Elementary notions of electrosurgery
- Radio frequency electric current
- Effects of high temperatures on cells
- The impact of high temperatures on tissues
- The electrical circuit of monopolar instruments
- The electrical circuit of bipolar instruments
- Chapter III
- Monopolar working modes of the electrosurgery unit
- Monopolar circuit and problems of its use in electrosurgery
- The issue of the integrated use of the electrosurgery unit and the risk of electromagnetic interference
- Chapter I: Introducere
We live in a world of electromagnetic radiation and we are surrounded by it wheter we realize it or not.
But how do we define electromagnetic radiation?
An electric field is generated around an electric conductor crossed by an electric current, and this (the electric field) generates a magnetic field. A varying electric field will generate a varying magnetic field, which in turn generates a varying electric field. In other words, the variable magnetic and electric fields generate each other, thus constituting what is called the electromagnetic field (electromagnetic waves).
Electromagnetic radiation is the propagation of electromagnetic waves in space, according to the graphic representation below. The two vectors, shown in red and blue, represent the electric vector, respectively the magnetic vector, which are perpendicular to the movement direction of the waves (fig. 1).
This model is for the understanding of the electromagnetic phenomenon, but we will never see this propagation, not even for waves in the visible spectrum. The sens of sight will convert electromagnetic radiation into sensations of light. Part of the electromagnetic radiation is accesible to the perception of the human eye as light in the visible spectrum, but light radiation beyond the extremes of the visible spectrum also exists – infrared and ultraviolet, just as there also is electromagnetic radiation that we cannot perceive in any way, all these composing the electromagnetic spectrum (fig. 2).
Fig. 2 – The electromagnetic spectrum
Electromagnetic radiation is oscillatory (undulating). It propagates in the form of electromagnetic waves. The oscillatory movement involves starting from a zero point, increasing to a maximum, decreasing to a minimum, then increasing to the starting point (zero) – see graph (fig. 3); this is a complete cycle. The complete number of cycles per second is called frequency and is measured in Hertz.
The measure associated with frequency is the wave length, which measures the space that the electromagnetic wave travels during a complete cycle. It is denoted λ and it is in an invers ratio with the frequency.
Electric current is an orderly movement of electrical charges. We frequently encounter it around us in the form of direct or alternating current. Direct current is typically produced by batteries (primary cells) which have a positive and a negative pole. When a consumer is connected to the circuit – see fig. 4 – the current will always flow in the same direction (direct current), from the negative pole to the positive pole.
Various commonly used devices generate direct current. For example, the bicycle dynamo produces direct continuous current, as do the photovoltaic cells in the solar panels. A special mention must be made for rectifiers that generate direct current by changing the parameters (rectification) of an alternating current – for example, mobile phone chargers.
Devices that use direct current for operation can be powered directly from a generator providing direct current or from batteries or accumulators. Although the terms are considered synonymous, there are significant differences between batteries and accumulators. Thus, according to definition, the accumulator is a source of electrical energy which can yield but also store energy through a reversible electrochemical process, and that can be recharged. Unlike the accumulator, the battery cannot be recharged (fig. 5).
From a constructive point of view, batteries are devices that, following chemical reactions, generate electric current.
The italian physicist Alessandro Volta is considered to be the inventor of the modern battery, in the year 1799. Volta’s battery was composed from a column of similar overlapping elemnets, the so-called voltaic elements – zinc discs alternating with copper discs and separated by a layer of felt or cardboard soaked in saline solution, which is a good electrical conductor (fig. 6).
A peculiar device whose utility could not be elucidated was discovered at an archaeological site near Baghdad, Irag, and has been dated to be about 2200 years old (from 250 BC). It is a clay vessel, waterproofed with pitch inside, which contains an iron electrode surrounded by a copper cylinder (fig. 7). When the vessel is filled with vinegar or another electrolyte solution, the device produces direct current with a voltage at the „battery” terminals of about 1.1 V, similar to current batteries that produce about 1.1 – 1.5 V per cell.
Nowadays, accumulators power mobile phones and various other portable devices, including power tools (drilling machines etc), cars and more recently, high-power accumulators power the motors of electric cars.
Direct current electrical sources (batteries or accumulators) are characterized by a measure called voltage which is measured in Volts (V) and which represents electrical potential difference between the positive and negative poles. Usually, the voltage of telephone and computer accumulators is around 5 V, and for cars 12 V.
Measures and Units of Measure that describe Electric Current
The electric current that crosses a circuit is characterized by intensity (I), which represents the number of electric charges that cross the circuit in the unit of time; intensity is measured in Amperes (A). In other words, it is the current flow. The intensity is also the ratio between the voltage (V) measured at the source terminals and the circuit resistance (R).
The formula that connects these measures to each other, I = V/R is Ohm’s law.
