The present day surgeon has a number of energy sources at his disposal, to help him to cut and coagulate tissues. These energy sources include electrical, laser, ultrasonic, and mechanical. Each of these has unique properties that determine its effectiveness and limitations when used during any kind of surgery, including minimally invasive surgery. The surgeon must realize that learning the use of a specific energy source, does not in itself practically lessen the chance of a complication. A complete understanding of the equipment, physics of the energy source, its potential hazards and limitations is essential, if energy source-related complications are to be reduced.
THERMAL TISSUE EFFECTS
Hyperthermia-induced tissue changes, start at, as early as 44°C in the form of tissue necrosis. Between 50°C and 80°C protein coagulation and collagen is converted to glucose. Between 80°C and 100°C, total desiccation of tissue occurs, and beyond 100°C, tissue is vaporized. With fulguration, when the temperature climbs to 200°C and above, carbonization starts and a visible black eschar can be seen (Fig. 1). The various energy sources utilized clinically, achieve varying degrees of hyperthermia. The ultrasonic wave achieves 80°C, the laser works at 200°C, and electrosurgery can achieve temperatures as high as 400°C. The final temperature acheived, however, also depends on the time that the energy source is applied to the tissue.
Hypothermia to −40°C and below, results in tissue freezing and in the postthaw period, there is vascular endothelial damage leading to thrombosis and cell membrane dysfunction. With temperature decreasing to −195°C below zero, there is intracellular and extracellular ice formation, leading to cell dehydration and shrinkage. With thawing, the melted extracellular water rushes inside the cell and the cell bursts.
- Electrosurgery uses an alternating radiofrequency current in the frequency range of 500,000 to 2 million Hz per second. The rapid reversal of this very high frequency alternating current means that ion positions across cellular membranes do not change. As a result, neuromuscular membranes do not depolarize, and there is no danger of muscle contraction or cardiac defibrillation at these high frequencies. On the other hand, household current, with its low frequency of 60 Hz can produce ventricular fibrillation and gives the typical shock.1,2
- The terms electrocautery and electrosurgery are often used interchangeably in modern surgical practice. However, these terms define two distinctly different electrical applications.3,4 Electrocautery is the use of electricity to heat a metallic object which then transfers the heat to the tissue helping to coagulate or burn, but, there is no current flow through the object being cauterized. In electrosurgery, the electrical current flows through the tissue and heats the tissue by the excitation of cellular ions.5,6
- There are 3 types of electrical currents in clinical usage:
- Direct current, which is unidirectional, is also known as galvanic current and is used in acupuncture and endothermy but not for electrosurgery.
- AC or alternating current where the flow changes in a sinusoidal fashion and is used in electrosurgery.
- Pulsed current where a high amount of electrical energy is discharged in a very short time. It is used for electromyography and nerve stimulation.
- Current flowing through the body takes the path of least resistance which in the human body means tissues with maximal water or in other words, the electrical resistance is in inverse proportion to water content of tissues. Thus blood is most conductive followed by nerve, muscle, adipose tissue and finally, least conductive is the bone. The path of the current in body tissues is not always a straight one. As soon as the current passes through a tissue it dries or it desiccates it, thus increasing its resistance and making it nonconductive. The current then takes the path through adjacent tissues which are still hydrated and thus have lesser resistance. Hence, the flow pattern of current through live tissue can never be predicted. Also this changing resistance of body tissues during the current flow requires that electrosurgical generators must deliver current at increasing voltages that should match the expected increase in tissue resistance of the human body, otherwise, current flow can be too low to produce the desired effect or too great, resulting in injury.
- The current density is an important variable determining the biological effect of the current and can be defined as amperes/area or amp/cm2. This explains why the pinpoint tip of an electrosurgical pencil works more effectively than a spatula. The less the area of contact, the more the density of the current at the point of contact and thus greater would be the effect (Fig. 2). Current flowing through the tissue raises the temperature of the tissue and generates heat. The amount of heat thus released is directly proportional to the resistance of the tissues.Fig. 2: Current density. Electrode 1 with a smaller surface area, generates current density more than under electrode 2, similarly the area of the ground pad, would determine the current density at its site of attachment. Larger surface areas for the ground pad are obviously better.
- The electrical current in electrosurgery can be delivered through two kinds of circuits. In the unipolar circuit, the ground pad (which is incorrectly called earth plate) takes the current back to the machine after traveling through the body.3,7 Thus it should be the aim to minimize the distance between the operating electrode and the ground pad. In the bipolar circuit, because both the positive and negative electrodes are near to each other, the current flow inside the body is minimal and is thus less damaging.
- Electrosurgical generator units (ESU) are essentially of two types: grounded and isolated (Fig. 3). The newer isolated generators eliminate the possibility of an alternate site burn by requiring the current to return to the generator.5,8 In the early grounded generators the current returned to earth via any contact point and thus caused inadvertent alternate site burns.
