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Electrical Surgical Unit
Dr Fadhl Al-Akwaa
[email protected]
www.Fadhl-alakwa.weebly.com
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ESU Importance
• Radio frequency current has been used for
many years to reduce time under anesthesia
and improve the clinical result. The ability to
simultaneously cut tissue and coagulate blood
vessels greatly reduces morbidity and
mortality, and enables a large number of
procedures that are otherwise not possible,
especially in neurosurgery.
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AGENDA
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81.1 Theory of Operation
81.2 Monopolar Mode
81.3 Bipolar Mode
81.4 ESU Design
81.5 Active Electrodes
81.6 Dispersive Electrodes
81.7 ESU Hazards
81.8 Recent Developments
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Terminology
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Cutting
Coagulation= fulgurate + desiccation
Desiccation OR contact coagulation. ‫تجفيف‬: process of drying food
Fulgurate: (fulgur is Latin for lightning). destroy using electricity
(such as a tumor, etc.)
Hemostasis: stoppage of bleeding
Blended mixed, merged, combined
choice of blend waveforms to allow the surgeon to select the
degree of hemostasis desired.
Bleeding
RF frequency 300 kHz and 5 MHz
Cautery: process of burning or scarring with a hot iron or other
implement ‫الكي‬
Ablating: remove by cutting
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Electrosurgery vs electrocautery
• Electrosurgery is sometimes erroneously referred to as
electrocautery.
• In cauterization the essential physical mechanism behind
the treatment is conduction heat transfer from a hot object
placed on the surface to raise the temperature high enough
to denature the tissue proteins.
• Cutting and coagulation by means of electrosurgery is also
accomplished by heating tissue to high temperatures, but
the essential difference is that the primary mechanism is
electrical power dissipation directly in the affected tissues
themselves, rather than heat transfer from an external hot
object on the tissue surface.
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Electrosurgery vs Diathermy
• Electrosurgery is also referred to as surgical
diathermy, particularly in Europe.
• diathermy literally means through-heating,
such as might be applied in physical medicine
for the relief of pain or in hyperthermia
therapy for tumor treatment.
• Electrosurgical devices in operating rooms are
designed and built for surgical use only.
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Clinical application
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Electrosurgery is commonly used in
dermatological,
gynecological,
cardiac,
plastic,
ocular,
spine,
ENT, Ear Nose & Throat
orthopedic,
urological,
neuroand general surgical procedures.
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Duty cycle=on time/off time
• Continuous
Interrupted
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Crest Factor
• The Crest Factor is equal to the peak
amplitude of a waveform divided by the RMS
value.
• Electrical engineering — for describing the
quality of an AC power waveform
Current density (high or low)
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Electrosurgical modes
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Electrosurgical modes
• Monopolar mode AND Bipolar mode
• The most noticeable difference between these two modes is
the method in which the electric current enters and leaves
the tissue.
• In the monopolar mode, the current flows from a small active
electrode into the surgical site, spreads through the body, and
returns to a large dispersive electrode on the skin.
• In the bipolar mode, the current flows only through the tissue
held between two forceps electrodes.
• The monopolar mode is used for both cutting and
coagulation. The bipolar mode is used primarily for
coagulation.
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History
• Development of the first commercial
electrosurgical device is credited to Dr. William
T. Bovie, who worked on it from 1914 to 1927
while employed at Harvard University[8] [9]
• The first use of an electrosurgical generator in
operating room occurred on October 1, 1926.
The surgery was performed by Dr. Harvey
Cushing.
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Theory of Operation: Temperature
• What is the general effects of heat on biologic
tissue?
• What happen when tissue temperature increase
from normal body temperature to 45°C?
• neither microscopic nor macroscopic changes,
• some cytochemical changes do in fact occur.
• the cells return to their normal function when the
temperature returns to normal values.
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Theory of Operation
• What is the general effects of heat on biologic tissue?
• Above 45°C,
• Normal cell functions was inhibited and lead cell was
death.
• Further increasing the temperature up to 100°C leads to
tissue drying; that is, the aqueous cell contents
evaporate. This process is called desiccation.
