Electrophysical properties of electrosurgery andcapacitive induced current

George Vilos, M.D.a, Kim Latendresse, M.D.b, Bing Siang Gan, M.D., Ph.D.b,c,d,*aDepartment of Obstetrics/Gynecology, University of Western Ontario, London, Ontario, Canada

bDepartment of Surgery, University of Western Ontario, London, Ontario, CanadacDepartments of Pharmacology and Toxicology, and Medical Biophysics, University of Western Ontario, London, Ontario, Canada

dHand and Upper Limb Centre, St. Joseph’s Health Care, 268 Grosvenor St., London, Ontario, Canada N6A 4L6

Manuscript received January 29, 2001; revised manuscript May 21, 2001

Abstract

Background: Although electrosurgery is one of the most commonly used technologies in the operating room, its electrophysical properties,including the potential for complications, are poorly understood by many surgeons.Methods: We describe the experimental simulation of a highly unusual complication that occurred during a surgical procedure requiringconcurrent use of monopolar and bipolar electrosurgery.Results: Capacitive induced current from an activated monopolar electrode to the bipolar cord was reproduced and consistently led tofull-thickness burns in our experiments.Conclusions: Surgeons should be familiar with the principles of electrosurgery, its electrophysical properties, and possible complications.© 2001 Excerpta Medica, Inc. All rights reserved.

Keywords: Electrosurgery; Electrosurgery complications; Capacitive induced current

Electrosurgery in the operating room (OR) was popularizedin the 1920s by the neurosurgeon Harvey Cushing using aspark-gap electrosurgical generator designed by WilliamBovie [1]. Although it is the most frequently used energysource in all ORs worldwide, it is the least understood bysurgeons and other OR personnel. Indeed, the use of elec-trosurgery is now so common that education about theprinciples of this technology is considered superfluous. Sur-gical residents in their most junior years start using thedevice almost without thinking about its potential compli-cations, and a feeling has become common that this is a“fool-proof” instrument. Considering the number of opera-tions performed annually, the rate of complications fromelectrosurgery is extremely low [2]. However, when such aninjury occurs it can be catastrophic when vital structuressuch as viscera are involved, and they may lead to unsightlyscars in superficial burns [3–7].

Electrical burns to patients are usually predictable andeasily preventable and have been reported to occur by in-

sulation failure of the active electrode, direct coupling fromthe active electrode to another conducting instrument, ca-pacitive leakage of current, or dispersive electrode padburns [2]. At times, however, the chain of events that leadsto adverse outcomes is complicated and could only havebeen avoided if the surgeon would have had a basic under-standing of the principles of electrosurgery and the properuse of the electrosurgery devices.

We were confronted by an unusual case where a numberof circumstances led to full-thickness skin burns on theforearm during secondary surgery on a 31-year old manwho had sustained a crush injury to his right index finger.Initial treatment involved debridement, microscopic repairof a digital nerve, and application of an external fixation fora comminuted fracture of the proximal phalanx. Two weekslater the patient was taken to the OR for iliac crest bonegrafting of this fracture. At this second surgery, the patientwas placed in the supine position, under general anesthesiawith separate preparation and draping of the right upperextremity and the left iliac crest. The left iliac crest bonegraft was harvested simultaneously with preparation of theright index proximal phalanx as the recipient site for thebone graft. Monopolar electrosurgery was used in the har-

* Corresponding author. Tel.: �1-519-646-6097; fax: �1-519-646-6049.

E-mail address: bsgan@lri.sjhc.london.on.ca

The American Journal of Surgery 182 (2001) 222–225

0002-9610/01/$ – see front matter © 2001 Excerpta Medica, Inc. All rights reserved.PII: S0002-9610(01)00712-7

vesting of the iliac crest bone graft. During dissection of theright index finger, a bipolar electrosurgical system was usedto maintain hemostasis in the finger. The surgery proceededuneventfully, and the patient was returned to the recoveryroom having undergone the planned surgical procedure. Inthe recovery room, however, two longitudinal third-degreeburns were noted on the right forearm and elbow eachmeasuring approximately 5 � 1 cm (Fig. 4). An incidentreport was filed and the OR safety committee examined theelectrosurgery instruments that were used and experimen-tally recreated the circumstances of the surgery.

Experimental investigation

The investigation revealed that during the procedure, asingle Valleylab Force-2 (Valleylab, Boulder, Colorado)electrosurgical unit (ESU) was used. The unipolar electrodewith a Valleylab dispersive split pad return electrode withreturn electrode monitoring (REM) system, and the bipolarleads were appropriately connected to the ESU. The poweroutput settings were 30 W for the coagulation and cuttingmodes and 15 W for the bipolar mode. The monopolarcoagulation was used to maintain hemostasis during thebone graft harvesting from the hip while the bipolar modewas required to maintain fine hemostasis in the right indexfinger. The two modes can function independently fromeach other and pose no electrical hazards when plugged intothe same ESU (Fig. 1). As the two cords, bipolar andunipolar, entered the sterile surgical field they converged,and they were clamped together with a towel clip to thedrapes, and subsequently diverged to their different desti-nations, the monopolar going toward the hip while thebipolar went to the hand (Fig. 2). Close inspection of theelectrical cord of the bipolar setup revealed a crack in theinsulation with partial exposure of one wire (Fig. 3). Be-cause only one wire was exposed, the burns could not havearisen from activation of the bipolar circuit. Thus, it wasconcluded that the burn arose through this crack from ca-pacitive-induced current initiated during the activation ofthe monopolar lead, with the split pad return electrodeserving as the return lead.

