Electrosurgery: Basics and Principles
Arash Taheri
Tuesday, February 25, 2014
Introduction
The term electrosurgery (radiofrequency surgery) refers to the
passage of a high-frequency (radiofrequency) electrical current
through the tissue in order to achieve a specific surgical effect
such as cutting or coagulation. Each electrosurgical device
consists of a high frequency electrical generator and two
electrodes (Figure 1). Adjacent to the active electrode, tissue
resistance to the passage of alternating current converts
electrical energy to heat, resulting in thermal tissue
damage.1,2 The large return electrode disperses the
current, reducing the current density to levels where tissue
heating is minimal.
Figure 1. An electrosurgery circuit in monopolar
biterminal mode (image from Taheri A et al.
Electrosurgery; basics and principles. Journal of American Academy
of Dermatology. In press.)

Basic mechanism of electrosurgery
Electrocoagulation occurs when tissue is heated below the
boiling point and undergoes thermal denaturation.3 A
slow further increase in temperature leads to vaporization of the
water content in the coagulated tissue and tissue desiccation. As
more superficial coagulated tissues dry out, they become less
electrically conductive leading to spark formation through
desiccated tissue. Desiccation is not a method or a distinctive
final result; it is only the final stage of coagulation that may or
may not happen.
A sudden increase in tissue temperature above boiling point
results in rapid explosive vaporization of the water content in the
tissue adjacent to the electrode. This leads to tissue
fragmentation and cutting (electrosection).4-6
Current waveforms
Electrosurgical generators are able to produce a variety of
electric waveforms (Figure 2). The name of each electrosurgical
waveform or mode does not necessarily translate to the final tissue
effect. The only variable that determines effects of a current is
the depth and the rate at which heat is produced. The wave-form,
voltage and power of electrosurgical current and the size of
electrode tip can affect the depth and the rate of heat production
and indirectly influence the final effect on the
tissue.3,7,8
Figure 2. Cutting mode uses a continuous waveform which
is able to provide the maximum output power of the generator. Other
modes use intermittent waveforms with lower maximum power than
cutting waveform. An intermittent waveform incorporates higher
voltage than a cut waveform at the same power
setting (image from Taheri A et al. Electrosurgery;
basics and principles. Journal of American Academy of
Dermatology. In press.)

Electrosurgical modalities
Electrocoagulation
Electrocoagulation can be performed in contact mode or in spray
(fulguration) mode. However, the term electrocoagulation is usually
used to refer to electrocoagulation in contact mode.
For superficial coagulation of small areas a fine-tip electrode
is used to concentrate a low power current to a fine point (Table
1). The current density in tissue rapidly decreases with distance
from the electrode (Figure 3); therefore, heat generation is
practically confined to the vicinity of the electrode tip on the
surface.9
When using a large-tip electrode with a large electrode-tissue
contact surface, a higher power output should be used (Figure
3).10 Current density decreases with distance from the
electrode surface more slowly compared to a fine electrode. A
higher power output and slower decrease in current density leads to
deeper tissue injury. A large electrode tip, therefore, should be
used only for deep coagulation (Table 1).11
In electrofulguration, the active electrode is held above the
tissue. Using an interrupted high-peaked-voltage output, an
electric discharge arc (spark) forms that rapidly dances from one
location to the other and spreads the current over an area larger
than the tip of the electrode.12 Each spark carries the
current to a very small point, acting as a very fine electrode.
Given a relatively low power, tissue destruction and coagulation
appears within a thin superficial layer of tissue. However, if
electrode is kept over a confined area, continuous heat production
on the superficial layers can cause heating of deeper layers and a
deep coagulation (Table 1).
Figure 3. Electrocoagulation (image from
Taheri A et al. Electrosurgery; basics and principles. Journal of
American Academy of Dermatology. In press.)

