Chapter 8 – Hysteroscopic Electrosurgery




Abstract




Surgical procedures using electrosurgery can be undertaken within the uterine cavity to address excessive menstrual blood loss and to enhance fertility. The insertion of specialised electrodes down hysteroscopic instruments enables the direct application of electricity to uterine tissue. The electrical energy is transformed into heat and, depending upon how this heat is focused, can be used to cut tissue and excise lesions, or cauterise and ablate tissue (Box 8.1). The larger hysteroscopic resectoscopes with outer diameters of 7 to 8.5 mm are generally, though not exclusively, used during inpatient procedures with a general anaesthetic or regional anaesthesia. The introduction of smaller electrodes (1.67 mm, or 5 Fr) has enabled therapeutic procedures to be undertaken using diagnostic hysteroscopes with an operating channel. This has supported the development of outpatient operative hysteroscopy for the removal of small intrauterine lesions.





Chapter 8 Hysteroscopic Electrosurgery



Mary E. Connor



8.1 Introduction


Surgical procedures using electrosurgery can be undertaken within the uterine cavity to address excessive menstrual blood loss and to enhance fertility. The insertion of specialised electrodes down hysteroscopic instruments enables the direct application of electricity to uterine tissue. The electrical energy is transformed into heat and, depending upon how this heat is focused, can be used to cut tissue and excise lesions, or cauterise and ablate tissue (Box 8.1). The larger hysteroscopic resectoscopes with outer diameters of 7 to 8.5 mm are generally, though not exclusively, used during inpatient procedures with a general anaesthetic or regional anaesthesia. The introduction of smaller electrodes (1.67 mm, or 5 Fr) has enabled therapeutic procedures to be undertaken using diagnostic hysteroscopes with an operating channel. This has supported the development of outpatient operative hysteroscopy for the removal of small intrauterine lesions.




Box 8.1 Operative Hysteroscopic Procedures Using Direct Application of Electricity




  • Endometrial ablation



  • Endometrial resection



  • Resection of submucosal fibroids



  • Resection of endometrial polyps



  • Uterine metroplasty for the septate uterus



  • Division of uterine adhesions


This chapter will focus on the various electrosurgical hysteroscopic procedures, the basics of electricity, the principles of electrosurgery and how to perform electrosurgical procedures safely.



8.2 Applications Relevant to Hysteroscopic Surgery



8.2.1 Endometrial Ablation


Treatment options for heavy menstrual bleeding (HMB) have significantly changed during the past few decades, with effective alternatives to hysterectomy now readily available. As a consequence, the number of hysterectomies performed in England for this indication fell dramatically from over 23 000 annually in the early 1990s to approximately 7000 in 2004/2005 [1]. From 1983, transcervical hysteroscopic procedures were developed for treatment of the uterine cavity [2, 3]. Initially, surgery was undertaken by looking down a resectoscope, which was a modified 9 mm urological endoscope with an attached light source; subsequently, cameras were added to provide an enlarged digital image of the uterine cavity displayed on a monitor. Electrodes inserted along the shaft of the resectoscope are manipulated under direct vision. Electricity passed through an electrode can resect, cauterise or vaporise tissue, depending upon the configuration of the electrode and how the electrical energy is used. The procedures continue to be performed using similar instruments, but with technological refinements.


Electrosurgery using a resectoscope consists of endometrial ablation using a rollerball electrode (rollerball endometrial ablation; REA) and endometrial resection using a loop electrode (transcervical resection of the endometrium; TCRE), performed either separately or in combination (see Figure 11.1). Strips of endometrium are either ablated or excised. A combination of both procedures involves REA at the uterine fundus and around the tubal ostia, where the myometrium is at its thinnest and therefore more vulnerable to perforation. The remaining endometrium from the thicker-walled anterior, posterior and lateral walls is then resected down to the level of the internal cervical os. Resection and ablation both destroy the endometrium and the basal layer from which the endometrium regenerates. As a consequence, menstrual blood loss is reduced, or may even cease. However, these first-generation procedures had little initial impact upon the number of hysterectomies performed for HMB [4], as, although effective, they required significant surgical skill, and complications such as fluid overload and uterine perforation occasionally occurred [5].