Let’s imagine an electric generator with voltage V at the terminals. By connecting a consumer to the generator terminals, we will create an electric circuit similar to the one in figure 4.
The electric circuit will be crossed by a current that will have a certain flow rate (intensity). At the same time, the electric circuit composed of conductors and consumers opposes the passage of the electric current by a certain resistance denoted by R. The resistance is measured in Ohm (Ω). The flow of current (which we will call intensity – I) is directly proportional to the voltage V and inversely proportional to the resistance R. Thus, for a circuit with a certain resistance R, if we double the voltage we will obtain a doubling of the intensity I. If we keep the voltage constant and double the resistance, we will get a halving of the intensity. It should be noted that the intensity of the current is the same at any point in the circuit.
In summary, the connection between intensity, resistance and voltage is given by Ohm’s law, which is expressed mathematically by the formula illustrated below – see fig. 8.
Resistance is a characteristic measure of direct current, and the counterpart for alternating current is called impedance (Z) (the resistance opposed to the passage of current in an alternating current circuit). Therefore, when discussing electrosurgery, because the circuits are crossed by radiofrequency current (alternating current), we will use the term „impedance” when we refer to the resistance of the tissue to the passage of the electric current.
For a circuit with a voltage V carried by a current I, we can define the dissipated power (P) as the product of V and I. The mathematical formula is P = V x I and is measured in Watts (W). To be able to keep a constant power, we will have to increase the voltage for a decrease in intensity, so that the product remains constant.
Why do we use alternating and not direct current?
The first plant to produce electricity was built by Thomas Alva Edison in 1882. It produced direct current, which was used both for industrial purposes and for lighting, using the first light bulbs invented by Edison in 1878. Electricity became a succes especially because of lighting and „entered” the homes of Americans with great speed due to the obvious advantages of electric lighting. In Edison’s network, the produced and transported current was around 110 V, the voltage at which the first incandescendent bulbs were powered.
A decade later, a new type of electric generator appears. It was invented by Nicola Tesla and produced alternating current. The first power plant similar to today’s is made by George Westinghouse and uses the motive force of the water of Niagara Falls to produce alternating current with the help of generators invented by Tesla. In the electrical network, the power plant “injects” an electric current with the same voltage as that produced by Edison, i.e. 110V.
In the following decade, a veritable media and commercial war would take place between Edison and Tesla over the advantages and disadvantages of alternating current versus direct current.
The transmission of electric current from the plant to the users requires the use of electric transport networks, networks on which losses are necessarily recorded due to the electrical resistance of the conductors that make up the network.
A simple calculation shows that the transfer of relatively large powers, of about 1MW (1 megawatt = 1,000,000 W) using a voltage of about 100 V from the power plant, would require a current of 10,000 A to circulate through the electrical conductors, according to Ohm’s law I = P/V. That is I = 1,000,000 W/100 V = 10,000 A. At such an intensity of carried current, even the best electrical conductors will experience a huge loss of power through carriage alone. This loss is calculated according to the formula P = I2 x R, where the power dissipated during the transport is directly proportional to the square of the intensity of the current carried. Thus it is observed that even in the case of using the best conductor that has an electrical resistance of at least 0.001 S, the calculation of the network loss shows that in the given situation for each transported megawatt, at least 100 kilowatts/second = 100 Kjoules are lost in the network in the form of the heat. This 10% loss will increase progressively, in proportion to the distance the electricity must be transported from the supplier to the user.
Unlike direct current, where increasing and decreasing voltage is extremely difficult, this change is extremely easy for alternating current, with the help of an electrical transformer. Thus, if we produce alternating current, we can raise its voltage from 100 V to 100,000 V immediately after production with the help of a transformer. Carrying the same amount of 1MW, at 100,000 V, the intensity of the network current will in this case be only 10 A, according to the form above, I=P/V = 106/105 = 10. And the power lost during the transport will be only 0.1 W according to the calculation form stated above (P = I2 x R) P = 102 X 0.001 = 0.1 W. Lowering of the voltage to “usable” values is done through successive transformer stations so that the transport of low voltages at which the losses become relatively high is done over the shortest possible distances.
The massive increase in electricity consumption led to the need to produce and transport more and more power, which led relatively quickly to the abandonment of industrial production of direct current in favor of alternating current, with Tesla finally winning the battle with Edison.
“Let the future tell the truth, and evaluate each one according to his work and accomplishments. The present is theirs; the future, for which I have really worked, is mine”
― Nikola Tesla
This is how it happens that although most devices, with some exceptions (electric motors – washing machines, refrigerators etc.), receive alternating current from the network, and their circuits operate inside with direct current obtained after the rectification of the alternating current.
Alternating current comes from sources that have alternating polarity, that is – one pole of the source is positive-negative-positive-negative, while the other pole is negative-positive-negative-positive etc. The frequency at which this polarity change occurs is the alternating current frequency and is measured in Hz (cycles per second). All household appliances are connected to the electrical network through a socket that delivers alternating current with a voltage of 220 V and a frequency of 50 Hz (in the USA the voltage is 110 V and a frequency of 60 Hz).
