Electrosurgery is the most commonly used form of energy in both open and endoscopic surgery. It is also one of the least understood form of energy forms used by the surgeon. The concepts of volts, current, resistance and their applications during surgery are often is understood. Moreover, the risks and dangers are also often not appreciated. In order to utilize electrosurgery optimally and to understand the hazards of electrosurgery, the surgeon must be familiar with the biophysics of electrosurgical energy.

Electricity is flow of electrons through a conducting medium. The electrons flow from one atom to the orbit of an adjacent atom. Depending on the direction of the current flow we call it direct or alternating current. When current flows continuously from one pole to the other pole of an electrical circuit, it is called direct current (DC). When the current flow changes its direction it is called alternating current (AC). There is no net gain of electrons at either pole of the electrical circuit. Household electricity is an alternating current and it changes its direction 50 times per second. This is called frequency of the current (50 Hertz).

Voltage is the force pushing the current through a resistance and it is measured in Volts.

Wattage. A watt is the rate of work. It is voltage multiplied by amperage. Electrosurgical generators display its power by the number of watts.

Resistance is the obstacle to the flow of current and it is measured in Ohms.

Bioeffects of electrical current. Household current cannot be used for electrosurgery. When it passes through our body it stimulates the nerves. The current causes exit of sodium and potassium ion and depolarization follows, resulting in the propagation of a wave and stimulation of the end organ. A sustained electrical field prevents reentry of sodium and potassium ions, repolarization cannot take place and results in paralysis of nerve and dysfunction of the end organ. So when an electrical current is applied to the human body, the Purkinjee fibers of the heart get paralyzed producing heart block and cardiac arrest. So any electrosurgical procedure should avoid stimulation of nerves. The depolarization is a relatively slow process measured in microseconds. The nerve stimulation and therefore paralysis can be avoided by applying the current for a fraction of time shorter than required to lower the threshold potential. This can be achieved by increasing the frequency of current to a level above 100 kHz (100,000 cycles per second). All modern electrosurgical units produce a current of 500 kHz to 2 MHz (2,000,000 cycles per second).

When a high frequency current is applied to the body tissue certain biochemical effects occur.Cells contain water, electrolytes and non-electrolyte particles. When a flow of electrons are applied to the cell, the positive charged particles (sodium and potassium ions) move towards it and negative charged particles move away from it. During the fast flow of these charged particles, it collides with each other or with other uncharged molecules producing friction and therefore heat. The temperature rises in the cell.If the tissue is heated very slowly the following events occur.

Below 45 degree C - The thermal damage is reversible.

Above 45degree C - The cell enzymes are denatured and tissue necrosis starts. There is no visible effect but can be assessed through cytochemical analysis. This type of injury to ureter or bowel can lead to delayed fistula formation or perforation of bowel.

70 degree C - The protein contents lose their quaternary configuration and solidify. This is seen as blanching of tissue. We call this as coagulation.

90 degree C - The liquid contents evaporate until tissue is completely dry- desiccation. This is seen as Shrinkage.

200 degree C - Carbonization starts. It refers to the end product of further heating of desiccated tissue. The solid contents of the tissue are reduced to carbon.

When the tissue temperature is increased instantaneously from 37 to 100 degrees C, the above steps are short-circuited. The liquid contents of the cell are converted into vapor (Steam) and the cell explodes producing a cutting effect.

In electrosurgery, our aim is to produce a combination of the above tissue effects. The tissue effect from heat depends directly on the temperature inside the tissue and the time required reaching that temperature. Clinician uses electrosurgery for cutting the tissue or coagulating it. To achieve this we have to use different types of current and electrodes.

Cutting Current

High frequency current generates intense heat in tissue when applied through a small contact area such as needle tip. As described earlier the tissue water is turned into steam and vaporizes the cells producing a cutting effect. A cutting current is selected for this purpose. Cutting current (unmodulated current) flows continuously throughout the time the generator is activated with the foot pedal. The peak voltage is low for this current, about 500 to 1000 V, which is beneficial .

Coagulating current

Traditionally we have been taught to use coagulating current (modulated current)
for coagulating a tissue. Coagulating waveform is nothing but an interrupted current. The current flow is for only less than 10% of the time the electrosurgical generator is activated. So the tissue is not heated up to the point of vaporization, instead it is desiccated. Coagulation currents may have peak voltages of 6000 V.

