Key points and recommendations
Key points and recommendations
a) Protection measures for the patient
The electrosurgical unit (ESU) should only be used by medical personnel after appropriate
training.
-
Inspect the ESU for damage, including insulation of all cables and electrodes, missing
components, and working lights and sounds (set on an audible level) prior to use.
-
The ESU should stand firm; no fluids should be placed on top of the ESU.
-
Do not use worn out or defective active electrodes, forceps or scissors.
-
Do not repair active electrodes, forceps or scissors.
-
Do not use the ESU in the presence of flammable material or substances (e. g. alcohol
or nitrous oxide).
-
The patient must be insulated against all electrically conductive parts. Make sure
that the patient does not come into contact with other metal parts not insulated from
the ground (e. g. operating table), although this concern is greatly diminished by
the use of isolated and/or balanced ESUs.
-
Place the patient on a dry, electrically insulating layer.
-
Pacemaker or defibrillator (all types): seek advice from competent authority prior
to endoscopy. Permanent ECG monitoring is recommended in these patients during electrosurgery.
The use of bipolar applications might minimize possible complications. If a monopolar
electrosurgical system is used, position the neutral electrode as close as possible
to the active electrode. Direct contact with the implanted device and the leads should
be avoided.
-
The power settings should be adapted to the type of procedure, tissue structure, patient
body mass index, endotherapy instrument used, and manufacturers’ recommendations.
Always use the lowest power setting possible that will accomplish the desired tissue
effect.
-
Before activating the ESU, the power settings should be rechecked and verbally confirmed
between the endoscopist and the assistant.
-
If current is not required, keep the foot away from the pedal to prevent accidental
pressing, or disconnect the electrode from the ESU.
-
If inadequate current output is observed, stop the procedure immediately. Use the
power switch as emergency stop for malfunctions. Leakage of current may be the result
of a malfunctioning endotherapy instrument, ESU or broken insulation of the endoscope
and may cause user and/or patient burns. Electrosurgical units that constantly monitor
leakage of current may help to ensure user and patient safety.
b) Staff safety
-
Avoid contact with the neutral electrode.
-
When applying current, always be sure to wear gloves and touch the equipment or patient
body with the entire palm of the hand, not with a single finger.
-
Electrosurgical equipment needs to be grounded in order to minimize interference with
videoendoscopic systems.
-
Smoke generated during electrosurgical procedures can be irritating and potentially
harmful to personnel; surgical masks and adequate ventilation of smoke may be useful.
c) Neutral electrode
-
Only patient neutral electrodes (plates or grounding pads) recommended by the ESU
manufacturer should be used. For example, some ESUs require split type plates to monitor
the quality of contact between the plate and the patient; single-use plates should
not be reused.
-
Check expiration date (if expired patient plates are used, the adhesive may fail to
maintain contact with the patient’s skin and burns may result).
-
Check the patient plate for any damage/modification or sharp edges.
-
The neutral electrode should not be attached over some structures, including bony
protuberances, metal implants or prosthesis, skin folds, scar tissue, hairy areas,
any form of skin discoloration/injury, limbs with a restricted blood supply, adjacent
to ECG electrodes or onto pressure areas/points.
-
The neutral electrode should be attached over well perfused muscle tissue; the skin
must be clean, dry, and free of hair to avoid loss of contact between the plate and
the skin. The electrode should not be completely wrapped around a limb. Overlapping
needs to be avoided. Ensure that the neutral electrode has full patient-skin contact.
-
The patient plate should be of appropriate size for the patient weight and should
never be cut to size.
-
Patient plates that have once been removed from the patient skin have to be replaced
by new ones.
d) Special situation: polypectomy or EMR
-
Adjust settings according to particular conditions (e. g. low power settings for small
bowel and cecum).
-
If polypectomy snare sticks in a polyp, increase cutting (see text above).
-
Do not touch metal parts, such as clips, with snare when applying current.
-
Do not touch the scope with metal parts of endotherapy instruments.
-
Watch out that snare tip does not accidentally touch the bowel wall opposite to mucosectomy.
-
Avoid deep coagulation of muscle layer (risk of late perforation).
-
Before applying current, make sure that the muscularis propria is not entrapped in
the snare loop.
