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ENTC 4350. ELECTROSURGICAL UNITS (ESUs). General Surgery. The electrosurgical unit (ESU) is generally used in surgery.

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entc 4350

ENTC 4350

ELECTROSURGICAL UNITS (ESUs)

general surgery
General Surgery
  • The electrosurgical unit (ESU) is generally used in surgery.
    • The laser is less efficient, less powerful, more costly, more bulky in the operating room and less understood due to a smaller case history data base work to discourage its use in many cases.
      • So much depends upon the skill of the surgeon in the use of any surgical knife, that the selection is often a professional judgement.
electrosurgical units
ELECTROSURGICAL UNITS
  • To do surgery, the electrosurgical unit (ESU) delivers, through an electrode, radio frequency (RF) currents in the range of 100 kilohertz to several megahertz.
    • It is capable of
      • Making incisions and excisions and
      • Performing
        • coagulation,
        • desiccation, and
        • fulguration.
slide4
It is the most efficient, powerful, and economical of the thermal knives presently available.
    • It is most widely used in general surgery and in cutaneous surgery.
    • It is capable of fast cutting through massive tissue and of effective hemostasis.
      • Its primary adverse side effect is thermal tissue damage.
slide6
The transformer, connected to the 60-cycle power mains, steps up the voltage, which is then applied across a gas tube.
slide7
The high voltage during the peak parts of the cycle ionizes the gas, lowering its resistance and thus drawing a current.
  • This, in turn, drops the voltage and extinguishes the gas, which then rises again in resistance.
    • This oscillation occurs at RF frequencies.
      • That oscillation is selected by the series capacitor and primary coil.
slide8
When a return plate is used in surgery, the voltage is taken off the primary coil shown in the figure.
    • The Oudin coil is a secondary coil that increases the voltage by transformer action, so that fulguration can be done without the return electrode.
      • For other surgical procedures the patient return plate is used.
slide9
During surgery, the RF current exits the relative sharp electrode, dissipating between 50 and 400 W of power into the tissue to make an incision.
    • The cutting electrode is about 0.1 mm thick and contacts several millimeters of the tissue.
      • The voltage, ranging from 1,000 to several thousand volts, sets up a line of small sparks and raises the tissue temperature such that the tissue parts as the cells vaporize.
slide11
The cells themselves form capacitors with a conductive electrolyte inside separated by a nonconductive membrane from the interstitial fluid.
    • That membrane passes the RF currents into the cell, causing itto vaporize.
slide12
If the voltage is high enough and is passed quickly enough through the tissue, the thermal damage is almost imperceptible.
    • However, if one goes slowly or if the voltage is too low, thermal tissue damage will result.
slide13
To achieve hemostasis, a certain amount of damage is desirable.
    • The control of this factor is key to good surgical technique using the ESU.
slide15
The device has several modes:
    • Cut mode—Pure sine wave, for cutting with the least coagulation.
    • Coag mode—Pulsed sine wave, low-duty cycle, for coagulating bleeding tissue.
    • Blend 1 mode—Modulated sine wave, for coagulating as the tissue is cut.
    • Blend 2 mode—Modulated sine wave, for coagulating as the tissue is cut.
slide16
The device has several modes:
    • Cut mode—Pure sine wave, for cutting with the least coagulation.
    • Coag mode—Pulsed sine wave, low-duty cycle, for coagulating bleeding tissue.
    • Blend 1 mode—Modulated sine wave, for coagulating as the tissue is cut.
    • Blend 2 mode—Modulated sine wave, for coagulating as the tissue is cut.
cut mode
Cut Mode
  • To cut tissue, the switch is usually set to the cut position
    • This connects the RF voltage to the amplifier, which then delivers to the active electrode 1,000 to 8,000 volts peak-to-peak AC at from 100 kHz to about 2 megahertz. High-density currents emerge from the active electrode to do the cutting.
slide19
A blade electrode is moved through the tissue like a knife to do the cutting.