Electrosection
The major advantage of electrosection over scalpel is that
hemostasis is achieved immediately upon incision by coagulation on
either side of the incision wall.
A thin needle can concentrate current on a small area and allows
the same cutting effect to be achieved with a lower power setting.
This leads to less heat production and less collateral tissue
coagulation compared with a thicker electrode.6,13
Therefore, a thin needle is used to make a relatively clean
incision with minimal coagulation and hemostasis on the incision
walls (Figure 4). A thick needle electrode can cut through the
tissue using a very high power current. Current density and
temperature decreases from electrode more slowly compared with a
thin electrode and results in a deeper coagulation margin (blend
cut; Figure 4).
When the cutting electrode comes in contact with the tissue, an
initial tissue heating and explosive vaporization of the water
around the electrode leads to isolation of the electrode from the
tissue. The current then passes through the vapor cavity by spark
without a direct contact between the active electrode and
tissue.4,9 The higher the peak voltage of the current,
the larger the sparks. Larger sparks spread current to a wider area
of tissue around the electrode and act as if a thicker electrode is
being used.14 Therefore, an interrupted
high-peak-voltage current provides a blend cut (Figure
4).3,15
In order to have less collateral tissue damage and coagulation
on the incision walls, contact time should be reduced to minimize
heat production and conduction.16 Therefore, the cutting
of the tissue should be brisk with the lowest effective power
setting.5,6
Figure 4. Electrosection. Left: A thin needle is able to
concentrate a low-peaked-voltage, low-power current (cutting
current with relatively low power). Middle: A thick electrode
provides deeper coagulation margins. Right: A high-peaked voltage
current (blend or coagulation waveforms) produces large sparks that
cannot concentrate the current (image from Taheri A
et al. Electrosurgery; basics and principles. Journal of American
Academy of Dermatology. In press.)

Bipolar versus monopolar electrosurgery
In electrosurgery, the prefix 'mono-' and 'bi-' polar refers to
the number of active electrodes. In monopolar electrosurgery an
active electrode carries current to the tissue (Figure 1). Current
then spreads through the body to be collected by a dispersive
electrode. In bipolar electrosurgery, however, the current passes
only through the tissue between the tips of a bipolar forceps
(Figure 5). A bipolar forceps acts as two active
electrodes.17,18
Figure 5. Bipolar electrosurgery circuit
(image from Taheri A et al. Electrosurgery; basics and principles.
Journal of American Academy of Dermatology. In
press.)

Biterminal versus monoterminal electrosurgery
The prefix 'mono-' and 'bi-' terminal refers to the number of
electrodes that are in contact with patient's body (Figure 1 and
Figure 6).
In so-called 'earth-referenced' electrosurgical units, the
return electrode is connected to earth and therefore, the earth and
all conductive objects around the patient's body can act as a
capacitive-type dispersive electrode (Figure 6). Electrosurgery can
be performed using these units regardless of whether a dispersive
electrode is attached to the patient. Performing monopolar
electrosurgery without using a dispersive electrode is called
monoterminal electrosurgery (Figure 6).
During monoterminal electrosurgery with an earth-referenced
unit, if an electrically conductive object such as a metal table or
surgical staff comes into contact with the patient's body, current
concentration at this point may result in a burn. For this reason,
monoterminal mode is used only on conscious patients who would be
aware of such complications.
The type of electrosurgical unit commonly used in operating
rooms today is floating or isolatedwith the dispersive electrode
isolated from earth. An isolated generator will not work unless the
dispersive electrode is attached to the patient.7 During
activation, if the patient's body comes in contact with an
environmental object, the risk of a burn is low.
Although a good dispersive electrode reduces the risk of distant
site burns, inadequate contact of the dispersive electrode with the
patient's body may result in a smaller contact area and current
concentration at this point may lead to a burn at this
site.3,7,19,20
Figure 6. Monoterminal electrosurgery using an
earth-referenced unit. The return electrode is connected to the
earth (image from Taheri A et al. Electrosurgery;
basics and principles. Journal of American Academy of
Dermatology. In press.)

