Things You Should Know About Radiosurgery in Small Animal Practice
Jeff Mayo DVM DABVP MANZCVS (Surgery)
www.jeffmayodvm.com
Abstract: RF Surgery has been available for use commercially since the 1950’s. In the 1980’s high frequency RF in the range of 4.0 MHz was introduced and revolutionized this technology for veterinary surgery. These units have become popular for use not only in intricate procedures, but for general practice as well. Over the years, misinformation has spread about their use creating the potential for improper use due to a poor understanding of how they really work.
This presentation will discuss things you should know about radiosurgery use and how to apply them to common surgical procedures in veterinary practice in a safe manner to minimize patient morbidity and complications.
Topics:
(1) How does radiosurgery work? Does RF surgery cause tissue damage? How does it compare to electrosurgery?
(2) How does RF surgery provide sufficient hemostasis?
(3) What is that “grounding plate” all about? What does it do and how important is it?
(4) What’s new in equipment, including generators and hand-pieces for both cutting and hemostasis?
(5) Review of common procedures using RF surgery in Small Animal Practice
Introduction:
Electrocautery is a term often applied to electrosurgery or radiosurgery, but the terms carry different meanings. Electrocautery simply implies the transfer of heat, and is often done using a battery to generate heat through a piece of wire. The temperature generated is usually in the 60-90 degree Celsius range which results in desiccation and coagulation of tissue, turning the blood from liquid to a gel. This was common practice during the 1800’s using a hot iron in order to coagulate blood vessels and tissue during traumatic amputations. Radiosurgery by definition uses a direct current to generate a frequency of 4 MHz, which does not create the foradic effect on tissue, or depolarization resulting in the shaking of muscles during use, or possibly stopping the heart. This electromagnetic energy is converted to kinetic energy, and ultimately thermal energy which is enters the tissue to create the desired effect, or vaporization of tissues through the vaporization of intracellular water. Frequencies in the 4 MHz range have been found to generate the least collateral trauma on tissue. Higher frequencies are thought to lead to channeling, while lower frequencies increase collateral trauma to the local tissue.
1. How Does Radiosurgery Work?
Radiosurgery works by taking voltage from a normal 60V direct current power source and using a generator, this voltage is increased to approximately 4 MHz alternating current. This energy is delivered from a small tip on a hand piece where it is highly concentrated and travels through the body towards the dispersion pad. This energy is focused in the immediate area of the surgical site, and will disperse as it travels towards the dispersion pad to be spread out over a much larger surface area where there will be no effect. The intracellular water, which comprises about 60-70% of the cell, absorbs this energy and begins to vibrate. As the water molecule vibrates faster, heat and friction are generated to the point that the water reaches a boiling point generating steam as the cell explodes. Temperatures generated in the tissue from 50-60 degrees celsius result in cell death in a few minutes. As the temperature increases to 90 degrees Celsius there can be instant cell death with desiccation and protein coagulation from denaturation, and the cell shrinks. Blood will change from a liquid to a gel and hemostasis will begin to take effect. Once the temperature reaches 100 degrees celsius, the water in the cell boils resulting in a steam envelope around the tissue you are cutting, termed vaporization. It is important to stay with this steam envelope to minimize collateral trauma to the tissues. Temperatures beyond that and approaching 200 degrees celsius result in carbonization and caramelization of tissues with extensive collateral trauma, often seen with improper usage of carbon dioxide lasers. While older machines were incapable of cutting through fat, tissue-matching technology™ in the new Soniquence® RF unit can cut through fat layers with minimal resistance.
Energy is delivered to the tissue in duty cycles, or the percent of a unit of time that the current is passing through the patient. Shorter duty cycles result in higher energy being delivered to the tissue over a shorter period of time and result in carbonization of the tissue, limiting the distribution of the heat by shielding. The cutting mode is a sine wave, resulting in the cleanest tissue edge in which current is moving through the tissues 100% of the time. The coagulation mode is a 6% modulated waveform which produces a very high current over a short period of time. The blended mode is a 50% duty cycle which spreads the current out over half of the duty cycle. The percent modulation can vary with different waveforms offered by different units. These higher voltages are also what results in interference with other devices in the operating room.
2. Does Radiosurgery Provide Sufficient Hemostasis?
Coagulation in RF surgery refers to white protein coagulation in the temperature range of 50-100 degrees Celsius. Within the cell, there is rupture and random reformation of intracellular hydrothermal bonds. This process occurs in conjunction with cellular dehydration and desiccation, which is exploited to seal the blood vessel.