    • The high-density currents disperse throughout the conductive fluids of the body and return at a low-current density to the patient return electrode to complete the circuit back to the ESU.
slide20
The return electrode is large in area and gelled to keep the skin resistance low and the region cool.
slide21
The RF circuit is usually isolated from ground; so if the patient’s body comes in contact with ground (through a metal operating table, for example), an alternative path for the return current would not be established.
slide22
In some machines, especially older models, the return electrode is grounded.
    • In this case, if the patient’s finger would also become grounded, an alternative path would be established, which could cause a burn on the finger.
slide23
In any case, at these frequencies, there is always some stray capacity that could connect the return lead to ground.
    • With proper design and careful operating procedure, this can be reduced to insignificance.
      • Because of this effect, one sometimes feels a tingle when touching a person who is receiving ESU treatment.
slide24
In the cut mode, the ESU continuously delivers its highest average power.
    • Thus, at every instant as the blade is moved along, the tissue receives the same treatment. This results in a smooth cut with no jagged edges.
coag mode
Coag Mode
  • In the coag mode, the average power delivered to the tissue is reduced from that delivered in the cut mode.
    • A blunt electrode may be touched to the tissue to produce a coagulum that establishes hemostasis.
slide26
The power per unit area at the tissue surface is lower than that from the blade in this case.
    • Therefore, the tissue is raised enough to produce coagulum without vaporizing it.
slide27
The coag mode may also be established by delivering pulsed energy at a low duty cycle (the ratio between the on time and the period between the starting times of successive pulses) of between 15 and 20 percent.
    • Automatically turning the voltage on and off like this slows the cutting process, and allows the heat to propagate into the tissue to form the coagulum.
slide28
The depth of coagulation depends on how long the electrode contacts the tissue, because tissue damage is caused by heat propagating into the tissue.
    • The edge of the cut will tend to be ragged, and some browning of the tissue will be visible.
    • There are low resistance paths for the electrical current and the heat, such as along a blood vessel or a nerve going through fat, which can cause deep coagulation.
blend modes
Blend Modes
  • The blend modes are used when one desires to cut and seal bleeders simultaneously.
    • The lower average power delivered reduces the cutting and increases the propagation of heat into the tissue to coagulate the blood.
slide30
In this mode, bursts of voltages high enough to establish a cutting spark are delivered at a duty cycle above about 25 percent.
    • In this case, cutting would occur about one fourth of the time; and the rest of the time, the heat generated would propagate into the tissue, creating a layer of coagulum along the incision to control bleeding.
      • The degree of coagulation can be monitored by observing the browning of the tissue.
slide31
The incision cut may be less smooth than in the cut mode.
    • The sloughing of the tissue under the cut may not be visible from the surface.
slide32
Less coagulation and faster cutting may be achieved by selecting the blend 2 mode, which may have a duty cycle of about 50 percent.
    • This would increase the time the cutting spark is activated and leave less time for coagulation to occur.
fulguration
Fulguration
  • The Latin word fulgur means “lightning,” and this is exactly what the fulguration spark is.
    • The air between the body and a sharp ESU electrode ionizes when the electric field intensity exceeds 3,000 kV/m.
slide34
When lightning strikes the earth, the bolt occurs when a charge on a cloud differs sufficiently from that in the earth.
    • With respect to an ESU needle electrode, the body is a charged mass of ionic fluid separated by an insulating layer of skin and air.
    • The inside of the body is the ground, just as the earth is ground for lightning.
slide35
It is not necessary to have a return electrode to the instrument any more than one would need a return path to the cloud during lightning.
    • The currents travel in and out of the body at the radio frequency of the ESU unit.
slide36
However, if one does use a return electrode, this adds another path for the current and increases the current in the spark.
