Electrosurgery in Therapeutic Endoscopy

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Chapter 6 Electrosurgery in Therapeutic Endoscopy

Marcia L. Morris, Ian D. Norton

Introduction

Endoscopic electrosurgery involves the use of electrical current to achieve a desired tissue effect (cutting, tissue ablation, desiccation, or a combination of these). Electrical energy to produce heating and tissue effect has been a part of endoscopy since the early 1970s.^1,² Common indications include biliary sphincterotomy, polypectomy, hemostasis and ablation of vascular lesions such as arteriovenous malformations, radiation proctopathy, and other forms of vascular ectasia. Other forms of nonelectrosurgical thermal effect may be achieved without the direct use of electrical current, such as laser photoablation and heater probe. Incorrect use of electrical equipment may contribute to poor patient outcomes, such as postpolypectomy serositis; colonic perforation; and biliary sphincterotomy–associated complications such as acute pancreatitis, hemorrhage, and duodenal perforation.

From the clinician’s point of view, this field has been hampered by problems with nomenclature (Table 6.1). First, there is often lack of uniformity in terms used by different manufacturers (e.g., blend may have quite different characteristics from one manufacturer’s generator to another). Second, the terms themselves may be misleading (e.g., a low duty-cycle waveform may be called pure coag but be capable of cutting tissue; this situation leads to statements such as “I only cut with coag”) Lastly, some terms in common usage are manufacturer specific (e.g., Endocut refers specifically to an ERBE [Marietta, GA] generator output). Usually a clinician becomes adept with the particular generator that he or she uses, and most modern generators have storable or preset parameters for common scenarios such as polypectomy and sphincterotomy. Problems may occur, however, when the clinician is confronted with a different generator (most likely to happen in an unusual and stressful environment, such as an emergency procedure in the operating room or emergency department or first list at a new appointment).

Table 6.1 Monopolar Output Names with Corresponding Duty Cycle*

A clinician with no electrosurgical “conscious competence” would be unable to troubleshoot generator problems or be flexible in unusual situations. Understanding the basic type of current delivery (bipolar vs. monopolar) has important implications for patients with implanted devices, such as pacemakers, defibrillators, and deep brain stimulators. For these reasons, the clinician should have a basic knowledge of electrosurgical generator principles. This chapter outlines the basic principles of electrosurgery pertaining to flexible endoscopy. As far as possible, the use of proprietary-specific terms is minimized.

Electricity and Tissue

Early pioneers of electrosurgical devices discovered that applying an electrical current to biologic tissue might produce different effects. The first effect was electrolytic. Charged molecules in the tissue flowed toward the opposite poles of an electrode if the current applied was direct or alternated slowly. Alternating the current more rapidly eliminated the electrolytic effect and produced heating at a cellular level. However, a current alternating at less than 100 kHz resulted in undesired neuromuscular effects (the result of applying household current of 60 Hz is well known). Alternating at very high frequency (300 kHz) eliminates neuromuscular effects but retains the desired cellular heating effects. This thermal effect is the basis for all electrosurgery.³

Endoscopic Thermal Modalities

Monopolar Electrosurgery

Monopolar output involves use of an electrode at the luminal site and a return electrode at a remote site (usually an adhesive pad placed on the thigh). The current flows from the electrode site, through the patient’s tissue to an electrode on the skin, and back to the generator, completing an electrical circuit. Monopolar is the most common form of endoscopic electrosurgery and is commonly used in hot biopsy forceps (HBF), polypectomy snares, sphincterotomes, needle-knives, and endoscopic mucosal dissection devices. As discussed subsequently, variables in current flow and current density result in different tissue effects, ranging from desiccation to cutting.

Bipolar (Multipolar) Electrosurgery

Bipolar (multipolar) electrosurgery uses technology similar to the monopolar circuit, but both electrodes are on the tip of the instrument. Current flows through a relatively small area of tissue, and there is no need for a return electrode on the patient’s skin. The common uses for this technology are coagulation of arteriovenous malformations and ulcer hemostasis. Bipolar (or multipolar) probes have been shown to be effective devices for hemostasis for bleeding peptic ulcers. Optimal results seem to be obtained by using forceful tamponade, large probes, low power settings (15 to 25 W) and prolonged contact times (10 seconds).^4,⁵ This technique uses relatively low power outputs (approximately 16 W) with limited depth of injury.⁶ Bipolar snares, biopsy forceps, and sphincterotomes have been developed but are not widely used. A new, important use of bipolar current is radiofrequency ablation catheters employed to ablate Barrett’s esophagus. In this situation, the current moves from one adjacent electrode on a balloon catheter to another. This energy passes via the mucosa and is sufficient to obliterate the mucosa, while being superficial enough to prevent significant submucosal damage, minimizing stricture formation.