- Both the unipolar and bipolar circuits can further be modified as open and closed circuit. Open circuit is typically formed when the electrode does not make contact with the tissues or the tissue in contact with the electrode is already desiccated. In the circuit the resistance increases and generator increases the voltage to close the circuit and the waveform also becomes erratic. The current in closed circuit is safe and delivers lesser voltage.
- Coagulation and/or fulguration
- Cutting: True electrosurgical cutting is a noncontact activity in which the electrosurgical instrument must be a short distance from the tissue to be cut. If there is contact, desiccation leading to mechanical cutting rather than pure-cutting ensues. True-cutting requires the generation of sparks between the electrode and the tissue, which generates extreme heat which leads to cell explosion.
- Fulguration: In this mode also, there is a no contact between the electrosurgical delivery device and the tissue. In contrast to cutting, fulguration requires short bursts of high voltage only 10% of the time to produce sparks but a low power to produce coagulation. Coagulation and fulguration thus utilize higher voltage than cutting but the pause between current flows is more (maximum pause in fulguration). Both cause coagulative necrosis of tissues and fluid.
- Desiccation: Is the process by which the tissue is heated and the water in the cell boils to steam, resulting in a drying out of the cell. Desiccation can be achieved with either the cutting or the coagulation current by contact of the electrosurgical device with the tissue because no sparks are generated. Therefore, desiccation is a low power form of coagulation without sparking, and it is the most common mode used by the surgeon.
- The blend current: The pure-cutting current will cut the tissue but will provide poor hemostasis. The coagulation current will provide excellent coagulation but minimal cutting. The blend current is an intermediate current between the cutting and the coagulation current, as one might expect. In actuality, it is a cutting current–the duty cycle or time that the current is actually lowing during activation of the electrosurgical delivery device is decreased from 100% of the time to 80–50% (Fig. 4).11,12 It is important to note that setting the generator to blend mode does nothing to alter the coagulation current that is provided. Only the cutting current is altered so that the duty cycle is reduced to provide more hemostasis.
- Use in laparoscopic surgery: It was initially believed that the use of electrosurgery in laparoscopic surgery would have unique problems. The low heat capacity of the insufflating gas would result in instruments not cooling as rapidly as in the open environment. In addition the high-water content of the insufflated gas would increase the conductive capacity of the medium. But evidence does not substantiate these beliefs. However, laparoscopic application of electrosurgery has other problems, giving rise to unique complications.3,13
Injudicious use of the ESU in open and laparoscopic surgery can be associated with:
- Grounding failures
- Alternate site injuries
- Demodulated currents
- Insulation failure
- Tissue injury at a distal site
- Direct coupling
- Capacitive coupling
- Surgical glove injury
Ground pad failures: The large surface area of contact of the return electrode with the body and prevents injury by dispersing the current over a larger surface area. Lack of uniform contact, however, can result in significant current concentration and damage, and any conductive low resistance object can then serve as the alternate conduit.
Fig. 4: Difference between pure cut and pure coagulation current. Pure cut is a low voltage continuous current, while a coagulation current is of very high voltage in very short bursts. Blend mode—only the cutting current is altered so that the duty cycle is reduced (i.e. time off becomes more than on) to provide more hemostasis.
Exit of current at these alternate sites can produce injury because of the high current density.
The application of the ground pad to a body surface which is uneven results in inadequate contact and causes tissue injury. Thus the pad is best not kept under the scapulas, heels or other bony structures such as the skull. It is always safe to keep it under the buttocks or thighs or the calf muscles.
Demodulated currents: Modern generators have filters that remove demodulated currents so that only electrical current of 250–2,000 kHz is delivered. Demodulated currents occur most commonly when an electrosurgical instrument is activated off metal and then touched to the metal, such as the common practice of “buzzing a hemostat.” Demodulated currents produce neuromuscular activity that is usually of no significance unless directly coupled to the heart through a catheter or during a cardiothoracic surgical procedure. Another example of demodulated current is muscle fasciculation at the site of application during the use of electrosurgery.
Insulation failure: Insulation failure is thought to be the most common reason for electrosurgical injury during laparoscopic procedures and more commonly seen with high voltage coagulation currents. The key factor that determines the magnitude of injury from insulation failure resides in the size of the break in the insulation.5,14 Paradoxically, the smaller the break, the more the chances of it being missed and greater the likelihood of injury on contact with tissue.5,15
This is related to the concept of power density. Protection against insulation failure is provided by the active electrode monitoring system, available in many machines and which switches the current off, if there is an insulation failure.5,16
Tissue injury: Current passing through structures of small cross-sectional area may have current concentrated there, with resultant unintentional thermal injury. For example, if the testicle and cord are skeletonized and mobilized from the scrotum, application of energy to the testicle can result in damage to the cord, because the current must return to the indifferent electrode (ground pad) through the small diameter cord before it is dissipated in the body through numerous pathways. Another example is of cutting an adhesive band from the gallbladder to the duodenum with electrosurgery. If the adhesion is wider near the gallbladder than on the duodenum, the current density will be greater on the duodenum injuring the duodenum (Fig. 5).