In laparoscopic surgery vascular structures like infundibulopelvic ligaments, uterine vessels and round ligaments are coagulated prior to division.. Coagulation is also employed for bleeding surfaces and endometrial implants.

Unlike cutting, the electrode is in direct contact with the tissue during coagulation. Although theoretically both coagulating or cutting current can be used for coagulation, a cutting or blended current is superior for practical reasons.

Blended current

Haemostasis will be poor if a pure cutting current is used. Haemostasis can be improved if a blended current is used during cutting. Blended current is an interrupted current, which flows for only part of the time .For example in Blend I, the current flows for 50 % of the time followed by no flow for next 50 % of the time in a second. So the time required for cutting will be longer and there may be more lateral coagulation producing haemostasis. So the haemostasis achieved is at the cost of more tissue damage. So use minimum blends with the cutting current. A blended current can have peak voltages of 2000 V.

To establish a circuit, current flow it has to come out through one terminal of the generator and reach the target area and flow back to the other terminal of the generator. The current from the generator can be applied to body tissues by two approaches - unipolar and bipolar system.

Unipolar system

In unipolar system, current flow is from the generator through the electrode to the tissue. Body tissue is a good conductor of electricity and current further spreads through the muscle, fat and then to skin. The circuit becomes complete only if this current flows back to the generator through the patient plate in close contact with the skin.

Bipolar System

In bipolar system the current comes out of generator through one lead of a cord and then through one prong of the bipolar instrument to the target tissue. The current comes out of the opposite side of the tissue and reaches the other prong of bipolar forceps and then flows back to the generator through other lead of the bipolar cord. The current flows only between the prongs of the bipolar forceps unlike the unipolar system. The bipolar generators are have less power output than unipolar generators. Most bipolar generators use unmodulated current although we use it for coagulation.

Variables Impacting Tissue Effect

Surgeons find a variable tissue response when he uses electrosurgery especially in the unipolar mode. This is expected because there are many factors, which come into play when actual electrosurgery is done.

The tissue effects of different waveform have been already discussed. A cutting current is used when tissues are to be divided. In endoscopic surgery a cutting current is used for adhesiolysis, myomectomy or salpingostomy. In open surgery a blended current is used for opening the abdomen because haemostasis with cutting is required. Blended current is not ideal in endoscopic surgery because it produces more tissue damage and therefore more smoke. Traditionally coagulating current is used for coagulating a bleeder.

In addition to waveform, power setting also alters the tissue effect. Higher wattage tends to produce quicker tissue response. Optimum wattage has to be selected depending on the other variables.

The smaller the electrode, the higher the current concentration for a particular power setting. In other words power density is more as the electrode size become smaller (Watts/contact surface area). Consequently, the same tissue effect can be achieved with a smaller electrode, even though the power setting is reduced. Conversely a coagulating effect can be achieved with a cutting current provided an electrode with large surface area is used. The power density is so low that the tissue cannot be heated to the point of vaporization. Many surgeons use the tip of a spatula electrode for cutting and flat surface for coagulation with the same power and waveform.

Time

At any given setting, the longer the generator is activated the greater the heat produced. The greater the heat, the farther will it travel to adjacent tissue (thermal spread). So the degree of coagulation of the incision surface dependents on the speed with which the incision is made. The slower the incision electrode is directed through the tissue, the greater is the degree of coagulation of the surfaces of the section.

Manipulation of the electrode

This can determine whether vaporization or coagulation occurs. When electrode is used to make a spark over the tissue, it cuts the tissue. When the same electrode touches the tissue and then activated it produces coagulation. This is because during sparking the current density is high enough to cut the tissue.

The usual sequence of touching the tissue and then activating the electrode is not the right method for achieving cutting effect. The electrode is first activated to produce a spark and then touched on the tissue to cut the tissue. In my practice I touch the tissue with the electrode and then withdraw for 2-3 mm to keep a sparking distance and then the cutting pedal of foot switch is pressed and moved over the tissue to be cut at a sufficient speed. Practically the force required to cut tissue is almost zero.

Type of tissue:

Tissues vary widely in density and resistance. Muscle can be cut much faster. Fibrous tissue takes longer since there is more resistance.

