Hysteroscopy: Visual Perspectives of Uterine Anatomy, Physiology & Pathology
3rd Edition

Chapter 10
Lasers and Electrosurgery in Hysteroscopy
Robert D. Tucker
Michael S. Baggish
The use of energy devices, such as laser and electrosurgery, in hysteroscopy for the treatment of intrauterine disease allows physicians to control tissue destruction, decrease bleeding, and minimize patient discomfort. Regardless of whether laser light or electricity is used, the underlying mechanism is the heating of tissue to cut, coagulate, or ablate. Power supplies have become commonplace in open, hysteroscopic, and laparoscopic procedures principally because they provide a dry surgical field and reduce surgery time. Since energy sources have advantages and disadvantages, physicians need to become intimately familiar with the technology that they use to achieve the desired results without complications. Although the following sections discuss the basic uses of each technology, the reader is urged to read the manufacturer’s operator’s manual for specific details.
Lasers
History of the Laser
In 1900, the German physicist, Max Planck, developed the quantum theory, which described energy traveling in packets rather than by waves. In 1913, Niels Bohr postulated that the hydrogen atom had a number of orbits in which electrons rotate around the nucleus. The far orbits correspond to high energy states (unstable), and when electrons dropped from an outer orbit to one closer to the nucleus, a packet (quantum) of light was emitted called a photon. The process of stimulated emission of radiation was first described by Albert Einstein in 1917. Charles Townes became interested in microwave spectroscopy while working on radar technology during World War II. In 1957, Townes and Schawlow investigated the possibilities of making an optical maser and in 1958 published their data. Fox and Li and Boyd and Gordon further supported the work of Townes and Schawlow. In 1960, Maiman at Hughes Research constructed a ruby laser, and in 1961, Javan, Bennett, and Herriott invented the helium-neon laser. The carbon dioxide laser was invented by Patel in 1964. Since that time, many varied types of industrial and surgical lasers have appeared on the market. Virtually every specialty in medicine ranging from dermatology to cardiovascular surgery uses lasers.
Lasers provide an alternative energy source to electrosurgery. Although several wavelengths exist, the neodymium–yttrium-aluminum-garnet (Nd-YAG) laser has been used most often for operative hysteroscopy (Fig. 10.1). The reasons for this are as follows:
  • The Nd-YAG laser offers a high power range.
  • The laser energy is delivered to the operative site by quartz or silicone fibers ranging in diameter from 600 to 1,200 μm.
  • The wavelength penetrates all liquid media.
  • The laser provides excellent hemostasis; it is predominantly a coagulator.
The laser does not require conduction through tissue as do electrosurgical devices. Therefore, lasers can be used with any liquid or gaseous medium. Typically, when the laser is selected as an energy-emitting accessory for hysteroscopic surgery, saline is chosen as the distending medium.
What Is a Laser?
When external energy such as electrical current, light, or heat is applied to an atom, i.e., pumping, part of the energy increases the random motion of the atoms and part is absorbed, causing the electrons orbiting that atom to jump to a higher energy level. This unstable condition lasts for a very short time, and when the electron returns to the ground state, a packet of energy is emitted in the form of a photon (Fig. 10.2A). If the atoms are stimulated in a medium with parallel mirrors at either end, the photon will reflect back and forth between the two mirrors. As these generated photons hit other atoms in the unstable state, additional photons will be emitted from the atom as electrons drop back to their lower energy level. The additional photons will be in phase (i.e., flow in the same direction and frequency as the photon that initially struck the atom) (Fig. 10.2B). Continuing to put energy into these atoms will cause more and more photons to be discharged, thus creating a beam of light that has three characteristics distinguishing it from ordinary light:
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Laser beams are collimated, or parallel, which creates a minimal amount of divergence as the light is transmitted from its source; the laser energy is coherent (i.e., all of the waves are in phase); and the laser light is monochromatic (i.e., a single color).
When a partially transmitting mirror is placed at one end of the optical resonator, a portion of the laser light can be released from the chamber in a controlled fashion (Fig. 10.3). Thus, we have light amplification by the stimulated emission of radiation, from which comes the acronym laser (Tables 10.1 and 10.2).
FIGURE 10.1 A: The electromagnetic spectrum pictured here schematically illustrates the commonly used lasers in gynecology, including the argon and KTP-532, which operate in the visible blue-green and green; the helium-neon operating in the visible orange-red; and the neodymium-YAG laser, which is principally used in hysteroscopy and emits in the near infrared. The carbon dioxide laser, which is not useful in hysteroscopy, emits in the far infrared. B: The most commonly used laser for hysteroscopy is the neodymium-YAG laser. Pictured is a modern, compact, high-powered neodymium-YAG laser. The fiber measuring approximately 2 to 3 meters is coiled on a supporting arm of the laser.
FIGURE 10.2 A: Orbiting electrons are stimulated to a higher energy level (metastable). The atom remains in the unstable state for a very short time, since the electron quickly drops to a more stable orbit (arrows). B: When a photon is driven into an unstable atom, it drives the electron (stimulated) into an inner orbit and liberates two photons traveling in the same direction and with the same frequency as the incoming photon.
FIGURE 10.3 A: Schema of a laser tube or optical resonator. Gas is excited by high-voltage current or radio frequency waves. Photons traveling parallel eventually leave the partially reflected mirror as a laser beam (i.e., coherent light waves). These can be focused through a lens to a fine point to exert a surgical effect. B: The absorption patterns of the commonly used lasers in gynecology: CO2 laser is virtually completely absorbed by water; therefore, the laser beam will exert a surface vaporization action. The KTP-532 and argon lasers exert intermediate vaporization effects, being less absorbed by water (i.e., the light penetrates water and other liquids). The neodymium-YAG laser, which is principally a coagulator, penetrates water and exerts a coagulation effect deep in the tissue.
Although the carbon dioxide laser has been used for many applications in gynecology because of its excellent tissue absorption, this laser has no applications for operative hysteroscopy.