A greater impact upon the number of hysterectomies was subsequently achieved with the development of the second-generation ablation devices. These produce uniform or global endometrial ablation (GEA) of the whole uterine cavity. They are often safer and quicker to perform than REA or TCRE, and can be more effective [6]. In England, since 2003, more ablation and resection procedures have been performed than hysterectomies for the surgical treatment of HMB; since 2005, more than half of these were with GEA devices [1, 7].


Most of the currently available GEA devices do not use electricity directly on the tissue, with the exception of the bipolar radiofrequency impedance-based device, NovaSure (Hologic, Inc., Marlborough, MA, USA). This consists of a fan-shaped gold-mesh active element that is inserted folded through the cervix, which has been previously dilated to 6 mm, then opened so that it expands and conforms to the shape of the uterine cavity (see Figure 11.2). Electricity passed through the device to adjacent endometrium causes it to vaporise until a pre-specified level of impedance of 50 ohms is reached, at which point treatment ceases. This impedance is equivalent to that of ablated superficial myometrium, indicating the removal of the more vascular superficial endometrium of lower impedance. A continuous vacuum applied to the cavity ensures close apposition of endometrium and electrode and removes blood and vaporised tissue. Treatment is completed within a maximum of two minutes and an average of 90 seconds. The short duration of active treatment, combined with the relatively small cervical dilatation, makes it appropriate for use as an outpatient procedure [8].



8.2.2 Submucosal Fibroids


At first it appeared that the GEA devices may supersede the more traditional TCRE and REA, but the global devices are generally only suitable for women with a normal sized and shaped uterine cavity. They are inappropriate for women with HMB who have a large or irregularly shaped uterine cavity, and this includes women with submucosal fibroids that distort the endometrium. Fibroids in this position are recognised as the cause of abnormal uterine bleeding and of impaired fertility, with reduced pregnancy and implantation. Loop electrodes passed down the resectoscope, and using either monopolar or bipolar current, can slice away fibroid protruding into the endometrial cavity. The fibroid chips are then physically removed from the endometrial cavity by withdrawing the resectoscope. One manufacturer has developed a system for aspirating the chips down the outflow channel of the resectoscope as they are produced, ensuring that a clear view of the uterine cavity is maintained (Figure 3.12b, Richard Wolf Princess resectoscope). An alternative electrosurgical method involves vaporising the fibroid using a specific electrode, such as the vaporising button (Figure 3.11b, Olympus vaporising button) or barrel, as this avoids the need for chip removal, though it does not allow for histological assessment of the removed tissue.


A systematic review of the literature with meta-analysis of appropriate results identified that women with submucous fibroids and infertility had lower pregnancy and implantation rates than infertile controls without fibroids. Importantly, removal of submucous fibroids in infertile women resulted in improvement of their delivery rates to that of the infertile women without fibroids [9]. When fertility is not a concern, removal of submucosal fibroids combined with resection or ablation of the surrounding endometrium is an effective treatment of HMB [6].


The removal of the smaller and more superficial submucosal fibroids, specifically those less than 2 cm in diameter and which are wholly or predominantly within the uterine cavity (type 0), can be accomplished in an outpatient setting using a diagnostic hysteroscope with an operating channel and a small bipolar needle electrode [10, 11], though in some centres a standard resectoscope is used [12]. The bipolar needle can be used to slice away the fibroid for later removal or vaporisation. The rate-limiting steps for outpatient removal of a submucosal fibroid are the presence of a significant myometrial portion, and the time taken for its removal. The time taken is dependent upon the volume of tissue to be removed [13], which is proportional to the radius cubed (4/3πr3) as shown in Figure 8.1. It is generally appreciated that patients are able to tolerate active treatment as an outpatient provided that it takes no longer than 15 to 20 minutes [14]. This usually limits outpatient removal of fibroids to those with a maximum diameter of less than 2.5 cm; an alternative may be to offer a two-stage procedure. The time taken to remove a fibroid is also important when planning removal of larger fibroids as an inpatient procedure.