1 Introduction
1 Introduction
Electrosurgery in endoscopy is an old technique, with urologists already using it
in an aqueous environment in 1926 [1]. Despite the availability of electrosurgical units (ESUs) with better safety profiles,
some practitioners still use electrosurgery under conditions that might be hazardous
with old technologies. In particular, ESUs with spark gap technology pre-date the
solid-state units introduced in 1968, and are no longer acceptable. Also obsolete
are ”grounded” or ”ground referenced” electrosurgical systems where the ground, not
the generator, completes the circuit. The replacement of this technology with isolated,
balanced, and return monitoring systems has virtually eliminated any risk to patients
that may arise from current division, in which all or part of the current seeks ground
through paths other than the neutral electrode, which could result in alternate site
burns. In addition to markedly greater patient safety, newer ESUs provide opportunities
for enhanced bipolar outputs and sophisticated neutral electrode safety monitoring
[2]. Moreover, the development of microprocessor-controlled ESUs has enabled more constant,
reliable or predictable qualities of current waveform, power output, and tissue effects.
2 Technical background
2 Technical background
2.1 Electricity and tissue effects
Electrosurgery is based on the transformation of energy from high frequency electric
current into heat, with the resulting effect of cutting and/or coagulating tissue
at the point of current application [3]. As current passes through tissue, electrons collide with various tissue components.
During these collisions, a certain amount of energy is dissipated depending on the
nature of the material traversed, which results in a rise in temperature. Electrosurgical
waveforms may be set to promote two types of tissue effects, namely coagulation (temperature
rises within cells, which then dehydrate and shrink) or cut (heating of cellular water
occurs so rapidly that cells burst). The proportion of cells coagulated to those cut
can be varied, resulting in a ”blended” or ”mixed” effect.
The rise in temperature is governed by Joule’s law:
Q = I2 × R × t
where Q is the heat generated by a current of constant intensity (I) flowing through
a conductor of electrical resistance (R), for a time (t) [3].
Tissue electrical resistance mostly depends on the degree of vascularization and water
content. For example, bone and fat present a higher electrical resistance than skin
and muscles. When electrosurgery is applied, progressive tissue desiccation increases
tissue resistance, which reduces current intensity.
2.2 Electrical circuit
Depending on the clinical indication and type of device used, energy may be transmitted
by ESUs in monopolar or bipolar mode.
-
In monopolar mode, the electrical current passes from the active electrode to the
target tissue, through the patient’s body, to finally exit the patient through a large
dispersive neutral electrode (also called a patient plate or return electrode) ([Fig. 1]).
Fig. 1 Monopolar electrosurgery. Electricity flows from the active electrode (usually inserted
through the working channel of the endoscope) to the neutral electrode placed on patient
skin.
-
In bipolar mode, the endoscopic device contains both the active and the neutral electrodes
in close proximity to each other. The electrical current passes directly from one
electrode to the other through a small amount of tissue in contact with both electrodes.
The current does not pass through the rest of the patient’s body and no patient plate
is required ([Fig. 2]).
Fig. 2 Bipolar electrosurgery. Electricity flows from the active to the neutral electrode,
both of them being located in close proximity on a single endoscopic device.
2.3 Current density and rise in temperature
Current density is the amount of electrical current per unit area of cross section.
In a monopolar circuit, current density is relatively high at the point of tissue
contact with the active electrode due to the small contact area; current density is
considerably lower at the point of contact between the patient and the neutral electrode
because the larger surface area of the latter disperses the current returning to the
ESU.
If we assume that tissue electrical resistance is uniform and heat conduction is negligible,
the increase in tissue temperature is directly related to the amount of electrical
energy absorbed by the tissue. This amount (QE) can be expressed by the equation:
QE = (I2 × R)/S
where R represents tissue electrical resistance, I the current intensity, and S the
surface of tissue in contact with the electrode.
When electrical current is applied for 1 second, tissue temperature increases according
to the following equation (assuming that all the electrical energy is transformed
into heat):
ΔT = (K × QE)/S = (I2 × K × R)/S2
where K is a tissue-specific heat parameter.
Tissue temperature increases with the square of the current intensity. QE may be adjusted
to cause an increase in tissue temperature at the level of contact with the active
electrode while thermal effect at the level of the neutral electrode, which is considerably
larger, is negligible. Conversely, if the patient is in contact with a small portion
of the neutral electrode, or if the neutral electrode is not correctly oriented, the
temperature at this level may rise and cause skin burn ([Fig. 3]).
