Basic principles: electrocautery and high-frequency currents in surgery

The description of electrocautery and high-frequency currents in surgery covers all basic principles. The key steps of the chapter are presented in a step by step way: use of electric currents, generation of use, tissue effect, types of cauterization, surgical equipment, complications of bipolar cautery, complications of monopolar cautery, Argon plasma coagulation, new electrosurgical techniques, lasers, ultrasonic dissectors.

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Basic   principles:   electrocautery   and   high-frequency   currents   in   surgery

Authors
D Mutter
Abstract
The description of electrocautery and high-frequency currents in surgery covers all basic principles.
The key steps of the chapter are presented in a step by step way: use of electric currents, generation of use, tissue effect, types of cauterization, surgical equipment, complications of bipolar cautery, complications of monopolar cautery, Argon plasma coagulation, new electrosurgical techniques, lasers, ultrasonic dissectors.
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2001-04
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E-publication
WeBSurg.com, Apr 2001;1(04).
URL: http://www.websurg.com/doi-ot02en227.htm

Basic   principles:   electrocautery   and   high-frequency   currents   in   surgery

1. Introduction
• Principle
Electrocautery devices use heat from an electric current to perform division and hemostasis of tissue. This heat is generated as high frequency electric currents pass through the resistance of organic tissue.
• Thermocoagulation
Heat has been used to cauterize tissues for more than 3000 years. The first application of electricity in surgery was thermocoagulation via heating of a wire placed between 2 electrodes. This produced a thermal increase within tissues due to direct contact with the hot wire.

(t = time)
• Electrosurgery
Modern-day electrosurgery uses tissue resistance to the passing of electric current to produce heat locally. The electrode of the electrocautery device is thus not heated: it only transmits the current from the electrosurgical generator to the target organ.
Nowadays, electrical current is used in several ways in surgery:
- monopolar cauterization;
- bipolar cauterization;
- other hemostasis devices.
2. Use/electric currents
• Definition
Electric current is defined by:
- the flow of electrons per second, measured in amperes (A);
- voltage: the force pushing current through a resistance, measured in volts (V);
- the resistance (r) of tissues through which the current passes, measured in ohms (O);
- the flow-induced force, measured in watts (W).

The power is delivered in a given time and is measured in Joules (J): J = V x A x t (t = time).
3. Generation/use
• Principles
When current flows through organic tissue, the resistance of the tissue induces transformation of the energy into heat due to the Joule effect. Heat that is generated within tissues (DQ) is proportional to the resistance, to the square value of the current intensity, and to the application time (DQ = A2 r t). The amount of heat delivered to tissues is inversely proportional to the surface area of the electrode in contact with the tissue. Depending on the intended action, electric currents are modulated via an adjustment in their amplitude (maximal voltage value), their frequency (cycles per second) or their power setting.
• Use of electric currents
Electrocoagulation was first used for therapeutic purposes in 1900. At the time, skin lesions were cauterized with a spark generated by an oscillating 10kHz current through a burst lamp. The first actual surgical application appeared with the device developed by Bovie: an apparatus working in a closed circuit that could perform cauterization and division.
In 1926, Cushing performed resection of a cerebrovascular myeloma using an electrocautery device and thus introduced electrocautery devices to the world of surgery. Electric current was used in the monopolar modality until 1966, when Wittmoser applied the bipolar variant in thoracoscopy.
• Generation of currents
A transformer supplies current of definite voltage, whereafter an oscillator creates alternating current (regularly changing direction, positive then negative) at a predetermined frequency. Presently, these currents are controlled by an all-in-one circuit composed of semi-conductors.
The current usually used in surgery has an intensity of 100 to 800mA and a voltage of 10 to 500V, with a frequency range between 50 and 300kHz (ie, a charge of 20 to 320W). This current generates heat, but avoids the faradic currents that can cause nerve stimulation. Electric arcing occurs at voltages higher than 19V.
• Danger
Monopolar cauterization presents a risk of unpredictable heating along the return path of the electric current. The current in monopolar cauterization follows the path of less resistance.