Figure 8.1 Fibroid diameter versus surgery time for removal of submucosal fibroids by hysteroscopic resection, with a tissue removal rate of 0.5 cm3/min [13].


(Courtesy of Elsevier.)

Removal of deeper type 1 fibroids and all type 2 fibroids remains the provenance of the more versatile resectoscope and within an inpatient setting. The deeper myometrial component can be separated from the adjacent myometrium by using the cold knife technique of Mazzon [15]. This stage is without electricity and so avoids damaging the adjacent myometrium while moving the fibroid portion into the uterine cavity for subsequent easier and safer resection. Haemostasis can be provided as necessary to larger blood vessels found deeper in the myometrium using electrosurgery [16].



8.2.3 Endometrial Polyps


Endometrial polyps are localised growths of tissue containing glands, stroma and blood vessels; they are common and occur more frequently with increasing age, obesity and tamoxifen usage. Polyps can be asymptomatic or the cause of abnormal uterine bleeding, including post-menopausal bleeding, and may interfere with fertility [17]. Abnormal uterine bleeding with an associated endometrial polyp improves with polyp removal [18]. Conservative management is regarded as reasonable for smaller asymptomatic polyps (<10 mm), particularly in pre-menopausal women, as up to 50% of these may regress spontaneously [19, 20]. The removal of larger polyps is advocated, as, although malignancy is uncommon (occurring in approximately 3% of cases [21]), the incidence is greater in larger polyps (>17 mm) even when asymptomatic [22].


Polyps can be removed with loop resection (monopolar or bipolar), but this usually requires dilatation of the cervix to 9 mm. Such use of the resectoscope is generally limited to an inpatient setting and is appropriate for the tougher and larger glandular polyps that may be difficult to remove through an undilated cervical os. For smaller polyps, the 5 Fr bipolar electrodes used with a diagnostic hysteroscope are potentially suitable for use in an outpatient setting [22] (see Figures 8.2 and 3.9). The bipolar needle can be used with saline to resect the polyp at its base, or to slice it to enhance its removal with small forceps or hysteroscopic graspers. The monopolar snare should be used with a non-ionising fluid for polyp excision. However, once the polyp is detached by any method, the snare can be used to remove the polyp from the cavity. Activation of the bipolar needle may stimulate the myometrium and cause pain, thus limiting its use in an outpatient setting, though lowering of the power setting can reduce the pain experienced [23].





Figure 8.2 Scheme for removal of intrauterine tissue such as endometrial polyps in the office setting before and after the introduction of tissue removal systems in the late 1990s. (a) Before 1998. (b) After 1998. [23]



8.2.4 Uterine Septa and Adhesions


Uterine metroplasty involves division of the central septum in the septate uterus and opening of the lateral sidewalls in the T-shaped uterus in order to improve fertility outcomes. It will be discussed in more detail in Chapter 14. Some regard hysteroscopic electrosurgery as providing the optimum technique for these procedures, as it gives the option of haemostasis if required [24]. Electrosurgical devices used include a 5 Fr bipolar needle down the operating channel of a diagnostic hysteroscope, a Cook needle down a resectoscope using either monopolar or bipolar electricity, or a monopolar or bipolar loop, again with a resectoscope [24, 25]. However, others consider non-electrosurgical methods preferable as they are concerned that the response of the endometrium to the electrical injury increases the risk of adhesion formation, thus reducing the effectiveness of the procedure [23]. Similar concerns are expressed about hysteroscopic adhesioslysis, with some authors advocating the use of scissors in preference to electrical energy [26].



8.3 The Basics of Electricity


Electricity is the presence and flow of electrical charge. In many circumstances, the electrical charge will be in the form of electrons; in tissue, the charge is carried as ions. The movement of charged particles (ions or electrons) over a period of time is electrical current (I) and is measured in amperes. The potential energy, or electrical potential difference, that determines the pressure that moves the ions or electrons around the electrical circuit is voltage (V), measured in volts. Resistance or impedance (R) describes the ease or difficulty with which the electrons or ions move through a given medium or tissue. There is a close relationship between voltage, current and impedance, and this is expressed as Ohm’s Law (Box 8.2). Given constant impedance, the current between two points is proportional to the voltage across the two points.