Accidental contact of a person with the household alternating current network produces electrocution, the parameters of the current allowing cellular depolarization.
Electrocution – definition cf. DEX – “the crossing of a living organism by an electric current of an intensity capable of causing injury or even death” (Fig. 9+/-10,11,12).
The risk of electrocution is one of the main risks associated with the use of alternating current and is inextricably linked to the configuration of the continuous change of polarity of the electric current. The intensity of the electric current carried in low-voltage networks (230 V) that are constantly used in the domestic environment and in medical facilities generally is 16-32 A. These values are 100-400 times higher than the approximately 100 mA required to produce ventricular fibrillation and death in case of accidental human contact with an electrical network that is not properly protected.
Beyond training staff to reduce risk exposure, a series of measures applied by electrical installation designers and also by equipment manufacturers exist today, in order to reduce the risk of electrocution. Among these, the most frequently used are the correct insulation of power cables and circuits, the creation of electrical networks with connection to the ground and the use of differential circuit breakers (fuses) (Fig. 10 – 11).
- Chapter II
II.1 RADIOFREQUENCY ELECTRIC CURRENT
Why is it necessary to know these notions and what is the importance of radiofrequency current in medical practice?
Alternating current with high frequency over 100 kHz does not cause electrocution of the patient due to chronaxy (the characteristic physiological time of excitability of each organ or tissue). Due to the rapid change of polarity in the case of radiofrequency current, the effect of tissue excitation cannot be practically obtained (Fig. 12).
Depending on the frequency, electromagnetic radiation behaves differently. At frequencies of hundreds of thousands of Hz, electromagnetic oscillations called “radio waves” are produced. Radio transmissions are based on the existence of radio waves (radio waves transmit the signal between the transmitter and the receiver antenna). For this reason the current with the frequency of hundreds of thousands of Hz is called radiofrequency current.
The effects of electric current on living tissue can be demonstrated using a cell between two electrodes as a model. Inside the cell there are electrolytes, positive ions (eg K+, Na+) and negative ions (eg Cl–);
- by applying a direct current to the electrodes, the positive ions will move to the negative electrode, and the negative ions to the positive electrode (plus and minus attract).
- if an alternating current is applied to the electrodes, during the time interval in which one of the electrodes is positive, the negative ions will be directed towards it. When the polarity changes, since the electrode becomes negative, the positive ions will be directed towards it while the negative ions will move away from it, approaching the other electrode, which has now become positive. A back-and-forth movement thus takes place, the positive and negative ions moving in the opposite direction to each other, alternately. This movement results in friction between the ions, and the friction generates heat.
At high frequencies (radio frequency) the cell will not have time to depolarize, so the electrocution phenomenon will not occur, the effects on the cell depending on the temperature reached under the action of the electric current.
|NOTE: the thermal effects on the cell depend only on the temperature reached, not on the method of producing the temperature increase.
II.2 EFFECTS OF HIGH TEMPERATURES ON CELLS
The effects are represented schematically in figure 13.
- Between 60-95 degrees Celsius, two different processes occur at the cellular level:
-> protein denaturation – there are bonds between protein molecules (hydrothermal bonds); these bonds break instantly at 60 degrees, but quickly re-form in a disordered manner; if the temperature drops, the restoration of the protein bonds forms a clot, in the process called coagulation.
-> dehydration (dehydration/ desiccation) – between 60-95 degrees Celsius the effect is dehydration, the cells losing water through the thermally affected cell wall; white coagulation is the result of a process similar to boiling the white of an egg – a homogeneous white clot; it has been shown microscopically that protein bonds are formed leading to the creation of a homogeneous gelatinous white structure (clot).
- Above 1000 Celsius, cellular vaporization occurs, the transition from the liquid state to the gaseous state, resulting in steam production. It causes a massive intracellular volume expansion that leads to the rupture of the cell membrane and the formation of a mixture of vapors, ions and organic material.
- Increasing the temperature above 2000 Celsius causes the molecules to degrade to caramelization (degradation of sugars) and carbonization.
The use of radiofrequency current in medical practice, especially in surgical disciplines, is based on the ability of protein denaturation, protein coagulation and vaporization – which translate into a coagulation/cutting effect of living tissue. In order for the effect to appear, the body must be crossed by the radiofrequency current, the thermal manifestation occurring in the place where the current density is maximum.
The maximum current density can be obtained in an area where contact with the tissue is made on a very small surface, therefore the instrument intended to cut or coagulate must be small in size (electric scalpel blade, Hook electrode). The current passing through the body will however be recovered by a plate electrode with a large surface area.