Fig. 3 Placement of the neutral electrode (”patient plate”) for monopolar electrosurgery.
a Correct plate positioning, with its ”long edge” directed towards the operative field.
b Wrong plate positioning, with the ”short edge” directed towards the operative field
(high current density at the plate corner might cause extended heating or ”asymmetry
alarm”). c Neutral electrode equipped with an equipotential ring requiring no particular plate
orientation.
Therefore, it is important to ensure that the patient skin is in good contact with
the entire surface of the neutral electrode and avoid any interfering matter (e. g.
cream, hair, scar) that could decrease conductivity and cause skin burns. A ”contact
quality monitor” (CQM) ESU system, combined with split patient plates, helps to prevent
the development of such burns as the CQM shuts down power delivery if the contact
surface becomes too small. The neutral electrode should also be positioned as close
as possible to the active electrode to reduce passage of electrical current through
the patient’s body.
2.4 Current frequency
Human myocardium is sensitive to household alternating electrical currents of low
frequency, with a risk of ventricular fibrillation and cardiac arrest. High frequency
current (> 300 kHz) is used in electrosurgery because myocardium sensitivity decreases
with increasing current frequencies. However, the risk of electrostatic losses increases
with increasing frequencies, thus reducing the efficiency of current application and
increasing the risk of burns to either the operator or the patient. Therefore, high
frequency currents in the range of 300 – 1000 kHz are usually employed during electrosurgery.
2.5 Current waveforms
High frequency currents generated by ESUs consist of one of the two following types.
-
Pure sinusoidal current waveform ([Fig. 4 a]):
– the ”crest factor” (ratio of the peak to the root-mean-square voltage) is constant
at 1.4 for every sinus waveform;
– higher peak voltages provide more intense coagulation/hemostasis effects;
– if the voltage peak (Vp) is below 200 V, it is insufficient for a cutting effect,
but it is ideal for soft coagulation;
– Vp of approximately 300 V enable a ”pure” cutting effect with the smallest possible
coagulation effect.
-
Amplitude modulated current waveforms ([Fig. 4 b]):
– the crest factor varies between 1.5 and 8, with increasing crest factors providing
deeper coagulation effect;
– in some ESUs, cutting and coagulation currents with these characteristics are named
”Blend Cut” or ”Dry Cut” and ”Fulgurate,” ”Forced Coag” or ”Spray Coag,” respectively.
Fig. 4 Current waveforms used in electrosurgery. a Pure sinus current waveform: continuous sinusoidal waveform with a crest factor (ratio
of the peak to the root-mean-square voltage) of 1.4; b Modulated current waveform: crest factor may vary between 1.5 and 8.
Some ESUs combine cutting and coagulation waveforms in one mode that alternates each
type of waveform (e. g. Endocut, Pulsecut) ([Fig. 5]).
Fig. 5 Endocut and Pulsecut modes, consisting of alternating cutting and coagulation currents.
3 Electrosurgical units
3 Electrosurgical units
All ESUs available for endoscopic use in Europe provide basic features including current
waveforms for cutting and coagulation of several characteristics, blended currents,
as well as CQM (provided that an adequate neutral electrode is used). In addition
to this, some ESUs provide modes that alternate cutting and coagulation phases (and,
in some units, adaptation of the current according to continuous measurements made
during the procedure, making a closed-loop feedback) or a bipolar cutting mode. Some
ESUs allow the user to modify many parameters of the current selected ([Fig. 6]), to connect optional modules that provide argon plasma coagulation (APC) or irrigation
through ancillary devices.
Fig. 6 Endocut settings that can be adjusted by the operator include the duration of the
cutting phase, the interval duration between cutting phases, and the coagulation effect.
Some ESUs also support the use of a single device that allows both injection and dissection
during endoscopic submucosal dissection (ESD). The size of the ESU may also be an
important factor in small endoscopy rooms. Additional information on ESUs is available
from Morris et al. [4].
