Describe the differences between electrosurgery and electrocautery.
Explain the effect of radiofrequency electricity on cells and tissue.
List the similarities and differences between monopolar and bipolar instrumentation.
Electrosurgery vs Electrocautery
Electrosurgery:
Uses radiofrequency electrical current to induce changes in tissue.
Results in tissue vaporization, coagulation, and desiccation for hemostasis.
Involves active and dispersive electrodes in the circuit.
Electrocautery:
Passive transfer of heat to tissue (e.g., branding cattle).
Not involved in the same electrical circuit; does not use radiofrequency current.
Example: Silver nitrate as chemical cautery.
Effects of Radiofrequency Electricity on Cells and Tissue
Radiofrequency alternating current causes rapid oscillation of intracellular ions and proteins in the tissue between two electrodes.
Incidence of Thermal Injuries: 1-2 thermal injuries per 1,000 laparoscopic surgeries.
Surgical Complications:
Common reasons for surgical complications include surgical burns and fires.
Tissue Temperature Effects:
50°C: Cell death occurs.
60°C - 95°C: Cell death imminent; water loss and protein denaturation.
100°C: Liquid to gas conversion leads to volumetric expansion and cell explosion (vaporization).
Elevated intracellular temperature via oscillation of radiofrequency improves coagulation.
Reducing tissue impedance (e.g., in fatty tissues) can lead to increased current and thermal injury.
Electrical Physics Principles in Electrosurgery
Current: Flow of electrons per unit time, measured in amperes.
Voltage: Electrical potential difference between two points, measured in volts.
Impedance: Resistance to the flow of electrons, measured in ohms.
Energy: Product of work and time, measured in joules, defined as the work done when a current flows.
Power: Amount of energy per unit time, $P = V imes I$ (measured in watts).
Ohm's Law: $I = rac{V}{R}$, stating current is directly proportional to voltage and inversely proportional to resistance.
Polarity of Electrical Sources
Constant Polarity Circuit (Battery): Fixed positive and negative ends.
Alternating Polarity Circuit: Oscillating positive and negative ends (common in radiofrequency electrosurgery).
Instrumentation Types
Monopolar Instrumentation
Requires both active and dispersive electrodes.
The patient is part of the circuit; energy oscillates between electrodes.
Bipolar Instrumentation
Only involves the tissue between active electrodes (two jaws).
Less area of the patient involved in the electrical circuit, reducing thermal spread risks.
Waveforms in Electrosurgery
Continuous Low Voltage (Cut): No breaks in the waveform.
Modulated Intermittent Waveforms (Coag): Gaps in current flow, preserving power and increasing voltage when current decreases.
Tissue Effects and Mechanisms
Vaporization & Cutting
Achieved with low voltage output focused with narrow electrodes; non-contact event.
Desiccation & Coagulation
Achieved with low voltage output and wider electrodes; requires contact with tissue.
Coagulation involves hydrothermal rupture of hydrogen crosslinks and tissue sealing.
Fulguration
Superficial hemostasis using a high voltage modulated current applied near tissue.
Summary of Electrosurgery Principles
Distinction between electrosurgery and electrocautery.
Radiofrequency electricity results in intracellular oscillation leading to thermal effects.
Bipolar and monopolar systems have different electrical circuit structures affecting thermal injury risks.
Complications of Electrosurgery
Mechanisms of Injury
Significant risk exists for radiofrequency electrosurgical injury, with a rate of clinically significant burns at approximately 3.6 per 1,000 cases.
Risks of Monopolar vs. Bipolar Instruments
Monopolar Instruments:
Higher risk of lateral thermal injury due to remote dispersive electrode.
Inadvertent tissue contact can result in deep injury.
Bipolar Instruments:
Reduced lateral thermal injury due to direct contact mechanism.
Less risk of lateral injury because both electrodes are in close proximity to the target tissue.
Specific Mechanisms that Lead to Injury
Lateral Extension of Injury: Current flowing beyond intended target tissue.
Inadvertent Tissue Contact: Accidental activation of the electrode in contact with non-target tissue.
Current Diversion: Unintended pathways leading to tissue injury (e.g., capacitive coupling, insulation failure).
Dispersive Electrode Injury: Occurs when dispersive electrode loses contact and current is concentrated at skin level.
Strategies to Mitigate Risks
Maintain low power settings to reduce injury risks.
Use low voltage cut waveform; avoid modulated high voltage for vessel sealing.
Ensure visibility of instruments during activation and avoid contact with other tools.
Ultrasonic Technology in Surgery
Mechanisms of Ultrasonic Instruments
Utilize ultrasound-based mechanical energy for tissue incisions and coagulation.
No risk of current diversion since electrical current does not pass through the patient.
Capable of causing lateral thermal injury similar to radiofrequency instruments.
Description of Ultrasonic Devices
Transducer converts electrical current to mechanical vibrations, typically oscillating at ~55,000 Hz.
Two oscillating components: passive jaw and active blade which can vary in excursion from 50 to 100 microns, allowing control over cutting vs. coagulation effects.
Lateral Thermal Injury and Comparison
Lateral thermal spread occurs due to:
Conduction: Heat transfer from heated tissue.
Cavitation: Vapor formation that dissects tissue, contributing to thermal effects.
Comparative Thermal Spread: Evidence suggests similar lateral thermal spread between ultrasonic and advanced bipolar devices.
Summary of Ultrasonic Instruments
Convert electrical energy to mechanical energy outside the patient.
Risk of lateral thermal injury remains, but no risk of capacitive coupling or current diversion.
Retain heat longer than radiofrequency instruments; instruments can exceed 60°C leading to immediate tissue injury if contact occurs.