Endoscopic Pyloromyotomy (G-POEM) and Per-Rectal Endoscopic Myotomy (PREM)

Symptom

None

Very mild

Mild

Moderate

Severe

Very severe

Nausea (feeling sick to your stomach as if you were going vomit or throw up)

Retching (heaving as if to vomit, but nothing comes up)

Vomiting

Stomach fullness

Not able to finish a normal-sized meal

Feeling excessively full after meals

Loss of appetite

Bloating (feeling like you need to loosen your clothes)

Stomach or belly visibly larger

For each symptom, please circle the number that best describes how severe the symptom has been during the past 2 weeks. If you have not experienced this symptom, circle 0. If the symptom has been very mild, circle 1. If the symptom has been mild, circle 2. If it has been moderate, circle 3. If it has been severe, circle 4. If it has been very severe, circle 5. Please be sure to answer every question

Please rate the severity of the following symptoms during the past 2 weeks

^aThis questionnaire asks you about the severity of symptoms you may have related to your gastrointestinal problem. There are no right or wrong answers. Please answer each question as accurately as possible

EGD and Imaging

Although most patients would have undergone an EGD earlier during the evaluation, EGD is important to rule out mechanical factors contributing to the gastric outlet obstruction, e.g., duodenal or pyloric ulcers, infiltrating malignancy, or extrinsic compression from surrounding structures. EGD can also assess the amount of gastric food stasis, which must be cleared before performing G-POEM.

CECT of the abdomen is often performed to rule out compression by extrinsic mass lesions and/or to also rule out proximal bowel obstruction which may sometimes mimic the symptoms of gastroparesis.

Gastric Emptying Scintigraphy (GES)

The conventional test for assessment of gastroparesis is gastric emptying scintigraphy (GES). GES is performed using a ^99mTc-sulfur colloid-labeled solid meal and is reported as the percent gastric retention at 1, 2, and 4 h [1]. More than 30% gastric retention is considered clinically significant. Patients must stop prokinetics or other medications that can interfere with gastric motility before they are subjected to GES.

EndoFlip and Pyloric Manometry

EndoFlip estimates the distensibility of the pylorus, whereas pyloric manometry can estimate the extent of pylorospasm. These tests, although described, are not routinely available, and their role in clinical management is unclear and uncommon.

Other less frequently performed tests include wireless motility capsule (WMC) (that measures pH, pressure, and temperature and assesses gastric emptying by the acidic gastric residence time) and breath testing (using 13C-octanoate or spirulina) [1].

Other Biochemical and Metabolic Workups

Patients must be evaluated for their diabetic status, presence of possible hypothyroidism, and other metabolic workups to identify the potential etiology of gastroparesis. Investigations to assess for fitness for general anesthesia are required; and metabolic abnormalities, especially electrolyte nutritional imbalance, must be optimally corrected before the patient can be scheduled for G-POEM.

Although not mandatory, most centers may offer a therapeutic trial of diet modulation, prokinetics, or even a trans-pyloric stent placement to assess symptom relief before scheduling G-POEM.

Technique and Variations of G-POEM

G-POEM is a relatively new and evolving procedure. The technique is therefore also evolving, and many operators are likely to have their own preferences when performing this procedure. The description that follows is one that the authors perform on a regular basis. Suitable variations based on individual anatomy and circumstances may be implemented depending on the operator’s understanding and training of the subject.

It is also important to note that G-POEM is a complex flexible endoscopic surgical procedure using the principles of third space endoscopy with inherent risks; and written, pictorial, and video descriptions cannot be a substitute for appropriate supervised training and credentialing for performance of third space endoscopy techniques.

Prerequisites and Preliminary Considerations

1.

G-POEM is performed under general anesthesia.
2.

Patients must be fasting overnight at least for 12 h; those with significant gastric stasis may require longer periods of fasting. A screening EGD is performed to confirm that the stomach is empty of all food and fluid residue.
3.

In patients with significant gastric solid food residue, it may be necessary to clean the stomach by nasogastric or endoscopic lavage 1 or 2 days prior to G-POEM.
4.

Unlike POEM, G-POEM may be performed in either the supine or the left lateral position. We prefer the supine position in most situations except when the stomach is grossly dilated, wherein the position of the antrum and pylorus is more accessible in the left lateral position.

Instrumentation

1.

High-definition gastroscope (GIF-HQ190, Olympus Corp., Tokyo, Japan).
2.