    • Likewise, stray capacity affects the size of the spark.
dessication
Dessication
  • If the ESU needle electrode is introduced into a mass, such as a vascular tumor, the currents will inject power that raises the fluids to above 100C, vaporizing and dehydrating the lesion.
    • Since lipids and proteins require more than 500 C to decompose, the surgeon has a mechanism to control dehydration.
      • He or she keeps the temperature below 500 C so as to not decompose the tissue while dehydrating it.
sealing bleeders
Sealing Bleeders
  • Bleeders up to 2 mm in diameter can be stopped if they are clamped with a metal hemostat.
    • To make instantaneous coagulation, the hemostat is touched with the ESU blade.
slide39
This process is also done with an electrocautery hemostat.
    • This device consists of a conductive forceps that serves as the active electrode.
      • The forceps is clamped over the bleeder, and the current is applied to seal it.
surgical techniques
Surgical Techniques
  • The surgeon has control of the cutting and coagulation by the stroke he or she uses.
    • One surgeon may prefer to use a coag-blend mode throughout the procedure and control the cutting and coagulation by the force exerted on the blade, the depth of the blade in the tissue, and the duration of contact.
      • The use of the ESU is a refined surgical skill, developed by practice.
slide42
The different ESUs from different manufacturers produce different waveforms.
    • The waveforms have different amplitudes, pulse duty cycles, and crest factors (the ratio between coag and cut waveform amplitudes).
      • Thus, a surgeon trained on one machine may have to be retrained to use another machine.
slide43
The practical consequence of this for attendants is that they should not change the ESU without informing the surgeon.
    • Even different machines from the same manufacturer can differ in subtle ways.
slide44
Also, calibration of the power levels is done into a test load of fixed resistance.
    • But, in practice, the tissue resistance depends upon its type as well as the electrode contact area pressure against the tissue.
      • All of these factors influence how much power actually gets into the tissue.
slide45
The energy then getting into the tissue depends on the duration of contact.
    • The effect of the RF current on the tissue cannot be controlled completely from the machine;
      • It must be controlled by the surgeon who has experience both in the procedures required and with the specific ESU being used.
patient leads
Patient Leads
  • Traditionally, the leads have been classified as either monoterminal or biterminal.
    • This is because some ESUs have only one lead and are used exclusively for fulguration.
slide47
The lead classifications are as follows:
    • Monoterminal—AnESU with one wire for patient contact.
    • Bitermmal—An ESU with two wires for patient contact.
    • Active electrode—The electrode that delivers treatment to the surgical field.
    • Patient electrode—The large surface area return electrode.
    • Monopolar electrode—An active electrode that uses a patient electrode to complete the circuit.
    • Bipolar electrode—Two electrodes in close proximity and of approximately the same size that are arranged so that the current tends to be confined to a small region between the two electrodes.
slide48
Each electrode is connected to a separate insulated wire but may be packaged in one cable.
    • This type of electrode is used for precise coagulation.
slide49
The arrangement of the patient leads on most modern ESUs is illustrated in (a).
    • The patient leads are usually isolated so that any leakage currents at power line frequencies would be suppressed.
slide50
The resistance of both leads to ground should exceed several megohms.
    • The effect of this would be that any alternative path from the patient to ground would not complete the circuit so as to cause burn injuries at the point of patient-to-ground contact.
slide51
However, because these are portable patient leads, one might inadvertently ground the return lead and provide an alternative path.
    • Someone may set the return plate on a radiator, or itmay make contact with a grounded bed or operating table.
slide53
Some manufacturers provide separate terminals for bipolar leads.
    • These leads often require lower power levels, and the separate terminals provide a measure of safety by making it less likely that the power would be inadvertently set too high.
electrosection
Electrosection
  • To do both incisions and excisions, a blade electrode or a needle electrode may be used. In both cases, a large-area patient return electrode is required.
    • The essential parameters that need to be controlled in this mode are adequate power, speed of cutting, pressure lightness, and deftness.
slide56
Short brushings with a clean electrode is considered most effective.