When making incisions using RF energy, historically it was that use of a mutated or blended wave would maximize hemostasis. The trade-off is that the tissue edges will be damaged and may result in delayed healing. The superficial coagulation and carbonization will insulate the tissue from more energy entering the tissue to provide a heterogeneous seal. Current theories suggest that we use a cutting mode which will produce a more homogeneous vessel seal as more energy can enter the local tissue area.
Hemostasis using traditional RF units is based on a lower frequency mutated wave being delivered through the surgical hand piece. The tissue is heated by the energy to a point of carbonization of the tissue and resultant seal of the blood vessel. The limitations of the vessel width are about 2 mm. Bipolar forceps utilized for this purpose require that the tips not be completely closed so that a spark gap is formed that will create a more efficient seal. There are RF generators on the market made specifically for this purpose and will measure the resistance of the tissue in order to optimize the seal up to a point of 7 mm, but this requires complete isolation of the blood vessel in order to maximize the effect. These dedicated units are expensive, and require costly hand pieces with limited reusability. Double seals are also recommended.
The current recommendations for RF devices are to use a cut mode for sealing a blood vessel. The reason behind this is that the coagulation mode will create a carbonization or char of the tissue that will insulate the energy from penetrating deep enough to seal the vessel. It is also recommended that the vessel be held in a forcep with just enough pressure to stop it from bleeding prior to making the seal. This process is called indirect coaptation. Soniquence® technology includes a bipolar mode that consists of a pure cut wave and the ability to achieve a much higher power output. Wet-field coagulation capabilities has improved hemostasis significantly with appropriate instrumentation and procedure.
3. What is that grounding plate all about? How does it work?
Historically, radio frequency generators were grounded to the patient during use using a metal plate that is supposed to keep the patient from being electrocuted. Safety issues were a concern when the generator would ground to other things in the operating room such as the table, or the ground resulting in patient burns. These plates worked best placed close to the surgical site, and on an area where there was little body fat. Burns could also result from the surface of the plate being scratched, or if there was a short circuit in the wire leading from the plate. As technology has improved, the current in the generator is now isolated which prevents it from grounding to something else, meaning that the current must return to the generator through a dispersive plate or it will not function. This prevents the patient from being electrocuted. Contact gel, or even wet towels are often used to improve this conductivity which in actuality could allow the development of burns. Newer technology from Soniquence® has led to the development of a rubber dispersive pad which requires no contact gel or other media. This reusable rubber dispersive pad may be though of as an antenna and does not need to be close to the surgical site to function appropriately in small animal procedures. Dispersive pads should not be placed close to other monitoring cable attachments on the patient to avoid coupling.
4. What’s new in equipment and hand pieces?
Radiosurgery requires a RF generator unit to bring the 60 Hz power at the plug up to 4 MHz. Historically, most generators were manufactured using very basic anode tubes and were adjusted using dials with relative numbers on them. These units create a significant amount of stray or scatter RF energy that can set off alarms on modern-day heart monitors and IV pumps. This stray energy also led to such clinical problems as delayed healing and failure to achieve the results of today’s technology. Newer radiosurgery generators contain more specialized modes of energy wave delivery to the tissue, the current is cleaner and more isolated, with capabilities of minimizing spread relative to the tissue being incised that has resulted in significant improvements in clinical results. Most modern-day generators are all digital in that controls are push button LED. Technology is controlled more by computer boards and upgradable firmware. These units also weigh significantly less than older technology yet generate significantly higher and cleaner power curves, an advantage appreciated by mobile surgical practices. All machines are now defined as dipole, meaning that the machine is one electrode, and the dispersive pad or other electrode defines if it is mono-polar or bipolar by wether the other pole of the current is the patient/dispersive pad or an instrument.
Modern day RF generators accomplish 3 things. First, they produce the 4 MHz power required for safe surgery. Second, they change the power relative to the unit of time, so if a unit is capable of 170 watts of power, remember that the relative power setting may only go up to 100. Lastly they change the duty cycle, or the percent time the unit is on during a given period. As technology continues to improve, the number of duty cycles or modes differs.
