Bangalore Endoscopic Surgery Training Institute & Research Centre[edit | edit source]
This is to describe the basic principles of Electrosurgery. Unlike lasers, there has not been any regulatory body on the use of electrosurgery. Traditionally the use of electrosurgery has been learnt from the seniors during surgery, and surprisingly there is hardly anything written about it in any of our standard textbooks of surgery. Inspite of its potential dangers, there is not enough effort to understand the occurrence and prevention of the complications of electrosurgery. This article attempts to give an insight into this topic of utmost importance to any surgeon today.
Definition[edit | edit source]
One common mistake that we often come across is that the terms "Electrosurgery" and "Cautery" is used for the same purpose while both of them are quite different. By definition, Electrosurgery is the use of radiofrequency alternating current to raise the cellular temperature as a way to vaporize or coagulate tissue. Cautery is a term derived from "Kauterion" which means "hot iron". It is the destruction or denaturation of tissue by a passive transfer of heat or application of a caustic substance.
Biological Effects of Electricity[edit | edit source]
There are primarily three types of effects produced on tissues by electrical energy. The first type is called Electrolytic effect where anions and cations in the body are attracted to opposite sides. This type of reaction is not conducive to life, and is produced by either low frequency alternating current or direct current. The second type of reaction is called Faradic effect which is produced by high frequency alternating current upto 20 KHz. This type of current causes stimulation of nerve-endings and muscles, and is commonly used by physiotherapists and neurologists, and sometimes by general surgeons during parotid surgery to detect the branches of the facial nerve, etc. The third is the Thermal effect which is produced by high frequency alternating current more than 300 KHz (also called radio-frequency AC).
There are basically three variable properties of electricity – Current, Voltage and Resistance.
Current (I) - is a measure of the electron moment past a given point in the circuit in a fixed period of time. It is measured as amperes.
Voltage (V) - is the pressure with which the electrons are pushed through the tissue. This is measured as volts.
Resistance (R) - is the measure of the difficulty that a given tissue presents to the passage of electrons, and is measured as ohms.
Power (W) - is the capacity to do work per unit time and is measured in watts.
All this can be very easily understood using Odell's Water-tower analogy.
An Electrosurgical Unit basically does two major functions. It converts a 60 cycles/second (60 Hz), low voltage alternating current into higher voltage radiofrequency (500 KHz to 3.0 MHz) current. Secondly it is capable of producing current with a variety of wave-forms.
Advantages of Electrocutting[edit | edit source]
- Reduced bleeding as there is simultaneous haemostatic effect.
- Preclusion of germ implantation, as there is heat produced in the vicinity, and as it is done by sterile technique.
- Avoidance of mechanical damage to the tissue.
- The possibility of using it in endoscopic surgery.
Types of Circuits[edit | edit source]
There are two types of circuits used to produce diathermy, Monopolar and Bipolar. In the Monopolar diathermy, the electricity travels from the ESU to the patient. The current enters the body of the patient and reaches the dispersive electrode (patient plate), which may be at a distance from the active electrode, and then returns the ESU. As alternating current is used, the direction of current keeps changing several times every second. In the bipolar diathermy, the current passes through one limb of the instrument and returns through the other limb of the instrument. While doing so, it travels through the tissue grasped between the two limbs of the instrument.
In the Monopolar type the effect of the current is seen at close proximity to the active electrode, as the energy is concentrated here, and gets dispersed as it travels towards the dispersive or return electrode. The advantages of using the Monopolar Electrocautery are that it is easy to use and surgery can be performed much faster as it can be used as both cutting and coagulating current. Hence it can be used to dissect tissues also. The disadvantage is that larger volumes of tissue are injured and sometimes distant burns can also occur. It requires a distant return electrode. It may also interfere with pacemakers.
To prevent complications it is important to place the return electrode (patient plate) as close to the operating field as possible, so that the circuit runs only for a short distance in the patient's body. Generally, it is advised to place the dispersive electrode around the arms or the thighs depending in which part of the body the surgery is being performed.
The advantage of using Bipolar Electrocautery is that small volumes of the tissue are injured and there will not be any distant burns. It is a safe mode when used in patients with pacemakers. It is also effective in wet fields. The main disadvantage is that more skill and time is required to use bipolar electrocautery, and that only coagulation current only is available. Hence there is no dissecting capability. But some of the recent machines have incorporated the cutting mode also. Bipolar offers more safety when being used at close proximity to bowel and other abdominal viscera.
