Tools and Accessories for ESD

Solution

Cushion duration^a

Cost

Viscosity (Pa.s)

Comments

Normal saline

0.0043

Cost-effective and readily available, but dissipates quickly

Hydroxypropyl methylcellulose

+++

0.0022

Relatively inexpensive with a durable lift

Hydroxyethyl starch (Voluven)

+++

0.0026

Commonly available and has a better lift than normal saline

Hydroxyethyl starch (Hetastarch)

0.0075

Similar to Voluven

Sodium hyaluronate

+++++

0.04

Gold standard, but costly and with limited availability

Eleview

++++

<0.02

New product, purpose designed for submucosal injection, costly

^aData suggests that although cushion duration is statistically different in normal saline compared to other injection fluids discussed here, the differences between other injection fluids (e.g., hydroxypropyl methylcellulose and sodium hyaluronate) are not statistically significant

Saline

Normal saline (0.9% NaCl) is isotonic and commonly used for most EMRs. Main advantages include familiarity and ease of use, availability, and cost-effectiveness. Normal saline is also safe to the surrounding tissue and with minimal specimen distortion on histology. The drawback of normal saline is that it diffuses quickly following initial submucosal injection, thereby requiring the need for multiple repeated injections for lift maintenance, which is not ideal for a long procedure like ESD.

Hypertonic solutions such as hypertonic saline (3.75% NaCl) as well as dextrose water have longer-lasting submucosal fluid lift when compared to normal saline but are on the whole still generally unsatisfactory with the additive risk of tissue injury due to high osmolality. Indeed, high concentrations of saline have been shown to give rise to delayed mucosal injury.

Carbohydrate-Based Solutions

Hydroxypropyl methylcellulose (Gonak 2.5%, Akom Inc., Somerset, NJ, USA) is a water-soluble polymer derived from cellulose. This provides readily available, lower-cost viscous fluid that is safe for injection. 15 mL of 2.5% solution is typically diluted with 85 mL of normal saline to make 100 mL of injectate [5]. This preparation has been demonstrated to provide a higher and more durable lift when compared to normal saline [6] and, in a retrospective study on EMR by Bacani et al., was shown to have longer lift effect (15–20 min) compared with normal saline (2–3 min) [7].

Hydroxyethyl starch (6% Voluven, Pfizer, NY, NY, USA; Hetastarch, Hospira, Inc., Lake Forest, IL, USA) originally used as a crystalloid solution for intravascular replenishment has a similar durability to hydroxypropyl methylcellulose in animal models. In clinical use, a comparative study by Fasoulas et al. showed that hydroxyethyl starch had more durable lift, required less solution, and resulted in a faster resection time compared with normal saline. There was no observed difference in safety or long-term outcomes in either arm [8].

Sodium Hyaluronate

The prototypical high-viscosity solution has been sodium hyaluronate (MucoUp, Boston Scientific, Tokyo, Japan), with extensive data from Japan where it is commonly used in ESDs. Not only has it been shown to provide one of the most sustainable mucosal lifts, but porcine data suggests that it also results in a steeper mucosal elevation compared with colloids or saline, which is useful in ESD as steeper borders facilitate snaring. The downside to sodium hyaluronate solutions would be the high cost of such preparations, which can come up to approximately 40 times that of carbohydrate-based solutions. Hyaluronate solutions are available in the USA in various preparations as a viscosupplement (Healon, Abbott Laboratories, Abbott Park, IL, USA; Hyalgan, Fidia Pharma USA Inc., Florham Park, NJ), but the cost is generally prohibitive for its use as a mucosal lift solution.

Eleview

Eleview (Aries Pharmaceuticals, San Diego, CA, USA) is a proprietary composition (Fig. 5.1) designed for use for submucosal lift in gastrointestinal endoscopic procedures and combines medium-chain triglycerides, poloxamer 188 (bulking agent), polyoxyl-15-hydroxystearate (surfactant), and methylene blue (dye) in suspension. Animal models suggests a mucosal lift superior to normal saline, and this is borne out by clinical data which suggests a small volume required per lesion as well as an overall faster resection time. As a new proprietary product, the cost of this would also be considerable.

../images/442926_1_En_5_Chapter/442926_1_En_5_Fig1_HTML.png — Fig. 5.1

Eleview . (Photo Credit: Olympus, Olympus America, Center Valley, PA, USA)

Caps/Distal Attachments

Lack of triangulation and tissue retraction are the main drawbacks of efficient tissue dissection during ESD. To facilitate tissue retraction and visibility, a cap or distal attachment is routinely used. The distal attachment is a clear transparent hood that is affixed to the end of the endoscope, to allow it to retract folds or resected tissue to get a clear view of the resection field. It also provides firm traction to the target tissue, allowing optimal dissection [2].