Argon Plasma Coagulation

Argon plasma coagulation (APC) is a newer technique in flexible endoscopy with many potential applications, including tumor debulking,⁷ ablation of vascular malformations,⁸ and coagulation of peptic ulcer bleeding sites.⁹ It also has a role in “tidying up” residual adenoma after piecemeal polypectomy, although overuse in this setting suggests poor polypectomy technique. APC is a unique means of energy delivery (Fig. 6.1). Argon gas flows from the catheter tip and provides a medium for current flow from the catheter tip to an adjacent mucosal surface (and via the patient to a remote return pad). APC is a form of monopolar electrocoagulation, unique in its noncontact nature. It can be used effectively either tangential or perpendicular to the mucosal surface. Side-firing catheters are available, but the standard end-firing catheter can be used for tangential and perpendicular applications.

Fig. 6.1 Argon plasma coagulation.

High current density at the mucosal surface leads to tissue effect. At high power output (e.g., 75 to 90 W), APC results in tissue debulking. At lower energy levels (e.g., 30 to 45 W), tissue desiccates with limited depth of injury.¹⁰ It has been theorized that as tissue desiccates, its electrical resistance increases, resulting in electrical arcing to adjacent, nondesiccated tissue. This mechanism could act to limit depth of injury. It has been shown, however, that APC can cause transmural injury at high power outputs,¹⁰ and there have been reports of perforation using this device.^11,¹² Nonetheless, the relative ease of use, nontouch technique, and relatively shallow depth of injury make this a versatile and useful instrument, especially in thin parts of the bowel such as small intestine and right colon.

Heater Probe

The heater probe unit (Olympus Corporation, Melville, NY) comprises a power source, catheter, and irrigation system. At the tip of the catheter is a heating coil within a polytef (Teflon) cap. This energy delivery is unique because it supplies a predetermined amount of energy (e.g., 30 J) to the cap without an electrical circuit flowing through tissue. Because this is a direct transfer of heat, it is an example of electrocautery, not electrosurgery. The main indications are ulcer hemostasis and coagulation of angiodysplastic lesions. Heater probe results in ulcer hemostasis in 80% to 90% of bleeding lesions.¹³ The energy and probe size are inadequate for tumor ablation indications, and this method cannot produce any electrosurgical cutting effect.

Principles of Electrosurgery

Electrical output from generators used in endoscopy are at high frequencies (300 to 950 kHz). The output is beyond the frequency range that causes neuromuscular stimulation, generally preventing muscular side effects and always preventing “electrocution.”

Tissue effect is determined by the rapidity of tissue heating. Rapid heating causes intracellular boiling and explosion of cells resulting in a cleavage plane (incision).¹⁴ In contrast, slow heating results in protein denaturization and desiccation or “coagulation” of tissue.¹⁵ Understanding the different characteristics of tissue heating under different circumstances is essential to understanding electrosurgery.

Variables in Electrosurgery

Many variables in electrosurgery can influence tissue effect.

Power Output

Power output is the amount of energy flowing through the circuit per unit of time (i.e., power = joules per second) measured in watts. The higher the power, the greater the tissue heating.

Two formulas, including Ohm’s law, elegantly relate all of the electrosurgical variables:

1 V = IR, where V is voltage, I is current, and R is resistance

2 P = I²R, where P is power, I is current, and R is resistance

Power and voltage are also directly related (e.g., P = V²/I).

