Electrical Surgical Unit Dr Fadhl Al-Akwaa [email protected] Please contact Dr Fadhl to use this material

Please contact Dr Fadhl to use this material

Electrical Surgical UnitDr Fadhl Al-Akwaa

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http://www.fadhl-alakwa.weebly.com/


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.


AGENDA

• 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


Terminology• 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


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.


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.


Clinical application• Electrosurgery is commonly used in• dermatological, • gynecological, • cardiac, • plastic,• ocular,• spine, • ENT, Ear Nose & Throat• orthopedic,• urological,• neuro- • and general surgical procedures.


Duty cycle=on time/off time

• Continuous Interrupted

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

http://en.wikipedia.org/wiki/Electrical_engineering


Current density (high or low)


Electrosurgical modes


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.


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.


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.


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.


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


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



Output values for ESUs,


Waveform

Continuous sine waveforms(e.g., those obtained from vacuum tube or transistor oscillators) have proven most effective for cutting.

Interrupted waveforms, such asexponentially damped sinusoids (obtained from spark gap or other relaxation-type oscillators) are effective for coagulationtechniques requiring fulguration, or intense sparking (fulgur is Latin for lightning).


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.


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.


high-frequency power amplifiers

• vacuum tube/ spark gap 1907, Lee De Forrest,• power transistors,• solid-state electrosurgical generators(Valleylab

and EMS) 1970


ESU Design

RF Generators for Electrosurgery“high-frequency power amplifiers”

control input switches,

safety monitor.

Power supplyMicrocontroller

Microcontroller

ElectrodesActive electrodereturn electrode,


Block diagram for typical solid stateESU



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


Electrosurgery Analyzers

QA-ES Electrosurgery Analyzer


Performance testing

• Tests include:• • Automatic power distribution measurement• • Crest factor measurement• • RF leak measurement• • Return electrode monitor (REM) test


Power Output Tests

• output current (A),• power (W), • peak-to-peak voltage (V),• crest factor values.


HF Current Leakage Test

• This test checks whether the active and dispersive leakage currents are within acceptable limits.


Measuring Leakage Current with HF Isolated Equipment


Measuring Leakage Current with Grounded HF Equipment


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

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

Documents

Electrical Surgical Unit Dr Fadhl Al-Akwaa [email protected] Please contact Dr Fadhl to use this material