4 Interference with other electrical equipment
4 Interference with other electrical equipment
Modern endoscopy units are equipped with several electrical devices and appliances
that may potentially give rise to electrical interferences. For example, the electrocardiograph
(ECG) can create a false ground and skin burns can develop at points of contact with
the electrodes if the electrode cables are placed close to, or entwined with, cables
leading to the active electrode.
In a patient with a cardiac pacemaker or an implantable cardioverter-defibrillator,
constant supervision must be maintained when applying high frequency current, particularly
in monopolar mode, as it can result in cardiac arrest in a truly pacemaker-dependent
patient. Monitoring of the patient ECG must include the possibility to detect pacemaker
discharges (artifact filter should be disabled) and peripheral pulse should be monitored
using a pulse oximeter [5]. Defibrillator equipment should be readily accessible. A preprocedure electrocardiogram
should be obtained and, if necessary, the device should be reset in ventricular asynchronous
(VOO) mode. This type of adjustment should be made by the appropriate personnel (e. g.
cardiologist or pacemaker technician), and once the endoscopic procedure is terminated,
the device is interrogated and reset to the preprocedure mode. During the procedure,
bipolar electrosurgery is preferred, if feasible. If the monopolar mode is used, pure
cut current may be preferable and the neutral electrode is positioned in a location
that minimizes the current crossing the pacemaker-heart circuit. In emergent situations,
placing a magnet close to the device temporarily ”reprograms” the pacer into asynchronous
mode if the device has a magnet mode (most have). A magnet marketed by one pacemaker
manufacturer is usually effective with other brands of pacemaker.
5 Electrosurgical settings
5 Electrosurgical settings
Heat generated in the digestive mucosa is directly proportional to the square of current
intensity (e. g. if current intensity is doubled, the heat generated increases by
a factor of 4). Understanding this relationship between current intensity, density,
and heat is essential for adequate ESU operation. As an example, the thermal effect
of current application to the base of a polyp is shown in [Fig. 7].
Fig. 7 Current densities during polypectomy at various levels of a polyp stalk. The density
of the monopolar current administered through the snare (and, hence, the rise in temperature)
varies according to cross-sectional areas.
All other things being equal, the larger the base of the polyp or the snare wire,
the more energy will be required to section it. Manufacturer-recommended settings
for various applications are presented in the Appendices available on line. Settings
can be adjusted before and during the procedure according to the endoscopist preferences
and desirable therapeutic response. For example, in the Endocut mode, no coagulation
is applied between cutting cycles if the lowest ”effect” level is selected, which
may be useful at limiting coagulation-related damage in the cecum. During ESD using
a Flush knife, coagulation may be switched from ”Soft Coag” to ”Forced Coag” to treat
a bleeding vessel.
6 Practical applications
6 Practical applications
6.1 Polypectomy
Although this section deals with colon polypectomy, the principles described here
are applicable to other polypectomy sites. Bleeding is the most frequent complication
of polypectomy, occurring in 1 % – 4 % of cases, compared with a 0.5 % risk for perforation
[6].
6.1.1 Polypectomy snares
Polypectomy snares of different size, shape, and wire characteristics are commercially
available. A snare with a particular diameter and shape is selected according to the
size of the polyp and bowel features (e. g. a small oval snare is preferable for removing
a small polyp in a diverticular-laden, narrow, colonic segment). It is important to
have a snare design that facilitates capture of the lesion; rotatable snares may facilitate
polyp grasping. Features of the snare wire may also influence the electrosurgical
outcome, as a thin or monofilament wire will favor cutting whereas a thick or braided
wire will favor coagulation. As manufacturer-recommended settings are not uniformly
based on a particular type of snare and wire characteristic, ESU settings may need
to be adjusted accordingly, depending on the type of snare used (e. g. by testing
on a piece of meat ex vivo). Thicker snares require higher power settings (powerful
cut with limited coagulation). Any alteration to the snare wire (especially fraying)
may lead to an increase in the contact area between the polyp and the snare, resulting
in decreased efficiency. Also, the speed of snare closure directly affects the efficacy
of the current applied and outcome. For example, closing the snare too fast might
result in insufficient tissue coagulation, resulting in bleeding.