II.3 THE IMPACT OF HIGH TEMPERATURES ON TISSUES
Understanding the changes produced by coagulation and dehydration at the cellular level is critical to explaining the effects obtained at the tissue level by electrosurgery, both those of vascular sealing and those of cellular vaporization that explain electrosurgical tissue sectioning.
Tissue coagulation occurs through protein remodeling and cellular dehydration, the cell shrinking its size through water loss. Through dehydration, the tissue decreases in volume, the proteins denature and rearrange, forming a clot that seals the blood vessels, achieving hemostasis. Effects occur at temperatures between 600 and 950C.
Tissue sectioning – the active electrode determines in contact with the tissue a limited area of vaporization followed, by moving the active electrode, by the linear expansion of this area keeping the active electrode in a gaseous envelope generated by tissue vaporization. The effect occurs at temperatures above 1000 C.
Observations with a practical role, ignoring which can cause intraoperative incidents/accidents:
- The notion of radiofrequency “current” is not to be confused with the notion of radiofrequency “radiation” (radiofrequency electromagnetic waves);
- Electric circuits are crossed by electric current, and in the circuit crossed by a radiofrequency current appears an electromagnetic field around the current-carrying conductor, which propagates in the form of radio frequency electromagnetic radiation. The radiation can be picked up by another electrical conductor where the electromagnetic field will generate a radiofrequency current. This phenomenon is the basis of radio transmissions: the radiofrequency generator emits radio waves, the antenna of the radio receiver will pick up the radio waves that will generate a current in the antenna, the current will be picked up, amplified and processed, generating the sound signal (fig. 14)
PRACTICAL APPLICATION – error 1:
A laparoscopic electrosurgical instrument with a diameter of 5 mm and a length of 30 cm (eg hook electrode) is a transmitter, while another similar laparoscopic instrument in parallel with the first (eg. forceps) can act as a receiving antenna; operating the active electrode out of contact with the tissue will induce the appearance of a radiofrequency current in the second instrument that will damage the tissue with which it is in contact, a situation very similar to the diagram in fig. 14. It is very likely that such tissue injury will not be observed intraoperatively.
The same phenomenon also occurs between the electrical cables that cross the operating field, which is why parallel arrangement of these cables is not indicated when the operating device is prepared. The phenomenon is encountered especially in “single port” laparoscopic surgery, where the instruments are very close to each other.
- attention to cable layout and chaotic operation of the electrosurgery unit outside the field of view and/or when the active electrode is not in contact with the target tissue
• severe cardiac events such as arrhythmias can occur by similar mechanisms when instruments or their connecting cables cross the implantation site of a pacemaker
PRACTICAL APPLICATION – error 2:
If the operating electrosurgery unit is set for a certain power and the current drops, the generator will automatically increase the voltage to maintain the required power. Since impedance (resistance) increases by removing water from the tissue, keeping the active electrode (electroscalpel blade/electrode hook) in contact with the tissue beyond the point of dehydration will result in a progressive increase in tissue impedance, a decrease in current intensity, and a compensatory increase in voltage to maintain power set with the progressive degradation of the tissue until charring.
Conclusion: higher voltage means more significant tissue injury, therefore THE ACTION OF THE ELECTRIC SCALPEL SHOULD ONLY BE DONE FOR THE DURATION NECESSARY TO ACHIEVE THE DESIRED TISSUE EFFECT.
II.4 ELECTRICAL CIRCUIT OF MONOPOLAR INSTRUMENTS
Let us observe the following electrosurgery circuit: the radiofrequency generator with two output terminals, one terminal connected to the active electrode (electric scalpel, hook electrode) through a conductor (electrical wire), the second terminal connected to the plate electrode/dispersion electrode through another connector cable. The plate electrode is in permanent contact with the patient by bonding, the active electrode comes into contact with the patient when used by the surgeon. Therefore, the electrical circuit is closed through the dispersion electrode, connected to the second pole of the device.
The notion of a monopolar circuit, although established and entered into the current terminology, does not correctly reflect the physical reality because in fact the patient’s body is connected to both poles of the generator, to one pole by means of the electric scalpel and to a second pole by means of the plate electrode.
Since the current is alternating with a high frequency, the patient’s body is crossed by the electric current from the blade to the plate electrode, but also from the plate electrode to the blade, without the electrocution effect occurring.
Analysis of this circuit in an extremely short time interval shows the following: the current leaves the generator, crosses the conductor to the electric scalpel in contact with the patient, crosses the patient’s body to the plate electrode, is recovered by the plate electrode and conducted through the conductor to the generator. In this way the circuit closes; the current in this circuit being alternating (radiofrequency current) and not continuous, with the frequency of 200,000-500,000 Hz = 200-500 kHz, it will change polarity every 1/200,000 – 1/500,000 of a second.