The argon laser was first developed for the treatment of diabetic retinopathy in 1965. This laser produces a visible blue-green light (488 and 515 nm), which is easily transmitted through clear aqueous tissues. Certain tissue pigments such as melanin and hemoglobin will selectively absorb argon laser light. The interaction of low levels of blue-green light with highly pigmented tissue results in coagulation of these pigmented tissues. The argon laser can be transmitted to tissue sites by way of fine quartz fibers and can efficiently be conducted through liquid media (Fig. 10.4). It is a highly effective system for endoscopic delivery. The KTP-532 (potassium titanyl phosphate) laser has similar characteristics to those of the argon laser but emits pure green light and has superior cutting features compared with the argon mixed wavelengths (Fig. 10.5).
TABLE 10.1 Lasers for Hysteroscopic Surgery: Physical Properties
Wavelength (nm) Color Spectrum Power (W) Absorption Aiming Beam
Argon 488–514 Blue-green 0–20 Hb1 melanin Argon
KTP-532 532 Green 0–40 Hb2 melanin KTP
Nd-YAG 1,064 Near infrared 0–170 Tissue protein Helium neon
W, watts; Hb, hemoglobin; KTP, potassium titanyl phosphate; Nd-YAG, neodymium–yttrium-aluminum-garnet.
The Nd-YAG laser is a solid crystal made up of yttrium, aluminum, and garnet (YAG) with surrounding neodymium (Nd). The Nd-YAG light emits in the near infrared region with a wavelength of 1,064 nm. The beam is transmitted through clear liquids, which allows its optimal use in water-filled cavities such as the eye, the bladder, and the uterus. Its absorption is not highly color specific as is the argon laser; however, the beam is efficiently absorbed by dark pigment. The Nd-YAG laser has a characteristic physical property of front scatter and penetrates deeply, resulting in a homogenous zone of thermal coagulation that may extend from 1 to 4 mm beyond the site of impact (Fig. 10.6). The Nd-YAG laser is an excellent tool for tissue coagulation and, like the argon laser, can be delivered through fiberoptic systems.
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Sculpted fibers have made it possible for an otherwise singularly coagulating device to become a focused cutting laser (Fig. 10.7).
TABLE 10.2 Lasers for Hysteroscopic Surgery: Clinical Features
Transmitted
by Fibers

Scattering
Passes
through Fluids
Penetration
(mm)

Coagulation

Cutting
Argon +++ + ++ 1–2 + ++
KTP-532 +++ + ++ ∼2 + +++
Nd-YAG +++ +++ ++ 3–4 +++ + (with sculpted tips ++)
FIGURE 10.4 A: An argon laser fiber is seen focusing on a myomatous mass. The blue-green beam can be clearly seen. B: As the laser is fired, an automatic shutter shields the eye of the operator, exposing only the red light. In fact, an intense blue-green scatter of light would make it almost impossible to see the image if the filter were not in place. C: The argon laser is fired initially onto a tongue blade. The blue-green aiming beam is quite apparent. The fiber, which extends approximately 1½ to 2 M, is coiled. This is a compact argon laser capable of attaining 20 W of power. D: A 600-μm fiber is inserted through the hysteroscope and will be used to cut the septum. Filter is not engaged. E: The automatic shutter has engaged, blocking the blue-green light waves as the laser beam cuts through the septum. Note the red hue.
FIGURE 10.5 A: A modern KTP-532 laser is combined with a neodymium-YAG laser. This laser can produce green visible or near infrared invisible light by the flip of a switch. B: Pure green light is seen traversing the quartz fiber of KTP-532 laser. This wavelength is almost completely absorbed by hemoglobin and therefore is excellent for coagulating vessels.
The holmium-YAG laser is a highly pulsed instrument that can cut tissues with minimal coagulation artifact when the fiber is maximally focused. When the fiber is defocused, the same laser is a superior coagulator. Holmium-YAG lasers have been used extensively in orthopedics but relatively uncommonly in gynecology (Fig. 10.8).
Tissue Effects
When laser light strikes an object including cellular tissue, it may be reflected, transmitted, scattered, absorbed, or a combination of these (Fig. 10.9). Because lasers are a special form of light, they obey all of the physical principles of light energy. The result when a laser beam strikes tissue depends on the wavelength, intensity, duration of the irradiation, and the type of tissue impacted (Fig. 10.10). To exert a biologic action, the beam must be absorbed.
Lasers can be used in a continuous mode, that is, allowing an uninterrupted stream of light energy to flow from the laser tube. This energy can then be focused or defocused by a lens system, thus altering the spot size (laser beam diameter). A larger spot size will diffuse the energy over a greater surface of the target tissue, thus allowing for less penetration. A focused laser beam, on the other hand, will concentrate the laser energy onto a very small area of the tissue, permitting deeper penetration. A deeper tissue effect can also be obtained by increasing the amount of laser light passing through the partially transmitting mirror (raising the power). Thus, the term power density best describes the quantity of laser energy absorbed per unit of tissue (Fig. 10.11). One can increase the power density by decreasing the spot size or by increasing the power that is transmitted from the laser. Tissue penetration is also controlled by length of exposure. If the laser is allowed to strike the tissue for a long time, the beam will penetrate deeper.
FIGURE 10.6 Typically, the neodymium-YAG laser produces front scatter with deep penetration into tissue. The longer the laser remains on the tissue, the wider the zone of coagulation.
The principal effects on tissue of the lasers used in gynecology are thermal (i.e., light energy is converted to heat). In many respects the thermal action of lasers and electrosurgical devices is identical. Cutting of tissue occurs when temperatures of 100°C are reached rapidly (i.e., vaporization or explosive evaporation) (Figs. 10.12 and 10.13).
FIGURE 10.7 A 1-mm ball-tip sculpted fiber. This bare laser fiber of relatively large caliber is ideal for endometrial coagulation and ablation.
FIGURE 10.8 A: The holmium-YAG laser operates between the neodymium-YAG wavelength and the CO2 wavelength. It is highly pulsed and an excellent cutting laser with very little coagulation effect when focused. When defocused, it produces excellent coagulation. B: The holmium-YAG laser beam is delivered by a fine fiber to the operative site. C: The uterine horn of the rabbit has been smartly cut by the holmium-YAG laser. Note the absence of char and the excellent hemostasis. D: Microscopic section of the crater produced by the holmium-YAG laser. Minimal thermal artifact is produced by this laser.
FIGURE 10.9 Laser light may be reflected, transmitted, scattered, or absorbed.