Another inadvertent method of tissue injury may occur as follows. Reapplication of current near anal ready desiccated or fulgurated tissue may create an unwanted exit route through a small contact area, which builds up a high current density. The typical example is during electrosurgical distal tubal cauterization. Initial cauterization of the tube near the isthmus produces an electrical nonconductive tissue.
Fig. 5: Tissue injury during adhesionolysis. The attachment of the adhesion has a narrower duodenal attachment as compared to the gallbladder end; hence there is greater current density at the duodenal end of the adhesion. This translates into greater chances of duodenal injury.
Fig. 6: Tissue injury at distal site. Because the first application 1 desiccates the tissue and makes it nonconductive, thus the second cauterization site denoted as 2 can only disseminate current through the tip of the appendix or the terminal end of the tubes. This would damage the adjacent structure to these sites and would present as delayed cautery burns and if the current passes to an intestinal segment in the vicinity, then usually perforation results. So after cauterization at site 1 further cauterization should not be done at site 2.
If further application is done toward the uterine side, the current exits through the uterus and out of the body. But if the current is reapplied towards the tubal side, the current can only flow out toward the ground plate through the fimbrial end and if the fimbrial end is in contact with a bowel loop it sets up a thermal injury (Fig. 6).
The tissue injury can also occur with other freely mobile or small area structures near to vital structures, such as infundibulopelvic, uterosacral, ovarian ligaments and the appendix.
Direct tissue injury is easy to recognize and repair. Indirect gastrointestinal tract (GIT) injuries are usually missed at the time when they occur only to manifest 72 hours later when coagulative necrosis is complete. Thus the clinical presentation is always delayed and the patient then presents with peritonitis.
- Sparking and arcing: Jumping of sparks from the electrode to tissues is the mechanism for fulguration and true electrosurgical cutting. However, it can also occur in an unintended fashion such that injury results, especially in laparoscopic surgery. Current can jump from any place on the uninsulated end of the electrode or an area of insulation break and not necessarily only from the tip. In addition, build up of eschar, or desiccated tissue sticking on the electrosurgical instrument may promote arcing from the shaft instead of the tip of the electrode leading to sparking to a secondary site. However fortunately, sparking with monopolar electric current is small because, under normal operating conditions at 30–35 W, 50% of the time, the spark jumps only 2–3 mm, and this is not enough to allow significant air or CO2 gaps to bebridged. However, the tip of the laparoscopic instrument should always be kept clean.
- Direct coupling: Direct coupling occurs when an electrosurgical device is in contact with a conductive instrument which then conducts electricity.9,17 Direct coupling can be reduced by using only insulated instruments and careful attention to avoid contact with any metallic object in the operative field and activating the electrosurgical electrode only inside the visual field and never near another metal object such as a clip, staple, laparoscope, or metal instrument (Fig. 7).
- Capacitive coupling: Capacitance is stored electrical charge that occurs between two conductors which are separated by an insulator (Fig. 8)3,18.Fig. 7: Direct coupling. Accidental direct contact between the cautery connected Maryland dissector and 2nd instrument.The capacitively coupled current wants to complete the circuit by finding a pathway to the patient's return electrode. The charge is stored in the capacitor until either the generator is deactivated or a pathway to complete the circuit is achieved. Capacitive coupling is greatest in the coagulation mode when there is no load on the circuit (open circuit). Capacitive coupling is considerably greater through a 5 mm cannula than through an 11 mm cannula and greater through a longer cannula. Every object in the room, the surgeon, the patient, the operating table, all have a small but finite capacitance to earth. In context to laparoscopic application it must be remembered that compound cannulas (metal with plastic sheath) should never be used. Because when capacitative current is set up in a metal cannula it must logically exit through the abdominal wall but if the plastic sheath is in place it separates the cannula from the abdominal wall and the current can only exit when the cannula tip comes in contact with any intra-abdominal structure causing unrecognized injury. Hence, the cannulas should either be only metal or only plastic, where no capacitive current is built up. Another example of capacitance can be seen with excessive length of the cautery cord lying on the table and the surgeons hand or instrument comes in contact leading to minor shock to the surgeon (Fig. 9).
A large number of the above complications can be reduced by using the electroshield system which shuts off the generator in the event of an insulation failure, or if capacitative coupled current has been generated.
Fig. 9: Capacitive current because of extra length of ESU cord, which generates electrical field on the adjacent instruments.
