This document summarizes key aspects of electrosurgical units used in surgery. It describes diathermy, which uses radiofrequency current to cut and coagulate tissue with limited blood loss. Monopolar diathermy involves current passing from the active electrode through the patient's body to a grounding plate, while bipolar diathermy confines current to tissue between instrument electrodes. Proper placement and monitoring of grounding plates is important to prevent burns with monopolar devices. Electrosurgical units use different waveforms and modes for cutting, coagulation, and desiccation of tissue.

1. Electrosurgical Unit

2. • Diathermy is the use of high frequency alternate polarity radio-wave electrical
current to cut or coagulate tissue during surgery. It allows for precise incisions to
be made with limited blood loss and is now used in nearly all surgical disciplines.

3. Monopolar Diathermy
• In monopolar action, the electrical current oscillates between the surgeon’s electrode, through the
patient’s body, until it meets the ‘grounding plate’ (typically positioned underneath the patient’s
leg) to complete the circuit.

4. • The active electrode is in the wound.
• The patient return electrode is attached somewhere else on the patient.
• The current must flow through the patient to the patient return electrode.
• There are four components of monopolar circuit.
1. Generator
2. Active Electrode
3. Patient
4. Patient Return Electrode

5. • In monopolar mode, good contact between the patient and the ground plate is essential.
• If this surface area is decreased, for example if the ground plate slips partially off the patient, then this
can result in severe burns. Fortunately, many modern machines monitor impedance and will stop
working if this occurs.
• The ground plate should be positioned as close to the operative site as possible, however it should not
be placed over a bony prominence, metal prosthesis, distal to a tourniquet, over scar tissue, on hairy
surfaces, or on pressure points, to minimise the risk of burns.
• The plate should also be kept dry.
• There is also the theoretical risk of smoke and contaminant inhalation when using diathermy, to both
surgeon and theatre staff, hence appropriate masks should be used in well ventilated areas.

6. Bipolar Surgery
• In bipolar diathermy, the two electrodes are found on the instrument itself. The bipolar arrangement
negates the need for a dispersive electrode, instead a pair of similar sized electrodes are used in
tandem.
• The current is then passed between the electrodes. Bipolar is most commonly used in operations of
the digits (to avoid monopolar current focused over a smaller region), in patients with pacemakers
(to avoid electrical involvement with the pacemaker), or in microsurgery.

7. • Active output and patient return functions are both accomplished at the site of
surgery.
• Current path is confined to tissue grasped between forceps tines.
• Patient return electrode should not be applied for bipolar only procedures.

9. Electrosurgical Cutting
• Electrosurgical cutting divides tissue with electric sparks
that focus intense heat at the surgical site.
• By sparking to tissue, the surgeon produces maximum
current concentration.
• To create this spark the surgeon should hold the electrode
slightly away from the tissue.
• This will produce the greatest amount of heat over a very
short period of time, which results in vaporization of
tissue.

10. Fulguration
• Electrosurgical fulguration (sparking with the coagulation
waveform) coagulates and chars the tissue over a wide area.
• Since the duty cycle (on time) is only about 6 percent, less
heat is produced. The result is the creation of a coagulum
rather than cellular vaporization.
• In order to overcome the high impedance of air, the
coagulation waveform has significantly higher voltage than
the cutting current.
• Use of high voltage coagulation current has implications
during minimally invasive surgery.

11. Cut
Low voltage waveform
100% duty cycle
Coag
High voltage waveform
6% duty cycle
Desiccation
• Electrosurgical desiccation occurs when the electrode is in
direct contact with the tissue.
• Desiccation is achieved most efficiently with the “cutting”
current.
• By touching the tissue with the electrode, the current
concentration is reduced.
• Less heat is generated and no cutting action occurs. The
cells dry out and form a coagulum rather than vaporize and
explode.

14. Cutting (Yellow button or pedal)
• Cutting uses a continuous waveform with a low voltage. In cutting mode, the electrode reaches a
high enough power to vaporize the water content. Hence it is able to perform a clean cut but is less
efficient at coagulating.
Coagulation or ‘Coag’ (Blue button or pedal)
• Coagulation alternatively uses a pulsed waveform with a high voltage. In coagulation, the waveform
is at a lower average power, not generating enough heat for explosive vaporisation, but enough for
thermal coagulation. The tip should be held slightly away from the tissue, however the sparks are
spread over a wider area causing charring rather than cutting.
• There is also a mixed (or blend) mode, acting in between as both cutting and coagulating, however
this is not widely used