Bipolar Vaporization of the Prostate

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Bipolar Vaporization of the Prostate

Ahmet Karakeci¹, Kyle Richards,² & Gopal H. Badlani³

¹ Department of Urology, Wake Forest University Baptist Medical Center, Winston‐Salem, NC, USA

² Department of Urology, University of Wisconsin‐Madison, Madison, WI, USA

³ Wake Forest University, Winston‐Salem, Madison, NC, USA

Introduction

Transurethral resection of the prostate (TURP) has long been accepted as the “gold standard” surgical treatment for benign prostatic hyperplasia (BPH). It is the measuring stick against which all other minimally invasive treatments for BPH are compared, being highly effective in improving urinary flow rates and decreasing symptom scores. The Agency for Health Care Policy and Research (AHCPR) panel guideline meta‐analysis showed that patients had an 88% chance of symptomatic improvement after TURP [1]. However, due to the morbidity associated with monopolar TURP, including the risk of bleeding, clot retention, impotence, urethral stricture, and transurethral resection (TUR) syndrome, as well as the length of hospitalization and catheterization, urologists have been tinkering with other minimally invasive treatments for BPH for decades.

Vaporization of the prostate was first described in the early 1990s using either conventional electrical surgery, termed electrovaporization, or laser techniques [2]. Transurethral vaporization of the prostate (TUVP) was first described by Kaplan and Te in 1995 [3]. The proposed advantages of TUVP included less blood loss, shorter catheterization time, and shorter hospitalization, all the while maintaining efficacy. Initially, electrovaporization techniques were performed using monopolar currents, but a monopolar current has its own associated problems. First, the use of a conductive irrigant, such as glycine or mannitol, is required, which may result in systemic absorption of hypotonic fluids, thus risking hyponatremia and TUR syndrome. Second, the patient is part of an electrical circuit that can pose a risk for patients with pacemakers and cause diathermy burns at the site of the return plate. Third, monopolar current does not allow simultaneous cutting and coagulation. To address these issues, bipolar electrocircuitry was developed for minimally invasive prostate surgery. Bipolar vaporization or resection allows normal saline to be used, which is isotonic, avoids the need for a return plate as the patient is not part of the electrical circuit, and allows simultaneous cutting and coagulation.

Bipolar electrovaporization of the prostate was first described in 2001 using a Gyrus device [4]. Since then, numerous centers have reported level 1 evidence for favorable short‐term outcomes using bipolar vaporization of the prostate. Herein we present a review of the mechanism of action of bipolar vaporization, various electrode and generator designs, clinical experience, and relevant comparative studies.

Mechanism of action

Vaporization is produced via the application of energy to the prostate, which results in heating of the tissues. The tissues are primarily composed of intracellular water, which subsequently boils at a rapid rate, thus producing steam. This results in cellular disruption and tissue destruction, leaving a void where the cells were previously present. In electrosurgery, the rate of electrical energy delivered (W) is measured in watts, the current (I) flows through the tissue, and the tissue creates electrical impedance (R). Heat is created due to the electrical impedance of the prostate to current flow, therefore:

Most of the energy delivered to the prostate results in vaporization of the surface layer of cells; however, some of the energy has been shown to disperse below the vaporization layer to create a zone of coagulation, resulting in improved hemostasis. This phenomenon of simultaneous vaporization/ablation and coagulation is the principal benefit of TUVP techniques. The actual depth of coagulation depends on system and electrode design. The technique employed by the surgeon will also impact the depth of coagulation as this is increased by increased pressure on and time in contact with the tissue. Importantly, coagulation has to take place with bipolar technology at lower peak voltages compared to those used for monopolar surgery (80–100 V for the PlasmaKinetic™ (PK) system) as higher voltages will convert the liquid into a gaseous phase, resulting in higher impedance. The impedance therefore is changed from a resistive to a capacitive mode, reducing energy flow, dissipating heat, and decreasing the final coagulation effect.

