How does capacitive coupling cause thermal injury?

From the Guidelines

Capacitive coupling causes thermal injury when electrical current from an active electrode transfers to nearby conductive materials through an insulating barrier, creating an unintended electrical circuit that generates heat in tissues. This occurs during electrosurgery when the active electrode's insulation is intact but in close proximity to metal instruments or tissue. The electrical energy creates a capacitor effect, allowing alternating current to flow through the insulation and into adjacent tissues or instruments. The resulting current density can create localized heating that damages tissue, particularly in areas where patients contact metal surfaces like the operating table or other instruments. These injuries often occur outside the surgeon's field of vision, making them particularly dangerous. The risk increases with higher power settings, longer activation times, and when the active electrode remains stationary against tissue. To prevent such injuries, surgeons should avoid contact between active electrodes and metal instruments, use lower power settings when possible, and ensure proper patient positioning to minimize contact with conductive surfaces 1.

Some key points to consider:

• Electric injuries can vary widely, from an unpleasant tingling sensation to thermal burns, cardiopulmonary arrest, and death 1.
• Thermal burns may result from burning clothing that is in contact with the skin or from electric current traversing a portion of the body 1.
• Injuries from electric shock result from the direct effects of current on the heart and brain, cell membranes, and vascular smooth muscle, as well as the conversion of electric energy into heat energy as current passes through body tissues 1.
• The severity of electric injuries can be reduced by turning off the power at its source and assessing the victim for CPR, defibrillation, and treatment for shock and thermal burns 1.

In terms of the options provided:

• A. Electric current transfer to organ touched by the metal torcher: This option is closest to the correct answer, as capacitive coupling can cause thermal injury when electrical current from an active electrode transfers to nearby conductive materials.
• B. Sandwiching: This option is not directly related to capacitive coupling and thermal injury.
• C. Wrong energy: This option is not specific enough to be considered a correct answer.
• D. Failure of insulation: While failure of insulation can contribute to electric injuries, it is not the primary cause of thermal injury due to capacitive coupling.

From the Research

Capacitive Coupling and Thermal Injury

• Capacitive coupling can cause thermal injury due to the transfer of electrical energy to non-targeted tissues, resulting in burns and other damage 2, 3, 4.
• This can occur even with intact instrument insulation, and is more likely to happen when an open circuit is formed during laparoscopic surgery 4.
• The amount of energy required to cause a visible burn can be as low as 3.8 J, and full wall thickness burns can occur with as little as 10 J of energy 2.
• Capacitive coupling can lead to electrical skin burn injury during laparoscopic surgery, and can cause collagen hyalinization, nuclear fragmentation, and coagulation necrosis in the affected tissue 4.

Mechanisms of Thermal Injury

• Thermal injury can occur due to the direct transfer of electrical energy to tissues, resulting in heating and damage to the tissue 5.
• Electric factors, such as electric charges and electrodynamic fields, can also play a role in wound healing and tissue damage 6.
• The understanding of these mechanisms is important for the development of strategies to prevent and treat thermal injuries.

Prevention and Treatment

• The use of shielded instruments with active electrode monitoring (AEM) can help to prevent capacitive coupling and reduce the risk of thermal injury 2.
• Careful manipulation of instruments and avoidance of open circuits can also help to prevent capacitive coupling and related injuries 4.
• New treatments, such as the use of electric currents and weak electric fields, are being developed to improve wound healing and reduce the risk of thermal injury 6.