    • In delicate situations, it may be necessary to wait five to ten seconds between strokes to limit heat damage to tissue.
      • This limits the average power that the tissue absorbs and reduces the likelihood of unwanted tissue damage.
slide57
If the cutting power is adequate, cutting can be done with no coagulation or thermal damage.
    • However, if the power setting is too low, the deep tissue damage can result in atypical healing of the wound and postoperative pain.
      • As a rule of thumb, if visible sparking occurs, the power is probably too high; and
      • If a noticeable drag occurs, the power may be too low.
slide58
Electrosectioning may be done in the cut mode of the ESU, or the blended modes may be used to keep the bleeding minimal.
electrocoagulation
Electrocoagulation
  • Electrocoagulation is done by choosing the coag mode of the ESU.
    • The current is applied through a wide-area active electrode and returned through a patient plate electrode.
    • The wide-area contact electrode spreads out the current, making a low current density, so that the tissue is heated rather than cut.
slide60
In one method, a ball-tipped electrode is put in momentary contact with the tissue and withdrawn.
    • Contact is repeated as deemed necessary.
      • A scrubbing motion should never be used, according to some surgeons.
      • A light tapping motion is recommended.
slide61
Coagulation may also be achieved with a bipolar electrode so the therapist can control the tissue destruction.
    • In this case, the currents are confined to a small region defined by the two electrodes at the tip of the surgical pencil.
      • A large-area return electrode is not needed.
slide62
This method is effective in confined areas, such as in the brain, where stray currents could cause serious injury to nerves or vessels.
    • Because the currents can be greatly confined, low power levels are effective.
      • Also, the confinement of the currents makes this electrode effective in coagulating bleeders in fluids such as blood.
slide63
It is effective in producing hemostasis arid sealing off bleeders in soft tissues.
    • It is used to destroy inoperable cancer masses.
slide64
Electrocoagulation can cause delayed bleeding if vessels are damaged.
    • Coagulation is complete when discoloration appears at the treatment site.
      • A popping sound is often heard when the vessel coagulates.
        • The current should be stopped as soon as coagulation occurs to prevent excessive thermal damage to the tissue.
electrodesiccation
Electrodesiccation
  • Deeply penetrating tissue dehydration can be done with Oudin currents (currents produced by a high-voltage coil that does not require a return electrode).
    • This can be safely used to remove many types of superficial lesions in cutaneous surgery.
      • A dehydrating current is applied to a motionless electrode penetrating the tissue to be desiccated.
        • This may be used either with or without a large area patient return electrode, depending on the machine used.
slide66
Heat radiates from the electrode into the tissue, dehydrating it.
    • It is very difficult for the operator to control the tissue destruction extending beneath the tissue.
      • Only long experience with particular cases can enable the surgeon to predict the effects.
slide67
This method is particularly dangerous near major vessels, which could hemorrhage from thermal damage, or near important nerves, which could be destroyed by the heat.
slide68
The hazards associated with this mode are also illustrated by the case in dentistry:
    • There it is unsuited except in a few clinical uses.
      • It is especially dangerous to the gingival mucosa (gums).
        • It is justified in emergency hemorrhaging in dire cases where local tissue destruction is preferable to severe injury to the patient.
fulguration1
Fulguration
  • The current is applied by permitting a spark gap by holding the electrode above the tissue.
    • If an Oudin coil is used, a patient return electrode may not be necessary.
      • The spark is moved in a rotary direction.
slide70
A leather mass, called eschar, is formed, or the tissue becomes charred and carbonized.
    • Appreciable destruction of adjacent and subadjacent tissue need not occur.
slide71
Fulguration is useful in destroying orifices of fistulae, papilomatous tissue, or fragments of necrotic or cystic tissue wedged between the teeth.
    • It is also useful in controlling bleeding.
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