These formulas illustrate that there is a relationship between power output and tissue resistance. As the resistance (or impedance) in the tissue increases (as it desiccates), power falls off unless either current or voltage is increased. Manufacturers addressed this problem by developing microprocessor-controlled generators that could measure resistance in the circuit and adjust output automatically (within certain set parameters) to maintain the desired tissue effect.¹⁶ Some power outputs are constant over a wide range of resistance; when this is graphically represented, it results in the so-called flat or wide power curve (Fig. 6.2). The initiation of an incision is problematic for generators, especially if the electrode is pressed firmly against the tissue surface because this presents a large surface area with low current density and low tissue impedance. The generator must supply particularly high power output to initiate the formation of microelectric arcs and commencement of the cutting effect. This initial power output is often greater than the output needed to continue the incision. Microprocessors can recognize this situation and transiently provide a high power output to initiate cutting.

Fig. 6.2 Typical power curves.

Voltage

Voltage refers to the potential difference between the two electrodes and defines the force making electrons move from one point in the circuit to another. Using the analogy of a waterfall, with current being the water flowing, voltage is analogous to the height of the waterfall. As one can see from the aforementioned formulas, voltage is an integral determinant of circuit behavior (and tissue effect). To complete a circuit, sufficient voltage must exist across the device-patient interface for microelectric arcs to occur between patient and tissue. Generally, a peak of at least 200 V is required. At greater than 500 V, tissue tends to char. Manufacturers have manipulated voltage in an attempt to create specific effects. In particular, increasing the voltage for a given continuous sinusoidal output (i.e., pure cut) varies the depth of coagulation adjacent to the cut; this has been termed cut effect 1, cut effect 2, and so forth (Figs. 6.3 and 6.4).

Fig. 6.3 Electrosurgical waveform patterns.

Fig. 6.4 Tissue effect changes with changing waveform.

Duty Cycle

Current flows for only a fraction of each second that the activating pedal is depressed. This fraction or percentage of time current flows is the duty cycle. A pure-cut mode delivers current during most or all of the activation period, whereas blended mode delivers current in an interrupted fashion (e.g., 25% to 50%). A pure coag mode may have a duty cycle of 6% to 10% (see Fig. 6.4). This mode gives tissue time to dehydrate (rather than rapid heating causing an explosive tissue cleavage seen in cutting mode). Some new generators have an alternating cut and coagulation mode (e.g., 50 msec of pure cut followed by 700 msec of coagulation). This mode results in a characteristic “staccato” type of incision. The aim of this type of output is to slow the rate of incision and prevent uncontrolled (“zipper”) cut¹⁷; whether this translates to improved patient outcome is yet to be determined.

Electrical Hazards

Electrical Shock

As mentioned previously, generator output is at a high frequency, which does not cause neuromuscular stimulation, but conduction of main power from faulty equipment via the patient could cause electrical shock. Leakage of faulty current can flow along any conductive pathway from an electrical instrument that is connected to a power line. This problem is prevented by grounding the external conducting surfaces and by isolating conductors in contact with the patient. There are strict standards relating to the use of electrical equipment with patients, and equipment should be checked at regular intervals.

High-Frequency Burn

The most common electrical complications associated with monopolar electrosurgery are burns to the patient and surgeon caused by the following:

Defective patient return electrodes

Insufficient patient contact with the return electrode

Poor technique.

In old machines, the return electrode was no more than a large flat metal plate on which the patient was positioned. Contact could easily become partial (resulting in increased current density and the risk of a skin burn). New return pads minimize the possibility of a burn at the return site by ensuring adequate patient contact (reducing the amount of energy passing through each square centimeter of skin—i.e., ensuring low current density). First, these are flexible adhesive pads, preventing the patient from partially rolling off the electrode during the procedure. Second, new pads comprise two electrically isolated pads. A small current flows from one side of the pad to the other. If this small circuit is lost (indicating poor skin contact), a return electrode fault registers, and the generator does not activate. Rarely, an alternating current in one appliance can induce a “capacitance” current in an adjacent conductive wire without there being an actual physical contact between the two wires. This occurrence is made possible by the flux of positive and negative charge in one circuit inducing an opposite electron flow in the other (e.g., if a nonshielded wire was used to maintain access to the biliary tree during sphincterotomy). An induced current in the access wire could cause a burn within the liver. This risk highlights the importance of using only guidewires approved for access during sphincterotomy. It is also important not to lay active cords, such as cords attaching a polypectomy snare to the generator, closely along the wire leads from patient monitor patch electrodes. Current can concentrate under the patch electrode causing a burn.