In veterinary surgery, some hand pieces are available in both consumable and reusable styles. The basic pencil-grip style still exists though has been improved significantly shortening the distance from the functional buttons to the tip. The tips have been modernized to decrease tissue adhesion, improve cut quality, and increase longevity. Many tip styles and shapes are available to fit the needs of the procedure at hand. Larger tips require higher power settings, as do other instruments with power settings increased proportional to the length of the instrument. Flat blade tips will have higher power densities when used on the side instead of the flat edge and provide some advantages over other tips for cutting tissue.
Significant advancements have been made in available hand piece devices to improve access to smaller areas and maximize cutting quality. Bipolar scissors are available that can cut and coagulate tissue simultaneously. Bipolar forceps are available in a number of sizes that can coagulate and cut tissue simultaneously to minimize surgical time and complications. Tissue can now also be shrunken using mutated waves and delivery devices in such areas as the nose and oral cavity.
5. Review of common procedures using RF surgery in Small Animal Practice
Skin tumors: It is of interest that historically, use of radiosurgery for skin incisions was frowned upon, citing literature that demonstrated that it led to higher infection rates and dehiscence of the surgical wound. These studies were completed using older technology and techniques that have been much improved upon today such as tissue-matching or the Soniquence smoothWave® technology that minimizes collateral spread of energy and improves incisional quality. It is now clinically accepted that radiosurgery provides for (1) cleaner incisions, (2) improved healing and wound strength, (3) less pain, and (4) improved cosmesis when applied appropriately to the skin incision. Loop electrodes are available for incisional biopsies or “curetting” out a tumor from narrow space areas.
In the dog, most benign tumors are lipomas, and most cancerous tumors (20%) are mast cell tumors. It is important preoperatively to know what type of tumor is involved in order to excise an appropriate amount of tissue and obtain a clean margin. Lipomas require minimal margins to remove, while mast cell tumors should include 1 fascial plane deep, and a minimal lateral margin of 2 cm for low grade tumors. Those located on areas difficult to close, such as below the knee or elbow, can be excised using a needle electrode, and covered with an appropriate local or free skin graft. In the cat, 90% of tumors are cancerous and should include a minimal margin of 2 cm, and up to 5 cm if an injection-site sarcoma is being considered as the diagnosis. Cat skin is thinner than dogs but can be grafted if care is exercised to develop the replacement flap.
Oral masses are seen much more frequently in the dog than cat. Unfortunately many are cancerous and potentially malignant and should be treated as such. Narrow-based tumors and those located in the lips or on the tongue tend to lend themselves to potentially complete excision using focused radiosurgery tips, both for cutting and hemostasis, along with well-planned grafts of skin from more local areas to replace or supplement missing mucosal tissue. Most canine melanomas are removable, while most feline oral squamous cell tumors are not.
Abdominal Procedures: As discussed above, skin incisions were historically frowned upon using radiosurgery, but evidence now exists that it is clinically acceptable. The skin incision should be preplanned prior to making it, with proper consideration given to (1) length, (2) depth, and (3) power setting and speed. Skin incisions should be slightly longer than the linea incision to better expose it for the laparotomy incision. Bleeding can be controlled using direct (touching a bleeder directly) or indirect (touching a clamp on a bleeder) and it is advisable to use the cutting mode for a constant power setting to avoid collateral trauma and skin coagulation. Either the needle tip or the blade tip may be used keeping in mind that the blade tip requires a higher power setting than the needle tip. The linea may be tented with a pair of forceps, a small incision made, then a cutting groove inserted to tent the linea and protect the organs underneath.
Most conventional and laparoscopic abdominal procedures in the dog and cat can be executed using radiosurgery. When performing the dog or cat spay, all incisions can be made with radiosurgery. Hemostasis can be achieved appropriately using direct or indirect coaptation supplementing transfixed sutures or with recently developed secondary instrumentation mentioned above. Liver and other organ biopsies can be effected using loop electrodes. Adrenal glands can be dissected out using bipolar micro dissecting forceps. Three-tie splenectomies can be performed using bipolar scissors and forceps to achieve control of blood flow and as supplementation to larger arterial flow ligations. As mentioned previously maximal hemostasis can be achieved by dissecting most of the fat away from the proposed area to coagulate, using a cutting mode to increase lateral spread of heat, and having a small gap between the ends of the forceps or turning the scissors sideways while performing the coagulum.