6.1.2 Current application
Prototype bipolar snares have been assessed in experimental studies, but monopolar
snare polypectomy is currently the standard of practice [7]. The use of blended or coagulation current, rather than pure cut waveforms, is recommended
for polypectomy. In a large multicenter study encompassing more than 9000 polypectomies,
the use of pure cut current was associated with the highest odds ratio for immediate
postpolypectomy bleeding along with inadvertent cold polypectomy (odds ratio of 6.95
and 71.15, respectively) [8]. In a single-center report of a large series of polypectomies using pure cut current,
the bleeding rate was acceptable (3.1 % of patients) but the authors insisted on the
need to have hemoclips readily available as these were used in 12 % of their patients
[6].
In a retrospective study that compared blended with coagulation current, the incidence
of postpolypectomy bleeding was similar in both groups of patients but the time interval
to bleeding was different. Immediate postpolypectomy bleeding was more frequent with
blended current, whereas delayed bleeding (2 – 8 days postpolypectomy) occurred more
frequently with coagulation current [9]. Patient circumstances may influence the selection of a particular current waveform,
as it may be more practical to treat immediate rather than delayed bleeding.
The type of current used may also affect the adequacy of resected polyps for histopathological
examination. A retrospective study compared polypectomy specimens obtained using two
different current settings: ”blended 2” current at a setting of 30 W (model not specified;
ValleyLab, Boulder, Colorado, USA) and Endocut with cutting and coagulation settings
of 120 W (ICC 200, Erbe, Tübingen, Germany). A dedicated pathologist blinded to the
resection technique found that resection margins were evaluable in 60.3 % vs. 75.7 %
of the polyps resected using blended 2 vs. Endocut current, respectively (P = 0.046) [10].
In the absence of firm evidence-based data, no specific recommendation can be made
regarding the selection of a particular electrosurgical current for polypectomy except
for the avoidance of pure cut current. A recent survey found that identical proportions
of endoscopists used coagulation current (46 %) and blended current (46 %) for polypectomy,
whereas only a small number of responders used pure cut (3 %) or modified the current
during polypectomy (4 %) [11].
Practical recommendations regarding the technique of snare polypectomy include the
following.
-
Once seized with a snare, the polyp should be tented away from the colon wall in order
to decrease the risk of perforation.
-
During polypectomy, tissue resistance will increase as desiccation occurs, and sectioning
the central part of the polyp base is therefore slower.
-
Contact between the surface of the polyp and the bowel wall should be avoided to minimize
contralateral burn. This may be difficult with a very large polyp, but wiggling the
polyp during current application will minimize damage of normal tissue in contact
with the polyp being resected.
-
A risk of snare entrapment in desiccated tissue exists for very large polyps. If the
area of contact between the snare and the tissue is large, current density may be
too low to efficiently section the polyp base. The natural tendency is to increase
snare tightening around the polyp but this may section the tissue without providing
enough coagulation or increase the area of contact between the snare and the tissue
surrounding the metal wire, further decreasing cutting efficiency. This situation
can best be avoided by not overly tightening the snare (strangulation) or attempting
polypectomy on a large pedicle with too low a power setting. Some theorize that using
a cut mode that provides automatic power adjustment (e. g. Endocut) may be of benefit,
but this has not been studied in a randomized trial. Otherwise, if entrapment occurs,
it may be beneficial to pause to allow the tissue to reabsorb some water and then
to adjust the power settings of the ESU in a stepwise manner.
6.1.3 Resection of small polyps with a hot biopsy forceps
Polypectomy using a hot biopsy forceps should be avoided as this technique leaves
residual neoplastic tissue in situ in 15 % of cases and the pathological examination
of resected specimens is severely hampered by thermal artifacts [12]. If the technique is nevertheless used to sample a large polyp or to resect a polyp
of less than 5 mm, the forceps should be tented away from the bowel wall to allow
for current concentration to a relatively small area and limit thermal damage to the
submucosa. As the area of contact between the metal cups of the forceps is relatively
large, the current in the tissue can be sizeable, resulting in a significant thermal
effect. A deep thermal effect can cause delayed wall necrosis and perforation, particularly
in areas where the digestive wall is thin, such as the cecum and ascending colon.