Tissue Effects of Electrosurgery[edit | edit source]
There are three types of tissue effects of the radiofrequency current, which is used for electrosurgery – Vaporization (or Cutting), Desiccation (or Coagulation) and Fulguration (or superficial coagulation). Vaporization and fulguration are non- contact procedures, and there is a small distance between the electrode and the tissue. The electrical spark travels through a steam bubble from the tip of the active electrode to the tissue to cause the particular effects on the tissue.
Mechanism of action (Cutting / Coagulation)[edit | edit source]
When an alternating current is used on a cell at a very high frequency (radiofrequency), the anions and cations move to and for within the cell with each cycle of the alternating current. This causes friction and results in increase in the intracellular temperature. Vaporization or cutting is caused by high current and low voltage. This causes a rapid heating of the cell and formation of steam inside. As a result there is an explosion due to the massive increase in volume of the intracellular contents, and lysis of the cell takes place. Coagulation is produced by a low current and high voltage. This is a damped current and the flow of current is interrupted. Though the increased voltage causes deeper penetration into the tissues, the low current causes slow heating of the cell. This in turn causes dehydration of the cell and the cell shrinks in size.
It is important to recaptulate the Ohm's Law, which says:
This, when applied to the formula: W=VxI,
where, I = Current, V=Voltage, R = Resistance, and W = Power.
Hence the amount of work done (coagulation performed) is directly proportional to the voltage used and is indirectly proportional to the resistance offered by the nature of tissue on which it is used. A higher voltage leads to a higher spark intensity and a higher spark intensity results in a deeper zone of coagulation during the cutting process.
The variables that affect the tissue effects of R-F Current are as follows:
- Generator output
- Power density (Size and shape of electrodes)
- Electrode-tissue proximity
- Tissue impedance
- Electrode speed / time on tissue
- Distension media.
Ideally when tissues have to be cut, a sharp electrode is used in the cutting mode, and the electrode is held at a small distance away from the tissue. Charring effect will be minimal when used in this way. When fulguration (superficial coagulation) is desired, as
while obtaining haemostasis over the liver bed, a ball electrode or a spatula is used in the coagulation mode, again holding the electrode at a small distance away from the tissue. If the electrode is pressed firmly over the liver surface, it would cause dessication or deep coagulation. When dissecting tissues and both cutting and coagulation are required, blended modes are used in different ratios of cutting and coagulation. The thickness of the electrode can be selected depending on how much coagulation effect is desired. The speed at which the electrode is moved determines the amount of contact and delivery of energy to the tissues, and thus the amount of coagulation and charring at the margins. In laparoscopy, the Carbon dioxide gas used is not as good a conductor of the electrical energy as air, and thus would alter the performance of electrosurgery.
Electrosurgical burns[edit | edit source]
During application of electrosurgery three main types of burns can occur:
Endogenous burns are always a result from a too high current density in the patient's tissue. At the active electrode there is a need for high current density in order to cut or coagulate tissue, but accidental pressing of the foot pedal or use of the electrocautery for a longer time or extent can cause burns. There are three mechanisms in which inadvertant burns can occur during use of monopolar electrocautery in laparoscopic surgery.
The common cause by which this occurs is when there is insulation failure or when the whole metal part of the instrument is not being visualised while using electrocautery. The instrument may be touching some other tissues outside the laparoscopic visual field, where the instrument may not be insulated adequately. At such a time the current passes to that tissue and causes burns there.
There can be another instrument which can conduct electricity (like telescope, grasper, etc.,), in close proximity to the instrument through which electricity is passing and the energy can jump and get transferred to this instrument also. Supposing there is some other tissue in close proximity to this instrument then there can be burns of this tissue, which is located far away from the site of surgery. This burn may go unnoticed.
