INTRODUCTION
Endoscopic spine surgery is a constantly evolving field with new innovations and experiences causing paradigm shifts in the way spine pathologies are treated and giving unmatched results compared to previous open surgeries. One of the challenges in full-endoscopic interlaminar spine surgery is the initial soft tissue dissection and control of bleeding. This challenge can effectively be overcome with the use of monopolar electrosurgery. To our knowledge, there is no literature on the use of monopolar electrosurgery in full-endoscopic spine surgery.
Electrosurgery has gained popularity in recent years and is now the most widely used form of energy in both open and laparoscopic surgery. This can be attributed to its lower cost compared to other forms of surgical energy, widespread availability, and versatile applications [1]. The conception of electrosurgery began in the early 19th century when the French physicist Becquerel first used electrocautery. He described a nonalternating current to heat wire, which, when applied to tissue, had a hemostatic effect, i.e., cauterization. In 1881, D. Arsonoval pioneered the use of alternating current [2]. It was not until the late 1920s that collaboration between the physicist William T. Bovie and the neurosurgeon Harvey Cushing resulted in the predecessor of today’s electrosurgical unit [3]. This model was used until 1968, when a smaller model was developed by Valleylab, which has since produced today’s platform of electrosurgical units. These electrosurgical units are called diathermy [2].
PRINCIPLES OF ELECTROSURGERY
Diathermy is a surgical instrument that uses electrical energy in a controlled manner, causing targeted thermal damage to tissues. Often “electrocautery” is used to describe electrosurgery. This is incorrect. Electrocautery refers to direct current (electrons flowing in one direction), whereas electrosurgery uses alternating current. Modern-day electrosurgery is the utilization of alternating current at radiofrequency levels. During electrocautery, current does not enter the patient’s body. Only the heated wire comes in contact with tissue. In electrosurgery, the patient is included in the circuit, and current enters the patient’s body. Electrical current flows when electrons from one atom move to an adjacent atom through a circuit. Heat is produced when electrons encounter resistance. For current to flow, a continuous circuit is needed. In the operating room, the circuit is composed of the patient, the electrosurgical generator, the active electrode, and the return electrodes. The electrosurgical unit is the source of the voltage [3-5].
There are 2 types of diathermy circuits, based on the electrodes used. In a monopolar system, the active electrode has a narrow tip, and the return electrode has a wide area of contact with the patient’s body, completing the circuit. A monopolar system causes a wider area of thermal damage. In a bipolar system, the active electrode and passive electrode (diathermy forceps) are separated by a small distance. The current runs only through the tissue held between the forceps tips, causing minimal thermal damage.
Electrical energy is converted to heat in tissue as the tissue resists the flow of current from the electrode. Three tissue effects are possible with today’s electrosurgical units—cutting, desiccation, and fulguration [6]. Factors modifying electrosurgical tissue effects include current waveforms, power output, electrode size, activation time, tissue impedance, and eschar [7].
1. Current Waveforms
The final determinant of how tissue responds to electrosurgery is the current type. Electrosurgical units produce 3 different waveforms: cut, coagulation, and blend.
A pure cutting (vaporization) waveform is a continuous, low-voltage sine wave producing a very small arc of electricity. It causes rapid heat generation, boiling intracellular water and vaporization of tissue.
A coagulation waveform is an intermittent, high-voltage sine wave producing a large arc of electricity, causing a wide area of thermal damage.
A blend waveform is a modification of the cutting waveform. It consists of a combination of both cutting and coagulation waveforms of varying proportions.
A cutting current power setting must be between 50 W and 80 W to be effective. Ideally, the electrode is held slightly away from the tissue to create a spark gap or steam envelope through which the current arcs to the tissue. This spark gap results from heating up the atmosphere between the electrode and the tissue [8]. The coagulation current is effective with the power settings in the range of 30 W and 50 W [5].
There are 3 modes of coagulation: desiccate, fulgurate, and spray [5].
(1) Desiccate dehydrates and destroys tissue without sparking or cutting. Because the active electrode directly touches the tissue, more current reaches the patient. Desiccation causes the deepest necrosis and greatest thermal damage. It places the greatest demand on the patient return electrode.
(2) Fulgurate coagulates tissue by sparking from the active electrode, through air, to the patient tissue.
(3) Spray affords optimum fulguration; penetration is less deep, and the tissue area is larger than with the fulgurate mode.
In monopolar electrodes, radiofrequency current flows from the generator through the active electrode, into the target tissue, through the patient, and through the dispersive electrode, and then returns to the generator [8]. The most common site of injury is at the patient return electrode. The return electrode must be of low resistance with a large enough surface area to disperse the electrical current without generating heat. If the patient’s return electrode is not large enough or is not completely in contact with the patient’s skin, then the current exiting the body can have enough density to produce unintended burns. Excessive hair, adipose tissue, bony prominences, and the presence of fluid and scar tissue compromise the quality of contact. To avoid this type of injury, contact quality monitoring systems were introduced in 1981. This system inactivates the generator if a condition develops at the patient return electrode site that could result in a burn [2].