FIGURE 10.10 The action of a given laser on tissue is a function of its wavelength. Penetration is greater for the short wavelengths and diminishes at the long end of the electromagnetic spectrum.
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Laser Techniques
Fiberoptically delivered lasers such as the Nd-YAG laser exert varied effects depending on the position of the fiber relative to the target tissue. For cutting purposes, the operator should select higher powers (i.e., 50 to 60 W) and position the tip of the fiber perpendicular or nearly perpendicular to the tissue. The fiber should be in light contact or 1 to 2 mm above the tissue (Fig. 10.14). This permits the beam to create the smallest spot possible, minimizing divergence. If a sculpted fiber is available, a pointed type should be selected for cutting. The key for cutting such structures as septa, submucous myomas, adhesions, and polyps is high-power density on the one hand and controlled depth on the other. The time expended for fiber movement across the surface that is to be cut is as important as the power density in determining the depth of tissue penetration. The slower the motion,
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the deeper the penetration. The shutter of the laser is controlled by the foot pedal. When the pedal is depressed, the laser fires and will continue to discharge until the operator lifts his or her foot from the pedal, which stops the laser emission.
FIGURE 10.11 The quantity (watts) of laser energy interacting per square unit of tissue area (cm2) is referred to as the power density. The CO2 laser is most efficiently absorbed. The neodymium-YAG laser penetrates deeply and creates the greatest area of coagulation.
FIGURE 10.12 The neodymium-YAG fiber is seen cutting through an adhesion. Bubbles of gas are liberated as the ablation of the tissue occurs.
For more precise control, the operator can pulse the laser, either electronically or manually. Electronic pulsing permits intermittent discharges of laser light lasting for fractions of seconds. The width of each packet of light (expressed as waves) can be set at 10 to 100 milliseconds, and the interval between pulses can be adjusted for a number per second time span (repetition rate) (e.g., 300 pulses per second) (Fig. 10.15). Allowing intervals of tissue cooling between laser pulses results in cleaner cuts, less thermally induced tissue injury, and greater precision. This property represents a strategic difference between lasers and electrosurgical devices.
FIGURE 10.13 The adhesion is completely and bloodlessly cut by the neodymium-YAG laser, revealing an open cavity behind.
FIGURE 10.14 The effect of focused, partially focused, and defocused laser beams. When the fiber is held close to the tissue (focused), it creates a sharp cut. On the far right, the beam is defocused by holding the fiber away from the tissue and creating a wide superficial crater. Intermediate between the two extremes is a slightly defocused beam. The power density varies with the focus of the beam.
FIGURE 10.15 A: A pulsed laser creates periods in which the laser energy is on the tissue for a short period of time. The peak power of the beam is much greater than that produced by a continuous-wave laser. The duty cycle of most of these lasers is between 10% and 20%. B: Pulsing creates less thermal artifact because the tissue can recover from the thermal action of the laser between pulses. (A: From Baggish MS. Basic and Advanced Laser Surgery in Gynecology. Norwalk, CT: Appleton-Century-Crofts, 1985, with permission.)
Tissue coagulation can be produced by lowering the power density. This is most effectively done by pulling the fiber back from the target tissue, causing the beam to diverge. As the beam diverges, the laser spot increases in diameter. Additionally, power can be decreased to 50 W.
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Deeper coagulation can be obtained by holding the fiber away from tissue and dropping power density, while at the same time allowing the laser to discharge for relatively longer periods of time (seconds) (Fig. 10.16). In this case, as the laser penetrates the tissue, a sphere of heat forms and expands peripherally as the time period lengthens. Initially the higher temperatures are closer to the fiber but extend outwards with time. Temperatures of 50°C to 70°C desiccate the tissue and result in coagulation (slower action compared with cutting). Coagulation results in cell death and rather typical gross and microscopic changes. The gross changes are seen as whitening or blanching of tissue (Fig. 10.17A). Microscopically, the cells and nuclei are distorted (Fig. 10.17B). The stromal tissues take on a deeper eosinophilic stain. Blood vessels are thrombosed. Tissue sloughing occurs subsequently over a variable period of time following the acute event.
FIGURE 10.16 A side-firing YAG laser illustrates scatter of the beam when distance from the fiber increases.
Photodynamic Therapy
Dougherty et al. have described the use of hematoporphyrin derivative for the treatment of cancer. Patients with malignant tumors will selectively take up hematoporphyrin derivative when this drug is injected intravenously. Normal cells will excrete this material after a lapse of 72 hours. When laser light emitting at 630 nm is applied to cells containing hematoporphyrin derivative, singlet oxygen forms, resulting in cell death (Fig. 10.18).
Photodynamic therapy for neoplasms previously sensitized with hematoporphyrin derivative provides a new modality of treatment. The first case of hysteroscopic photodynamic therapy was reported by McCaughan et al. in 1985. Patients were given 2.3 to 3 mg of hematoporphyrin derivative per kilogram of body weight 2 to 6 days prior to photodynamic therapy. A tunable dye laser system using 20 W of argon power coupled with a rhodamine B tunable dye laser was used to provide a 630-nm light source. Malignant lesions involving the uterine cavity can be treated with this system, so long as one realizes that the penetration of the 630-nm light is limited to 1.5 to 2.0 cm into the tissue.
FIGURE 10.17 A: A myoma has been largely cut away by the neodymium-YAG laser beam. Only a small portion of the myoma remains intact and recognizable. B: A microscopic section shows tremendous coagulation necrosis and thrombosis produced within the myoma by the action of a defocused neodymium-YAG laser beam.
Safety Considerations
Hysteroscopic laser surgery presents certain risks that may not be considered with conventional hysteroscopic surgery. The YAG, frequency-doubled Nd-YAG, and argon lasers carry a risk for the doctor as well as the patient. Eye injury from backscatter following tissue impact is a danger for the surgeon (Fig. 10.19); therefore, use of special safety filters with the hysteroscope is mandatory. For the patient, the principal risk is occult damage to pelvic contents if the beam penetrates through the uterine wall. If the surgeon follows the principles of power density that have been outlined in this chapter, this risk should be kept to a minimum. The extremely thick muscular wall of the uterus provides a significant safety factor for the gynecologist when compared with other laser surgeons using similar laser energy in the bladder, bowel, or stomach. Although the safety record of hysteroscopic laser surgery to date has been good, more
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widespread use by inexperienced persons will cause the complications rate to rise. It is mandatory that all surgeons be trained by attending specific hands-on courses, in addition to thorough didactic instruction; surgeons must read the manufacturer’s manual and instructions prior to using the laser; and finally, prospective hysteroscopic laser surgeons should attend preceptorship programs sponsored by surgeons experienced in hysteroscopic laser techniques.