Cardiac Pacemakers and Implanted Defibrillators

Guidelines for endoscopic electrosurgery in the presence of cardiac pacemakers and implanted defibrillators have been published by the American Society for Gastrointestinal Endoscopy (ASGE).²⁰ Electrosurgical units should be used with caution in patients with these devices. Although there have been no reports of serious adverse events in endoscopic applications, monopolar electrosurgical energy in urology and general surgery has been reported to cause pacemaker dysfunction, especially in older pacemakers. In short, the electrical current flowing through the body could be misinterpreted by an implanted defibrillator as a tachyarrhythmia, leading to an unnecessary shock, or could interfere with pacemaker sensing. General principles for the use of electrosurgery in the presence of a permanent pacemaker are as follows:

1 Power delivery should be kept to short bursts (<1 second) with at least 5 seconds between each activation.

2 Try to keep the path from active electrode to return pad distant from the permanent pacemaker and its leads.

3 If possible, consider using bipolar circuitry or a heater probe.

4 Permanent pacemakers can be put into a safe default mode by placing a strong magnet over the pacemaker box for the duration of the procedure.

5 The patient should have continuous electrocardiogram (ECG) monitoring during the procedure.

Implanted defibrillators should be turned off for the duration of the procedure, and the patient should have continuous ECG monitoring during the procedure.

Deep brain electrode stimulation is increasingly used for refractory Parkinson’s disease. Although no adverse effects with electrosurgery have been reported, manufacturers and neurologists are very reluctant to allow patients to have any monopolar electrosurgery. There is a single case report of severe lancinating pain experienced by a patient with one of these devices while undergoing dermatologic surgery with a monopolar instrument.²¹

Endoscopic Electrosurgical Techniques

Biliary and Pancreatic Sphincterotomy

Transpapillary division of the biliary sphincter has become a routine part of endoscopic retrograde cholangiopancreatography (ERCP) to facilitate biliary access, remove calculi, improve drainage in biliary dyskinesia, prevent biliary stenosis after ampullectomy, and aid in stent placement. Sphincterotomies are done using monopolar current. Most sphincterotomies are performed using a “pull” type of sphincterotome. The tip of the instrument has an exposed wire (20 to 30 mm) that forms a bow with the catheter when a handle is tightened; this puts tension between the cutting wire and the roof of the papilla. Only the tip of the exposed wire is used for cutting (to increase current density and improve operator control of the incision). Most procedures are wire guided, that is, with a shielded guidewire in the bile duct to ensure that the pancreatic duct is not inadvertently incised.

Cutting may be performed with either pure-cut (100% duty cycle) or blended (approximately 50% duty cycle) current. Use of pure-cut current results in a more rapid incision with less edema of surrounding tissues but less hemostasis. Several studies have shown reduced risk of pancreatitis in patients having pure-cut sphincterotomy compared with coag current.^22,²³ As would be expected with less coagulation, increased mild hemorrhage is seen, but this does not translate into clinically significant bleeding.^22,²³ However, because of the potential for less control of a rapid incision with pure-cut current, great care must be taken with this current output. As mentioned earlier, new generators automatically switch between cut and coag settings or interrupted pulses of cut current alone during the course of the incision. As with colonic polypectomy, excessive tissue desiccation should be avoided because this may lead to stalling of the incision.

Needle-Knife Sphincterotomy

Needle-knife sphincterotomy employs a fine, stiff wire projecting approximately 5 mm beyond the tip of a catheter. This type of sphincterotomy is used to cut a pathway into the bile duct and is usually reserved for cases of failed cannulation in which biliary access is of particular importance.

Complications of Sphincterotomy—Link with Electrosurgery

Common complications of endoscopic sphincterotomy include pancreatitis, hemorrhage, and perforation. Each complication may be influenced by the type of current used.

