ESU (Electrosurgical unit)

Introduction

• An ESU (Electrosurgical unit) is a generator capable of producing a cutting and/or coagulating (control bleeding) clinical effect on tissue by the use of alternating current at a high frequency (RF - radio frequency, also known as radio surgery) through an active electrode. 
• Voltages and currents may vary depending on the desired clinical effect.
• ESU is one of the most important tools in all kind of operation rooms.

Types of ESU are:

• Monopolar (unipolar) unit
• Bipolar unit
• Monopolar/Bipolar unit

Effect of RF on cell

One of the effects of electric current is heat generation.

If the current intensity exceeds a limit, it might cause evaporation of inter-cellular fluid and subsequently, blast of cell membrane and disintegration of the cell.

As a result of this factor, following changes take place in the tissue:

1. Blast of cells and release of their internal contents.
2. Evaporation of tissue fluids that lead to tissue accumulation.
3. The proteins of blood cells and tissues transform into clots. 

Principle of Monopolar Unit

• There is only one electrode is mounted on the device and the entire patient is interposed between this “active electrode(cautery pencil)” and the large dispersive electrode that is also attached to the ESU, but located relatively distant from the target tissue, typically on the thigh or back. 

Monopolar Modes:

• Cut
• Coagulation
• Blend

Monopolar Modes

Electro surgical generators are able to produce a variety of electrical wave forms. As waveforms change, so will the corresponding tissue effects.

Cut

A continuous, low-voltage waveform to vaporize or cut tissue. This waveform produces heat very rapidly.

Coagulation 

Using an intermittent (high voltage) waveform, like coagulation causes the generator to modify the waveform so that the duty cycle (on time) is reduced. This interrupted waveform will produce less heat. Instead of tissue vaporization, a coagulum is produced.

Blend

A blended current is not a mixture of both cutting and coagulation current but rather a modification of duty cycle. As we go from blend 1 to blend 3 the duty cycle is progressively reduced. A lower duty cycle produces less heat. Consequently, blend 1 is able to vaporize tissue with minimal hemostasis, whereas blend 3 is less effective at cutting but has maximum hemostasis.

Bipolar unit

• Bipolar electro surgery uses 2-tined bipolar forceps.
• One tine of the forceps serves as the active electrode, and the other tine serves as the return electrode.
• A grounding pad is not needed for bipolar-only cases.

Block Diagram