In bipolar and monopolar cutting, the generator must initiate a momentary high‐energy spike to initiate a plasma vapor layer. This layer is ionized in the form of a nonequilibrium plasma, where plasma ions and electrons are responsible for current flow. In monopolar circuitry, the current arcs to the tissue and passes through the patient to a large‐surface return electrode on the skin, heating the intervening tissue by ohmic resistance. However, in bipolar surgery, the active and return electrodes are in close proximity to each other, separated by an insulator. The electron emission from the smaller active electrode heats and vaporizes the adjacent intracellular water to form a thin gas layer (plasma pocket) that grows and forms a larger bubble containing energetic species that can dissociate both water and organic molecules, resulting in the net tissue effect [5]. It is likely that the thermal effect noted with bipolar surgery takes place at much lower temperatures (<70 °C) than those in monopolar surgery (300–400 °C). Once the plasma vapor pocket is formed, it can be maintained at low voltages (100–350 V_rms) as the electrode is close to making contact with the tissue. Tissue destruction ensues due to the breakdown of carbon–carbon and carbon–nitrogen bonds. This results in the production of elementary molecules and low molecular weight gases, including carbon dioxide, oxygen, nitrogen, and hydrogen. Intraoperatively, the effect is precise cutting and vaporization with minimal collateral damage as the charged sodium ions contained within the plasma vapor pocket have only a short estimated range of penetration (50–100 µm). This is largely due to electrosurgical principles as minimization of collateral tissue damage is dependent upon resistive heating caused by any current flowing through tissue and by limiting thermal transfer from the electrode sources. The final result in the human prostate is precision tissue cutting/vaporization with minimal charring and burnt prostate odor traditionally equated with monopolar TURP.

Specialized generators were developed along with the bipolar technology using radiofrequency (RF) energy output. The initial bipolar vaporization of the prostate used a Gyrus device and generator designed with a 200 W capability with an RF range of 320–450 kHz and a voltage range of 254–350 V [4]. However, the Vista Coblation system (ACMI Corporation, Southborough, MA, USA) used RF energy output from a specialized electrosurgical generator that is one‐fifth that of monopolar generators (100 kHz square wave) [6]. The initial Olympus SurgMaster generated an RF output of 350 kHz and a recent report used the UES‐40 SurgMaster (Olympus Medical/Winter & Ibe GmbH, Hamburg, Germany) with a power output of 290 W and 120 W for vaporization and coagulation, respectively (Figure 152.1) [7]. The frequency of the newest system from Karl Storz (Autocon® II 400 Electrosurgical System, Karl Storz, Tuttlingen, Germany) (Figure 152.2) generates an RF output of 350 kHz with a power output of 120 W for coagulation.

Image described by caption and surrounding text. — **Figure 152.1** UES‐40 Electrosurgical Generator.

*Source:* Olympus America Inc. Reproduced with permission of Olympus.

Photo of Karl Storz Autocon® II 400 Electrosurgical System. — **Figure 152.2** Karl Storz Autocon® II 400 Electrosurgical System.

*Source:* Karl Storz Endoscopy‐America, Inc., California, USA. Reproduced with permission of Karl Storz Endoscopy‐America, Inc.

Electrode and generator design

The bipolar technology was developed with the active and return electrodes in close proximity to one another, separated by an insulator. Energy from the generator travels through the active electrode, through the plasma pocket, through the conductive solution to the tissue bed, and returns via a thicker electrode to the active cord to the ground. Hence, there is no need for any energy to travel through the patient to a return electrode on the skin, eliminating the risk for inadvertent burns from inadequate contact. Also, the low operating frequency and voltage of bipolar surgery should eliminate any potential for interference with cardiac pacemakers.