Box 8.2 Ohm’s Law V = IR


The greater the resistance or impedance to the flow of ions, the greater the voltage required to push the same amount of current through a given material. Tissue with readily accessible ions due to a high electrolyte content, such as muscle, blood vessels and blood, has a low impedance, and electricity flows through it easily. High-resistance tissues are where the electrolyte content is low, such as bone, fat and scar tissue. Another feature of electricity is that it takes the easiest path available, so it will pass along blood vessels in preference to higher resistance fatty tissue. The impedance of tissue changes during electrosurgical procedures as the tissue dries: its ions become less accessible and the impedance rises, so the path taken by electricity during a surgical procedure will change.


There is a useful analogy between electricity and the flow of water. The movement of ions with current is analogous to the volume of water flowing past a point. The voltage is equivalent to the potential energy provided by the difference in height of water flowing from one place to another. The impedance to the flow of electrical current is represented by the resistance to water flowing across the surface of rocks or through a narrow pipe. Both water and electricity take the path of least resistance: water flows downhill and electricity flows to where there is least impedance.


Electrical charge flows within a closed pathway or circuit returning to its source. The ground or earth can form part of the circuit, demonstrated dramatically when lightning reaches the earth. The ground can inadvertently become part of the electrosurgery circuit; the significance of this is discussed in Sections 8.4.2 and 8.4.3.


Power (W), or the rate at which electrical charge is moved, is measured in watts, also defined as joules per second. It is the result of moving a given electrical current (I) through a particular electrical potential difference (V); this can be expressed as W = V × I. Using Ohm’s Law to substitute current, so that W = V  (V/R) or W = V2/R, it can be seen that the power delivered rises exponentially with increases in voltage, and that it also rises inversely with impedance. The significance of this is that as the tissue is heated and dries, the impedance will increase and, for a fixed power output, the voltage will fall.


Historically, the first use of electricity was in the form of direct current (DC), with all the electrical charge flowing in one direction. This remains the case for electricity derived from batteries and solar panels. However, mains electricity delivered into our homes is transmitted as alternating current (AC), where the direction of the electrical current periodically changes direction at a rate of 50 cycles per second (hertz, Hz). AC is used for transmitting mains electricity over long distances as it is more efficient than DC – the same power can be delivered with a lower current at very high voltages. The lower current results in less heat loss; the high voltage is achieved with a transformer. Before use in both domestic and industrial settings, the dangerously high voltage is reduced to a safer, more manageable level.


Moving charge creates an electromagnetic field. The change in direction of the charge in AC gives rise to the emission of electromagnetic waves, and these form part of the electromagnetic spectrum (Figure 8.3). The wavelength is determined by the frequency of the AC cycle. All electromagnetic waves move at a fixed speed – the speed of light – so the higher the wave frequency, the shorter the wavelength.





Figure 8.3 The position of electromagnetic waves, as used in electrosurgery, within the electromagnetic frequency spectrum.


(All rights reserved. Used with the permission of Medtronic.)

Electricity has different effects on tissue depending upon how it is delivered. DC with charge flowing in a constant direction has no medically useful action. The effect of AC depends upon the frequency of the cycle change and the length of the electromagnetic waves emitted; at low frequencies, cell depolarisation occurs with muscle contraction and this can cause death due to heart muscle fibrillation (electrocution), nerve stimulation and heating of tissue. Muscle and nerve stimulation occur at low electromagnetic frequencies, but this ceases at frequencies above 100 kHz when the change in direction of the current is too rapid to depolarise the cells. As neuromuscular stimulation is a most undesirable effect, electrosurgical units (ESUs) are designed to generate high-frequency (HF) electricity in the range of 200 kHz to 3.3 MHz (Figure 8.3).

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Sep 17, 2020 | Posted by in GASTROENTEROLOGY | Comments Off on Chapter 8 – Hysteroscopic Electrosurgery
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