2. Power Output
As expected, the greater the current that passes through an area, the greater the effect will be on the tissue. A power setting of between 50 W and 80 W is recommended for effective cut mode, whereas a setting of between 30 W and 50 W is recommended for effective coagulation mode [9].
3. Electrode Size
With respect to electrode size, smaller electrodes provide a higher current density and result in a concentrated heating effect at the site of tissue contact. Reducing the contact area of the active electrode by a factor of 10 increases the current density by a factor of 100 without changing the power setting [10].
4. Time
The length of time a surgeon uses an active electrode determines the tissue effect. Too long an activation will produce wider and deeper tissue damage. Short activation time causes less tissue damage.
5. Tissue Impedance
Tissues vary widely in their impedance. Tissues with high water content, such as muscles and skin, pose less impedance to current flow. By contrast, scarred tissue and fat pose very high impedance [11].
UNDERWATER USE OF ELECTROSURGICAL INSTRUMENTS
Endoscopic electrosurgery is useful for treating tissue in cavities of the body and is normally performed in the presence of a distension medium. When the distension medium is a liquid, this is commonly referred to as underwater electrosurgery, this term denoting electrosurgery in which living tissue is treated using an electrosurgical instrument with a treatment electrode or electrodes immersed in liquid at the operation site. In spine endoscopy, normal saline is used as the distension medium.
USE OF MONOPOLAR ELECTROSURGERY IN SPINE ENDOSCOPY - OUR EXPERIENCE
1. Materials and Methods
We have used self-designed monopolar electrosurgery for over 2,000 full-endoscopic interlaminar spine surgical cases for initial soft tissue and muscle dissection. Patients with cardiac pacemakers were excluded from the study. We have used spray mode or cutting mode. Fulguration and desiccation modes also work but produce more thermal damage and carry more risk of burns. The deal power setting was determined by trial. We start with lower power and then increase it if necessary, depending on the machine used. Low input voltage machines require higher power settings compared to high input voltage machines. 50-W power in spray mode works well with most diathermy machines. We have used monopolar coagulation for initial exposure and dissection once the dura is exposed, we switch to radiofrequency (RF) coagulation.
2. Parts of the Monopolar Electrosurgery System
(1) The tip – monopolar tip is 0.8 mm in diameter, L shaped, noninsulated, and soldered to the shaft (Figure 1).
(2) The shaft – 3.5-mm diameter with insulation and a 30-cm shaft which can go through the endoscope. This configuration allows the use of the same probe with a discoscope and a stenoscope. This probe was custom-made by Om Surgicals, Mumbai, India (Figure 2).
(3) Connecting cable – female end connects to the shaft of the monopolar probe and the male end to the diathermy machine (Figure 3).
(4) Diathermy machine – any high-frequency monopolar diathermy can be used in either coagulation/cut mode. Coagulation mode is used in spray mode between powers of 50 and 60 W.
(5) Return plate – connected to the thigh of the patient. The thigh is the preferred area because of the short distance between the operating field and the plate. The thigh provides a large surface area for contact, minimizing the risk of thermal injury.
3. Temperature Variation
Use of electrosurgery generates heat. In full endoscopy, saline is used for irrigation. Saline medium dissipates the heat generated during electrosurgery, thereby minimizing collateral damage. We measured the temperature variation of the fluid used during endoscopy before and after the use of monopolar electrosurgery. The temperature of the normal saline fluid used was 27° centigrade. Post use of electrosurgery, the temperature rose to 30°C. This temperature is safe to use for spine surgeries without causing harm to the dura.
4. How It Works
Monopolar electrosurgery works as an active electrode and is used in the operating region, and a conductive return plate is secured on the patient’s skin. With this arrangement, current passes from the active electrode through the patient’s tissues to the external return plate. Since the patient represents the significant portion of the circuit, the input power levels have to be high (typically 150–250 W). This high power compensates for the resistive current limiting of the patient’s tissues. The electric junction between the active electrode and tissues is supported by wetting of the tissues by normal saline during endoscopic surgery. This ensures that the surgical effect is limited to the tip or the active electrode, with the electric circuit between the 2 electrodes being completed by the tissues.
Normal saline is the preferred distension medium in underwater endoscopic spine surgery. Although normal saline has an electrical conductivity somewhat greater than that of most body tissues, it has the advantage that displacement by absorption or extravasation from the operative site produces little physiological effect. The high voltages used in this application result in very low penetration of the electrosurgical effect, making it the only technique suitable to control bleeding from multiple small blood vessels. This electrosurgical instrument is useful in dissection, desiccation, vaporization, and coagulation of tissues and combinations of these functions. All these functions help in easy clearing of tissues and control of bleeding till we reach the ligamentum flavum.