Electrosection versus scalpel surgery
Electrosection is used as an alternative to scalpel surgery.
While many studies support better outcomes using scalpel surgery,
there is also literature favoring electrosection.21-24 A
general concept is to avoid electrosection for cutting skin when a
primary closure is planned.
Electrosection results in some histologic distortion of surgical
margins. For specimens requiring histopathological analysis,
scalpel surgery is preferred.
Electrosurgery versus CO2 laser surgery
Coagulation of tissues such as warts or skin tumors can be
achieved using electrosurgery or CO2 lasers. Both
methods can provide superficial destruction, however
electrocoagulation can be used more easily for deeper tissue
destructions. While a CO2 laser is more predictable and
controllable for superficial destructions, in experienced hands,
electrosurgery has more flexibility for choosing the depth of
injury.
Similar to electrosection, CO2 lasers can provide
coagulation of the incision walls and hemostasis. Both techniques
are operator dependent and cannot be standardized. Therefore,
comparing these modalities in clinical settings is not easy. Some
studies show more collateral coagulation using electrosection,
while others report the opposite results.23-31
Conclusion
Superficial coagulation of small areas can be performed with a
fine-tip electrode. A large-tip electrode is used for deep
coagulation. Making a relatively clean incision with little
hemostasis (pure cutting) needs a thin electrode and a cutting
current (cut mode). Blend cutting can be performed using an
interrupted current (blend or coagulation mode).
In regards to safety, monoterminal mode may be limited,
especially when using a high power on an unconscious
patient.
Table 1. Settings of an electrosurgical unit for
destuction/coagulation of different skin targets
Depth of tissue injury |
Area |
Method of application of current |
Electrical current of mode of choice |
Alternative currents or modes |
Setting |
Possible indications* |
Superficial destruction |
Small area |
Fine-tip electrode in contact method |
Continuous current (cutting mode) |
Interrupted current (blend or coaulation modes) |
A very low power setting is used. The power is started very low
and is increased until a reasonably fast movement of the electrode
on the tissue can be attained. Coagulated materials can be wiped
off and a second pass be performed |
Seborrheic keratosis
Dermatosis papulosis nigra or small skin tag
Freckle or lentigo
Plane wart
Common or genital wart
Molluscum contagiosum
Cherry angioma
Spider angioma and telangiectasia
Sebaceous hyperplasia
Syringoma
|
Large area |
Fine-or large-tip electrode in fulguration# (spray)
method |
Interrupted current (fulguration mode) |
Interrupted current (coagulation mode) |
A low to medium power setting is used. The power is started low
and is increased until a reasonably fast movement of the electrode
on the tissue can be attained. Coagulated materials can be wiped
off and a second pass be perfomed |
Seborrheic keratosis
Verrucous epidermal nevus
Rhinophyma
|
Medium depth destruction |
Small to large area |
Medium-size-top electrode in contact method; or
fulguration# (spray) method |
Depending on the method (see above) |
Interrupted currents (blend or coagulation modes) |
Needs more power than superficial destruction |
Gential wart@
Actinic keratosis
Bowen's disease
Rhinophyma
Mucous cysts
Pyogenic granuloma$
|
Deep destruction (used as an alternative to excision) |
Medium to large area |
Large-tip electrode in contact method |
Continuous current (cutting mode) |
Interrupted currents (blend or coagulation modes) |
Medium to high power setting. The power should be enough for a
slow desiccaton (hearing a popping sound after a few seconds) |
Basal cell carcinoma$
Keratoacanthoma$
Squamous cell carcinoma$
|
Loop excision |
Medium to large area |
A thin wire in loop shape |
Continuous current (cutting mode) |
Interrupted currents (blend or coagulation modes) |
Setting should be selected depending on the amount of desired
hemostasis |
An alternative to shave excision + hemostasis. Not suitable for
histopathologic evaluation |
* Electrosurgery can be used for the mentioned indications,
however it is not necessarily the treatment of choice.
@ Becuase of risk of viral transmission through the
smoke, electrofulguration is not a preferred treatment of viral
warts.
# Depending on the power and the speed of movement of
the electrode on the tissue, electrofulguration can potentially
induce either a superficial or a relatively deep destruction.
$ Fragile tumors can be treated using curettage +
electrodesiccation as an alternative to excision. However,
depending on variables such as tunor type, location, and size, in
many cases, excision may be preferred.
|
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