The principal tissue effect achieved with bipolar electrosurgery is tissue coagulation through the process of desiccation. Bipolar electrosurgery can coagulate vessels up to 7 mm diameter%.5,19
In contrast to unipolar circuits, bipolar shows a 50% reduction in the overall amount of tissue damage, but requires more time. With the bipolar mode, there is reduced depth of penetration, less smoke is generated and the risk of perforation is less also decreased lateral spread.5,20 Another obvious advantage of bipolar over monopolar electrosurgery is the absence of a return electrode on the patient which eliminates the possibility of ground pad or alternate site burns, and capacitive coupling.3,21 In addition, it almost eliminates the risk of insulation failure. Finally, direct coupling can occur only if metal is grasped or placed between the electrodes in a bipolar circuit or extremely close to the electrodes. But the bipolar, too, has its share of problems. The visual appearance of surface coagulation may not correspond to actual full-thickness desiccation and thus there are chances that there may be over desiccation or under desiccation, both of which are problematic. As the outer layers of tissue desiccates, the resistance to current flow increases which results in lateral spread of current almost 3–4 mm and tissue heating over an additional 2–3 mm, in all directions, because of steam dispersion through tissue (Fig. 10).
With under desiccation the coagulation may cease before it is completed. This can result in bleeding. Inadequate coagulation canal so explain, in part, the occasional high rates of pregnancy following bipolar sterilization, where the tubes may be incompletely blocked.
Fig. 10: Bipolar current effects red area–extent of current flow (usual 3–4 mm), green area denotes extent of thermal effect (up to 3–5 mm). Lifting the tissues before current is switched on minimizes the thermal damage to underlying structures.
It canal so result inside wall injury of vessels both because of current and thermal effect. Thus retraction and lifting up of tissue from vital structures is essential. A significant problem with bipolar electrodes is tissue sticking. This can be reduced or eliminated by irrigation of the bipolar electrodes at the time of activation. The irrigant not only cools the electrodes but also the tissue, thereby minimizing conducted thermal injury. Nonelectrolytic solutions such as glycine or weakly electrolytic solutions work best.
This problem can be overcome by the use of an attached ammeter which denotes optimal desiccation indirectly by showing a cessation of current flow through that tissue. Under desiccation leads to obvious failure to achieve the desired effect.
Electrosurgery in patients with metal implants or pacemaker has to be used with care. Preferable mode to be used should be bipolar mode. In unipolar mode the ground plate should be as near to the site of surgery, as away from the implant or pacemaker, minimum time of activation and under electrocardiogram (ECG) monitoring, and care should be taken that the unit should be stopped on the slightest change in cardiac rhythm.
Do's and Don'ts
- Inspect insulation carefully
- Use lowest possible power setting
- Use a low voltage waveform (cut)
- Use brief intermittent activation versus prolonged activation
- Do not activate in open circuit
- Do not activate in close proximity or direct contact with another instrument
- Use bipolar electrosurgery when appropriate
- Utilize available technology, such as a tissue response generator to reduce capacitive coupling or an active electrode monitoring system, to eliminate concerns about insulation failure and capacitive coupling
- Maximum contact between body and ground plate preferably under gluteus, thigh or leg
- Do not use under bony structures such as scapula, heel or head.
Use of Electrosurgery in Laparoscopic Applications
A few safety precautions would be helpful:
- Use up to 30 W of power.
- Choose a smaller contact patch to achieve cutting and a larger contact patch to achieve coagulation.
- Use the thin wire electrodes to cut and the tissue has to be placed on tension to achieve cutting and for precise bloodless dissection.
- The foot switch or hand switch should be activated for short periods only. If the current is on long, the chance of remote site electrical injury is increased (in the event, there is an unrecognized insulation failure).
- If the surgeon observes blanching of tissue, a precursor of charring, too much power is being used. Charring should be avoided. In the liver bed, this will result in the liver tissue adhering to the electrode and, when the electrode is moved, it will tear the liver tissue.
Recent Technological Advances in Electrosurgery
With the development of newer generators and innovative instrumentation, better delivery of the appropriate amount of energy resulting in better sealing of vessels, can now be achieved by a number of methods.