Experimentally, we reproduced the electrosurgery-pa-tient arrangement using porcine tissue on a REM dispersiveelectrode (Fig. 3). Whereas bipolar electrosurgery activationdid not cause a burn through the exposed wire, every timethe monopolar mode was activated, we were consistentlyable to reproduce a burn of the tissue through the singleexposed wire of the bipolar electrosurgery cord, suggestingthat the most likely cause of the burn was capacitive-leak-age current from the monopolar cord into the bipolar cord.The REM alarm did not activate, as the total current goingout through the monopolar electrode equalled the total cur-rent returning to the ESU via the split pad return electrode.

Discussion

Our investigation revealed that several avoidable errorsled to the described complication. As is often the case, eacherror may not have caused a problem in itself, however,their simultaneous occurrence led to the described adverse

Fig. 1. Valleylab Force-2 electrosurgical unit with monopolar and bipolarleads attached.

Fig. 2. Experimental configuration of bipolar and monopolar cordsclamped together over the sterile drapes, situating the wires in closeproximity.

Fig. 3. Insulation defect (arrow) in proximity of porcine tissue that issituated on a return electrode monitoring (REM) dispersive electrode.Activation of the monopolar pencil electrode consistently resulted in spark-ing through the crack of the bipolar wire resulting in burns of the tissue,whereas bipolar activation did not.

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outcome. Nevertheless, if the principles of electrosurgeryhad been more widely known among the surgeons and theOR personnel, this kind of complication may have beenavoided. Our investigation demonstrated that the followingprinciples of electrosurgery were not well understood andthat ignoring the basic properties of the ESU power inter-actions contributed to the accidental burn.

Capacitive leakage current

Electrophysics defines a capacitor as two nearby conduc-tors separated by a nonconducting medium. For example,two people standing next to each other without touchingform a capacitor and may store electrical energy. Forcingthe two cords of the monopolar and bipolar set-ups in closeproximity to each other created the first condition for apotential burn by inducing capacitive leakage of electricalcurrent from the monopolar cord to both wires of the bipolarcord. (Fig. 2). The intended radiofrequency (RF) alternatingcurrent (AC) flowing through the active pencil monopolarelectrode and back to the ESU through the patient and thedispersive return plate induces RF unintended (stray) cur-rent in any conductors in close proximity with the unipolarcord. This process is frequently referred to as capacitanceeffect, and it occurs without direct electrical contact of theconductors [8–12]. The magnitude of current induced fromone conductor to another depends primarily on the proxim-ity and surface area of the two conductors’ interface, thevoltage and frequency of the intended current, and thedielectric constant (the insulation) of the cords. Capacitivelycoupled currents are eliminated in bipolar cords since theytravel in opposite directions and cancel each other.

The second condition for this patients’ skin burn was aninsulation defect (a small crack) in one of the wires of thebipolar cord, which, as it happened, was in contact with thepatient’s forearm. (Fig. 4). Frequent use and resterilizationof electrical cords and instruments can cause the layer ofinsulation to break down or crack. Tiny, visually undetect-

able tears are actually more dangerous than large cracks,because the current escaping from these miniscule breaks ismore concentrated and therefore capable of causing sparks.The temperature of these sparks has been measured to be upto 700°C and can cause tissue burns and even start fires inoxygen-rich or flammable environments.

It is unlikely that the burn was caused during activationof the bipolar mode, as a bipolar circuit must be completedbetween the two electrodes of the bipolar coagulation setup.This normally occurs by interposition of the patient’s tissuebetween the two tips of the microbipolar forceps. As onlyone of the bipolar cords was damaged, no such circuit couldhave formed, and additionally, we were not able to repro-duce this possibility experimentally.

It is clear that surgeons need not obtain a degree inphysics prior to using electrosurgery. However, the imple-mentation of several safety strategies may minimize futureadverse occurrences. Firstly, some basic level of knowledgeshould be mandatory for users of the ESU. Both OR nursingpersonnel and surgeons must have access to a succinct andbrief explanation of the physical background of electrosur-gery. This may perhaps be easiest to ensure by mandatingthat a small booklet remains attached to the unit, so that newusers can familiarize themselves with these principles. Aprominent warning label on the generator will help in di-recting new users to read the accompanying booklet. Theunderstanding of these principles should lead to the avoid-ance of problems associated with capacitive induced cur-rents. For example, it should be avoided that multiple cordsare attached to the drapes parallel and in close proximitywith a single towel clip. Such a measure will avoid acapacitance effect not only from one cord to the other butalso from one cord to the towel clip, which, if inadvertentlyin contact with the patient’s skin, can also be a source ofcapacitance induced burns.

Several other relatively simple precautionary measuresmay also help in avoiding other electrosurgery complica-tions. The volume of the audible tone upon ESU activationshould never be turned off. This will avoid that the audiblewarning signals will never be drowned out by other warningbeeps in the OR. If multiple foot pedals are used for acti-vation of electrosurgery, it should be clear to the operatorwhich pedal activates which instrument. In addition, thelowest settings that are effective should be used. This willnot only minimize adjacent tissue damage but also minimizethe capacitance effect. Finally, when using electrosurgeryduring laparoscopic surgery, it may be best to use an ESUdevice that is equipped with a conducting capacitanceshielding and active electrode monitoring system. This willreduce the risk of capacitance effect that can be induced intothe laparoscopic cannulae.

In summary, capacitive induced current is a little knownentity and a possible source of perioperative complications.Given the high frequency of electrosurgery use in the OR,surgeons and ancillary OR personnel should understand the

Fig. 4. Skin burns on the forearm and elbow of the patient (arrows) causedby the crack in the bipolar cord. The bipolar forceps and cord are placed ontop of a photograph of the burn for illustrative purposes.

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principles of electrosurgery and be aware of the potentialdangers.

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