There is certain amount of energy that leaks on to the reducer if it is made of metal, and usually if the reducer is in contact with a metal canula on its outer aspect, the energy is dissipated on the abdominal wall. In turn the energy goes to the dispersive plate and returns to the E.S.U. But if the reducer is not able to let out the energy (because the outside canula is made of a non-conducting material, like plastic), it gets accumulated in the reducer. When a loop of intestine or some other viscera comes in close proximity to the reducer, it suddenly discharges all the energy to that tissue and can result in burns there. This can be prevented by either using both metal reducer and canula, or both being made of nonconducting material. The risk of capacitive coupling burns exists when a combination of metal and plastic ports is used. Certain modifications are incorporated in some new Electrosurgical units, like Electrosheild and monitoring devices which are capable of either preventing accumulation of extra energy in the portals or carrying back this energy to the E.S.U.
The usual causes of endogenous burns other than those mentioned are as follows:
- Patient plate is too small
- Patient plate is not covering the patient's tissue with its entire area. (at least 75% area should be in contact)
- Unintentional contact to other electrically conductive parts, e.g., drip stand or metal parts of the operation table, etc.,
Sometimes there may be concentration of energy at the patient plate or at areas where the patient comes into contact with electric-conductive parts. The current density becomes so high as to burn the patient's tissue.
EXOGENOUS BURNS[edit | edit source]
Exogenous burns are caused from the heat of burning substances such as skin-cleansing lotions, degreasants and disinfectants, also anaesthetics, which have been ignited by sparks between the active electrode and the patient's tissue. Note that alcohol usually burns as invisible flames, since the operating lamp lights brighter than the flame does. This way the patient-burn can only be recognized after it happened.
PSEUDO BURNS[edit | edit source]
From time to time minor or major necrosis are found with patients and are regarded as burns but without finding any explanations or reasons of how these burns have been caused.
Endogenous burns can be excluded when the patient did not have contact with electric-conductive parts at the area where the necrosis is found.
Exogenous burns can also be excluded when before or during electrosurgery no flammable substances were used.
The causes of these burns must be found out by differential diagnosis:
Necrosis caused by pressure to the patient's tissue:
During long operative procedures pressure to the patient's tissue can cause necrosis, for example, during heart surgery when the patient is hypothermic a large tissue necrosis was found post-operatively.
Pressure to the patient's skin caused by rubber-straps being used to fix and attach the patient plate or by contact-clamps being put underneath the patient can again cause necrosis. In many cases this is erroneously diagnosed as patient-burn.
During electrosurgery patient-burns can only occur when the before mentioned facts are existing. It is possible to prevent patient-burns safely when the operating team knows and observes the causes as well as pays attention to these before and during electrosurgery.
SAFETY PRECAUTIONS[edit | edit source]
The following steps should be followed carefully while using electosurgery:
- All connections are carefully checked before the ES unit is put on.
- The patient plate used is always one recommended by the manufacturer.
- The patient plate must always be applied by covering the patient with its entire area as best as possible.
- The conductive surface of the patient plate must always be clean and free from corrosion.
- If gelled patient plates are used, it is most important that the gel is evenly applied over the entire conductive area of the patient plate.
- Prior to use, the patient plate must be checked for damage, especially patient plates made of aluminum foil.
- It is important that the patient plate is applied with the electrically conductive surface to the patient's skin and not with its wrong side.
- The patient plate is applied as close to the operative site as possible.
- Care must be taken that no electrical conductive fluids come between the patient's skin and the patient plate.
- The patient is insulated against all electrically conductive objects by a thick, dry, electrically insulating sheet, placed between the patient, the operating table and the supports. The sheets must not become damp. Areas subject to considerable secretion of sweat, body extremities lying against the trunk or skin-to-skin contacts should be separated by the application of a dry cloth. Drain off urine with catheter.
- During electrosurgery always sparks exist between the active electrode and the patient's tissue
Therefore do not use flammable or explosive substances or gases during electrosurgery. If flammable or explosive substances have been used, these must be completely removed before activating the electrosurgical unit.
A special precaution to be taken during laparoscopic surgery is that electrosurgery should not be taken during laparoscopic surgery is that electrosurgery should not be used whenever there is bowel perforation. Bowel contains Methane gas, which is released into the peritoneal cavity whenever there is a bowel perforation, and if electrosurgery is used at such a circumstance, it may lead to an explosion.
Assuming good surgical technique and good endoscopic instrumentation with intact insulation, correct connection of cables and proper placement of neutral electrode would go a long way in making this efficient tool safe and a boon to the surgeon especially in this era of laparoscopic surgery.
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