Transparent distal attachment (Olympus) – various shapes are available; our preference is the straight cap.
3.

Carbon dioxide insufflator.
4.

Endoscope flushing pump.
5.

Injector needle 25G with short bevel.
6.

Injectate – normal saline stained with indigo carmine or methylene blue solution. Do ensure that the solution is light sky blue in color and is not very dark, as a dark solution hampers dissection and hemostasis within the tunnel.
7.
Diathermy settings – ERBE Vio II™ (200D or 300D) or Vio III™ workstation (ERBE GmBH, Tubingen, Germany):
1. (a)
  
  Incision – EndoCut™ effect, 2; cut duration, 3; cut interval, 3
2. (b)
  
  Submucosal dissection – spray coagulation, 50W; effect, 2. Or forced coagulation, 60W; effect, 2
3. (c)
  
  Coagulation – soft coagulation, 80W; effect, 4
4. (d)
  
  Myotomy – spray coagulation, 50W; effect, 2. Or forced coagulation, 60W; effect, 2
8.

Alternatively, ESG 400™ (Olympus) diathermy can also be used.
9.

Knife – a choice of knives is available. The most commonly used knives are the HybridKnife™ (ERBE GmBH) or the triangular tip (TT) Knife™ (Olympus). The HybridKnife™ has to be used in conjunction with the ERBEJet™ injector workstation that has the ability for high-pressure injection resulting in rapid mucosal elevation, and the knife can inject and cut using the same instrument. An injector version of the TT Knife™ is also available in some countries – TT-J Knife™ (Olympus). The TT-J Knife™ permits injection and cutting using the same instrument similar to the HybridKnife.
10.

Insulated tip (IT)-2™ Knife (Olympus) – for dissection at the pylorus and myotomy.
11.

Hemostatic forceps – Coagrasper™ (Olympus).
12.
Closure devices:
1. (a)
  
  Mucosal clips (Olympus, Boston Scientific Corporation, Cook, or similar).
2. (b)
  
  Over-the-scope clips (OTSC™ clip, Ovesco, Germany) or Padlock™ (US Endoscopy, USA) are preferred by some operators.
3. (c)
  
  Endoscopic suturing (OverStitch™, Apollo Endosurgery Inc., USA) is also an alternative if closure is difficult using clips.

The G-POEM Procedure (Video 21.1)

1.

The air pump on the endoscope processor is turned off and carbon dioxide is used for insufflation.
2.

After a screening EGD, the endoscope is withdrawn into the gastric antrum.
3.

A mucosal incision site is selected approximately 3–5 cm proximal to the pylorus.
4.

Submucosal injection is performed using a 23 or 25G injector needle to raise a sizeable submucosal cushion (Fig. 21.1). It is recommended to inject approximately 20–25 ml of injectate to raise this cushion. Smaller volumes may also be used but the elevation can disappear rapidly and make entry into the submucosal tunnel difficult.
5.

A longitudinal mucosal incision approximately 15–20 mm in length is made using either the HybridKnife™ or TT Knife™ and the diathermy settings are done as described above. Gastric mucosa is thicker than esophageal mucosa and therefore the cut should be deep enough for the blue-stained submucosa to be visible (Fig. 21.2). A good mucosal incision is one that cuts the mucosa and muscularis mucosae so that the mucosal edges separate and the stained submucosa is visible.
6.

Some workers prefer a transverse incision to a longitudinal one because it is easier to close the incision using the OverStitch™ device (Apollo Endosurgery Inc., USA).
7.

Using the principle of POEM, the mucosal edges are undermined to create space in the submucosa, especially toward the apex of the incision. Care must be taken to ensure that the muscle layer is not damaged during this step; otherwise there is a risk of full-thickness perforation (Fig. 21.3).
8.

Once adequate space has been created, the gastroscope is gently maneuvered using rotatory and pushing movement using the big wheel and shaft so that the scope enters the submucosal space. The stomach is a much roomier organ than the esophagus, and therefore the scope may require some maneuvering before one can enter the tunnel. A simple trick is to tip the scope down in such a manner that the mucosal flap disappears from the screen and then the scope is pushed further. This prevents the scope from slipping out into the gastric cavity.
9.

Once inside the tunnel, dissection is continued in a plane close to the muscle layer so that the circular muscle fibers are clearly visible. Gastric submucosa is much thicker and fibrotic as compared to esophageal submucosa which is supple. Point to note is that if the circular muscle fibers are not seen, it is likely that the plane of dissection is superficial and needs correction (Fig. 21.4).
10.

