What is the mechanism of electrocautery and how do coagulation and cutting modes differ?

Mechanism of Electrocautery and Differences Between Coagulation and Cutting Modes

Electrocautery uses high-frequency radiofrequency alternating electrical current passed through tissue to generate heat, which produces different surgical effects depending on the rate and depth of heat production—with cutting achieved through rapid explosive vaporization above 100°C and coagulation through slower thermal denaturation below the boiling point. 1, 2

Basic Mechanism of Electrosurgery

Heat generation is the fundamental mechanism underlying all electrosurgical effects. When radiofrequency current passes through tissue, the tissue's resistance converts electrical energy into heat adjacent to the active electrode 2. The specific tissue effect achieved depends entirely on two variables: the depth of heat production and the rate at which heat is generated 2.

Monopolar vs. Bipolar Systems

• Monopolar electrocautery involves current flowing from the active electrode through the patient's body to a grounding pad (indifferent plate), typically placed on the thigh 1
• Bipolar systems confine the current between two closely spaced electrodes, eliminating the need for a grounding pad 1
• Bipolar systems generate less electromagnetic interference and are safer for patients with pacemakers or ICDs 1

Cutting Mode: Rapid Vaporization

Cutting occurs when tissue temperature suddenly rises above 100°C (the boiling point of water), causing rapid explosive vaporization of intracellular water content, leading to tissue fragmentation. 2

Technical Parameters for Cutting

• Voltage requirements: Above 200V with a duty cycle >50% (typically activated by yellow pedal) 3
• At these voltages, electrical sparks become electric arcs that cause superficial cell explosion 3
• The rapid heating prevents lateral thermal spread, resulting in precise tissue division 2
• Pure cutting current produces minimal coagulation but increases immediate bleeding risk 4, 5

Clinical Application

• Pure cutting current causes rapid transection with minimal hemostasis, often requiring additional intervention for bleeding control 4
• Most commonly used in procedures requiring precise tissue division with minimal thermal damage to margins 4

Coagulation Mode: Thermal Denaturation

Coagulation occurs when tissue is heated below the boiling point (below 100°C), causing thermal denaturation of proteins without vaporization. 2

Technical Parameters for Coagulation

• Lower voltage with intermittent delivery (duty cycle <10%, typically blue pedal for forced coagulation) 3
• Below 200V, current heats tissue until steam from boiling stops the current flow 3
• Slower heating over a larger contact area results in deeper coagulation 3
• Desiccation occurs when slow temperature increase leads to vaporization of water content in already-coagulated tissue 2

Types of Coagulation Current

• Soft coagulation: Lower voltage, controlled output (capped at 19 volts in some systems to prevent deep injury) 1
• Forced coagulation: Higher voltage with duty cycle <10%, preventing arcing while achieving deeper coagulation 3
• Spray coagulation: Highest voltage for superficial coagulation over larger areas 3

Blended Current: Combined Effects

Blended currents combine cutting and coagulation by using voltages above 200V with intermediate duty cycles, producing simultaneous tissue division and hemostasis. 4, 3

Microprocessor-Controlled Units

• Endocut mode alternates short cutting bursts with prolonged coagulation periods, limiting peak voltage based on impedance feedback 4
• Provides superior hemostasis compared to pure cutting while maintaining adequate tissue division 4
• Recommended settings for cervical procedures: Endocut Q mode, effect 2-3, cut duration 1, cut interval 4, maximum 30-50 watts 4

Advantages Over Pure Modes

• Reduces immediate bleeding compared to pure cutting current 4, 5
• Maintains better margin evaluability than excessive coagulation 4
• Balances tissue cutting with hemostasis while minimizing char formation 4

Critical Safety Considerations

Electromagnetic Interference with Cardiac Devices

• High current generated near pacemakers or ICDs can cause device malfunction, including inappropriate pacing inhibition or ICD firing 1
• Risk increases when the cautery device is close to the device or when current path lies along the pacemaker lead axis 1
• Bipolar cautery significantly reduces electromagnetic interference risk 1

Common Pitfalls to Avoid

• Never use pure cutting current alone when hemostasis is important, as it causes rapid transection with minimal coagulation 4
• Avoid excessively high wattage settings, which increase thermal damage and char formation, compromising pathologic margin evaluation 4
• Do not use coagulation current for cutting, as it produces excessive thermal artifact and tissue destruction 4
• Ensure proper grounding pad placement in monopolar systems to prevent burns 1, 6

Practical Application in Endoscopy

According to the ERS/ATS guidelines, electrosurgery can achieve both coagulation and vaporization depending on energy settings 1. The technique is widely used for:

• Debulking endobronchial lesions (success rates ~90% for tracheal/main bronchi lesions) 1
• Treating benign tumors and cicatricial stenoses 1
• Hemostasis control during therapeutic procedures 1

Argon plasma coagulation represents a specialized non-contact monopolar coagulation technique using ionized argon gas as the conductive medium, producing more homogeneous but superficial thermal effects 1.