the sealing time varies between about 2 and 10 seconds. Subsequently, the cutting mechanism of the laparoscopic tool can be triggered, and the sealed tissue bisected. Depending on the thickness of the pedicle that is to be ligated, and the presence or absence of major vessels, multiple firings can be done before division. We typically use two to three applications per major vascular structure or with thicker bites of tissue, dividing the tissue at its distal-most seal (Figure 3.8). These multiple applications provide an increased length of tissue seal, and also allow for direct inspection of the sealed area, which is often translucent, adding confidence in the hemostasis before cutting.

The vessel seal created by the LigaSureTM provides bursting strengths that are well above physiologic range. In an in vitro model using

Three Steps HemostasisThree Steps Hemostasis
Figure 3.7. Vessel sealing devices (LigaSure™) A 10 mm and B 5 mm, each with a cutting mechanism.
Ligasure Sealing Machine Machine
Figure 3.8. Ligation of the ileocolic vessels using the LigaSure™ 10 mm instrument.

porcine renal arteries, bursting strengths were demonstrated to be greater than 400 mm Hg - comparable to clips and ligatures, and superior to ultrasonic and bipolar devices.16 Furthermore, the seal created is permanent, and intrinsic to the vessel itself. The surgeon does not need to rely on a luminal clot and does not need to fear a clip becoming dislodged or a tie being too loose on an edematous tissue pedicle.

The quality of hemostasis is demonstrated again in the reliability of the device. In a study involving a variety of open and laparoscopic general surgical cases, with over 4200 applications of the LigaSure™, Heniford et al.17 demonstrated a 0.3% rate of post-application bleeding that required alternative hemostatic techniques. In 98 cases studied, they had no postoperative bleeding complications. We have had similar success at our institution, only encountering difficulty with hemostasis in the infrequent setting of a heavily calcified vessel, and finding exceptional benefit in the setting of Crohn's disease. Further discussions in its use will come in the procedure chapters.

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Responses

  • norma
    How to increase haemostasis during cutting?
    5 years ago
  • Mehari Yonas
    What is a ligasure machine?
    5 years ago
  • Isotta Genovesi
    What heat temperature does tissue desiccation occur?
    5 years ago
  • Marko
    What does a cut waveform look like in a HF surgical device?
    4 years ago

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