Pancreatitis

Acute pancreatitis is the most common complication of endoscopic sphincterotomy, occurring in at least 5% of cases.^24,²⁵ Development of pancreatitis may be partly a function of iatrogenic trauma to the periampullary region. This trauma results in edema and obstruction to pancreatic flow. Post-ERCP pancreatitis may be reduced by the use of pure-cut current instead of the usual blended current.²²

Hemorrhage

Hemorrhage during endoscopic sphincterotomy is due in part to inadequate coagulation effect of tissue during the incision. Mild oozing at the sphincterotomy site at the time of endoscopic sphincterotomy is common, settles spontaneously, and is of no clinical significance. Minor bleeding at the time of sphincterotomy may be more common with pure-cut technique.²² Significant hemorrhage occurs in 1% to 3% of patients²⁶ with an associated mortality of less than 1%.²⁶^–²⁸ This hemorrhage is due to incision of a significant vessel, which is partly “bad luck” and sometimes due to poor orientation of the incision, cutting into a diverticulum or overcutting the incision. Arterial bleeding is not prevented by one electrosurgical output versus another. It is believed, however, that a half-incised vessel (the ends of which cannot retract) bleeds much more than a fully cut one, implying that cutting a little more may be useful in this situation.

Perforation

Duodenal perforation during endoscopic sphincterotomy is usually the result of a poorly aligned or too long incision beyond the boundaries of the intramural common bile duct. Clinically significant perforation occurs in less than 1% of sphincterotomies.^24,²⁹ The risk of perforation may be 8% in patients with a small papilla and patients with papillary stenosis.³⁰ Asymptomatic perforation may be more common, possibly occurring in 15% of sphincterotomies.³¹ Duodenal perforation may occur during a rapid, uncontrolled cut of the sphincter (“zipper cut”). The occurrence of this type of rapid incision is a function of current delivery to the tissue and operator experience.

Polypectomy

Polypectomy is most commonly used to remove colonic polyps, either in one piece or piecemeal. Polypectomy and other thermal ablative techniques such as hot biopsy and ablation have the potential to cause transmural damage, resulting in either serosal inflammation (postpolypectomy syndrome) or perforation. Perforation occurs in 0.1% to 0.8% of colonoscopic polypectomies.^32,³³ Serositis without perforation occurs in 1% of polypectomies³²; it manifests 6 hours to 5 days after the procedure with pain, fever, and leukocytosis. The right side of the colon is particularly at risk because of its thinner wall.

Immediate hemorrhage occurs in about 1% of polypectomies, and delayed bleeding may occur in 2% of polypectomies.³⁴ Significant hemorrhage is much more likely when cutting through a thick stalk. Delayed bleeding may occur any time up to 2 weeks after the procedure. From the preceding discussion, it can be seen that sphincterotomy and polypectomy complications may be related partly to either an overrapid, poorly controlled incision or an overdesiccated, poorly progressed incision. Modern generators use bursts of cut alternating with coagulation to progress the incision in a predictable fashion. Microprocessor-controlled feedback varies generator output in response to changes in tissue resistance (i.e., increasing desiccation) to prevent stalling of the incision.

Osmotic sugar preparations (e.g., mannitol) should be avoided because gut fermentation generating hydrogen could cause explosion during colonic electrosurgery. This risk has been greatly reduced with the introduction of nonfermentable preparations. Nonetheless, to reduce risk of explosion further, preparation should be optimized to reduce fecal residue and colonic gas (i.e., hydrogen and methane). Explosion has also been reported with the use of APC of the rectum after enema preparation.³⁵^–³⁷ If cautery must be performed on an unprepared colon, effort to exchange the gas in the colon with repeated insufflation and suction should be undertaken. Carbon dioxide (CO₂) insufflation, mainly used for patient comfort, may reduce the risk of gas ignition further.

Hot Biopsy Forceps

HBF have been a popular means of removing diminutive polyps for many years.³⁸ HBF employs monopolar circuitry. Blended or coagulation current should be used, at a relatively low setting and applied only until blanching of the tissue occurs (1 to 2 seconds). The bowel should be deflated before power application, and care must be taken not to touch other parts of the bowel wall with the cups while coagulating. Postpolypectomy syndrome, perforation, and significant bleeding all have been reported after removal of diminutive polyps using HBF.³⁸ This technique is relatively poor at removing all polyp tissue.³⁹

Cold Snare Technique

Chopping polyps off without using any thermal energy has been advocated for polyps less than 5 mm.^40,⁴¹ The technique is fast, but, more importantly, it does not leave a significant thermal ulcer, which may take 2 weeks to heal. This technique has particular appeal for patients requiring anticoagulation after the procedure.