Overtubes have the ability to facilitate luminal access during POEM and potentially limit oropharyngeal trauma with repeated esophageal intubation throughout a procedure. An overtube is a semirigid plastic sleeve-like conduit device with a soft, tapered, distal tip. The inner diameter is larger than the endoscope, with the distal end tapering to closely match the diameter of the endoscope to minimize the likelihood of mucosal entrapment between the two devices during exchanges [14]. Overtubes vary in length and caliber depending on the indication and route of access. To protect the cricopharyngeal area or airway, such as in POEM, the length needs to be 20–25 cm [14]. Overtubes are intended to facilitate endoscopy by protecting the mucosa from trauma during scope insertion, maintaining linear stability, and reducing the risk of aspiration [14]. Additionally, the sealed distal end may limit proximal gas loss (CO₂ or air) and maintain better insufflation during the procedure. We utilize a 25 cm Guardus overtube (US Endoscopy) (Fig. 3.2a) during POEM and secure it to the patient with umbilical tape (Fig. 3.2b).

Specifically for POEM, the overtube acts to stabilize the endoscope and maintain consistent access for repeated reinsertions. This limits transmission of pushing forces applied to the mucosa and may limit mucosal laceration and gaping, especially at the esophageal mucosotomy site during POEM [7, 13]. During POEM, a diagnostic upper endoscopy is first performed without the device to ensure that the overtube does not interfere with the initial insertion and obscure markings on the endoscope [14]. The overtube can be preloaded onto the endoscope, and once the diagnostic exam is complete, it is advanced over the endoscope to promote procedural efficiency and avoidance of reinsertion. Liberal use of lubricant to the endoscope and inner and outer surfaces of the overtube prior to insertion is helpful, and any resistance during passage necessitates reassessment [14]. Although water-based lubricants are commonly used, they can desiccate during the extended time required to complete the POEM procedure in many cases. Medical grade olive or vegetable oils are available alternatives and maintain lubricant features for prolonged periods, thus facilitating device movement. Complications such as mucosal abrasion and tears have been reported, with overtube use secondary to the large diameter or pinching of the mucosa between the overtube and endoscope. Proper insertion techniques over a bougie or endoscope reduce this risk [14].

Carbon dioxide (CO₂) gas insufflation is utilized during the procedure with a CO₂ insufflator CO₂MPACT™ (Bracco Diagnostics, USA) (Fig. 3.3) at our institution, or Olympus UCR (Olympus, USA) [2, 9, 11], and a standard low-flow insufflation tube (MAJ-1742, Olympus America) [2] (Fig. 3.4). The use of a CO₂ gas insufflation unit is preferred for performance of POEM as regular room air insufflation may lead to unique complications. Utilizing CO₂ insufflation with a low controlled gas flow of 1.2 L/min is beneficial for decreasing the risk of the gas dissecting through small holes in the longitudinal muscle causing pneumomediastinum, pneumoperitoneum, and air embolism [13, 15]. If dissection does occur, however, CO₂ is rapidly absorbed [15]. It is important to ensure that the standard endoscopic room air pump is turned off (Fig. 3.5) during the entire procedure to avoid room air being supplied in conjunction with CO₂ insufflation, thus eliminating the safety advantage of CO₂ utilization [16]. This differs from ESD where it may not be essential to turn the room airflow off, as the muscular layers are kept intact limiting mediastinal emphysema and pneumoperitoneum [13]. The abdomen should be exposed during the procedure to allow periodic examination to ensure no excessive distension is present, potentially representing capnoperitoneum. Large volumes of intraperitoneal CO₂ may result in abdominal compartment syndrome and potential hemodynamic collapse if left untreated. A decompression needle (typically large-gauge angiocatheter with cannula or Veress needle) should be readily available to perform abdominal wall puncture and aspiration if significant capnoperitoneum is present [13]. When needed, needle decompression is performed on either side of the abdomen in the subcostal area. Once successful decompression has been performed, the cannula or Veress needle is often left in place for the remainder of the procedure to evacuate any further accumulated gas.

There are two main monopolar knives utilized during POEM. Depending on endoscopist preference, either of these knives can be used alone for both the initial mucosotomy, submucosal dissection and myotomy. The most commonly used endoscopic knives are the triangle-tip electrosurgical knife (KD-640 L, Olympus, USA) and the HybridKnife^® (ERBE USA) Table 3.1.

The triangle-tip electrosurgical knife (Fig. 3.6) is a monopolar energy device with a noninsulated 1.6 mm triangular electrode plate at the tip of a 4.5 mm long cutting knife. The three sharp angulations at the tip permit smooth spraying of monopolar energy over a wide circumferential range [13]. This enables submucosal dissection and myotomy to be carried out without any direct contact of the knife with the tissue, which makes the dissection more efficient with less bleeding [13, 16]. This technique also minimizes tissue accumulation on the knife, thus decreasing the number of instrument exchanges needed for cleaning, and overall improving the visual field during dissection and muscle division. The triangle-tip electrosurgical knife was the knife used in the original description of POEM [2]. Care must be taken to avoid perforation due to the relatively large distal electrode. Additional knife tip shapes, including L shape and ceramic-insulated triangle tip, are alternative options which can be selected based on operator preference.

The HybridKnife^® has the potential ability to singularly accomplish all aspects of POEM including initial mucosal lift and dye injection during the submucosal dissection owing to its central capillary within the cutting knife. This feature allows the knife to function as an ultrafine 120-μm water jet that is powered by a foot pedal-activated, jet lavage unit: the ERBEJET^®2 system (ERBE USA). The pressurized water jet has the ability to diffuse within the mucosal layer in a needleless fashion to create a submucosal lift [12]. There are three different tip configurations of the HybridKnife^®, all with a 5 mm long cutting knife. The I-type is straight without an additional tip. The T-type has a noninsulated 1.6-mm diameter disk-shaped electrode at the tip. Finally, the O-type has an insulated, hemispherical, domelike tip. Only the I-type and T-type knives are approved by the US Food and Drug Administration and currently available in the United States [12], and the T-type has been the model described for use in POEM [10] (Fig. 3.7).

Bleeding during POEM is not uncommon and can significantly obscure visualization during dissection. Normally, minor bleeding can be controlled with the application of coagulation current from the triangle-tip electrosurgical knife or HybridKnife^®. More significant bleeding may require management with an endoscopic coagulation forceps. Small vessels identified during submucosal dissection can also be coagulated prophylactically with the knife [12].

The electrosurgical generator unit (ESU) facilitates therapeutic endoscopy by delivering high-frequency electrical current to the endoscopic device. The ESU transfers electrical current through the endoscopic device to thermal energy for use within the tissue [17]. Currently available ESUs contain sophisticated microprocessors and software that allow them to generate multiple different electrosurgical waveforms and settings based on the application specific to various endoscopic procedures, including POEM.

The electrosurgical generator utilized for POEM at our institution is the ERBE VIO 300D (ERBE USA) (Fig. 3.8). This is a radiofrequency surgical energy system, which supports spray-coagulation mode for noncontact tissue dissection during both the submucosal dissection and myotomy [13]. This unit is compatible with both the triangle-tip electrosurgical knife and the HybridKnife. The settings can be adjusted as needed during the procedure. The most frequently reported settings for the various stages of POEM are depicted in Tables 3.2 and 3.3. In general, low-voltage (>200 V) settings are used for tissue coagulation, medium-voltage settings (200–600 V) are used for tissue cutting, and high-voltage settings (>600 V) are used for tissue ablation.