Various diathermy machines that we have used are listed in Table 1.
The monopolar electrosurgery does not work with some low-frequency electrosurgical machines that have low input power, i.e., less than 150 V; for example, the CONMED SABRE GENESIS model with low input power (100 V). This machine lacks spray mode, which adds to the disadvantage.
DISCUSSION
Monopolar electrosurgery and its use in the surgical field have been well known and well researched. However, the use of monopolar electrosurgery in endoscopic spine surgery has never been researched. There is a misconception among surgeons that monopolar electrosurgery will not work in full-endoscopic spine surgery. This is true in low-power machines below 200 W; however, in high-power machines with >200-W power, monopolar electrosurgery works very well in endoscopic spine surgery.
Monopolar electrosurgery works by concentrating the current at the active electrode to produce the desired thermal tissue effect and dispersing it at the return electrode to prevent thermal injury. Reducing the radius of the active electrode by half can result in a 16-fold increase in thermal change without changing the power setting [12]. The monopolar L hook has a tip diameter of 0.8 mm, making it very effective under saline irrigation.
Electrosurgery can interfere with cardiac implantable electronic devices (CIEDs) such as permanent pacemakers and implantable cardioverter defibrillators. Such interference can damage or inhibit the CIED, burn the myocardium, or cause arrhythmias and asystole [13,14]. In these patients, it’s better to use alternative techniques such as radiofrequency/ bipolar electrosurgery.
We have used monopolar electrosurgery for 2,000 cases of full-endoscopic interlaminar endoscopy since 2018. The procedures included discectomy, decompression, fusions, para-percuteneous stenoscopic lumbar decompression, and excision of spinal cord tumor. We have used monopolar electrosurgery in the lumbar, dorsal, and cervical spines. We have used monopolar coagulation for initial exposure and dissection. Once the dura is exposed, we switch to RF coagulation. Monopolar electrosurgery is not safe over the dura or the roots. We do not use monopolar electrosurgery in transforaminal endoscopy for 2 reasons. Firstly, proximity of exiting nerve root. Secondly, there is limited soft tissue to clear during transforaminal surgery. The advantages of this technique are faster soft tissue dissection, decreased surgical time, and improved vision as it controls bleeding well. An experienced surgeon can clear soft tissues in less than 5 minutes using a monopolar probe in interlaminar endoscopic surgery (Figure 4). One major advantage of monopolar electrosurgery is in revision cases. The electrosurgery probe is extremely effective in going through the fibrous tissues in revision cases. Monopolar electrosurgery can be used to control bone bleeding also. The cost advantage of monopolar electrosurgery is because of 3 reasons. Firstly, monopolar probes are far cheaper than any other probes. Secondly, monopolar probes last longer than any other probes. Thirdly, the requirement of an RF/bipolar probe is greatly reduced when we use monopolar electrosurgery. High-frequency diathermy machines are routinely available in operation theatres. Even if one has to buy a diathermy machine, the cost of it will be covered by the cost of 2 RF probes.
The incidence of laparoscopic electrosurgical injuries is 2–5 per thousand procedures [15]. About 40,000 patients each year receive electrosurgical burns [16]. We did not encounter thermal injury in any patient of spine endoscopy.
Electrosurgical complications in spine endoscopy can occur from (1) active electrode injury by direct application/inadvertent activation/residual heat; (2) insulation failure – closely inspect the probe for any loss of insulation; (3) direct coupling – when the active electrode touches the cannula or endoscope; (4) return electrode injury due to poor contact.
Tips to avoid thermal injury are as follows.
(1) Correct placement of return electrode over the thigh with good contact over a wide surface area. Avoid metal patient plates.
(2) Use the lowest possible power setting, generally 50 W for most machines.
(3) Use only spray mode or cutting mode.
(4) Avoid activation of electrosurgery when the probe is touching the cannula or endoscope.
(5) Avoid monopolar electrosurgery once the dura is exposed.
(6) When not in use, keep the monopolar probe away from the patient on the Mayo trolley.
(7) Never use damaged probes and cables.
Monopolar electrosurgery helps in the control of bleeding, reduces surgical time and improves vision in full-endoscopic spine surgery. We did not have any complications due to monopolar electrosurgery. Comparative studies are required with other techniques such as radiofrequency, bipolar, and plasma in terms of time, blood loss, vision, cost, and complications.
CONCLUSION
Monopolar electrosurgery use in endoscopic spine surgery helps in quick clearance of soft tissues and excellent control of bleeding in full-endoscopic interlaminar spine surgeries. Monopolar electrosurgery is the most cost-effective ablation device available. There is a need for more awareness among spine surgeons to use this technique to its fullest potential and reduce surgical time and bleeding significantly to give a better patient outcome. However, all precautions should be taken to avoid complications.
PDF Links
PubReader
ePub Link
XML Download
Full text via DOI
Download Citation 
Print 