Therefore, if we analyze the circuit over time, we will find that every fraction of a second, the direction of the current changes, the generator delivering the current to the dispersion electrode, the patient’s body is crossed to the active electrode, and then it returns to the radiofrequency generator through the active electrode conductor.
NOTE: the direction of the current changes very quickly, with a frequency of 200-500 kHz so that the patient’s body and the plate electrode are crossed in both directions by the electric current.
The idea of electric current flowing exclusively from the active electrode to the plate electrode is wrong. The neutral electrode terminology for plate electrode is also wrong.
Once the circuit is made, the intensity of the electric current is the same at any point in the circuit. In other words, the rate at which the electric current crosses the circuit is the same at any point in it.
Let us now consider the behavior of electric current when it crosses circuit areas with different sections (contact surfaces); the same current flow that crosses the contact area between the active electrode and the tissue will also cross the contact area between the plate electrode and the tissue. Let us now notice the important difference in surface area for the two contact areas: an extremely small area of contact between the active electrode and the tissue (could be about 1 mm²) and the contact area of the plate electrode, of 20×10 cm = 200 cm² = 20,000 mm² , i.e. 20,000 times more than the surface of the active contact!
We define current density (not to be confused with flow = intensity) as the ratio between current intensity and surface area. It is obvious that the current density for the same current value gets higher as the section of the circuit at that point gets smaller (Fig. 15a, 15b).
The effect of the electric current will be maximum at the level of the active electrode, although the same intensity of current passes through the patient’s body and the plate electrode, due to the very small section of the blade of the electric scalpel or hook in relation to the contact surface of the plate electrode.
The same current also flows through the plate electrode.
Since the surface current density is very low at the plate electrode level, the thermal effect at this level is negligible. If the surface area of the plate electrode is reduced, for example an electrode cut off or in partial contact with the skin, the current density increases because the current remains constant, but the contact area decreases (Fig. 15b).
The thermal effect is dependent on the current density, but also on the contact time. A prolonged contact time increases the degree of thermal injury, excessively dehydrates a tissue, increasing its impedance, thus forcing the device to deliver higher voltage to achieve the set power. (This is the law of radiofrequency current density.)
II.5 ELECTRICAL CIRCUIT OF BIPOLAR INSTRUMENTS (Fig.16)
For bipolar forceps, the circuit is different due to the particular construction of the working tool. This time, the working tool is a forceps similar to the anatomical forceps from classical surgery, which has each arm (jaw) separately connected to one terminal of the generator, and the arms (jaws) are electrically isolated from each other.
When the forceps grabs tissue between its arms (jaws), the circuit closes as follows: generator – cable – arm 1/tool jaw – tissue – arm 2/tool jaw – cable – generator.
Unlike the monopolar circuit in which the patient’s body is crossed by the electric current between the monopolar electrode and the plate electrode, in the bipolar circuit a small amount of tissue – the one caught between the arms of the instrument, is crossed by the current.
The same constructive principle is also used to make the bipolar forceps utilized in laparoscopic surgery.
It is important to note that in current electrosurgery generators all types of circuits are actually bipolar.
What differs is the shape, the destination of the electrodes (for monopolar the active electrode is the scalpel electrode, the Hook electrode with a very reduced section to obtain the desired effect, while the second electrode is represented by the plate electrode) and the amount of tissue between the two electrodes (in the case of the bipolar forceps – the tissue between the two jaws is included, and in the case of monopolar – the patient’s body is between the two electrodes).
At first glance both the monopolar electrode and the bipolar forceps connects to the generator through a cable. For the monopolar circuit the cable contains a single conductor, and for the bipolar circuit the cable contains two conductors. From the above description of the circuits it turns out that the bipolar clam does not need the dispersion electrode because the circuit closes directly between the jaws of the instrument.
Even if the electrical circuit closes between the jaws of the instrument, leading to the idea that only the tissue between the jaws will undergo thermal changes, in reality the thermal effect is also transmitted tot the neighboring tissue (lateral thermal injury) over a distance of a few millimeter. Moreover, if the effect of the tissue lengthens excessively, the tissue carbonizes, impedance (resistance) increases greatly, and the electric current will look for other ways of propagation – the most direct way is now the neghboring tissue that still has a good ability to conduct the current, so that it will also be subject to thermal effect, it will progressively dehydrate, thus extending the thermal injury area (Fig. 17).
To prevent this phenomenon, modern generators of electrosurgery have the ability to measure the opposite resistance of tissue to the electric current (impedance) during the action of the bipolar brush and modulating or interrupting the delivery of electric current when the ideal thermal effect has been achieved.