Gastric submucosa is also quite vascular. Submucosal vessels in the stomach often require formal coagulation using Coagrasper™ rather than contact coagulation by the knife.
11.

Dissection is performed in a direction perpendicular to the circular muscle fibers. Stomach is a roomy organ and your tunnel needs to narrow down and point toward the pylorus. Unless the direction of dissection is carefully monitored, it is easy to lose direction. Frequently withdrawing the endoscope from the tunnel into the gastric lumen to check the direction of dissection is helpful.
12.

Tunnel length for G-POEM is much shorter as compared to esophageal POEM; and unless the direction is wayward, one should reach the pylorus quite quickly.
13.

Identification of the pylorus/pyloric ring – this is the most crucial step of the procedure (Fig. 21.5). As dissection progresses toward the pylorus, the circular muscle fibers start narrowing down to form a tight ring at the pylorus. A change in the mucosa is also seen, which becomes initially more adherent and then suddenly thins out beyond the ring. This is the undersurface of the duodenal mucosa as seen from the tunnel. Dissection at the level of the pyloric ring can be difficult as the duodenal mucosa is firmly adherent to the circular muscle; repeated injections and patient dissection are the key to circumvent this problem.
14.

The duodenal mucosa is seen almost vertical in relation to the pyloric ring (Fig. 21.5). Care should be taken at this point to prevent injury to the duodenal mucosa. It is recommended to change to an IT-2 Knife™ at this point to minimize this risk. The dissection is continued for another 5 mm (it is not necessary and not recommended to continue tunneling beyond the pyloric ring as in esophageal POEM wherein the tunnel is continued for 2–3 cm beyond the gastroesophageal junction).
15.

The endoscope is withdrawn and is passed across the pylorus into the duodenal bulb to confirm mucosal staining at the pylorus and just beyond it (Fig. 21.6).
16.

Once adequacy of the tunnel has been confirmed, the endoscope is reintroduced into the tunnel. A full-thickness pyloromyotomy is performed using the IT-2 Knife™ by hooking the instrument onto the pyloric muscular ring and pulling it from distal to proximal (Fig. 21.7). This direction of myotomy is important to prevent inadvertent duodenal mucosal injury. The pyloric ring can be quite thick; full-thickness myotomy must be ensured to achieve the desired result.
17.

Pyloromyotomy should be approximately 2–3 cm in length; it is not recommended to perform a longer myotomy due to the risk of damage to the gastric pacemaker situated in the antrum. On completion of the pyloromyotomy, the duodenal mucosa can be seen prolapsing into the tunnel (Fig. 21.8).
18.

Care should be taken to avoid damage to the branches of the gastro-epiploic vessels which are in close relation to the pylorus at this location. Bleeding from these vessels can be brisk and severe, and the vessels can continue to bleed into the peritoneal cavity if left unattended.
19.

Once myotomy is completed and hemostasis has been confirmed, the endoscope is again withdrawn and passed into the duodenal bulb to rule out mucosal injury. While passing across the pylorus, one may feel reduction in the resistance to the scope, in spite of the distal cap attached to it, though this is less clearly appreciable as compared to esophageal POEM wherein the gastroesophageal junction is wide open after the myotomy.
20.

Closure of the mucosal incision is the final step of G-POEM. As in esophageal POEM, this can be achieved by applying serial mucosal clips, the first clip being applied beyond the distal incision angle and then progressing proximally to approximate the mucosal edges (Figs. 21.9, and 21.10). As compared to esophageal POEM, the mucosal edges in G-POEM tend to separate laterally and are difficult to approximate. The incision also frequently elongates to some extent, possibly because the gastric mucosa has folds and is loosely attached to the submucosa. To prevent clips from slipping, care must be taken to ensure an adequate bite of the mucosa and to apply the clips close to one another so that the tension is distributed evenly. Several clips may be necessary to achieve an optimum closure.
21.

In case of severe tension on the mucosal edges, alternative techniques like OTSC clips or OverStitch™ closure may be considered. It is imperative that the mucosal closure is secure, failing which, there may be a risk of leakage of gastric contents and peritoneal contamination.
22.

In very severe cases when the operator is unsure about the secureness of the mucosal closure, a nasogastric tube may be inserted to decompress the stomach post-procedure. Alternatively, a triple lumen nasojejunal tube is placed temporarily to aspirate the stomach as well as achieve feeding into the intestine.

