Diathermy and Metal Implants — FRCA Final MCQ

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HardAnaesthetic Equipment & SafetyDiathermy and Metal ImplantsFRCA Final

A 50-year-old man is undergoing elective arthroscopic shoulder surgery. He has a passive metal-on-metal hip prosthesis. The dispersive electrode can be positioned on the upper torso so that the prosthesis is outside the intended monopolar current pathway. All other relevant factors being equal, which energy mode has the greatest propensity for capacitive coupling and an unintended remote thermal injury?

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Correct answer: E — Monopolar spray coagulation (fulguration)

Monopolar spray coagulation (fulguration) uses an interrupted, high-peak-voltage waveform and is commonly activated without direct electrode–tissue contact. These features increase capacitive coupling and the risk of unintended remote thermal injury. Experimental comparison found greater coupling with coagulation than cutting current and markedly greater coupling during fulguration or open-air activation than during desiccation. Pure cut is a lower-voltage continuous waveform. Soft coagulation is a low-voltage contact technique, although it can cause deep local heating. Bipolar current is largely confined between the forceps tips, while ultrasonic dissection does not pass radiofrequency current through the patient. A passive hip prosthesis is not itself an absolute contraindication to monopolar electrosurgery; safe dispersive-electrode positioning should keep the implant outside the intended current pathway.

Reference: Robinson TN et al. Surgeon-controlled factors that reduce monopolar electrosurgery capacitive coupling during laparoscopy. Surgical Laparoscopy, Endoscopy & Percutaneous Techniques. 2010;20(5):317-320. https://pubmed.ncbi.nlm.nih.gov/23659748/