- Chapter III
The electrosurgery generator (ESU = electrical surgery unit) is the device that generates radiofrequency current for surgical purposes. It is connected tot the electrical network with a voltage of 220-240 V and a frequency of 50 Hz, common to the domestic applications. The generators can be set for certain working powers and for certaing working modes. Elementray ways of working are CUT and COAG. Intuitively, cut would suggest cutting effect, and COAG coagulation effect. In reality, things are more complicated: the devices also have an intermediate mode between CUT and COAG, called BLEND; they may have preselected levels for the CUT effect; may have submodes for COAG (soft, forced, spray); they can display the power in W or in increments, or they can provide complex information about voltage, power, working mode, suggested guidelines for the chosen working mode, customized programs for the operator or programs selected for categories/types of interventions.
The working principles presented here help understand the basic functions of generators, every user is required to fully understand the working mode of the generator they are using.
If there are several types of generators in the operator’s block, the personnel must be familiar with the correct operation of each.
The generators are coupled to the grid, they are turned on, the power and the way of working are set, the working instruments are connected (monopolar scalpel, plate electrode, bipolar clam); now the generator is ready to be used, but no current crosses the patient’s body. The surgeon orders the delivery of current to the patient manually (activates a button attached to the instrument) or using a pedal. There is a color code, always the yellow button/pedal will trigger the CUT current, while the blue button/pedal will trigger the COAG current (Fig 18). The time interval when the button/pedal is operated is called a work cycle.
Pressing both butoons/pedals simultaneously is considered an error and the device emits an alarm beep without delivering current to the patient.
III. 1 MONOPOLAR WORKING MODES OF THE ELECTROSURGERY UNIT
- CUT mode – high frequency current, with low voltage, the current is delivered throughout the operation of the control button/pedal (yellow color). Therefore, the current is delivered 100% of the work cycle: in other words, if the surgeon acts for 1 s, the patient’s body is crossed by the current for one second (Fig.19).
The cellular effect is vaporization, the macroscopic appearance is of net cut with minimal adjacent tissue injury.
|NOTE 1: The CUT module also performs coagulation on the section trench, but with little depth. Around the blade of the electric scalpel, through the phenomenon of vaporization, a vapor tire is created. If the speed at which the blade crosses the tissue is adequate, the blade is surrounded by vapors throughout the tissue crossing, also performing hemostasis; if the speed of the blade is too high, it will come out of the vaporization zone, the tissue effect being different and increasing the risk of bleeding.
B. COAG mode – by pressing the blue pedal, the electrosurgery unit will deliver a high-frequency and high-voltage current, the current being delivered only for a limited time (about 6%) of the work cycle (Fig. 20).
Therefore, when the pedal is pressed for 1 second, the current will be delivered for about 0.06 seconds. In this short interval, a rapid increase in tissue temperature occurs. The rest of the time, even if the button is pressed, the generator does not deliver electricity. During this time interval (94% of the work cycle) the tissue reshuffles after the short application of electricity, and the tissue temperature has time to decrease. Cellular and tissue changes are more extensive than in the case of partial CUT mode and due to the coagulation effect. The hydrothermal bridges between proteins are broken, the proteins are reconfigured and bind new structures – coagulum, the process being similar to the boiling of the egg white. The temperature developed in the tissue for this phenomenon to occur is more than 40 degrees Celsius, but below 100 degrees Celsius.
|OBSERVATION 2: Operating the circuit in COAG mode for a long time produces an increase in temperature, gradually achieving caramelization (approx. 200 degrees) and carbonization (approx. 400 degrees), and the tissue changes color becoming brown and then black, a sign that the correct coagulation time has been surpassed.
CONSEQUENCE 1: Since the greatest tissue injury is obtained in COAG mode, it is recommended to use mainly CUT mode set at the lowest power that provides the desired electrosurgical effect (usually 25-30 W).
The CUT mode ensures a low-depth coagulation on the trench as the working tension is reduced; as coagulation advances in depth, the impedance of the tissue increases and the intensity that crosses the tissue decreases.
In order to obtain a more efficient coagulation mode, but without the tissue damage generated by the COAG mode, electrosurgery generators can deliver a current with intermediate characteristics called BLEND mode (Fig. 21).
CONSEQUENCE 2: If we want a deeper coagulation at the level of the trench, the tension must be higher, which ensures better penetration of the tissue with an adequate current. BLEND mode offers these characteristics, the cut current form, but with higher voltage delivered in work cycles of 60-80% of the button/pedal operating range.
Therefore the BLEND mode is not a mixture of cutting current with coagulation current as the name would suggest.