Airway surgery is becoming more commonplace in English and French Bulldogs. Frequently these patients come in with clinically evident snoring and stenotic nares, along with gastrointestinal problems. Acute respiratory failure may be evident during summer months due to excessive environment health. Oral examination often shows stenotic nares and advanced laryngeal collapse in the French Bulldogs, to include a thickened soft palate that may be evident on a lateral radiograph of the larynx, requiring a folded-flap palatoplasty. Everted laryngeal saccules are often evident, indicating stage I or higher laryngeal collapse. Tonsils may be swollen and exteriorized from their crypts.
All surgical procedures involving the airway may be performed using the basic instrumentation available with the Soniquence® radiofrequency unit. More advanced instrumentation is available upon request with the Soniquence® unit to enhance tissue ablation and removal of the soft palate with minimal collateral trauma and hemorrhage. Nare resection should be performed on the ventral aspect of the alar fold and the mucosal edges sutured together. The soft palate should be excised at the mid-to-caudal aspect of the tonsilar crypt. The tonsils can be excised and bleeding controlled with bipolar forceps. Everted laryngeal saccules can be shrunk using a blended wave and tissue ablation forceps, but tearing them should be avoided as it can cause inadvertent swelling requiring extended intubation or placement of a tracheostomy tube to stabilize the airway.
Rear-end surgery in the dog and cat includes such things as perianal tumors and hernias, and various urethrostomies to relieve urinary obstruction. Perianal tumors in the dog can be very bloody requiring the use of radiosurgery to cauterize as it cuts. Perianal hernias in the dog and cat might benefit from a colopexy prior to hernia reduction to improve clinical outcomes. Most perianal hernias can be supplemented with an internal obturator “roll-up” technique to protect the repair, as primary suturing is rarely sufficient. It is of note that the cat does not have a sacrotuberous ligament to support primary hernia repair. Both canine and feline urethrostomies can and should be performed using radiosurgery to improve hemostasis, incisional accuracy, and decrease clinical morbidity during recovery.
Safety Issues
“Plume” is the name given to the smoke generated by energized surgical devices. Much attention and concern has been given to it as of recent by nurses in human operating rooms as their use of radiosurgery can generate significant amounts of it. Analysis of the plume (human studies) has generated some cause for concern and led to more diligent use of the smoke evacuator during use of energized surgical devices. The plume content of veterinary-generated smoke has not been studied as of this writing. The general recommendation is to avoid inhaling it as it can cause irritation of the airways and produce a cough.
Oxygen, anesthetic gases, endotracheal tubes, and surgical preparation solutions containing alcohol can all contribute to fires in the operating room. Mistakenly, oxygen is thought to be combustible by some, but it should be considered an accelerant. The trapping of anesthetic gases and oxygen underneath surgical drapes can increase their concentrations in areas and increase the opportunity for them to ignite. Theoretically it is possible (though seemingly improbable) that trapped methane gases in the colon could present a problem during open abdominal procedures involving the colon and distal bowels, resulting in an explosion of fire, though this is more likely to be a problem with laparoscopic or endoscopic procedures.
Many doctors that have experience in the past using RF generators are aware that the units will interfere with various devices in the operating room such as IV pumps and older Doppler devices. This occurs due to a process called antennae coupling, which is the emission of energy from the RF device captured by another power cord or monitoring cable. Most of these devices are not adequately shielded, thus this stray energy is easily captured. You can demonstrate this using a light bulb by wrapping the hand piece power cord around the light bulb, it will turn on. None of this stray energy is considered dangerous to the patient. Antennae coupling can be sometimes be limited or stopped by the use of separate outlets for the RF generator, increase the separation between wires, avoid the wires running parallel to each other, utilizing lower power energy devices, or the use of a RF choke on the power code of the RF generator. Higher voltages during certain duty cycles can also interfere with other medical devices.
Very rarely, if you have a patient with a implanted cardiac device, RF surgery is not recommended on this patient. If hemostasis is required, electrocautery may be better suited, or the use of another non-electrical method of hemostasis. Patients with diabetes or liver disease, and procedures close to the eyeball should be avoided without advanced clinical experience.
In summary, radio frequency surgery is a mainstay in veterinary surgery. While many of the much older units are still in existence and being used in veterinary practice, many of them are no longer generating 4 MHz, their instrumentation is no longer available, and service is not being provided. Newer technology has greatly extended our capabilities to provide more advanced procedures to our patients. There have been significant improvements in technology that minimize potential complications, decrease patient morbidity, and will advance the average veterinary practice skill set.