Electrosurgical Principles and Techniques

Electrosurgical Principles

• The learner should be able to:

  • Describe the differences between electrosurgery and electrocautery.

  • Explain the effect of radio frequency electricity on cells and tissue.

  • List the similarities and differences between monopolar and bipolar instrumentation.

Differences Between Electrosurgery and Electrocautery

• Electrocautery:

  • Passive heat transfer to tissue.

  • Example: Branding of cattle.

  • Chemical cautery example: Silver nitrate.

• Electrosurgery:

  • Involves application of radiofrequency electrical current to tissue.

  • Produces tissue vaporization, coagulation, and desiccation for hemostasis.

  • Converts electromagnetic energy to kinetic energy to thermal energy within tissue.

Effect of Radio Frequency Electricity on Cells and Tissue

• Radiofrequency alternating current causes:

  • Rapid oscillation of intracellular ions and proteins.

• Thermal injuries in surgery:

  • Common causes include surgical burns and fires.

  • Estimated incidence of thermal injuries in laparoscopic surgery: 1-2 per 1000 patients.

Concepts of Electrical Physics in Electrosurgery

1. Current:

   • Definition: Flow of electrons past a point in a circuit per unit time.

   • Measured in amperes.

2. Voltage:

   • Definition: Difference in electrical potential between two points in a circuit.

   • Measured in volts.

3. Impedance:

   • Definition: Resistance to the flow of electrons or ions; measured in ohms.

4. Energy:

   • Definition: Transferred to tissue as a product of work and time.

   • Measured in joules.

5. Power:

   • Definition: Amount of energy per unit time; measured in watts.

   • Adjusted on electrosurgical generator units (ESU).

6. Ohm's Law:

   • Relation between current (I), voltage (V), and resistance (R): I = \frac{V}{R}.

   • Water tower analogy:

     • Height of the water (voltage), width of pipe (resistance), volume flowing per unit time (current).

     • Increasing voltage increases current and vice versa depending on impedance.

Polarity of Electrical Energy Sources

• Constant Polarity Circuits:

  • Example: Battery with positive and negative ends.

• Alternating Polarity Circuits:

  • Example: AC electricity with cyclical switching of polarity.

  • Important for radiofrequency electrosurgery.

Monopolar vs. Bipolar Instrumentation

• Monopolar Instruments:

  • Utilize one active electrode and one dispersive electrode.

  • Energy oscillates between electrodes with the patient as part of the circuit.

• Bipolar Instruments:

  • Have two active electrodes (jaws), running only through a small part of tissue.

• Waveforms:

  • Continuous low voltage waveform (cut).

  • Intermittent modulated waveform (coagulation).

Thermal Effects on Cells and Tissue

• Cellular temperature effects due to radiofrequency:

  • 50°C: Cell death begins.

  • 60°C to 95°C: Protein denaturation and coagulation occur.

  • 100°C: Vaporization occurs, leading to massive volume expansion.

• Mechanisms of Thermal Injury:

  • Increased intracellular temperature results from oscillation of RF.

  • Two processes: Desiccation (water loss) and coagulation occurs simultaneously.

  • When focused correctly, cutting or vaporization is achieved.

Tissue Effects During Laparoscopic Procedures

• Best methods for achieving hemostasis near vessels include:

  • Low voltage output for vaporization and cutting.

  • High voltage for coagulation with careful energy focus.

  • The focus of energy affects tissue response (vaporization vs. desiccation).

• Factors affecting depth of thermal injury include:

  • Thickness of electrode, speed of instrument movement, and tissue impedance.

Ultrasonic Technology Overview

• Mechanism of Operation:

  • Ultrasound instruments cut and coagulate using mechanical energy.

  • No electrical current passes through the patient, minimizing current diversion risks.

  • Oscillating blades at approx. 55,000 Hz produce tissue friction, leading to thermal effects.

Risks Associated with Ultrasonic Technology

• Lateral thermal injury can occur from:

  • Conduction through heated tissues.

  • Cavitation causing vapor formation and tissue dissection.

• Comparisons to RF instruments show similar risks of lateral thermal injury.

Strategies to Reduce Risks in Electrosurgery

• Use the lowest effective power settings.

• Avoid using high voltage for coagulation during fulguration.

• Ensure clear visibility of the instrument tip at all times.

• Prevent unintended contact with other instruments during operation.

Summary of Complications Associated with Electrosurgery

• Monopolar instruments:

  • Higher risk of capacitive coupling and direct coupling injuries.

• Bipolar instruments:

  • Lower risk of injury but still carry some degree of risk.

• Common mechanisms of injury:

  • Over-extension of injury beyond target tissue, inadvertent contact, current diversion, and dispersive electrode injuries.