III. 2 MONOPOLAR CIRCUIT AND THE PROBLEMS OF ITS USE IN ELECTROSURGERY (Fig. 22)
It is noticed that the circuit is interrupted with two electrodes located at a distance from each other (Fig. 23). The air between the electrodes is a pretty good insulator under certain conditions so we can consider the circuit open (the current intensity is zero, no current passes through the circuit). If, however, the voltage between the electrodes is quite high and the distance is small, the air between the electrodes will be ionized, with an electrical discharge being produced between the electrodes, the current crosses this space, being visible as a blue light. The flow of electric charges that cross the space between the electrodes is the electric arc. The electric arc phenomenon can be produced not only in the air (open surgery), but also in the environment of carbon dioxide (laparoscopic surgery). The phenomenon frequently occurs in nature (lightning, thunder), in the ignition system of cars equipped with gasoline engines (“spark” emitted by the spark plug), in piezoelectric lighters or in the ignition system of the modern stove. When using electrosurgery, the electric arc is obtained using the “spray” mode, in which the applied voltage is very high and the active electrode is kept at a short distance from the tissue, but without touching it. The phenomenon of ionization and electrical discharge (fulguration) obtained in spray mode achieves a phenomenon of superficial electrocoagulation, relatively extensive in the surface, useful in the hemostasis of diffuse bleeding.
|OBSERVATION 1: if the active electrode is kept at a short distance from the tissue, an electric arc can be obtained in the other working modes as well.
OBSERVATION 2: if the active electrode is in the vicinity of a metal element (clip, mechanical suture clip) an electric arc will be produced if the circuit is active (pedal – CUT/COAG button pressed); the metal element (clip, mechanical suture stapler) will heat intensely, being able to reach the melting temperature, and the thermal insult is remarkable.
THEREFORE, IT IS FORBIDDEN TO USE ELECTROSURGERY IN THE VICINITY OF METAL ELEMENTS OF MECHANICAL SUTURE, METAL CLIPS OR IN CONTACT WITH THEM.
OBSERVATION 3: the accidental activation of the electrosurgery circuit by operating the CUT/COAG button/pedal without the active electrode touching the tissue can create the conditions for the appearance of an electric arc between the active electrode and any metal element in the operating device, in contact with the tissue, but possibly outside the visual field captured by the video camera/telescope (trocar, telescope, vacuum cleaner etc.). Since the tissue can be any anatomical element located in the surgical perimeter, we can understand how an intestinal lesion, for example, can occur through this mechanism without being recognized/observed intraoperatively, but with the potential for subsequent manifestation – fistula, peritonitis.
Alternative ways of propagation of electric current in electrosurgery
When the surgeon activates the button/pedal of the monopolar electrosurgery circuit, the generator will deliver radiofrequency current with the desired current form (CUT, COAG, BLEND) at the set power. The current will choose the path with the lowest resistance. If the active electrode is in contact with the tissue, the circuit closes through the body of the dispersion electrode-probe with a thermal effect at the level of the point of contact between the active electrode and the tissue. This is the ideal circuit, but in practice there are other secondary ways through which the current can propagate; these pathways usually have very high electrical resistances, which is why they are not preferential pathways. The situation changes dramatically when the surgeon operates the electrosurgery unit without the active electrode being in contact with the tissue; in this case, the current will propagate using another pathway to close the circuit and if a secondary path is available, it will be used. It is important, then, to understand what these secondary pathways are and how they can generate accidents and intraoperative incidents.
There are at least two categories of secondary transmission pathways for radiofrequency electricity:
- Category I – radiofrequency current crosses components that can be assimilated to electrical resistances
- by accidental transmission (chaotic pedal drive, e.g.)
- by intermediate transmission – contact with other metallic elements/instruments
- by electric arc – explained above
2. Category II – the radio frequency current generates electromagnetic radiation received by another element that behaves as an antenna
- via capacitive transmission (capacitive coupling)
- by induction (by antenna effect)
Explanations for accidents/incidents caused by category 1 situations
These propagation pathways such as direct coupling (the active electrode touches the metal part of another instrument which in turn is in contact with the tissue, the thermic effect manifesting itself at this point of contact) are intuitive, easy to understand.
The explanation is simple – the electric current will propagate through the metal of the interposed instrument as through any other metal conductor.
The formation of the electric arc is easy to understand, moreover, the electric arc is visible!
What escapes the immediate perception is that if the electric arc is made between the active electrode and a metal clip, it will result in an increase in the temperature of the clip to the melting point, and the local thermal aid is stretched in surface and depth; if the metal element is part of a line of digestive mechanical suture, the result at the distance may be a fistula.
Explanations for accidents/incidents caused by category 2 situations
A. Incidents/accidents caused by capacitive coupling
For understanding the capacitive coupling (mediated by a “capacity” = capacitor), it is necessary to present the scheme and operation of a capacitor. A condenser (capacitor) is an electrical device consisting of two armatures (surfaces of conductive material), separated by an insulating/non-conductive area (dielectric), which can store an electrical charge (capacity) (Fig 24).
In the direct current circuit, the electric capacitor interrupts the electrical circuit, while in alternating current it will behave as a resistance that allows the passage of current (capacitive reaction Xc, measured in Ohm).
In the simplest form, a capacitor is represented by two metal plates separated from each other by an insulator (the insulator can be air or a solid material that does not allow the passage of electric current). This is a flat capacitor.