6.1.4 Risk of explosion during colon polypectomy
Several case reports have described explosions occurring at the time of electrosurgery
in the colon. The risk of explosion exists when combustible gas concentrations are
elevated in the colon (methane > 5 %, hydrogen > 4 %, and oxygen > 5 %) [13]. These conditions may be present in poorly prepped or unprepped colons, or when
mannitol-based bowel preparations are used [14]. With the advent of polyethylene glycol or sodium phosphate-based preparations for
bowel cleansing, this concern has markedly decreased. Using carbon dioxide for gut
distension during endoscopy can also minimize the explosion risk.
6.2 Sphincterotomy
6.2.1 Sphincterotomes
Sphincterotomes consisting of monofilament or braided cutting wires are commercially
available. Monofilament sphincterotomes may provide a more clear-cut incision with
less risk of heat injury at the sphincterotomy edges and the ampullary area but, to
our knowledge, a prospective randomized trial comparing the two devices has yet to
be performed. One of the available sphincterotomes (CleverCut, Olympus Inc., Tokyo,
Japan) has the proximal part of the exposed wire covered with insulation material
to decrease contact between the wire and the endoscope or surrounding tissues. Sphincterotomes
may have one, two or three independent lumens to accept the cutting wire, a guide
wire, and contrast medium. Single-lumen sphincterotomes are rarely used as the guide
wire should be removed during sphincterotomy (electric short circuits may develop
between the cutting wire and the guide wire if guide wire insulation is defective,
inducing lesions at the distal end of the guide wire) [15]. A double-lumen sphincterotome equipped with an angled Tuohy-Borst valve (DASH,
Wilson Cook Inc., Winston-Salem, North Carolina, USA) allows injection of contrast
medium when a guide wire has been inserted into the sphincterotome because the valve
prevents spillage of contrast medium during injection. Rotatable sphincterotomes (e. g.
Autotome, Boston Scientific Inc., Natick, Massachusetts, USA) may be useful, particularly
in difficult situations such as Billroth II anatomy.
6.2.2 Current application
Factors associated with a higher effectiveness for cut initiation and propagation
during biliary sphincterotomy in an experimental setting include a smaller diameter
of the electrode wire, a shorter length of wire in contact with the tissue, a higher
force applied with the wire onto tissue, and higher power settings [16]. Practical issues related to sphincterotomy are as follows.
-
If no effect is observed within one or two seconds after current application, it may
be useful to reduce the length of wire in contact with the surrounding tissue.
-
Uncontrolled rapid cutting (”zipper effect”), a potentially dangerous event, may develop
as the length of wire in contact with the tissue decreases (e. g. once tissue has
been cut) or if the force applied with the sphincterotome is high.
The type of current used for sphincterotomy (pure cut vs. blended) does not influence
the incidence or severity of pancreatitis, the most frequent complication of sphincterotomy,
as shown in a meta-analysis of randomized trials [17]. One of the trials in the meta-analysis, in which the Endocut mode was used to provide
blended current, failed to show any significant difference in terms of postsphincterotomy
pancreatitis with Endocut vs. pure cut current [18]. However, pure cut current was associated with a higher incidence of bleeding. Blended
current is recommended for biliary sphincterotomy, particularly in patients at high
risk of bleeding [19]. Current modes that provide alternating cutting and coagulation phases (e. g. Endocut,
Pulsecut) are increasingly being used, in part due to the impression that they provide
better control of the cut. The Endocut I mode has been specifically designed for sphincterotomy
but has not been validated in controlled trials.
As heating related to coagulation is thought to favor the development of local edema
that might obstruct pancreatic outflow, the combination of current waveforms has been
explored as a potential means to reduce postsphincterotomy pancreatitis (e. g. pure
cut current for sphincterotomy initiation followed by blended current after having
cut 3 – 5 mm of tissue). However, comparative studies of combined current waveforms
vs. pure cut or blended current used throughout sphincterotomy have found no difference
in the outcome of postsphincterotomy pancreatitis [20]
[21].
6.3 Hemostasis
All ESUs offer coagulation modes that can be applied immediately during a cutting
procedure using a nonspecific device (e. g. applying coagulation current at the bleeding
edge of a biliary sphincterotomy using the sphincterotome wire) or to treat a spontaneously
bleeding lesion with a specific device (e. g. bipolar coagulation probe).