Eschar:

Eschar is relatively high in resistance to current. Keeping electrodes clean and free of eschar will enhance performance by maintaining lower resistance.

Patient Return Electrodes

The function of the patient return electrode is to remove current from the patient safely. A return electrode burn occurs when the size or conductivity of the patient return electrode does not safely dissipate the heat produced, over a time.

The ideal patient return electrode safely collects current delivered to the patient during electrosurgery and carries that current away. To eliminate the risk of current concentration, the pad should present a large, low impedance contact area to the patient. Placement should be on conductive tissue that is close to the operative site. Again, the only difference between the "active" electrode and the patient return electrode is their relative size and conductivity. Concentrate the electrons at the active electrode and high heat is produced. Disperse this same current over a comparatively large patient return electrode and little heat is produced. If the surface area contact between the patient and the return electrode is reduced, or if the impedance of that contact is increased, a dangerous condition can develop. In the case of reduced contact area, the current flow is concentrated in a smaller area. As the current concentration increases, the temperature at the return electrode increases. If the temperature at the return electrode site increases enough, a patient burn may result. Surface area impedance can be compromised by excessive hair, adipose tissue, bony prominence, fluid invasion, adhesive failure, scar tissue and many other variables.

Pad Site Location

Choose a well-vascularized muscle mass close to the operating area. Avoid less vascular areas, hairy areas, irregular body contours and bony prominence. A pelvic surgeon may place the electrodes on the thigh muscles.

Electrosurgery Safety Considerations during MIS

When electrosurgery is used in the context of minimally invasive surgery, it raises a new set of safety concerns. Some of these are insulation failure, direct coupling of current, and capacitively coupled current.

Direct Coupling

Direct coupling occurs when the user accidentally activates the generator while the active electrode is near another metal instrument. The secondary instrument will become energized. This energy will seek a pathway to complete the circuit to the patient return electrode. There is potential for significant patient injury.

Insulation Failure

Many surgeons routinely use the coagulation waveform. This waveform is comparatively high in voltage. This voltage can spark through compromised insulation. Also, high voltage can "blow holes" in weak insulation. Breaks in insulation can create an alternate route for the current to flow. If this current is concentrated, it can cause significant injury.

You can get the desired coagulation effect without high voltage, simply by using the "cutting" current while holding the electrode in direct contact with tissue. This technique will reduce the likelihood of insulation failure.

Capacitive Coupling During Endoscopy

Metal Cannula System

Capacition occurs whenever a nonconductor separates two conductors. During MIS procedures, an "inadvertent capacitor" may be created by the surgical instruments. The conductive active electrode is surrounded by nonconductive insulation. This, in turn, is surrounded by a conductive metal cannula. A capacitor creates an electrostatic field between the two conductors and, as a result, a current in one conductor can, through the electrostatic field, induce a current in the second conductor.

Plastic Cannula System

Capacitance cannot be entirely eliminated with an all plastic cannula. The patient's conductive tissue completes the definition of a capacitor. Capacitance is reduced, but is not eliminated.

Hybrid Cannula System

The worst case occurs when a metal cannula is held in place by a plastic anchor (hybrid cannula system). The metal cannula still creates a capacitor with the active electrode. However, the plastic abdominal wall anchor prevents the current from dissipating through the abdominal wall. The capacitively coupled current may exit to adjacent tissue on its way to the patient return electrode. This can cause significant injury.

Guidelines for use of electrosurgery

Pre operative

1	Study your diathermy unit in detail. Identify the switches and power setting tools for the cutting, coagulating, blend and bipolar current.
2	Check whether the patient plate, unipolar and bipolar cables match your unit and the laparoscopic hand instruments. Keep extra cables for emergency.
3	If operator is not familiar with that particular diathermy and if time permits, check the probable power settings by placing a wet soap on the patient plate and experimenting with the cutting, coagulation and bipolar currents. This can be set as the preliminary setting to begin the surgery.
4	Place the patient plate in appropriate position before anaesthetizing the patient in all cases For pelvic surgery, plate is usually kept below the buttock. Please take care not to place it in the curved low back. A rubberized plate is better than rigid steel one. Don’t attach the patient plate directly over large blood vessels close to skin.Use no jelly, instead use a clean plate. Please keep an extra plate ready. Please make sure no cloth or drape comes in between the patient and the plate.
5	While positioning the patient it is better to avoid contact of patient to any metal part of the table. A thick ,dry, electrically-insulating sheet must be placed between the patient, the operating table and supports.
6	While draping the patient please don't put the sterile drapes between the patient and the plate.
7	Do not use towel clips to fix the diathermy cables. Use sterile bandages to fix the cables
8	It is better to have a regular OT technician who is well instructed.
9	Periodically check for the integrity of the insulation of the electrodes.