Argon Beam Coagulator
Argon gas is an inert, noncombustible and easily ionized gas that is used in conjunction with monopolar electrosurgery to produce fulguration. Essentially, the electrical current ionizes the argon gas, thereby making a more efficient pathway for the current to flow because the gas is more conductive than air, therefore providing an efficient bridge between the tissue and the electrode. The plasma beam is conducted to the area of lowest resistance during fulguration. Thus, when it is used, rising resistance in desiccated tissue, beam will move to an adjoining area of relatively lower resistance result in more limited and uniform area of eschar formation. This eschar formed with ABC is more stable and depth of 2–3 mm coagulation is achieved depending on the power- and gas-flow settings.22,23 Since ABC is non-contact in nature, it ensures that the eschar created is not pulled away which normally occur with conventional diathermy. Also less smoke is produced with the argon beam coagulator. Despite these advantages, the argon beam coagulator suffers from on every significant drawback in laparoscopic surgery, namely, high flow infusion of argon gas into the abdominal cavity which not only increases the intra-abdominal pressure to potentially dangerous levels, but can also result in fatal gas embolism. The effect is obviously not seen in open surgery, where it is extensively utilized in hepatic resection or for hemostasis in any solid organ.22,23
Vapor Pulse Coagulation
A unique technology called vapor pulse coagulation (VPC) produces faster, more uniform results with pulsed energy instantly delivered in a controlled manner. The energy delivery device generates up to 200 W of radiofrequency output. The energy curve is sinusoidal, with variable amplitude between 320 kHz and 450 kHz. VPCs pulse-off periods allow tissue to cool and moisture to return to the targeted area, greatly reducing hotspots and coagulum formation. This technology also results in evenly coagulated target tissue, minimal thermal spread, less sticking, and enhanced hemostasis. This technology is only available in the Gyrus PK Tissue Management System with its own innovative generator, which works in tandem with the Gyrus PK instruments. The delivery device has several settings for different applications. For the current usage, it is set up for coagulation with an adjustable setting for maximum energy delivery. In addition, energy delivery has an integral pulse-off, making delivery intermittent and thereby allowing for tissue cooling and preventing desiccation. This, in addition to a bipolar mode, enhances its safety due to minimal lateral spread of energy.24
Smart Electrode Technology
The Surg Rx EnSeal System incorporates Smart Electrode Technology. The EnSeal instruments adjust dose energy simultaneously to various tissue types in a tissue bundle each with its own impedance characteristics. This electrode consists of millions of nanometer-sized conductive particles embedded in a temperature-sensitive material. Each particle acts like a discrete thermostatic switch to regulate the amount of current that passes into the tissue region with which it is in contact, thereby generating heat within it. To keep temperature from rising to potentially damaging levels, each conductive nanoparticle interrupts current flow to a specific tissue region engaged by the electrode region. When temperature dips below the optimal fusion level, the individual particle switches back on, reinstating current flow and heat deposition. The process continues until the entire tissue segment is uniformly fused without charring or sticking. Less heat is required to accomplish fusion, as the tissue volume is minimized through compression energy, is focused on the captured segment and the vessel walls are fused through compression, protein denaturation, and then renaturation.25
Modified Bipolar Electrosurgery
The Ligasure System or LVSS (Ligasure vessel sealing system) utilizes a new bipolar technology for vascular sealing with a higher current and lower voltage (180 V) than conventional electrosurgery. It uses a unique combination of pressure and energy to create vessel fusion. This fusion is accomplished by melting the collagen and elastin in the vessel wall and reforming it into a permanent, plastic-like seal. It does not rely on a proximal thrombus as the classic bipolar electrocautery. A feedback-controlled response system automatically discontinues energy delivery when the seal cycle is complete, eliminating guess work and minimizing thermal spread to approximately 2 mm for most LigaSure instruments. This unique energy output results in virtually no sticking or charring, and the seals can withstand 3 times normal systolic blood pressure seals vessels up to 7 mm.26,27 This system also requires a designated generator that works with several different specific instruments designed by the company.
Today virtually all laparoscopic procedures and many open surgical procedures can be performed safely and efficiently without the use of electrosurgery by utilizing ultrasound. Furthermore, ultrasonic surgery has also replaced mechanical surgical clips and scissors in many laparoscopic procedures.28
Physics of Ultrasound
- Audible sound waves are confined to the frequency range of 20 cycle per second (Hz) to about 20,000 cycles per second. A longitudinal wave, whose frequency is above the audible range is an ultrasonic wave. When ultrasonic waves are applied at low power levels, no tissue effect occurs, as is the case for diagnostic ultrasound imaging. However, higher power levels and power densities can be harnessed to produce surgical cutting, coagulation, and dissection of tissues. This involves mechanical propagation of sound (pressure) waves from an energy source through a solid, liquid, or gaseous medium to an active blade element (longitudinal mechanical waves).
- Ultrasonic dissectors are of two types—low power which cleaves water-containing tissues by cavitations leaving organized structures with low-water content intact, e.g. blood vessels, bile ducts, etc. It does not coagulate vessels and is used as cavitational aspirators for liver surgery and neurosurgery (Cusa, Selector) and high power systems which cleave loose areolar tissues by frictional heating and thus cut and coagulate the edges at the same time. High power systems (Autosonix, Ultracision) are used extensively, especially in advanced laparoscopic surgery. The harmonic scalpel and the AutoSonix system operate at a frequency of 55.5 kHz.
- Therapeutic ultrasurgical devices are composed of a generator, hand piece, and blade. The handpiece houses the ultrasonic transducer, as tack of piezoelectric crystals sandwiched under pressure between metal cylinders. The transducer is attached to amount, which is then attached to the blade extender and blade. The harmonic scalpel cools the hand piece with air while AutoSonix and Sonosurg systems rely principally on large diameter hand piece made of heat dissipating materials to remove the heat and prevent heat buildup.28,29
Ultrasonic Cutting, Coagulation and Cavitation
- The basic mechanism for coagulation of bleeding vessels ultrasonically is similar to that of electrosurgery or lasers. The difference is that with ultrasonic probes vessels are sealed by tamponading and coapting with a denatured protein coagulum by mechanical energy of the vibrating probe as opposed to thermal injury.
