Gastroenterological Endoscopy. Группа авторов
the rest of the time has a 50% duty cycle. Continuous sine waves, often labeled as “Cut,” have a 100% duty cycle, whereas waveforms with duty cycles ranging from 20 to 80% often have labels such as “Swift Coag,” “Blend,” and “Blend Cut.” Waveforms named “Coag” typically have duty cycles of 6 to 12%, and although current is not flowing during much of the activation period, voltage spikes are well above 1,500 Vp when current does flow and therefore some electrosurgical cutting occurs especially with wire electrodes, such as polypectomy snares. Operators who utilize the “Coag” output and smoothly close a snare through polyp tissue are taking advantage of this cutting action along the snare wire, coupled with marked hemostasis promoted by the long rest periods in the cycle and the high voltage peaks that drive coagulation into tissue.
As an alternative to duty cycle, the crest factor can also be used to quantify waveforms. Crest factor takes into consideration average and peak voltages, as well as the frequency of the modulation, and becomes a better indicator of the expected depth and intensity of coagulation relative to the duty cycle for modulated waveforms. Continuous sinusoidal waveforms have a constant crest factor of 1.4 and in this instance the maximum peak voltage should also be stated. Highly modulated, high-voltage waveforms typical of “Coag” types (6% duty cycle) have crest factors in the range of 5 to 7. In general, high duty cycles correlate with low crest factors indicative of waveforms designed to produce more cutting with limited coagulation, whereas low duty cycles correlate with higher crest factors that predict increasing depth of coagulation and hemostasis (
Specialized proprietary microprocessor outputs are available in some ESUs. For example, the “ENDO CUT” (Erbe Electromedizin, Tubingen, Germany) mode fractionates (pulses) the current output to promote controlled cutting of tissue and provide a well-defined and constant zone of coagulation during the entire cutting process. The “ENDO CUT” mode consists of an initial incision (cut) phase followed by phases of alternating cutting and coagulation current (
7.4 Practical Applications
7.4.1 Snare Polypectomy
The optimal electrosurgical settings for “hot” snare polypectomy that maximizes resection efficiency and minimizes adverse events, such as bleeding and transmural burn syndrome, have not been established. Comparisons among available studies are hampered by the qualitative labels of the current waveforms used during polypectomy. Polypectomy practice and the electrosurgical method utilized vary among endoscopists. According to a U.S. survey, most endoscopists use “Pure Coagulation” (46%) or “Blend” (46%) current and a minority utilize “Pure Cut” (3%) or modify the current waveform (4%) during polypectomy.8
Although the risk of transmural burn syndrome might, in theory, be increased with a “Pure Coagulation” current as it drives coagulation deeper into tissue, that type of current has been used in a relatively safe manner for resecting large colon polyps (> 2 cm).9,10 A comparative study of “Blend” versus “Continuous Coagulation” current showed similar rates of adverse events overall, but timing of postpolypectomy hemorrhage was related to the current waveform utilized. All immediate or very early (< 12 hours) bleeds occurred when blended current was utilized, and all delayed bleeds (2–8 days) occurred when coagulation current was used.11 In one study, the postpolypectomy bleeding rate was relatively low at 1.1% when “Pure Current” was applied, although prophylactic endoscopic loop or endoscopic clip placement was undertaken in 12% of the polypectomy defects to minimize the risk of bleeding.12 The use of “Pure Cut” current as opposed to “Blend” or “ENDO CUT” current was found to be a risk factor for immediate postpolypectomy bleeding in a large, prospective, multicenter study.13 The use of proprietary current outputs, such as “ENDO CUT,” is promoted by some experts in the field of endoscopic resection.14 The use of “ENDO CUT” resulted in significantly less deep thermal ulceration, necrosis, and acute inflammation relative to a low-power coagulation current in an animal model,15 as well as in better assessment of the resection margins and histologic quality of the specimens relative to a blended current.16
Fig. 7.8 ENDO CUT mode. After an initial incision (cut) phase, bursts of cutting alternating with coagulation current are delivered. The duration of the cutting cycle, the interval duration between cutting cycles, and the intensity (effect) of the coagulation cycle can be adjusted. (This figure is provided courtesy of ERBE Inc., Marietta, GA.)
Findings from the above-mentioned studies are consistent with predicted outcomes based on the principles of electrosurgery. In general, a “Pure Cut” current leads to increased immediate bleeding, whereas overuse of a “Pure Coagulation” current increases the risk of delayed postpolypectomy hemorrhage and transmural burn syndrome. In addition to the current waveform, the speed of snare closure and type of snare utilized will influence the polypectomy process. A thin (monofilament) snare will deposit a higher current density than a thick snare wire, resulting in faster transection. ESU settings or operator technique may need to be adjusted accordingly based on the selected snare.
From a practical perspective, a reasonable approach for all polyp types is to constrict the polyp without overtightening, begin current application, and then smoothly close the wire using a low duty cycle waveform that enables cutting and coagulation at the same time (Video 7.2). For standard polypectomy, interrupted waveforms with duty cycles of 4 to 12% and broad power-to-impedance curves are suitable, with power outputs averaging 20 W. These waveforms have high-voltage peaks that allow some electrosurgical cutting along the wire, while at the same time driving coagulation adequately through snared tissue. Tenting of the polyp away from the wall prior to current activation may decrease the risk of perforation, and moving the ensnared polyp back and forth during transection will minimize contact between the polyp surface and intestinal wall, hence decreasing the risk of contralateral burn injury (Video 7.2). The use of submucosal fluid injection to provide a safety cushion against deeper tissue heating is also reasonable, particularly during resection of large sessile polyps. Snare entrapment in desiccated tissue can be minimized by avoiding excessive snare strangulation or by resecting a thick stalk polyp with too low a power setting. If entrapment occurs, the snare should be loosened and a pause taken prior to resuming the transection process, with stepwise adjustments in power setting or electrosurgical waveform toward mostly a cutting current.
7.4.2 Hot Biopsy
The use of monopolar hot biopsy forceps (Video 7.3) is discouraged due to the 15% rate of residual polyp tissue, thermal artifact interfering with histopathological evaluation, and risk of delayed bleeding and perforation due to deep thermal damage attributed to the large cups of the forceps, particularly in the thin-walled right colon.6 However, the reported experience with the hot biopsy forceps utilized predominantly coagulation current. The use of a soft coagulation or “Cut” current is more appropriate since both waveforms have lower peak voltages, resulting in less intense coagulation and overall thermal injury. Moreover, utilization