Intraoperative.

1	Use the minimum current settings for cutting and coagulation. Use a low voltage waveform (cut). Since almost all undesirable side effects such as carbonization of tissue, burns to the patient, sparking, destruction of fine electrodes etc. are observed in case of excessively high power, the attempt should be made to reduce the power to bare minimum necessity.
2	Use bipolar electrosurgery when appropriate
3	Connect the cables to hand instruments only when necessary. Disconnect immediately after use
4	Keep the foot switch in a safe place for the operating surgeon so that no body accidentally stamps on it. Do not transfer the foot switches while the electrode is inside the peritoneal cavity. Inadvertent pressing of the switch can damage the vital organs.
5	Use brief intermittent activation vs. prolonged activation
6	Activate the electrode only when a panoramic vision is achieved. A bowel touching on the non-insulated area of the forceps may not be visible at close up view). Observe the entire length of the non-insulated part of the instrument. When dividing a broad adhesion between a bowel and a non-vital organ, using electrode always divide near the bowel first and then excise the adhesion . If the adhesion is separated first from the non-vital organ and then divided near the bowel the current has to flow through the bowel to the return plate damaging it.
7	Evacuate the smoke periodically for proper vision.
8	Clean the electrode frequently for efficient use. Dirty tip of the electrode requires increase in the power setting with inadvertent damage to the tissues.
9	When making incisions for myomectomy, salpingostomy, make a trial movement first and then only activate the electrode.
10	Select an all-metal cannula system as the safest choice. Do not use hybrid cannula systems that mix metal with plastic..

Difficulties

1	Too much smoke: Smoke cannot be totally avoided. When too much smoke is present reduce the current settings to minimum. Avoid using blended current. Use the thinnest electrode possible. Periodically suck out the smoke with suction probe.
2	Desired coagulating effect is not seen for the usual settings. The electrode tip may not be clean or may be holding a thick chunk of tissue. Occasionally the bare area of the electrical instrument is touching some other tissue, which is not seen. Have a panoramic view and check. The cable connections or even the cable may be faulty. Try to use a sterile spare cable.
3	Sticking of the tissues to the instruments. This happens especially when coagulating a bleeder with a bipolar during salpingostomy or a bleeder near the tubal fimbria. Continue to activate the electrodes while detaching from the tissue. Make sure to use a clean forceps. A sterile tooth brush is a good instrument for cleaning the electrodes
4	Coagulated vessel bleeds when divided. This happens with larger pedicles like infundibulopelvic ligament is coagulated. Use smaller power settings for longer period of time. When high settings are used initially outer tissue gets dried up and there is no flow to the depth of the vessel. Another alternative is to incise the peritoneum over the pedicle first and then apply coagulation.

Summary

Electrosurgical energy has by far the most diverse capabilities when compared to other energy sources and is among the least expensive of them. Recent technological advancements in performance and safety have positioned this technique as one of the more useful tools in a surgeon's armamentarium.
As with any surgical tool , education and skill are required in order to use it safely.

Suggested Reading

1	Luciano AA, Soderstrom R M, Martin DC. Essential principles of electrosurgery in operative laparoscopy. Am Assoc Gynecol Laparosc 1994; 1:189-195.
2	Sacks E. Monopolar electrosurgical safety during laparoscopy. Health Devices 1995; 24(1): 3-27.
3	Soderstrom RM. Electrosurgery's advantages and disadvantages. Contemp Ob/Gyn.1990;35:35.
4	4. Roger C. Odell. Physics and clinical application of electrosurgery. In: C.Y.Liu ,ed. Laparoscopic hysterectomy and pelvic floor reconstruction, Blackwell Science ,1996.