FIGURE 10.18 A photochemical response is produced by the administration of hematoporphyrin derivative. The derivative concentrates in cancer cells while being removed by normal cells. A pump-dye laser delivers light at 630 nm. This action creates oxygen singlet formation and destruction of the cancer cells while leaving the normal cells undisturbed.
FIGURE 10.19 A: Protective eyewear is used with lasers operating in the visible or near visible. The filters for each laser are different. B: A surgeon operating a holmium-YAG laser with protective goggles.
FIGURE 10.20 A: The touch technique allows the fiber to contact the endometrium, creating furrows in the tissue. B: The blanch technique allows the fiber to dwell above the surface, creating a whitening of the otherwise pink mucosa.
Summary
Recent technical advances in laser surgery combined with improved hysteroscopic techniques have provided a basis for a new horizon in hysteroscopic laser surgery. The Nd-YAG, argon, KTP-532, and tunable dye lasers have been used effectively in treating intrauterine disease via the hysteroscope. Ablation of the endometrium has proved to be an effective alternative to hysterectomy for patients with chronic menorrhagia refractory to medical and surgical therapy (Fig. 10.20). Hysteroscopic excision with lasers can be accomplished with substantial hemostatic benefits. Tunable dye laser therapy incorporating hematoporphyrin derivative has been shown to be effective in treating some forms of malignant disease. The future of laser hysteroscopy will be determined by the advances in laser biophysics as they are coupled to the needs of the practicing physician. The approach of laser hysteroscopy offers the advantages of simplicity and decreased costs. Physicians should become familiar with both the difficulties and the potential benefits of this technology.
Electrosurgery
Electrosurgery is the use of radio frequency (RF) alternating currents (AC) to cut and coagulate tissue (Fig. 10.21A, B). RF currents are supplied by a generator to an active electrode at the operative site, the current flows through the tissue at the site, tissue resists the flow of current, and heating occurs, producing the surgical effect. The current disperses through the patient and is collected by a return electrode, typically placed on the patient’s thigh or buttocks, and returned to the generator to complete the circuit; this is termed monopolar electrosurgery (i.e., one active electrode) (Fig. 10.22). Although most physicians refer to electrosurgery as electrocautery, the terms are not synonymous. True electrocautery uses a direct current (DC) battery to heat a wire that, in turn, heats tissue by conduction; electrocautery cannot cut tissue but rather can only coagulate. Electrosurgery uses alternating currents, supplied by a generator, that flow through patient tissue to both cut and coagulate.
History
Modern electrosurgery began in the late 19th century when d’Arsonval, a French physicist, demonstrated that alternating currents at frequencies of 2 kHz (2,000 cycles per second) to 2 MHz (2,000,000 cycles per second) could be used to heat tissue without causing muscle or nerve stimulation. At the turn of the century, surgeons such as Riviere, Clark, and Doyen were routinely using RF currents in treating intractable ulcers and removing benign and malignant tumors of the head, neck, breast, and cervix. Endoscopic electrosurgery was pioneered by Edwin Beer; in 1910 he reported the use of high-frequency sparking delivered through a cystoscope to destroy bladder tumors and growths at the bladder neck.
By the mid-1920s, the medical literature contained many reports on devices for RF current cutting, coagulating, and ablating of tissue. However, it was not until the collaboration
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in Boston of William Bovie, an Assistant Professor of Physics at Harvard, and Harvey Cushing, Director of Neurosurgery at Peter Bent Brigham Hospital, that a machine capable of both cutting and coagulating was commercially produced. Their work, published in 1928, described desiccation, cutting and coagulation using RF currents and led to the acceptance of the technology by many surgeons.
FIGURE 10.21 A: An active electrode (AE) conducts electric current (I) to its terminus at which point an arc (F) is discharged, producing a temperature >100°C. The tissue is vaporized. The current passes through the tissue (G) and returns to the generation via the neural electrode (NE). (Courtesy of ERBE USA.) B: Radio frequency (RF) currents are those that exceed 100,000 cycles per second. Electrosurgical generators operating at frequencies >100,000 cycles per second are called RF generators. (Courtesy of ERBE, Tubingen, Germany.)
FIGURE 10.22 A: Monopolar current travels from the generator through an electrode and then is conducted through the patient, usually via large blood vessels, to a return electrode (ground plate) and back to the generator. B: A patient with a return electrode appropriately attached to the thigh. (Courtesy of Everest, Minneapolis, MN.)
Improvements made over the last several decades have increased electrosurgery utility and safety, thereby reducing patient complications. These improvements include solid-state
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isolated generators with specialty outputs, return electrode monitoring, and many procedure-specific electrodes.
Biophysics of Electrosurgery
Electrosurgical Variables
Although a complete description of electrosurgery is beyond the scope of this chapter, we will discuss the important variables and their effect on tissue. For a more complete discussion of the topic, the interested reader should refer to Pearce (1986) for a discussion on engineering aspects and Wattiez et al. (1995) for a discussion on clinical aspects.
Current Density
Current is the flow of electrons or ions over a period of time. This current enables electrosurgery to heat tissue and produce cuttings and coagulation. As the current flows through the tissue, the tissue resists the flow, resulting in tissue heating. If heating is rapid and >100°C, vaporization of extracellular and intracellular water occurs, thereby producing a cutting or vaporization action with little coagulation effect. If heating is slower and at temperatures <100°C, tissue desiccation occurs, producing coagulation. The current is measured in amperes (A); typical multipurpose generators can supply approximately 1.0 A of current operating in the monopolar mode.
Current density is one of the most important variables affecting the clinical outcome and is directly under the control of the surgeon. This variable is defined as the RF current (I) that flows through a specific cross-sectional area of tissue (a) (i.e., I/a). Current density can be controlled by the choice of electrode size and the contact areas between tissue and the active electrode.