4. Tissue effect
• Principles
The characteristics of the current determine the tissue effect. Its action on the cell, ie division or cauterization, is dependent on the intensity and waveform (or frequency) of the current.
• Current for dividing tissue
Division of tissues is performed using a current that produces a rapid rise in temperature to above 100°C in the cell: the water that it contains is vaporized and the cell explodes. The current used has a high intensity, but it has a low voltage, a low power setting, and it is non-modulated and steady. This ensures that the right temperature to vaporize the cell is quickly reached.
• Cauterization current
A highly modulated and intermittent current of low intensity will induce a temperature lower than 100°C in the cell, usually 60° to 80°C. Beyond 55°C, proteins are denatured irreversibly, yet the temperature remains lower than the vaporization temperature within the cell. The protein coagulum and the retraction of dehydrated cells induce hemostasis.
• Types/modulated currents
• Principles
Three types of modulated currents can be used in surgery: this is decided by a combination of voltage and modulation. A high frequency current, with a high voltage and a highly modulated frequency may produce an electric arc between the tissues and the electrode, away from the tip of the electrode.
This phenomenon permits the use of electrosurgery for vaporization purposes.
5. Types/cauterization
• Use of electric current
There are 2 basic ways in which electric current can be used in surgery:
- monopolar cauterization,
- bipolar cauterization.
• Monopolar cauterization
The monopolar electrosurgical modality is used in more than 85% of laparoscopic procedures undertaken by general surgeons but less frequently in gynecology.
Electric current flows from an active electrode to a neutral one. In the monopolar modality, the electric current goes through the body from the active electrode (handle of the electrocautery device) to the neutral return electrode. This return electrode is the ground plate of the generator, and allows for current dispersion.
Monopolar cauterization requires a high power setting to bridge the resistance related to the large gap between the 2 electric poles. It ensures deep cauterization within tissues.
• Dispersion electrode
Its surface is large, more than 100 cm2, to avoid burns due to the high-frequency electric current passing through the skin.
It is composed of 2 conductive areas.
• Bipolar cauterization
• Principles
The bipolar electrosurgical modality appeared in 1966.
The same instrument has 2 electrodes close to one another.
The electric current does not go through the body but flows directly from one electrode to the other.
Bipolar cauterization constitutes only about 10% of the use of high-frequency surgery.
It requires a lower power setting than monopolar electrosurgery. This modality makes it possible to perfectly control the passage of current between the 2 electrodes. The current only flows through the target tissues while the adjacent tissue is protected.
This modality can also be used in ionic liquids owing to the low resistance of the liquid to the current flow.
• Benefits
The main benefit of bipolar cauterization is a result of the absence of a neutral electrode at a distance from the site of cauterization. As a result, there is no general or skin risk. However, the bipolar cauterization instruments are fragile. They do not permit the same applications as monopolar electrosurgical devices.
Bipolar cauterization does minimal damage to adjacent tissues, as the depth of cauterization is limited to the area between the 2 electrodes.
6. Surgical equipment
• Monopolar surgery
• Conventional
The monopolar modality can be used with any type of current-conducting instrument.
• Laparoscopic
The monopolar modality is most often used with a hook, scissors or a fixed grasper.
• Bipolar surgery
• Conventional
Bipolar instruments are uncommon and include:
- large and small bipolar graspers,
- bipolar scissors.
Recently, scissors designed for conventional surgery were introduced. This permits the simultaneous application of cutting and bipolar cauterization. These scissors are equipped with 2 blades set apart from one another to form active electrodes. This allows a range of uses that goes further than simple cauterization. Thin tissues can be cauterized over a wide area before being cut without changing instruments, and rapid hemostasis of small localized bleeders is possible. This type of device is not yet available for laparoscopic surgery, however.
• Laparoscopic
Bipolar graspers are the only instrument utilizable in laparoscopic surgery.
They are recommended in laparoscopic surgery to prevent current-induced accidents.
• Vessel-sealing devices
Vessel-sealing devices (hemostasis devices) are new high-frequency current applications.
7. Complications/bipolar
• Complications
Electric currents can lead to severe complications if instruments are misused due to lack of knowledge. Some complications in laparoscopy are specifically related to the use of electrocautery.
During a survey conducted by the American College of Surgeons, complications related to electrosurgery were reported by 18% of surgeons. Amazingly, more than 50% of surgeons knew of a colleague who had experienced such a complication. Complications occurred once or twice per 1000 procedures.
• Prevention
Complications
- rise in local temperature

Prevention
- dissection of tissues to be cauterized,
- no blind cauterization.
• Close-proximity burns
As the flow of current is well defined, complications arise due to the prolonged application of bipolar cauterization in the close vicinity of a structure vulnerable to a rise in temperature. Indeed, as the currents used have lower intensity, the duration of cauterization is longer. This results in a rise in temperature in the periphery of the cauterized area.