• If the temperature is increased beyond 100°C, the solid
contents of the tissue reduce to carbon, a process
referred to as carbonization.
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Bioheat equation
• Where T and To are the final and initial temperatures
(K),
• σ is the electrical conductivity (S/m),
• ρ is the tissue density (kg/m3)
• C is the specific heat of the tissue (Jkg-1k-1)
• J is the current density (A/m2), and
• t is the duration of heat applications
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Bioheat equation
• The bioheat equation is valid for short application
times where secondary effects such as heat transfer to
surrounding tissues, blood perfusion, and metabolic
heat can be neglected.
• the surgeon has primarily three means of controlling
the cutting or coagulation effect during electrosurgery:
• the contact area between active electrode and tissue,
• The electrical current density, and the activation time.
• output power vs. tissue impedance
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Output values for ESUs,
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Waveform
Interrupted waveforms, such as
exponentially damped sinusoids (obtained
from spark gap or other relaxation-type
oscillators) are effective for coagulation
techniques requiring fulguration, or
intense sparking (fulgur is Latin for
lightning).
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Continuous sine waveforms
(e.g., those obtained from vacuum tube
or transistor oscillators)
have proven most effective for cutting.
Cut/Coag
• Cut/Coag Most wet field electrosurgical systems
operate in two modes; Cut where the tissue is
vaporized and Coag where the tissue is dried.
• Cut If the voltage level is high enough then the heat
generated can generate a vapour pocket. The vapour
pocket typically reaches temperatures of
approximately 400 Degrees Centigrade which vaporizes
soft tissues.
• Coag When the system is operating in coag mode the
voltage output is usually lower than in cut mode and
less power is delivered. This therefore generates less
heat and a vapour pocket is not generated.
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Why high frequency?
• sensitivity to electrical stimulation decreases with
increasing frequency in the kHz range and above.
• Neural and muscle cells are electrically-excitable,
i.e. they can be stimulated by electric current. In
human patients such stimulation may cause acute
pain, muscle spasms, and even cardiac arrest.
• To minimize the effects of muscle and neural
stimulation, electrosurgical equipment typically
operates in the radio frequency (RF) range of 100
kHz to 5 MHz.
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high-frequency power amplifiers
• vacuum tube/ spark gap 1907, Lee De Forrest,
• power transistors,
• solid-state electrosurgical generators(Valleylab
and EMS) 1970
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ESU Design
control input
switches,
RF Generators for
Electrosurgery
“high-frequency
power amplifiers”
safety
monitor.
Microcontroller
Power supply
Microcontroller
Electrodes
Active electrode
return electrode,
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Block diagram for typical solid state
ESU
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Safety Appliances.
American National Standard for Electrosurgical Devices
• the return electrode losing its attachment to
the skin>> skin burns at the dispersive, or
return, electrode site.
• Patient return monitor circuit
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Electrosurgery Analyzers
QA-ES Electrosurgery Analyzer
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Performance testing
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Tests include:
• Automatic power distribution measurement
• Crest factor measurement
• RF leak measurement
• Return electrode monitor (REM) test
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Power Output Tests
• output current (A),
• power (W),
• peak-to-peak voltage (V),
• crest factor values.
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HF Current Leakage Test
• This test checks whether the active and
dispersive leakage currents are within
acceptable limits.
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Measuring Leakage Current with HF
Isolated Equipment
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Measuring Leakage Current with
Grounded HF Equipment
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REM Alarm Test
• The REM (Return Electrode Monitoring) alarm
test ensures that the ESU sounds an alarm if
the resistance between the two neutral
electrodes exceeds its specified limit
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Electrosurgery Analyzers
• Typical measurement parameters:
– RF current (ma)
– RF power (watts)
– Crest Factor (CF) – the measure of Vpeak / VRMS
• 1.414 to 1000 range
– Duty cycle (pulsed waveforms)
• 1% - 100% range
– Through “non-inductive” test loads from 0Ω to >
5000Ω
– 5th generation parameters include
• Frequency
• Pulsed parameters such as time on, time off, total cycle time,
duty cycle