If we curve this trilaminar structure to obtain a cylinder, we will actually have a cylindrical metal reinforcement on the outside, a cylindrical reinforcement on the inside with a smaller diameter and an insulator between them. This is a cylindrical capacitor (Fig. 25).
Laparoscopic surgery, through the presence of tubular instruments and cannulas, offers numerous situations in which the association of metal trocar – electrosurgery instruments can constitute “capacitors” (Fig 26, 27).
PRACTICAL APPLICATION 1 (Fig. 26):
An insulated metal instrument in a 5 mm cannula:
– the outer reinforcement (cannula)
– interior reinforcement (metal instrument)
– dielectric (instrument insulation)
PRACTICAL APPLICATION 2 (Fig. 27):
An insulated metal instrument in a 5 mm cannula:
– the outer reinforcement (cannula), anchored to the wall with the help of a plastic fastener
– interior reinforcement (metal instrument)
– dielectric (instrument insulation)
It is important to understand how a capacitor in radiofrequency current can look and work because the phenomenon is counterintuitive, naturally the surgeon believes that an insulator (dielectric) between two metal plates interrupts the circuit, in reality things happen exactly the opposite – if he is not warned, he will never identify these ways of inadvertent transmission of radiofrequency energy and will be able to create risks for his patients; the surgeon will not recognize the incident at the time of its occurrence and will not even have an explanation at a post-factum evaluation.
B. Incidents/accidents caused by induction (by antenna effect)
For an unsuspecting practitioner, it is not possible to propagate the electric current between two isolated conductors at a short distance from each other, although, as we have indicated, this occurs in radiofrequency current through the antenna effect (Fig. 28).
III. 3 THE PROBLEM OF INTEGRATED USE OF THE ELECTROSURGERY UNIT AND THE RISK OF ELECTROMAGNETIC INTERFERENCE
The use of various electrically powered devices in the operating room exposes the patient to the appearance of electromagnetic interference. Their appearance can alter the correct functioning of devices affected by interference.
|HENCE THE NEED FOR A CAREFUL ANAMNESIS ABOUT THE EXISTENCE OF SUCH AN IMPLANTABLE ELECTRONIC DEVICE, BEFORE ANY SURGERY.
|SUCH A SITUATIONS WILL BECOME MORE AND MORE COMMON IN THE FUTURE.
Among the frequently used equipment, the most important effects, due to potential risks, involve the use of monopolar electrosurgery in patients who have implanted heart rate control devices – pacemakers or implantable defibrillators.
Besides these, patients can also have various other types of stimulants such as nerve stimulators or cochlear implants.
The effects of electromagnetic interference on heart rate control devices are variable and dependent on the intensity, frequency and shape of the signal wave generated by the energy source – for us, the electrosurgery unit.
In addition to these factors dependent on the electrosurgery unit, there are a number of variable circumstances that can more or less severely influence the heart rate control device:
- distance between the power source and the connections of the pacemaker
- how the stimulator’s connections are oriented in relation to the electromagnetic energy field
- interference can more severely influence a stimulator with malfunctions in operation or with the low battery, which may otherwise function seemingly normally.
|ALTHOUGH NEW GENERATION PACEMAKERS ARE GENERALLY SHIELDED AGAINST ELECTROMAGNETIC INTERFERENCE, THE RISK OF POTENTIAL INTERFERENCE WITH THE CORRECT FUNCTIONING OF THE DEVICE OR OF INJURY TO THE CARRIER PATIENT ALWAYS EXISTS.
Risk of ventricular fibrillation
The risk of ventricular fibrillation in the case of using monopolar electrosurgery is primarily determined by the possibility of intersecting the route of cardiac electrostimulation with the route of the electric current in the monopolar circuit between the active and dispersing electrodes (Fig. 29). It is considered that the risk of significant electromagnetic interference is about 20% in surgery of the supraumbilical region, 2.5% in interventions below the umbilical region and up to 68% in cardiac surgery.
For this reason, a set of rules on the positioning of the dispersion electrode in relation to the place of the surgical procedure exist today (Fig. 30 a-e).
Fig. 30 a-e Positioning of the dispersion electrode according to the premises of surgery in patients with a pacemaker
GLOSSARY OF TERMS
Usual nomenclature vs. correct designation:
plate electrode – not neutral electrode
plate electrode or dispersion electrode
electrosurgery unit – not electrocautery
radiofrequency electrosurgery – not cauterization
cauterization = direct transfer of heat from a high-temperature instrument to the living tissue
coagulation = alteration of the protein structure under the action of the increased temperature, regardless of the way the increase occurred
stray current = aberrant route of the electric current
inductive coupling = means of transfer of electric current in the absence of a direct connection to close the electrical circuit
capacitive coupling = means of transferring the electric current in the absence of an apparent connection to close the electrical circuit
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