A range of devices are available for either monopolar or bipolar coagulation. These
devices include APC probes, coagulating forceps, and bipolar probes. These latter
devices require contact with tissue and allow for immediate hemostasis by compressing
the bleeding vessel (tamponade). APC is particularly useful in treating large surface
areas; it should be used with caution in the vicinity of hemostatic endoclips, as
the latter are current conductors.
APC is a noncontact, monopolar, electrocoagulation technique that works by applying
high frequency current to the tissues through ionized argon (argon is an inert gas
that requires to be ionized to conduct current). As the current exiting the tip of
the APC probe follows the path of least resistance, tissues that are already coagulated
(and, hence, of increased electrical resistance) receive less current than surrounding
tissues. The high frequency current is applied while attempting to avoid direct contact
between the probe and the bowel wall in order to avoid gas injection into tissue (pneumatosis).
Compared with contact methods of coagulation, APC provides a more homogeneous tissue
effect and can treat large surface areas more rapidly. Also, it may harbor a lower
perforation risk because the penetration depth is limited to 1 – 3 mm [22]. However, APC lacks the mechanical (tamponade) hemostatic effect of contact techniques.
APC is mainly used for:
-
coagulating superficial vascular lesions (e. g. sporadic angiodysplasias, gastric
antral vascular ectasia, radiation proctitis);
-
palliative ablation of tumors, in particular tissue ingrowth/overgrowth of esophageal
stents;
-
ablation of residual polyp tissue after piecemeal resection of large sessile polyps
[23];
-
transection of metal stents at high power settings (e. g. migrated biliary stents
impinging onto the contralateral duodenal wall, causing obstruction and ulcers) [24].
Practical recommendations regarding APC use include adequate bowel cleansing (for
colonic applications), avoidance of APC in the vicinity of metallic devices (e. g.
clips), and intermittent suctioning of the argon gas to minimize gut distension.
6.4 Endoscopic mucosal resection and submucosal dissection
Endocut and Pulsecut are commonly used settings for endoscopic mucosal resection (EMR)
and ESD, although some endoscopists use pure cut waveforms. Compared with EMR, ESD
is technically more challenging and time consuming but enables en bloc resection in
most cases. The instruments (knives) used for dissection and the type of current waveforms
and power settings selected are influenced by various parameters, such as lesion location,
tissue characteristics, and operator preferences. As the technique of ESD is not yet
standardized, endoscopists mainly rely on personal or reported experience thus far.
7 Monopolar vs. bipolar accessories
7 Monopolar vs. bipolar accessories
All ESUs used in digestive endoscopy provide monopolar and bipolar modes; few provide
bipolar cutting current. This is due to the limited availability of devices adapted
for bipolar use apart from coagulation probes. Prototype bipolar polypectomy snares
[7], hot biopsy forceps [25], sphincterotomes, and needle knife for ESD [26]
[27] have been developed to profit from their theoretical advantages over monopolar devices
(i. e. less power to achieve similar effects and more superficial delivery of energy
with decreased risk of perforation) [25]
[28]. However, these bipolar devices are not widely available, in part due to their more
complex design and fabrication costs relative to their monopolar counterparts.
Bipolar mode is currently used almost exclusively with catheter probes designed for
hemostasis of nonvariceal bleeding lesions. This type of probe provides treatment
outcomes similar to other effective modalities [29]. Bipolar probes usually permit irrigation, which is particularly useful if an endoscope
with a single working channel is used.
8 Conclusion
8 Conclusion
Digestive endoscopy has been developing as a therapeutic tool for more than 30 years,
with electrosurgery being an essential part of this development. In electrosurgery,
high frequency current is used to produce heat in tissue. Various parameters, including
current waveform, power setting, type of active electrode, and duration of current
delivery allow control of tissue heating and the resulting outcome of cut and/or coagulation
of tissue. The safe and effective performance of electrosurgery during endoscopy requires
an understanding of these parameters.
Acknowledgment
Acknowledgment
The authors thank P. Dumonceau for assistance with generating the figures.
Competing interests: Representatives from the following companies participated in an advisory capacity:
J. Raiser (Erbe Elektromedizin, Tübingen, Germany), I. Mesecke-von Rheinbaben (Olympus
Europa, Hamburg, Germany), T. Carter (Boston Scientific, Hemel Hempstead, UK), and
C. Tockweller (Gebruder Martin GmbH, Tuttlingen, Germany).