The cap does slightly decrease the peripheral endoscopic visual field, but this trade-off is inevitable given the need for retraction and adequate visualization of the resection field.

The cap, being a simple plastic tube, is not difficult to manufacture; and a variety of brands and designs are available, with a straight cap being the most commonly used and widely applicable. Caps are also available with the edge being tapered like a short funnel for entering narrower spaces, as well as angle tips which have a beveled edge that offers better retraction of tissue mainly in one direction, for example, in the peroral endoscopic myotomy (POEM) procedure.

The soft distal attachment (Olympus America, Center Valley, PA, USA; Fig. 5.2) is one of the more commonly used caps and offers a drainage hole which is usually placed at 12 o’ clock with respect to the screen which would allow drainage of excess fluid at the site opposite to the scope suction channel which usually comes out at 7 o’ clock [5].

../images/442926_1_En_5_Chapter/442926_1_En_5_Fig2_HTML.png — Fig. 5.2

Distal attachments used in ESD. (a) Olympus distal attachments. (Photo Credit: Olympus America, Center Valley, PA, USA). (b) Short-type (ST) hood. (Photo Credit: Fujifilm America, Valhalla, NY, USA)

The short-type (ST) hood (Fujifilm America, Valhalla, NY, USA; Fig. 5.2) is a cap with a tapered tip, which is useful for accessing a submucosal tunnel, such as in the POEM procedure or resections employing the tunnel technique. It also has a drain design allowing flow of fluid around the cap for better visibility.

Electrosurgical Generators and Electrical Currents

ESD requires a modern electrosurgical generator to provide the modulated current options that help deal with various phases of the resection. These produce high-frequency (>100,000 Hz) current to avoid neuromuscular depolarization, at varying energy levels to achieve tissue effects.

At slow heating of tissue at lower energy levels, the tissue gradually heats to beyond 50 °C and dries out, and this desiccation causes shrinkage of tissue resulting in a coagulation effect. Because energy transfer is lower, direct contact is required.

At rapid heating of tissue at high energy levels, water in tissue vaporizes to steam beyond 100 °C; and this vaporization disrupts cell structures, causing a cutting effect. Because the energy transfer is high, the current sparks from the electrode to the tissue, and the effect can be achieved at a very short distance from the electrode.

Generator Unit

Modern electrosurgical generators are able to alternate between the two modes and have options to have a combination of both effects, which is termed a blended current. This allows fine-tuning of the current to the stage of the procedure and greatly enhances the speed and hemostasis of the dissection. The ESGs available in the USA that are suitable for ESD are the ICC 200E, the VIO 200S and VIO 300D (ERBE USA, Marietta, GA, USA; Fig. 5.3), and the ESG 100 (Olympus America, Center Valley, PA USA).

../images/442926_1_En_5_Chapter/442926_1_En_5_Fig3_HTML.png — Fig. 5.3

ERBE VIO 300D generator unit . (Photo Credit: ERBE USA, Marietta, GA, USA)

Current Modes

The various modes of electrosurgical generators have been reviewed extensively in an ASGE review [9], and a synopsis focusing on the ERBE electrosurgical unit is outlined in Table 5.2, and these are used to discuss steps in ESD. It must be noted that some variations in the use of electrosurgical modes exist among experts, due to differences in the type of knife used, as well as some local practice differences (types of ESD performed, mucosal lift solution used, the typical amount of fibrosis encountered, etc.).

Table 5.2

Summary of electrosurgical generator modes and utility in ESD

Mode	Features	Some uses in ESD
Endo cut	A cutting mode with alternating cut coagulation modes cycling to achieve cut and a concurrent, milder hemostatic effect	Mucosal incision Dissecting dense fibrotic tissue in the submucosal space
Dry cut	A cutting mode similar to endo cut but with enhanced coagulation, consequently with greater thermal effect	Precise submucosal dissection Mucosal incision when bleeding is a problem
Forced coagulation	A coagulation mode with high voltage	Submucosal dissection in vascular tissues
Soft coagulation	A coagulation mode with relatively low voltage. As tissue desiccates, resistance increases and the current falls, allowing the tissue to fall off with less char and controlled energy application	Hemostatic forceps Lesion marking
Swift coagulation	A coagulation mode with enhanced cutting properties. Less hemostatic than forced coagulation, but more hemostatic than dry cut (and less cutting effect)	Pinpoint hemostasis of vessels Creating a divot during coagulation
Spray coagulation	A coagulation mode with a continuous very high voltage resulting in arcing to surrounding tissue, similar to argon plasma coagulation	Non-contact hemostasis POEM procedure for ease of submucosal tunneling with concurrent non-contact hemostasis

Mucosal Markings

Careful inspection is the first step to any resection to determine the edge of the lesion, also termed the demarcation line, which is the junction between the lesion and the surrounding normal tissue. This is typically done with image-enhanced endoscopy (such as narrow band imaging or blue laser imaging) and chromoendoscopy employing methylene blue, indigo carmine, or, in the case of squamous lesions of the esophagus, Lugol’s iodine.