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig1_HTML.jpg — Fig. 21.1

Submucosal cushion created in the distal antrum approximately 6 cm proximal to the pylorus

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig2_HTML.jpg — Fig. 21.2

A triangular tip knife is used to make a longitudinal incision on the elevated mucosa

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig3_HTML.jpg — Fig. 21.3

The mucosal edges are undermined by dissecting the submucosa, thereby creating space to introduce the endoscope into the tunnel

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig4_HTML.jpg — Fig. 21.4

Submucosal dissection is performed in a direction perpendicular to the circular muscle fibers (arrow)

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig5_HTML.png — Fig. 21.5

Pyloric ring seen through the submucosal tunnel. The duodenal mucosa is seen stretched vertically beyond the ring (arrow)

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig6_HTML.jpg — Fig. 21.6

Confirm adequacy of the submucosal tunnel by inspecting the blue staining of the duodenal mucosa beyond the pylorus (arrow)

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig7_HTML.jpg — Fig. 21.7

Full-thickness myotomy is performed using the IT-2 Knife™. The insulated ceramic tip of the instrument protects against inadvertent duodenal mucosal injury

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig8_HTML.png — Fig. 21.8

Completed pyloromyotomy as seen from the submucosal tunnel. Note the prolapsing duodenal mucosa after myotomy (arrow). A short myotomy approximately 2 cm in length is recommended (thick arrow)

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig9_HTML.jpg — Fig. 21.9

The first clip is applied just beyond the distal angle of the incision. This lifts the mucosal edges and facilitates subsequent clip placement

../images/442926_1_En_21_Chapter/442926_1_En_21_Fig10_HTML.jpg — Fig. 21.10

Completed closure of mucosal incision by serial clips

Post-procedure Care and Instructions

1.

Patients are maintained nil orally for at least 24 h post-procedure, longer in cases when security of mucosal closure is suspect.
2.

Intravenous broad-spectrum antibiotics are administered for 48 h post-procedure.
3.

Some workers prescribe proton pump inhibitors in the post-operative period; however there is no clear justification for their routine use. Although their use may reduce risk of post-operative hemorrhage, acid secretion is suppressed and thus may increase the risk of post-operative infection.
4.

Patients are monitored for hemodynamic and respiratory instability, which may indicate ongoing hemorrhage, infection, or peritonitis. It is important to note that hemorrhage after G-POEM may not always occur inside the gastric lumen and therefore may not present as hematemesis, but may present as progressive abdominal distension, pain, and hemodynamic instability indicating an ongoing intraperitoneal bleeding.
5.

Most patients do not complain of significant post-procedure pain. Analgesic requirements are minimal and often on demand. Most post-operative pain is due to gaseous distension that disappears within a few hours. Care must be taken while administering narcotic analgesics to patients with diabetic gastroparesis since this may further affect their gastric dysmotility.
6.

It is our policy to get a hematocrit estimation 12 h post-procedure. A dropping hematocrit indicates ongoing blood loss and needs prompt evaluation.
7.

An upper GI series using either barium or water-soluble contrast medium is performed after 24 h to rule out a leak.
8.

After confirming absence of a leak, patients are instructed to start liquids and soft low-residue diet is gradually initiated within 48 h.
9.

Patients are usually discharged on the second post-operative day with instructions to contact the unit in case of emergency.
10.

Patients are advised to continue soft diet for 8–10 days, after which they can resume normal diet.
11.

The first follow-up visit is usually scheduled between 4 and 6 weeks. In addition to GCSI estimation, an EGD and a GES are repeated at follow-up to assess the response to G-POEM.

Adverse Events and Technical Challenges

G-POEM is an endoscopic surgical procedure and carries potential risk of adverse events. If performed following the instructions detailed above and adhering to surgical principles, it is a remarkably safe procedure with minimal adverse events and quick recovery. However, the following potential adverse events have been reported and are possible:

1.

Capnoperitoneum – Mild capnoperitoneum is common and almost invariable during G-POEM due to the insufflated CO2 gas that escapes through the tunnel into the peritoneal cavity. Most often it is insignificant and asymptomatic.
2.