Tissue Resistance
As current flows through any material, there is a resistance to the flow that is characteristic of the material; the amount of resistance is measured in ohms. In the case of tissue, the resistance is inversely proportional to the electrolytic content. Therefore tissue such as liver, which has a high content of blood, has a low resistance, whereas fat has a high resistance. Typical tissue resistances are as follows: blood, 30 to 50 ohm/cm; muscle, 200 to 400 ohm/cm; bowel wall, 150 to 250 ohm/cm; and fat, 800 to 1,000 ohm/cm. During cutting and coagulating, these values do not remain constant; for example, initially the tissue resistance may be 200 ohms, but after a few seconds of electrosurgical desiccation, the value may rise to 1 to 3 kohm. Tissue resistance is very important in determining where current flows through tissue because current follows the path of least resistance.
To be correct, the term resistance applies only to direct current flow. For alternating currents, the term is impedance; which consists of two components: magnitude and phase angle. This is a result of tissue having membrane capacitances, as well as resistance. At electrosurgical frequencies, the phase angle values are small, and simply using resistance measurements introduces only small errors.
FIGURE 10.23 A: A Valley Laboratories generator operating at approximately 500 kHz. B: An ERBE generator operating at approximately 350 kHz.
Voltage
Voltage is the amount of work a generator must perform to force the current through the resistance of the tissue. For example, high voltages are necessary to force current through high-resistance tissue such as fat. If the procedure is performed with the electrode in contact with tissue, higher voltages also produce deeper thermal effect in the tissue. Generator voltage alternates from positive to negative at the operating frequency of the generator. The frequency varies from manufacturer to manufacturer and among models from a given manufacturer. However, in general the frequency is designed to be from 350 kHz to 3 MHz (Fig. 10.23).
Generator voltages are measured in volts (V), and multipurpose generators produce maximum peak-to-peak voltages (Vp-p, measured as the value from the maximum positive value to the maximum negative value) from 6 to 10 KV. Most older generator output voltages are not constant, but rather, vary as the tissue resistance varies; however, new generators, controlled by microprocessors, are able to control their voltage and hold the voltage constant to a specific value over a wide range of resistance to achieve their desired surgical effect (Figs. 10.24 and 10.25). Typically, the highest generator voltage output is achieved when the generator is activated in the open circuit condition with the electrode not in contact with the tissue.
Power Density
The power output of the generator is controlled by the front panel setting. The higher the generator power setting, the higher the generator output voltage. The
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amount of heat produced by RF current flow in the tissue is directly proportional to the power (measured in watts) dissipated in the tissue. Power density (P) equals the current density squared times the tissue resistance, or P = (I/a)2R.
FIGURE 10.24 Ordinary electrosurgical generator voltages vary. Initially the voltage is high, but as resistance increases it drops. (Courtesy of ERBE, Tubingen, Germany.)
This relationship has important implications in surgery. If current is confined to flow in a small cross-sectional area such as an adhesion, the power dissipated as heat in the tissue can be extremely high. Conversely, current applied by a small active electrode and allowed to disperse throughout a large volume, such as coagulation on the liver, produces only localized heating as the current quickly spreads over a large cross-sectional area from the application site.
Although both of these examples are true on a macroscopic level, the analysis does not adequately describe the microscopic power dissipation. Consider the coagulation of a bleeding vessel on the liver surface. Since current follows the path of least resistance, the blood vessel carries most of the initial current; however, since the resistance is low, little power is deposited. If the vessel bifurcates or decreases in diameter, the resistance increases and heat is dissipated. As tissue destruction occurs, resistance increases, causing further power dissipation and destruction. Finally, the resistance level becomes sufficiently high that current flows to other paths. Microscopically, this event can be seen as perivascular damage surrounded by normal tissue. Such submillimeter changes are not clinically important and only aid in distinguishing electrosurgery damage from other causes.
This relationship is also seen in the surgeon’s selection of electrodes. Small area electrodes, such as needles, will produce high-power densities and thus high heat, yielding cutting action or vaporization of tissue. Using the same power, a larger area electrode produces significantly less power density and lower thermal effect, creating a desiccating action. It should be noted that the choice of generators can also affect the power density. Older generators set at a given power level will vary power output with changing tissue resistance, and therefore power density will change over time. Many newer generators with computer control of the output can maintain a near-constant power with changes in tissue resistance, giving the surgeon more consistent feel and surgical effect over a wide range of tissue resistances.
FIGURE 10.25 A constant-voltage generator, such as that pictured in Figure 10.23B, regulates voltage continuously by an onboard computer. As can be seen in this diagram, the voltages remain constant. (Courtesy of ERBE, Tubingen, Germany.)
Energy
The time (t) that current flows through the tissue multiplied by the power level is defined as the energy (E) delivered to the tissue: E = Pt, where E is measured in joules (J). Substituting the power density, (I/a)2R, the energy dissipated in the tissue becomes (I/a)2Rt. Although total energy delivered to the tissue is proportional to thermal necrosis, the time course of power delivery is also important. For example, for a given electrode area, 1 W delivered over 40 seconds (40 J) will cause less destruction than 40 W delivered over 1 second (40 J). However, variables such as blood flow also have significant effects on tissue necrosis, and, in the above example, power at low levels delivered over a small area, as by a needle electrode, can cause tissue destruction.
Summary
RF electrosurgery analysis is complicated by variables changing rapidly with each cycle of the generator operating frequency; these changes occur in the microsecond time frame, making cellular microscopic analysis extremely difficult. Although no single variable dominates the phenomenon, macroscopic analysis over time periods of
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1 or more seconds can be made by considering the variables discussed. It must always be remembered that the surgeon controls most of these important variables: voltage by generator setting, power density by both the generator setting and the choice of electrode area, and energy by power density and application time.
Electrosurgical Waveforms
Waveforms vary their voltage and current characteristics over time, thereby presenting different surgical effects. In general, cutting action is produced by rapid heat >100°C, which vaporizes water and explodes cells, whereas coagulation is produced by heating at temperatures of 60°C to 100°C. Coagulation can be produced by desiccation, in which the active electrode is firmly in contact with the tissue, or fulguration, in which the electrode does not touch the tissue, but rather, sparks jump from electrode to tissue. Waveform names (i.e., cut and coagulate) are misnomers because low-power settings of the cut waveform produce excellent contact desiccation and high-power settings of the coagulation waveform produce cutting.