There are several challenges to electrode design, including establishment of a reliable plasma corona preferentially at the distal active electrode, how to achieve a plasma condition with short delays from the time of foot‐switch activation by the surgeon, how to provide adequate hemostasis from both cut and coagulation sources of foot‐switch operation, and how to maintain this under all surgical conditions. With these challenges in mind, manufacturers and urologists are still in search of the “ideal” electrode for bipolar TUVP. The commercially available electrodes vary in size and configuration; however, in general, the active component is slightly thinner and separated from the thicker return electrode component by an insulator. The commercially available systems also vary in terms of resectoscope sizes, design of electrode housings, and coupling mechanism between active and return cords.

The Gyrus PK system was the first bipolar vaporization technology reported in the literature and therefore had to address several of these early technical issues. For bipolar vaporization to occur at the time of foot‐pedal activation, the active electrode must be in close proximity to the tissue because if the gap is too wide or if there is insufficient power, current flow is dissipated by the large volume of electrolyte solution in a full bladder and there is no effect on the tissue. Furthermore, if the power/voltage spike is not great enough to maintain the plasma pocket, cutting and vaporization of the tissue will occur in a stuttering fashion, depending on the quality of tissue contact.

With these limitations and challenges in mind, the initial Gyrus PK system was modified, resulting in a second‐generation model called the PK SuperPulse® Generator. There are several advantages of this system. First, this device is preconfigured for maximal allowable current under low impedance conditions. Second, the surgeon can choose between two sets of preset cutting voltages. Third, the generator is designed to recognize the active electrode offering default settings that are optimal for a wide range of conditions at the tip. Lastly, the PK SuperPulse generator is equipped with a row of internal capacitors acting as an energy reservoir to ensure sufficient voltage for instantaneous fire‐up and for power ride‐through under challenging conditions of impedance. These modifications have resolved the issue of stuttering cutting/vaporization that occurred previously. The capacitor reservoir can provide up to 4000 W of power for short periods of time (10 ms) if the tip impedance is low enough. This may be important because under conditions of high flow with cold saline, more power than normal is required to create and maintain the initial plasma pocket at the active electrode tip.

At baseline, prior to RF voltage application, the impedance differential between bipolar active and return electrodes is between 23 and 60 ohm with variability due to the irrigation temperature and the proximity of the active electrode to the tissue bed. The PK SuperPulse generator can generate a high enough power (4000 W) at low impedance (23 ohm) to sustain a voltage of close to 300 V_rms that boils the saline immediately surrounding the active loop in a matter of milliseconds. This phenomenon is largely due to the electrode design. The electrical current crowds the reduced surface area of the active electrode, which results in a nonequilibrium vapor pocket containing charged sodium ions. The activated sodium ions form the plasma inside the vapor pocket and produce the orange glow that is visible to the naked eye. There is a time delay of 1–2 µs from the initial negative current spike until light is emitted. Once the plasma is formed, the impedance increases greatly from 500 to 3000 ohm, depending on whether the electrode is in contact with the vapor pocket or the irrigant, and/or the length of the vapor pocket (as there is higher impedance with longer plasma vapor pocket lengths). The power delivery now becomes focused around the active electrode and is not dissipated in the surrounding saline solution and prostate tissue, and therefore much less power is required to sustain the plasma vapor pocket. The energy reservoir can then be replenished as the output voltage falls by being repeatedly formed during each half cycle of the high‐frequency exciting voltage waveform.

The PK SuperPulse generator has two sets of preset cutting voltages (termed SP1 and SP2). At the lower preset voltage of SP1, plasma volume is smaller and impedance is lower, and detected intraoperatively as a less intense orange glow around the active electrode. The SP2 setting can be used during suboptimal operative conditions when cutting/vaporization becomes difficult, to allow for an increased plasma volume and slightly higher preset voltage. Foot‐pedal activation and fire‐up should take no longer than 20 ms as a result of the energy reservoir of the internal capacitors. Once an activated electrode is in contact with tissue, in vivo studies have demonstrated that no more than 100 W are usually required to sustain the user‐defined maximum voltages.

Clinical experience

Bipolar TUVP has been in clinical use for a decade. The initial experience was reported in 2001 by Botto et al. using the Gyrus device and a rolling‐type electrode (Axipolair®) [4]

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