- Ultrasurgical hook, or spatula blade can coagulate blood vessels in the 2 mm diameter range without difficulty and the scissors can coagulate vessels up to 5 mm in diameter. Heat generated with the use of dissector is limited to temperature below 80°C. The overall temperatures achieved by the dissector, even after prolonged use, remains well below the 250–400°C achieved with electrosurgery and laser surgery. This results in reduced tissue charring and desiccation and also minimizes the zone of thermal injury. Skin incisions made with the ultrasonically activated scalpel or cold steel scalpel heal almost identically and are superior to electrosurgically made incisions. The minimal tissue damage may explain the marked reduction in postoperative adhesions to the liver bed following laparoscopic cholecystectomy with the ultrasonically activated scalpel, when compared with electrosurgery or laser surgery.
- Although coagulation produced by ultrasonic surgery is slower than that observed with either electrosurgery or laser surgery, nonetheless, it is as effective or even more effective, because despite the slower rate of tissue coagulation, the entire process of tissue coagulation combined with transection, the ultimate goal of surgery, is faster with the ultrasonic scalpel than with other energy modalities. However, greater depth of thermal injury can result with ultrasonic dissection ultrasurgery, as compared to electrosurgery, if activation of the probe persists for more than 10 seconds.
- The mechanisms of coagulation also offer an advantage for ultrasonic surgery over electrosurgery with regards to the sidewall of a blood vessel. Blood vessels are usually not coapted significantly by electrosurgery because of the concomitant reduction in power density. Furthermore, the blood within the vessels has a high heat capacity and acts as a heat sink, which allows one side to coagulate prior to the other, with resultant bleeding from a hole in the wall of the vessel that was in contact with the electrosurgical device. But with the ultrasonic shears the blood vessel can be gripped and then coagulated (Fig. 11).
- Absence of coagulated tissue sticking to the active element, because of the vibration of the active blade, is another unique feature of ultrasurgical coagulation compared with other energy modalities. In addition, the grasper blade allows unsupported tissue to be grasped and coagulated without difficulty, or cut and coagulated as with scissors.
- The cutting mechanism for the ultrasonically activated scalpel is also different from that observed with electrosurgery or laser surgery. At least two mechanisms exist. The first is cavitational fragmentation in which cells are disrupted. This occurs primarily in low protein density areas such as liver. This mechanism is utilized by the cavitational ultrasonic aspirating device (CUSA). The device is composed of an ultrasonic generator that vibrates at 23,000 Hz. When coupled with powerful aspiration device, the ultrasonic aspirator fragments cells and aspirates the resulting cellular debris and water. This action leaves collagen rich tissues such as blood vessels, nerves, and lymphatic intact. Thus, there is no cutting or coagulation with the ultrasonic aspirator. In marked contrast, the ultrasonically activated scalpel not only coagulates and cavitates, it also cuts high protein density areas such as collagen or muscle rich tissues. This occurs via the second cutting mechanism, which is the actual “power cutting” offered by a relatively sharp blade vibrating 55,500 times per second over a distance of 80 µm.
- A major advantage of the ultrasonically activated scalpel's coagulation ability is the absence of melting and charring of tissues. This allows the tissue planes to be clearly and sharply visualized at all times. The ultrasonically activated scalpel can also be used as a blunt dissector to aid in identifying tissue planes. However, the high power ultrasonic dissection systems may cause collateral damage by excessive heating and this is well documented in clinical practice. Ultrasonic surgical dissection allows coagulation and cutting with less instrument traffic (reduction in operating time), less smoke and no electrical current.28–30
(LASER: Light Amplification through Stimulated Emission of Radiation)
The laser beam is generated in a cavity (Fig. 12). By using a foot pedal, the surgeon has three options as to how the laser beam can be released from the cavity. The first mode is known as the continuous wave (CW) where the beam continues to be emitted at a steady rate. In the pulse mode (PW), the pulse is released for a limited period of time at a higher peak power and the Q switched mode where the energy is released in exceedingly narrow pulses in very high peak power. This type of laser is used frequently in ophthalmologic procedures and the power in these lasers tends to be measured in milliwatts. High power and short pulse duration are the hallmark of ophthalmologic lasers (Fig. 13).
Unique Properties of the Lasers (Table 1)
- First the light is monochromatic. The laser emits light over a very narrow, well-defined wavelength.
- Second, the light is coherent. Because of the properties of stimulated emission, laser light is perfectly in phase; that is each peak and valley of the sine wave curves align exactly.
Finally laser beam is virtually nondivergent (up to 1° of divergence), giving a highly focused beam.
Biophysical Principles of Lasers
The biophysical effects can be described as:
- Electromechanical: Dielectric breakdown in tissue caused by shock wave-plasma expansion resulting in localized mechanical rupture.
- Photothermal: Laser light generates heat which heats and vaporizes tissues.
- Photochemical: Target cells are induced by laser light to chemical reactions.
- Holmium laser vaporizes water inside the stone causing thermal expansion and calculus disintegration.
There are a number of types of laser available. The major types of medical lasers available commercially today, are all named after the medium in the laser cavity.