Circumferential mucosal markings are typically placed for gastric and esophageal ESDs (although not always for rectal ESDs) at the start of the procedure approximately 5 mm from the demarcation line to guide subsequent injection and dissection. This key first step helps to ensure adequate lateral margin. The tissue is lightly touched with the tip of the ESD knife with soft coagulation or endo cut modes to create a visible superficial burn mark. Alternatively, argon plasma coagulation can also be used to mark the margins, but this adds additional cost and necessitates switching instruments. Use of forced coag current should be avoided because it creates extensive tissue damage which may compromise lateral margin evaluation and can also serve as an escape point of the submucosal injectate.

Incision

Mucosal incision , both the initial incision and the circumferential incision, separates the lesion’s lateral borders from the rest of the tissue and allows access to the deep submucosal space. This can be achieved with endo cut (ERBE)/pulse cut (Olympus), although dry cut or swift coagulation modes have also been deployed, depending on the knife and type of tissue dissected.

Dissection

Classically, forced coagulation has been used to dissect through the generally vascular submucosal space, particularly under a lesion with neovascularization with fine vessels; and a good coagulative effect is desirous. If the submucosa is less vascular, swift coagulation or dry cut modes can also be used, with the advantage of creating less carbonization.

Fibrotic tissue has less water content and easily carbonizes with coagulation modes; hence, careful application of a cutting mode , for example, endo cut or dry cut, should be employed because submucosal lift cannot be achieved and the margin of error above the muscularis propria is small.

Hemostasis

When it comes to hemostasis , an ounce of prevention is worth a pound of cure. Preemptively identifying and addressing vessels in the submucosal space keeps the dissection field clean and clear and eventually leads to faster resections. Every attempt should be made to effectively coagulate vessels before cutting through the area and causing active bleeding.

The general rule of thumb for vessels smaller than 1 mm would be to use the same electrosurgical knife and switch to a coagulating mode (forced coagulation, dry cut, or swift coagulation). It is worth remembering that total energy delivered is a function of both power and time, and adequate time has to be spent in the particular spot for the coagulation mode to work.

For vessels larger than 1 mm, it is often worth the while to change out to hemostatic forceps such as the Coagrasper (Olympus America, Center Valley, PA USA), grasp the vessel, and use soft coagulation to deliver a controlled burn to the target. The same is typically applied to bleeding vessels, with grasping of the bleeding spot, careful retraction to achieve gentle tenting of the spot, and application of soft coagulation until adequate hemostasis. Importantly, only soft coagulation current should be used with coagulating forceps.

For hemostasis of active bleeding during resection, the same principle applies. For low-level bleeding such as a small vessel or venous ooze, the same ESD knife can be employed with consideration to switch to a more coagulative current. For brisk bleeding, usually from a sizable artery, the coagulating forceps should be employed. As blood accumulates and obscures the endoscopic view, the earlier the bleed is dealt with, the better. The use of a through-the-scope water jet is advisable if not mandatory to flush away the blood to identify the bleeding point for effective hemostasis.

It should be emphasized that electrosurgical settings are a very important component of safe and effective ESD, yet multiple other factors contribute to the final tissue effect. Some of these factors are related to the device in use (material and thickness of the ESD knife electrode), some are related to the endoscopist technique (the speed of movement of the electrode, the amount of contact between the tissue and the electrode, the pressure applied by the electrode, the amount of time the generator stays activated), and finally some are dependent on the type of target tissue itself (water content and degree of fibrosis). Therefore, frequent change of electrosurgical unit settings is typically not needed because the endoscopist can vary many of the factors listed above. Furthermore, this complex environment highlights the fact that there is no one “best” electrosurgical unit set of settings.

ESD Knives

At the heart of the specialized instruments that make ESD possible are the ESD knives . These are essential for dissection of the submucosal plane and come in a wide variety of forms (Fig. 5.1). Categorizing them broadly by form, we have needle knives which are bare, metal fine-tip knives, insulated-tip (IT) knives which have a ceramic non-conducting tip that limits current at the very tip of the knife and mainly allows controlled dissection along the shaft, and scissor-type knives which resemble a pair of shears in design and function. These are available in various forms from different manufacturers and are elaborated in detail in the following [2] and summarized in Table 5.3.

Table 5.3

Characteristics of selected ESD tools

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