ENTC 4350

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ENTC 4350

• ELECTROSURGICAL UNITS (ESUs)

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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.

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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.

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• 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.

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• The original ESU was invented by William Bovie.

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• The transformer, connected to the 60-cycle power
  mains, steps up the voltage, which is then
  applied across a gas tube.

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• 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.

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• 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.

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• 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.

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• The electrodetissue interface is illustrated
  below.

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• 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 it to vaporize.

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• 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.

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• To achieve hemostasis, a certain amount of damage
  is desirable.
• The control of this factor is key to good
  surgical technique using the ESU.

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• An RF oscillator forms the basis for a modern
  ESU.

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• The device has several modes
• Cut modePure sine wave, for cutting with the
  least coagulation.
• Coag modePulsed sine wave, low-duty cycle, for
  coagulating bleeding tissue.
• Blend 1 modeModulated sine wave, for coagulating
  as the tissue is cut.
• Blend 2 modeModulated sine wave, for coagulating
  as the tissue is cut.

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• The device has several modes
• Cut modePure sine wave, for cutting with the
  least coagulation.
• Coag modePulsed sine wave, low-duty cycle, for
  coagulating bleeding tissue.
• Blend 1 modeModulated sine wave, for coagulating
  as the tissue is cut.
• Blend 2 modeModulated sine wave, for coagulating
  as the tissue is cut.

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• Front panel switches enable the operator to
  select the mode desired.

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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.

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• 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.

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• The return electrode is large in area and gelled
  to keep the skin resistance low and the region
  cool.

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• The RF circuit is usually isolated from ground
  so if the patients body comes in contact with
  ground (through a metal operating table, for
  example), an alternative path for the return
  current would not be established.

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• In some machines, especially older models, the
  return electrode is grounded.
• In this case, if the patients finger would also
  become grounded, an alternative path would be
  established, which could cause a burn on the
  finger.

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• 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.

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• 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.

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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.

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• 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.

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• 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.

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• 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.

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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.

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• 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.

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• 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.

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• 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.

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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.

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• 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.

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• 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.

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• 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.

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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.

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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.

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• 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.

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• The current returns to the ESU through a
  large-area patient electrode.

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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.

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• 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.

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• 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.

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• 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.

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• 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.

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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.

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• The lead classifications are as follows
• MonoterminalAn ESU with one wire for patient
  contact.
• BitermmalAn ESU with two wires for patient
  contact.
• Active electrodeThe electrode that delivers
  treatment to the surgical field.
• Patient electrodeThe large surface area return
  electrode.
• Monopolar electrodeAn active electrode that uses
  a patient electrode to complete the circuit.
• Bipolar electrodeTwo 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.

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• 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.

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• 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.

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• 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.

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• 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 it may make contact with a grounded bed or
  operating table.

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• Safety is most effectively ensured by careful and
  informed operating procedure.

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• 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.

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• ELECTROSURGICAL TECHNIQUES

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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.

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• 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.

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• 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.

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• Electrosectioning may be done in the cut mode of
  the ESU, or the blended modes may be used to keep
  the bleeding minimal.

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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.

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• 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.

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• 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.

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• 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.

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• It is effective in producing hemostasis arid
  sealing off bleeders in soft tissues.
• It is used to destroy inoperable cancer masses.

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• 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.

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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.

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• 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.

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• 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.

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• 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.

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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.

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• A leather mass, called eschar, is formed, or the
  tissue becomes charred and carbonized.
• Appreciable destruction of adjacent and
  subadjacent tissue need not occur.

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• 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.