Laser Tissue Interaction
It depends upon:
- Power density
- Exposure time (3 types available) Q-switched, pulsed and cautious wave
- Absorption and scatter.
Depth of penetration denotes extinction length or the tissue thickness at which 90% of laser beam has been absorbed. The effect generated:
- Is directly proportional to the time of application more than the power rating.
- Is inversely proportional to distance from tissue.
- Some cooling at the surface of application results in lesser vaporization at surface and deeper penetration (blooming effect).
- Nd:YAG, CO2 and argon lasers.
- All three of the above lasers work fundamentally by thermal action. When tissue is heated by any of these lasers up to 60°C, there is no permanent or visible damage to the tissue. By 65°C, denaturation of protein occurs. The tissue will visibly turn white or gray and will disintegrate approximately 4–7 days later. This is the temperature range in which the Nd:YAG laser works. Once tissue has been heated to 90–100°C, there is tissue drying, some shrinkage, and permanent damage due to dehydration. Over 100°C, carbonization or blackening of tissue occurs. As the temperature rise continues, there is evolution of gas with tissue vaporization. This is the temperature in which the CO2 and argon laser works.
- Argon-pumped dye laser: The only laser system that does not work by the thermal cavity is combined with hematoporphyrin derivative. In this laser system, hematoporphyrin derivative is administered intravenously 48 hours prior to therapy. The hematoporphyrin derivative is concentrated within the tumor cells in preference to the normal cells in certain organ system of the body including the bladder. When exposed to the red light, the hematoporphyrin derivative is excited and cleaves oxygen to from singlet oxygen within the mitochondria, leading to cell death. This is a nonthermal effect.
- Excimer laser uses rare gas halides as the medium. It lies in the ultraviolet spectrum. Maximum usage in ophthalmology and laser angioplasty.
- KTP/YAG laser (wavelength 532 nm) is the green light laser. Potassium-titanyl-phosphate which is used to guide the beam of Nd:YAG laser is visible as green light. It is used in prostatectomy, and skin lesions.33
Visible and Invisible Lasers
- Visible lasers are located in the wavelength between 400–700 nm. Best examples are argon and KTP laser.
- Invisible lasers are located in the range of 700 nm or more. The best examples are Nd:YAG laser, carbon dioxide laser.
- Skin related—skin burn.
- Photokeratitis, skin malignancy
- Eye—thermal retinal damage, corneal burn and cataract.
High-Velocity Water Jet Dissection or Hydro-dissection
Pulsatile high-velocity high-pressure water or crystalloid jet dissection involves the use of relatively simple device, produces clean cutting of reproducible depth. In hydrojet technology very thin water jet produced which acts almost like a cutting knife. It requires a special hydrojet generator and produces high-pressure jet of between 20 BAR and 60 BAR. Water stream under high pressure (hydrojet) is used to facilitate tissue dissection and release adhesions. Other advantages are the cleansing of the operating field by the turbulent flow zone and the small amount of water required to complete dissection. A relatively hemostatic method which exposes the blood vessels or biliary channels, once parenchymal dissection has occurred, which can then be dealt with appropriately.34,35 Specific problems were identified with the use of this modality. The “hail storm” effect results in excessive misting which obscures vision. This has been solved to some extent by incorporating a hood over the nozzle. Difficulty in gauging distance and thus poor control of the depth of the cut are drawbacks. The spraying of tissue fragments also renders the procedure oncologically unsound. The present use of water-jet dissection is limited to dissection and resection of parenchymal organs, including liver, gallbladder, brain, kidney, prostate, lymphadenectomy and pleurectomy in thoracoscopic surgery and to cleaning wounds.34,35 Other uses include, in orthopedic surgery for cutting and endoprosthesis and bone, in dental use for cutting and grinding of dental materials, in plastic surgery for cleaning skin graft, removal of tattoos, and liposuction and for dermatological lesions. The fluid used can be combined with an anesthetic agent or an antibiotic to reduce the pain and prevent infection. Microwave water jet scalpel is another application of the water flow. It is used for minimally invasive removal or resection of tumors. It is a combination of a microwave scalpel and a jet system.
Radiofrequency (RF) ablation is a minimally invasive method that uses thermal energy to destroy tumor cells in organs such as the lung, liver, kidney, benign bone tumors, pancreatic cancer and also biliary cancer. The tumor is located by a computed tomogram or an ultrasound scan. Energy is then delivered through a metal tube (probe) inserted into tumors or other tissues, under ultrasound guidance. When the probe is in place, metal prongs open out to extend the reach of the therapy. RF energy causes atoms in the cells to vibrate and create friction. This generates heat (50–100°C) and leads to the death of the cells. However, temperature controlled RFA can also be used. The efficacy of treatment is assessed by CT scan one month following treatment. Retreatments are often necessary. Risks of the procedure include bleeding, although this is extremely rare. It also finds use in heart tissue to destroy abnormal electrical pathways that are contributing to a cardiac arrhythmia. Thus it is used in recurrent atrial flutter (Afl), atrial fibrillation (AF), supraventricular tachycardia (SVT), atrial tachycardia, multifocal atrial tachycardia (MAT) and some types of ventricular arrhythmias.