Prevention of this complication involves the perfect dissection of the structures to be cauterized, avoiding cauterization of large blocks of tissue.
Bipolar cauterization is sometimes the fallback option to control hemorrhage in an area where clips cannot be applied or monopolar cauterization cannot be performed. Once more, there is a risk of blind cauterization of structures that have not been dissected.
• Postoperative skin sloughing
Bipolar cauterization does not protect from the risk of postoperative skin sloughing of wounds.
8. Complications/monopolar
• Complications
• Origins
Numerous complications have been described. They are related to defective equipment or non-compliance with basic safety rules. This usually occurs due to a lack of knowledge about the principles of high-frequency surgery.
• Insulation defect 1
The most frequent yet also the most easily avoidable complication is related to compromised insulation on the electrocautery device. This occurs especially in instruments that have been through several sterilization cycles. Breaks in insulation can be minimal and invisible to the naked eye. The current flows through this break in insulation to tissues, and not via the tip of the instrument.
• Insulation defect 2
When a defect in the insulation of an instrument is outside the visual field, unrecognized tissue burns (skin or organs) can occur, with dramatic consequences if diagnosis is not made and treatment is not immediate.
In practice, this implies that one should be wary when there is a need to increase the generator power during a procedure to obtain adequate cauterization. This permits detection of anomalies. This may mean that a part of the current is escaping through an insulation defect.
• Direct coupling
Direct coupling is another form of unwanted contact where the electrical stream is transmitted by a conductive element from the active electrode to tissue. Once the electrode, be it hook, grasper, or scissors, is activated, it can touch another metal object, such as the scope.
If the latter is in contact with the wall via a metal trocar, it will discharge over a wide area without damage. Conversely, if it is isolated from the wall, it can come into contact with an intestinal loop on a restricted surface and thus produces a thermal lesion with a risk of secondary fistula.
• Leakage currents
• Monopolar current
The use of monopolar current implies the return of the current toward the generator via a return electrode situated at a distance from the operative field. During its course, the current can discharge toward regions of lesser resistance before it reaches the electrode and induces a heating along with cauterization or division of these tissues at a distance from the operated zone.
• Gynecological surgery
During cauterization of the Fallopian tubes, the current usually travels through the uterus and the broad ligament.
If the current cannot flow to the uterus or the broad ligament, it traverses the tube and can then escape through a close-lying intestinal loop. If this contact between the tube and the intestinal loop occurs over a very small surface, punctate cautery damage can occur.
• Bile duct surgery
The current will always take the path of least resistance. If cautery is used on the cystic duct, this can be the common bile duct, with damage resulting in:
- secondary stenosis,
- secondary fistula after sloughing of the skin at the wound site.
• Specific cases
The leakage current can be transmitted by electric arcing to the adjacent tissues when high power currents are used.
Leakage currents on the exterior of the patient result from contact between the patient and a metallic part of the operating table.
They are responsible for skin burns. Modern electrosurgical generators detect such currents and automatically stop the generator from functioning.
• Capacitive coupling
• Principles
Capacitive coupling is related to the formation of a capacitor by the metal and insulated layers of the electrocautery device. The active part of a hook covered with its insulated sheath constitutes a capacitor when it crosses a metal trocar. This capacitor generates an induced current. Such current charges the capacitor, which in turn discharges when in direct contact with tissues (in such a case through the patient’s abdominal wall without evidence of lesion).
• Risk
However, if the trocar is isolated from the wall, for instance by a plastic fixation device, the induced current will not be able to discharge through the wall, but through the closest tissue.
This type of capacitive coupling can also occur with an active electrode placed on a suction-irrigation device crossing a metal trocar.
• Pacemaker
There are risks when using electrocautery in a patient with a pacemaker: high-frequency currents can cause a break or a random alteration in the programming of the pacemaker, resulting in rhythm disturbances.
This risk is related to the way the pacemaker responds to electric and magnetic interferences caused by high-frequency currents flowing through the body. These currents can either be generated by the electrosurgical device or be induced.

A Ministry of Health (France) memorandum notes that if an electrocautery device is indispensable for a surgical procedure, the bipolar modality is preferable.
When monopolar cauterization has to be used, the ground plate on the patient must be positioned so that a cone composed of the tip of the active electrode and the plate remains perpendicular to the plane formed by the pacemaker and the pacing probe. In all cases, the functioning of the pacemaker is monitored postoperatively.
• Prevention of complications
• Recommendations 1
Any instrument with a visible defect should be removed from the operating room.
The use of insulated electrocautery devices is preferred, even if they are not intended for use with an electric generator, owing to the risks of direct coupling.
In electrosurgery, low-voltage currents (less than 200V) are preferred. These are currents for division. Only high-voltage cauterization currents (more than 200V) are capable of generating electric arcs. They may provoke tissue burns at a distance from the operative field.
• Recommendations 2
The electrode must only be activated once contact between tissues and the electrode has been established.
A good view of the operative field with a high quality video camera and an adequate pneumoperitoneum can reduce the risk of unintentional burns.
• Safety features
Modern generators are equipped with safety features which:
- limit the duration of activation,
- automatically stops delivery of energy when the impedance of the circuit increases. This impedance rises when tissue resistance increases (ie, when cauterization is performed). It is therefore impossible to carbonize tissues.