Pure Cutting
In general, most generators use a sine waveform for the pure cut setting (Fig. 10.26A). The generator voltage causes ionic breakdown of air and produces small arcs over the short distance from the active electrode to the tissue; these arcs yield high current density and high tissue heating for tissue vaporization. If the active electrode is placed in contact with tissue, cutting will not be initiated until the tissue is desiccated and slightly shrinks from contact with the electrode; then arcing will occur and cutting will begin.
Approximately 500 Vp-p are necessary to ionize air and establish cutting action. The sine wave produces two arcs each cycle: one at the maximum voltage and one at the minimum voltage. Therefore, for a generator operating at 500 kHz, one million arcs occur each second. The rapid arcing rate between the electrode and tissue does not allow sufficient time for the ions to diffuse from the area. This produces a tight pencillike arc that yields a clean cut with a small amount of hemostasis (Fig. 10.27). If the voltage is increased, current density increases, producing high temperatures and greater thermal damage lateral to the cut. At very high voltages, the sidewalls of the cut become charred and necrotic. Higher amperage and lower voltage (peak to peak) create a cleaner cut with less surrounding tissue necrosis. As wattage (power) is increased using a constant voltage generator—i.e., voltage is constant—the amperage will increase according to the following formula: W = I × V, where I = amps, V = volts. This may be stated differently using Ohm’s law: R (ohms) = V/I and substituting: W = I2R.
FIGURE 10.26 A: Typical waveforms of pure cut, blend cut, and coagulation. The peak-to-peak voltages are shown for each waveform. B: Pure cut at one, blend cut at two with intermediate coagulation, and blend cut at three with still greater coagulation. The zone of coagulation increases with elevation of the peak-to-peak voltage.
Blended Cutting
In many surgical situations, it is necessary to obtain more coagulation on the sidewalls lateral to the cut than pure cut provides. This can be accomplished by using a blend cut waveform. These waveforms use higher voltages than cut waveforms, yet the generator does not supply current continuously with the exception of constant voltage generators. Blend cut waveforms are intermittent, and the generator supplies current only during 50% to 80% of the activation time. Intermittent supplying of current is termed the duty cycle. For example, a waveform that
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continuously supplies current (i.e., a sine wave) is said to have a 100% duty cycle, whereas a waveform supplying current 50% of the activation period is said to have a 50% duty cycle. Typically, the lower the duty cycle, the higher the voltage. Higher voltages produce greater hemostatic effect, since more force is available to push current deeper into the tissue (Fig. 10.26B), whereas a lower duty cycle allows heat to be removed by adjacent retained blood flow and aids in minimizing charring.
FIGURE 10.27 Submucous myoma being shaved down to plane of endometrial cavity. The loop electrode is offset at approximately 90 degrees. The generator (ESU) is set at pure cut or blend one.
Coagulation
Coagulation of tissue can be accomplished by two methods: contact desiccation, in which the electrode is touching the tissue, and fulguration (spray coagulation), in which the electrode does not touch the tissue and sparks are generated between the electrode and tissue. Coagulation waveforms have a low duty cycle, usually between 5% and 50% (Fig. 10.26).
Contact Coagulation
To perform contact coagulation, the surgeon has two options: the traditional coagulation waveform or the cut waveform at a low power setting. The typical coagulation waveform uses a high voltage to cause relatively deep thermal effects. As the tissue under the active electrode desiccates, resistance increases dramatically. If high power settings (high voltage) have also been used, sparking to tissue may occur. Simple observation shows the spark is not contained to a compact area, as in cut sparking, but rather, the sparks originate from different positions on the electrode and strike various spots on the tissue. This spray is a result of the low duty cycle allowing ions to diffuse from the site and necessitating the establishment of a new spark path. Voltages vary from 500 Vp-p to several thousand volts.
A less used technique for contact coagulation uses the cut waveform. If low voltages are used, Vp-p <500, no arcing will be possible and a desiccation rather than a cut will occur. Deep thermal effects occur with longer application times (Fig. 10.28).
Fulguration (Spray Coagulation)
The fulguration waveform is used for noncontact coagulation; it uses very high voltages, up to 10 kVp-p, to allow sparking to the tissue from up to 10 mm. The typical duty cycle is approximately 5%; this leads to highly random sparking. The spark strikes the tissue, creating a high resistance area; thus, the next spark will strike a lower resistance area on the tissue (Fig. 10.29). Spray coagulation leads to superficial tissue damage; therefore, it is clinically useful for the control of bleeding of small vessels over a large area, such as in lobe resection of the liver. It is also an attractive technique for coagulation of retracted vessels hidden in fissures and not directly accessible. Fulguration does not work well on larger bleeding vessels where vessel coaptation or tamponade is needed.
During coagulation, the highest temperatures are reached in the vicinity of the electrode. As the heat spreads into the tissue distal to the electrode, the temperature in the tissue progressively diminishes. The longer the current flows, the wider is the surrounding conductive zone of injury (Fig. 10.30).
Electrosurgical Generators
Generator Types
The two types of electrosurgical circuits are monopolar and bipolar (Fig. 10.30). In the monopolar circuit, current flows from the generator to an active electrode at the surgical site. Current disperses from the surgical site and flows through the patient to a large area return electrode, whereupon it is returned to the generator to complete the circuit. In the bipolar circuit, the patient return electrode is eliminated by placing a second small area electrode within several millimeters of the active electrode. Current flows from the first electrode to the tissue, then to the second electrode, which returns the current to the generator to complete the circuit. This design confines current flow to a small volume of tissue around the two electrodes. Therefore, bipolar electrodes damage significantly less tissue than monopolar electrodes (Fig. 10.31A). Since few bipolar electrodes have as yet been developed for procedures such as endometrial ablation, we will concentrate on the characteristics of monopolar generators; readers desiring further information on
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bipolar electrosurgery are referred to Kaplan (1978) (Fig. 10.31B). Bipolar generators are typically safer because the monopolar return electrode and its associated problems are eliminated. Few electrodes have been developed for bipolar endometrial ablation. One specific bipolar electrode that fills
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the uterine cavity is mesh constructed in two parts. Current flows from one mesh section to the endometrium and then to the second mesh section to return to the generator and complete the circuit. The current is continued until the endometrial tissue reaches a predetermined value that indicates complete ablation, whereupon the generator automatically terminates current flow.
