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ENTC 4350
ELECTROSURGICAL
UNITS (ESUs)
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

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.

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.

The original ESU
was invented by
William Bovie.

The transformer, connected to the 60cycle power mains, steps up the voltage,
which is then applied across a gas tube.

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.

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.

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.

The electrode—tissue interface is
illustrated below.

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.

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.

To achieve hemostasis, a certain amount
of damage is desirable.
• The control of this factor is key to good
surgical technique using the ESU.

An RF oscillator forms the basis for a
modern ESU.

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.

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.

Front panel switches enable the operator
to select the mode desired.
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.

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.

The return electrode is large in area and
gelled to keep the skin resistance low
and the region cool.

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.

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.

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.

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

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.

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.

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.

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

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.

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.

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.

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

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.

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.

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.

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

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

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.

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.

The current returns to the ESU through a
large-area patient electrode.
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.

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.

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.

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.

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

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.

The lead classifications are as follows:
•
•
•
•
•
•
Monoterminal—An ESU 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.

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.

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.

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.

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.

Safety is most effectively ensured by
careful and informed operating
procedure.

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.
ELECTROSURGICAL
TECHNIQUES
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.

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.

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.

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 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.

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.

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.

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.

It is effective in producing hemostasis
arid sealing off bleeders in soft tissues.
• It is used to destroy inoperable cancer
masses.

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

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.

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.

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.

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.
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.

A leather mass, called eschar, is formed,
or the tissue becomes charred and
carbonized.
• Appreciable destruction of adjacent and
subadjacent tissue need not occur.

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.