Tension capnoperitoneum with resultant respiratory compromise and rising end-tidal CO2 (Et-CO2) – This can occur due to over-insufflation during tunneling or myotomy. If the respiratory compromise is mild, the procedure can be halted for some time, the endoscope is withdrawn, and the anesthetist hyperventilates the patient so that the carbon dioxide is washed out. In case of severe respiratory distress, abdominal paracentesis can be performed using a wide-bore needle (16G) to decompress the abdomen and improve ventilation. In most situations, ventilation will improve using these measures. In the rare event that the patient continues to remain unstable, the procedure may have to be aborted. Significant capnoperitoneum reported as adverse event was reported on one occasion by Khashab et al. and on two occasions by Gonzalez et al. in their series [17, 18].
3.

Hemorrhage – Gastric submucosa is vascular and bleeding can occur during the procedure and must be suitably arrested. Significant post-procedure hemorrhage is uncommon if optimum measures for hemostasis have been undertaken during the procedure. It can occur due to rebleeding from one of the submucosal vessels, or from subserosal vessels during myotomy. It is important to note that post-procedure bleeding may not always become clinically evident by presenting with hematemesis but may rarely continue within the peritoneal cavity and present as hemorrhagic shock. Appropriate resuscitation measures including transfusion of blood products may be required. Repeat EGD with reentry into the tunnel after removal of the clips, evacuation of blood clots, and arrest of bleeding source may be required if ongoing bleeding is suspected. Surgical exploration or interventional radiology support may also be required if endoscopic measures fail to stop the bleeding. Schlomovitz et al. reported bleeding in one patient that was treated by hemoclips; and Kahaleh et al. reported bleeding inside the tunnel that required coagulation using Coagrasper™ forceps [19, 20].
4.

Infection and peritonitis – G-POEM breaches the integrity of the gastrointestinal tract. Although the submucosal flap valve technique has been shown to be exceedingly safe against leakage of bowel contents, peritoneal contamination or infection can occur. The integrity of the mucosal closure is paramount. Broad-spectrum antibiotics may usually be adequate for mild infections; however surgical exploration and peritoneal drainage may be required for severe cases. The risk of infection appears to be infrequent however, with no study to date reporting significant infection or peritonitis.
5.

Gastric ulcer – Pre-pyloric ulcer has been occasionally reported as an adverse event after G-POEM [17, 20]. The mechanism is poorly understood but may be related to de-vascularization of the mucosal flap during tunneling. Khashab et al. reported severe atrophic gastritis as a possible contributory factor, whereas Kahaleh et al. reported that the ulcer was possibly a residual mucosal defect. Therapy using proton pump inhibitors and sucralfate was adequate.

Apart from these specific issues, adverse events related to anesthesia, intubation, and the endoscopic procedure are potentially possible. G-POEM however appears to be a safe procedure with a low overall incidence of adverse events of 6–7% in most series.

Status of G-POEM

G-POEM was conceptualized and reported by Kawai et al. in a porcine model in 2012 [15]. Subsequently, Khashab et al. reported the first successful human G-POEM in 2013 in a patient with refractory diabetic gastroparesis [12]. The initial 2 years saw several case reports and short case series being published endorsing the safety and feasibility of this procedure. G-POEM was reported for various indications – Chaves et al. and Chung et al. reported it for early post-operative gastroparesis, whereas we reported it for delayed post-operative gastroparesis [21–23]. Mekaroonkamol et al. reported a successful series of three patients of varying etiologies – idiopathic, post-infectious, and post-operative gastroparesis [24]. There was also a case report of combined POEM and G-POEM for recurrent achalasia and refractory gastroparesis wherein POEM was preceded by the G-POEM so as to mitigate the risk of severe reflux because of gastroparesis [25]. Pham et al. have reported this procedure in a patient with primary pyloric stenosis [26]. Shlomovitz et al. demonstrated successful G-POEM in six out of seven patients and also documented normalization of gastric emptying in five patients [19].

In the last 2 years, larger patient series have been reported in the form of single- or multicenter studies. Current literature on G-POEM is summarized in Table 21.2. The first multicenter study by Khashab et al. demonstrated success of G-POEM in a retrospective cohort of 30 patients [17]. Adverse events were few (6.7%) and length of hospital stay was short (mean 3.3 days). Symptom improvement was seen in 26/30 (86%) patients during a median follow-up of 5.5 months, and patients with symptoms of nausea and vomiting responded the most. The study concluded that G-POEM was safe and effective in the treatment of refractory gastroparesis.

Table 21.2

Summary of current G-POEM literature

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