Recent advances in treatment of varicose veins include varicose vein ablation by RF delivered with the help of a thin catheter. So also nerve ablation can be done to reduce the chronic pain of arthritis or lower back pain. Chronic lower back pain (CLBP) is also an area amenable to RF. The causes of CLBP tend to be multifactorial. Arthropathy of the lumbar facet joints is thought to be a common etiology (15–45%). RFA of the medial branch nerve of the facet joint is a well-established treatment modality used to decrease facet joint pains. A wide range of temperature is being used (70–90°C) but the optimal temperature that provides the best patient outcomes with the least side effects is not well established in the pain management literature.36,37
An alternative means of producing thermal coagulation of tissue involves the use of microwaves (MW) to induce an ultra-high-speed (2,450 MHz) alternating electric field, causing the rotation of water molecules. Although the use of MV for tissue ablation is not new, the majority of the clinical experience with technique is with ablation of liver tumors. Percutaneous microwave ablation (PCMWA) was first used as an adjunct to liver biopsy in 1986, but it has since been used for hepatic tumor ablation. As with RFA, MWA involves placement of a needle electrode directly into the target tumor, typically under US guidance. MW energy spectrum ranges from 300 MHz to 300 GHz to produce tissue-heating effects. Each ablation also produces a hyperechoic region around the needle, similar to that observed with RFA. Unlike RFA, however, no retractable prongs are used, and the resulting ablation tends to be much more elliptical. For isolated, nonmetastatic lung tumors, surgical resection remains the treatment of choice. However, many patients are precluded from surgery due to poor cardiopulmonary function, advanced age, or extensive disease burden. For these patients, minimally invasive therapeutic options such as RFA, MWA, and cryoablation have emerged as possible alternatives. Tumor ablation of thoracic malignancies should be considered a viable treatment option for patients with early stage, primary or secondary lung cancers who are not surgical candidates or for patients in whom palliation of tumor-related symptoms is the intent. MWA is regarded as a particularly efficient option for the treatment of lung tumors since unlike RFA it does not rely on impedance to generate heat, rather electromagnetic microwave waves heat matter by agitating water molecules in the surrounding tissue, producing friction and heat.38,39
Cryotherapy uses the principle of rapid freezing and slow thawing of the tissue in multiple cycles. These temperature changes affect several intra- and extracellular mechanisms leading to cell membrane disruption and thrombi formation in the blood vessels inducing apoptosis and ischemia.40 Delayed effects include loss of microcirculation leading to anoxia and stimulation of cytotoxic T cells.41 The cryogens used are liquid nitrogen, nitrous oxide and liquid carbon dioxide. Liquid nitrogen has became the most popular cryogen as it is easily available, lack explosive potential, freeze tissue up to –197°C and predictable effect. The application is carried out through 3 mm or less probes. The application of ultracold liquid causes damage to the treated tissue due to intracellular ice formation. The osmotic gradient created by these crystals facilitates cell destruction by drawing water out of the cells. In addition, the cell membrane composed of lipid bilayer is also sensitive to hypothermia. During the cooling process, the membrane becomes highly permeable and allows mass transfers of ion, resulting in destructive changes in the ionic composition of the cell. The thawing process is the final step when the crystals dissolve due to increased temperatures, creating a reverse osmotic gradient. Water reenters the cells, causing swelling and rupture. Furthermore, it has also been hypothesized that freezing results in vascular injury by causing stasis in blood flow. The resulting ischemia causes cell death by necrosis. The degree of damage depends upon the minimum temperature achieved and the rate of cooling. The gas is then switched off once the desired temperature is achieved. The tissue is allowed to thaw which leads to the cell destruction by hemorrhagic infarction. The cycle of freezing and thawing may then be repeated, a process known as “double freezing.”
The uses of cryotherapy are esophageal premalignant lesion, bone tumors, hepatocellular carcinomas, precancerous condition of cervix, nephron-sparing kidney cancers prostate cancer, retinoblastoma and in the palliation of hepatocellular carcinoma (HCC) and liver metastsis.40–42 It is also widely used in various skin conditions such as skin cancer, actinic keratosis, warts, moles, skin tags, and solar keratosis. The application of cryotherapy can be in both by open and, laparoscopic surgery. Cryotherapy can also be applied as ice-pack therapy, cold spray anesthetics and whole body cryotherapy.
In present era, wide range of energy devices are available, which are appealing and also safe alternative for cutting, coagulation and dissection. Its use in surgical practice has increased the versatility of the surgical procedure and decreases operating time. The use of energy devices in surgical practice depends on the task, surgeon experience, availability and cost. Monopolar and conventional bipolar electrosurgery are used freely, as it has wide range of dissection capability and cost effective. Because among the most commonly used sources, there is no major difference among their results. The only reason to select one over the other would be the site of application and the requirement.
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