FIGURE 10.28 A: Soft coagulation is produced when voltages are <200 peak-to-peak. The tissue temperature remains relatively low, with no sticking of tissue to the electrode. B: Forced coagulation produces deeper penetration as the voltage exceeds 200 peak-to-peak. This is useful for coaptation of deeper and larger vessels. Typically, the electrode sticks to the tissue. C: Spray coagulation is equivalent to fulguration where the electrode remains off of the tissue and the spark jumps the interface between air and tissue.
FIGURE 10.29 An argon beam coagulator exemplifies spray coagulation.
FIGURE 10.30 The coagulation electrode produces the highest temperature readings in the vicinity of the electrode. As the conduction spreads, the temperatures decrease in the peripheral tissue.
Early monopolar electrosurgery generators were ground referenced (i.e., the patient return electrode was directly connected to earth ground). This produced a potential hazard to the patient. If the patient return electrode became disconnected from the generator, the RF current would seek an alternate path to ground. These paths could be a grounded metal touching the patient (e.g., operating table or metal stand) or through another piece of medical equipment connected to the patient (e.g., an ECG electrode and monitor). This type of generator led to many patient burns (Fig. 10.32).
FIGURE 10.31 A: A bipolar circuit differs substantially from the monopolar. The current leaves the generator through one insulated wire via the active electrode. Tissue action is exerted between the two poles of the electrode. The second pole is a neutral or return electrode. Only the tissue between the two electrodes conducts the current, which is then returned to the generator. (Courtesy of Everest, Minneapolis, MN.) B: A 3-mm diameter bipolar ball electrode can be used for endometrial ablation.
Isolated generators were next developed to eliminate the potential for patient alternate-site burns. In these generators the patient return electrode was not connected to earth ground, but rather, the return was isolated from earth so virtually all current would flow to the generator, not ground. If a break occurred in the return electrode–generator connection, no electrosurgical current would flow. However, these generators could not prevent burns from occurring under the patient return electrode. For example, if the return electrode became partially disconnected from the patient such that only a small contact area remained, all the return current would flow through the small area, potentially creating high current density and high heat.
To prevent return electrode burns, a return electrode monitor (REM) circuit was developed that monitors the contact area between the electrode and the patient. If the area is reduced to an unsafe level, the generator is disabled and an alarm is sounded. The REM circuit requires a special two-part return electrode; the electrode–patient contact resistance is compared between the two separate sections. REM generators and REM return electrodes eliminate this class of burns. Unfortunately, non-REM return electrodes also fit REM generators, and when used, the system will provide no protection; therefore, it is imperative that operating
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room staff be trained to recognize and use the correct electrode (Fig. 10.33).
FIGURE 10.32 A: An intraoperative picture of an omental burn that occurred during laparoscopic cholecystectomy. The damage was caused by capacitive coupling from a metal suction irrigator with a monopolar electrosurgery electrode used through an irrigator. The device was used through a plastic cannula. B: A photomicrograph of a full-thickness burn of the small bowel. The mucosal surface is at the top and is normal on both right and left sides. Center burn shows a complete loss of normal architecture. This injury occurred during a gynecologic operative procedure. C: A photomicrograph of a full-thickness burn and perforation in the colon. Mucosal surface top appears normal; however, at the center there is a perforation and a loss of normal architecture. This injury occurred during a gynecologic operative procedure. D: A photomicrograph of an electrosurgical burn in animal tissue. The tissue was stained with picrosirius red and is viewed with polarized light. Normal tissue on the left side and top is birefringent and appears to fluoresce, whereas the coagulated tissue that has been denatured is dark. This stain is particularly useful in tissue that has been excised immediately or shortly after surgery. This stain is not useful for viewing morphology.
Generator Outputs
Generator characteristics vary from model to model. Therefore, surgeons are urged to become familiar with the generators they are using by reading the manufacturer’s manuals.
No manufacturer produces a generator in which the output power is constant. Therefore, when a surgeon selects a given power setting such as 50 W, the actual level varies. Figure 10.34 displays the power output versus resistance for a typical multipurpose generator in pure cut, blend cut, and coagulate modes. These curves demonstrate that peak powers are produced in the average tissue impedance range of 300 to 500 ohms. However, the power drops after several thousand ohms for all modes. Coagulation power drops faster, since less power or heat is needed to desiccate the tissue compared with the high heat required for the vaporization action of cutting.
FIGURE 10.33 The return electrode monitor (REM) circuit monitors the contact area between the electrode and the patient. If the area is reduced to an unsafe level, the generator is disabled. (Courtesy of Valley Laboratories, Boulder, CO.)
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Summary
Radiofrequency electrosurgery is a safe and cost-effective method to provide hemostasis and cutting. It allows surgeons a dry surgical field and decreased surgical time compared with other energy sources. Surgeons who understand the technology can use it more safely and with enhanced outcome.
Tissue Interaction of Thermal Devices
Energy devices such as lasers and electrosurgery units (ESUs) produce their effects by conversion to heat energy. Before proceeding, the authors wish to point out some common ingrained misnomers associated particularly in respect to electrosurgical instruments. The term cautery or electrocautery is unfortunately a common parlance descriptively used by many surgeons. Cautery devices are rarely, if ever, used in modern medicine and surgery. A cautery literally is a piece of metal heated red hot and touched to tissue to coagulate bleeding tissue. The term could conjure up a picture of a Civil War–era hospital following a battlefield amputation in which a hot poker is applied to control bleeding from the severed vessels. An electrocautery is more akin to a charcoal starting device or the heating coil on an electric range than it is to a modern electrosurgical unit. Cold coagulation is a thermal device producing desiccation and coagulation at relatively low peak to peak voltages, e.g., 200 volts. It is not cold in the sense that cryosurgery freezes tissues but is a thermal device producing coagulation at 60°C to 70°C.