They generate controlled energy: the quantity of energy delivered by the electrode does not depend on the depth of cauterization or on its duration.
The generator is automatically switched off when low-frequency currents are generated.
The generators constantly control the quality of the contact established between the neutral electrode and the patient. A defect in the contact or an inadequate contact area can lead to skin burns at this site.
9. Argon plasma coagulation
• Equipment
Coagulation with Argon plasma (Argon Plasma Coagulation, APC) can perform hemostasis of diffusely bleeding surfaces.
It conducts monopolar electrosurgical current to tissue via an ionized Argon gas stream.
- Argon gas supply;
- high-frequency current: the source of energy;
- high-frequency electrode: inside the Argon applicator and connected to the monopolar outlet of the electrosurgical device.
• Principles
If the voltage is high enough and the tissue is conductive, the gas stream (ie, electrically ionized Argon plasma) allows the current to flow between the applicator and the tissue.
The density of the current applied to the tissue induces thermal coagulation. This transfer of energy is performed without the slightest contact between the instrument and the tissue. The Argon plasma beam acts not only axially along the axis of the applicator, but also laterally and radially.
• Benefits
Given that the current has a tendency to run to tissue that is still inadequately coagulated (low impedance) and that tissue impedance increases with coagulation, the Argon plasma is automatically diverted to non- or slightly-coagulated areas and brings about a more homogeneous cauterization of surface tissues than with any other technique. The low depth of penetration and the absence of carbonized tissues permit its use on delicate areas.
10. New electrosurgical techniques
• Principles
Very high-frequency electrosurgery represents a new method of applying electrical power that which could change the face of electrocoagulation: vessel-sealing systems using high-frequency current.
It is a new approach to the use of electrical currents in surgery:
- utilizing both the effect of mechanical pressure on tissues,
- and the transfer of electrical energy to create fusion between tissues.
• Properties
- ability to control vessels up to 7 mm in diameter;
- heat diffusion restricted to less than 2 mm from the application area;
- utilizes lower energy, therefore less tissue adheres to the jaws of the instrument compared to conventional bipolar cauterization.
The generator regulates the energy delivered depending on the thickness and type of tissue.
The surgeon only activates the generator once the grasper has been applied to the vessel to be cauterized.
The generator sends a diagnostical impulse that enables it to determine tissue impedance. It then applies an electrical charge adapted to the specific tissue.
This energy is delivered sequentially. A new assessment of residual impedance is performed between each energy pulse. This permanent tissue monitoring avoids both an excess or a defect in tissue cauterization.
The energy used is lower than with other systems; this reduces the diffusion of heat away from the application area.
• Results
• Resistance
The tissue effect is the result of an alteration of the vascular wall structure with fusion of collagen and elastin making up a solid, scarcely deformable aggregate. There is little localized heat and no thrombosis.
The bursting pressure of the arterial cauterization was assessed at 360 mm Hg: that is, 3 times an estimated 120 mm Hg mean arterial systolic blood pressure. It is higher than hemostasis obtained via an ultrasonic scalpel or via bipolar cauterization: the efficacy is similar to that of ligation.
• Disposable graspers
The disposable graspers used in laparoscopic surgery are expensive. Widespread use of this system could lead to a decrease in their cost.
11. Lasers
Laser types
Lasers can supply heat to tissues without the use of electric current:
- the neodymium yttrium-aluminium-garnet (Nd:YAG) laser with infrared emission;
- the potassium titanyl phosphate (KTP) laser with green emission;
- the Argon laser with blue emission.
As yet, lasers have not been shown to be superior to conventional electrosurgical systems. In addition, they are more expensive and not widely available.

Principles
The principle of laser-assisted dissection is based on the capacity of light energy to stimulate tissue molecules, causing a rise in local temperature. This induces tissue dehydration and coagulation of protein.
The final result is comparable to that obtained with cauterization.

Hazards
Known hazards of laser use are a poorly controlled rise in local temperature with a risk of contact burns.
For instance, Nd:YAG lasers are likely to induce a rise in temperature over more than 3 to 4 millimeters of depth and can provoke tissue burns away from the area of cauterization.
12. Ultrasonic dissectors
This new generation of devices induces a rise in the temperature of tissues secondary to the application of a 'blade' vibrating at a frequency of 25 000 to 55 000 Hz. The vibration is generated by a piezo-electric system. No electric current crosses the tissues.
13. Conclusion
Proper use of electrosurgical devices and an in-depth knowledge of their functioning enable surgeons to optimally benefit from the use of high-frequency currents in surgery. This also prevents accidents.
Some alternative technologies to high-frequency currents have been suggested for use in surgery, but none have yet proven superior.