6.5 – Electrosurgical Units (ESU)
Principles of ESUs
A basic understanding of electricity is needed to safely apply electrosurgical technology for patient care. Often “electrocautery” is used to describe electrosurgery. This is incorrect. Electrocautery refers to direct current (electrons flowing in one direction), whereas electrosurgery uses alternating current. Modern day electrosurgery is the utilization of alternating current at radiofrequency levels. During electrocautery, current does not enter the patient’s body. Only the heated wire comes in contact with tissue. In electrosurgery, the patient is included in the circuit and current enters the patient’s body.
Electrical current flows when electrons from one atom move to an adjacent atom through a circuit. Heat is produced when electrons encounter resistance. For current to flow, a continuous circuit is needed. In the operating room, the circuit is composed of the patient, the electrosurgical generator, the active electrode and the return electrodes. The electrosurgical unit is the source of the voltage.
Electrical energy is converted to heat in tissue as the tissue resists the flow of current from the electrode. Three tissue effects are possible with today’s electrosurgical units—cutting, desiccation, and fulguration. Achieving these effects depends on the following factors: current density, time, electrode size, tissue conductivity, and current waveform.
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Current density: As expected, the greater the current that passes through an area, the greater the effect will be on the tissue.
- Time: The length of time a surgeon uses an active electrode determines the tissue effect. Too long an activation will produce wider and deeper tissue damage. Too short an activation will result in absence of the desired tissue effect.
- Electrode Size: With respect to electrode size, smaller electrodes provide a higher current density and result in a concentrated heating effect at the site of tissue contact. Following the same principle, the patient return electrode used in monopolar electrosurgery is large in relation to the active electrode in order to disperse the current returning to the electrosurgical unit and minimize heat production at this return electrode site.
- Tissue Conductivity: Various tissue types have a different electrical resistance, which affects the rate of heating. Adipose tissue and bone have high resistance and are poor conductors of electricity, whereas muscle and skin are good conductors of electricity and have low resistance.
- Current Waveforms: The final determinant of how tissue responds to electrosurgery is the current type. Electrosurgical units produce 3 different waveforms: cut, blend, and coagulation (see Figure 6.5.1)
Figure 6.5.1 – Wave forms of ESUs with different tissue effects
Table 6.5.1 provides an overview of the tissue effects of the two traditional (Monopolar and Bipolar) and two innovative energy modalities (Advanced Bipolar and Ultrasonic).
Table 6.5.1
Comparison of Tissue Effects of 4 Energy Modalities
| Monopolar | Traditional Bipolar | Advanced Bipolar | Ultrasonic | |
|---|---|---|---|---|
| Tissue Effect | Cutting, Coagulation | Coagulation | Cutting, coagulation | Cutting, coagulation |
| Power Setting | 50–80 W | 30–50W | DEFAULT | 55,000 Hz frequency |
| Thermal Spread | Not well assessed | 2–6mm | 1–4mm | 1–4mm |
| Maximum Temperature | >100°C | >100°C | Not well assessed | <80°C |
| Vessel Sealing Ability | Not applicable | Not applicable | Seals vessels ≤7mm | Seals vessels ≤5mm |
| Technique | Not applicable | Not applicable | Tension free application | Tension free application |
In monopolar electrodes, radiofrequency current flows from the generator through the active electrode, into the target tissue, through the patient, the dispersive electrode and then returns to the generator (see Figure 6.5.2). The most common site of injury is at the patient return electrode. The return electrode must be of low resistance with a large enough surface area to disperse the electrical current without generating heat. If the patient’s return electrode is not large enough or is not completely in contact with the patient’s skin, then the current exiting the body can have enough density to produce unintended burns.
Figure 6.5.2 – Example of a monopolar circuit
In bipolar electrosurgery the active and return electrodes are located at the site of surgery, typically within the instrument tip (see Figure 6.5.3). The classical example is the two tines of forceps that are the active and return electrode and represent the entire circuit. Most bipolar units use a lower voltage waveform to achieve hemostasis and avoid collateral tissue damage. Bipolar electrosurgery has a more limited area of thermal spread compared with that of monopolar electrosurgery, and is similar to that of a laser.
Disadvantages of bipolar electrosurgery include the increased time needed for coagulation due to a low power setting, charring, and tissue adherence with incidental tearing of adjacent blood vessels
Figure 6.5.3 – Example of a bipolar circuit
Troubleshooting ESUs
There are many different manufacturers of ESUs and each will have their own recommended set of preventative maintenance and repair guidelines. You can find information on 33 different brands of ESU’s by clicking on the link. Each company may provide you with information regarding the different models they offer. For example, in BTEC 315 we use the Valleylab ESU and if you click on the link, you can find information on 13 different products. Specifically, you will be working with the Valleylab Force 2 and if you click on the final link you can find information regarding its user and service manual, technical and preventative maintenance guidelines, schematics and instruction manual. Figure 6.5.4 demonstrates a flow chart of troubleshooting an ESU.
https://bmet.ewh.org/server/api/core/bitstreams/84f43d0c-b2a5-4f69-9aca-46077ddb8bb1/content
Figure 6.5.4 – Flow chart of ESU repair and troubleshooting
Attributions
Portions of this chapter were shared from Principles and Safety Measures of Electrosurgery in Laparoscopy by Alkatout et. al. is licensed under CC BY-NC-ND 4.0
References
- Figure 6.5.4 ESU Repair and Troubleshooting by Engineering World Health., All Rights Reserved. Used with permission.