FIGURE 10.34 Maximum generator power output versus impedance (resistance) for pure cut, blend cut, and coagulation are shown. Note that the true generator power output varies dramatically with the tissue impedance for cutting waveforms; only in the coagulation waveform does the generator power approximate the setting at most tissue impedances.
The tissue actions of energy devices typically produce characteristic wounds. An electrosurgical loop electrode cuts through tissue by rapid heating of the cells to 100°C, causing these cells to explosively evaporate (explode) and disperse in a cloud of vapor (smoke). CO2 gas is released from the exploding cells, producing gas bubbles within the hysteroscopic liquid medium together with discolored cellular remnants. Eventually this debris will cloud the view of the
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operator until shaking the hysteroscope dissipates the bubbles. Subsequently, the reduced debris is flushed away by the constant interaction of fluid leaving the field via the outflow channel of the operating hysteroscope or resectoscope and infusing fresh fluid via the intake channel of the same instrument. Tissues in close proximity to the cut are macroscopically blanched white as the peripheral spread of the heating produces coagulation and necrosis.
If the cutting proceeds at a slow pace, superheating and carbonization will be seen. Microscopically, the actions of heating are characteristic. Cells nearby show cytoplasmic and nuclear distortion. Lines of fine carbon may also be seen. Cells that have not exceeded thermal relaxation may be injured but do not die and may recover from the injury. The following is a graphic example of this action. If one passes a finger through a candle flame rapidly, no injury to the skin occurs and no pain is experienced. Next, if the subject slows down the passage, some heating discomfort is felt and the skin may be warmed but still no injury is evident. Finally, if the hand is held directly over the flame for a count of say 3 seconds, intense pain will be experienced and the foolish person will have sustained a clinical burn. If the same individual counts to 10, then the wound will be carbonized (i.e., a substantial third degree burn will have occurred). Lasers transmit so rapidly that instantaneous pain and a third- degree thermal wound will jolt any unfortunate operator who passes his or her hand between an invisible beam and the target.
Electrosurgical Hazards
Given that electrosurgery is used in millions of procedures per year (estimates are as high as 18 million) and the number of important injuries is extremely small (estimated at <500 per year), the clinical use of the technology is quite safe. However, all surgeons and operating room staff should be familiar with the potential hazards with the use of electrosurgery.
One class of potential problems is explosion and fire. Although many improvements in operating rooms have been made to prevent explosions, such as explosion-proof switches and plugs and antistatic flooring and shoe covers, staff must be aware of the potential hazard when using anesthetic gases that are explosive. Explosions involving bowel gases have also been reported and demonstrate the need for adequate bowel preparation in some surgical procedures. The use of 100% oxygen also requires special attention to avoiding igniting other materials. Flammable liquids such as alcohol should not be allowed to pool near the patient.
Stimulation of nerves and muscles does not occur at electrosurgical frequencies; however, low-frequency currents are created during the arcing and sparking process and these frequencies do stimulate. Such stimulation is usually a nuisance, but in two instances, they can be problematic. High-voltage activations can stimulate abdominal muscles or the obturator nerve, and few surgeons relish performing surgery on a moving patient or being kicked in the face during surgery. There have been reported cases with ventricular fibrillation induced by electrosurgery during chest surgery or in patients with indwelling cardiac catheters. These problems can be reduced by using low-voltage/low-power settings, by not activating the electrode when it is not in contact with tissue, and by using bipolar electrosurgery when possible.
Interference with monitoring devices and pacemakers can also occur during electrosurgery. Most equipment and pacemakers now have filtering circuits or shielding to eliminate this class of problems. As with stimulation of muscle and nerves, these problems are exacerbated by high-voltage/ high-power activations and can be minimized by similar steps.
The most important hazard with the use of electrosurgery is alternate-site burns. Although alternative-site burns from return electrodes have virtually been eliminated by return electrode monitoring, other burns are more problematic. The most dangerous of these burns are those that occur outside the view of the surgeon. This class of unintended injuries is most common in minimally invasive surgery where events outside the area may not be seen. Injuries occur by three mechanisms: insulation failure, direct coupling, and capacitive coupling. Insulation failure can happen with reusable or disposable cables/electrodes and in open as well as minimally invasive procedures. It is prudent for the surgical staff to inspect all cables/electrodes before and after use for any breaks in the insulation. Any cables or electrodes with defects should be saved and the patient closely examined. Direct coupling exists if the active electrode touches any other metal instrument in the operative field; such contact makes the metal instrument electrified as long as there is a current. This situation also can occur through tissue as in the monopolar electrosurgical cutting or coagulation of thin adhesions; current is confined to flow in the conductive adhesion back to its attachment to complete the circuit. The authors have seen multiple cases of bowel burns caused by this direct coupling in tissue. Capacitive coupling primarily happens in monopolar electrosurgery. Capacitors are two conductors separated by an insulator; they prevent the flow of direct current but pass a substantial amount of RF electrosurgical current. For example, if a monopolar electrode passes through an operative scope or metal cannula, current will be induced on the metal of the scope of cannula through capacitive coupling every time the electrode is activated. Typically, this current passes harmlessly to the patient over the large area of contact with the scope or cannula. Problems can exist if the scope or cannula is insulated from the patient by a nonconductor such as a plastic abdominal wall anchor on a metal cannula. The authors have seen many bowel burns occur by this coupling. The use of all metal accessories with the electrosurgical electrode, low-voltage/low-power settings and bipolar electrodes help to minimize the capacitive coupling problems.
If an energy device should perforate the uterus when the instrument is activated, then the surgeon is obligated to
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perform an immediate laparotomy to completely and carefully “run” both large and small intestines. This exploration should be done with the intent of compulsively exploring every visible surface of the intestines to examine these structures for signs of injury. The peritoneal surfaces covering the urinary bladder and ureter should likewise be carefully examined. Should any sign of injury be identified, the underlying retroperitoneal space should be opened and explored. Any sign of hematoma formation should trigger retroperitoneal exploration of the great vessels, preferably in concert with vascular surgeon consultation. These maneuvers are designed to permit early diagnosis of collateral injury to a perforated uterus and to ameliorate the serious ramifications of such an injury.
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