Perform standard bowel preparation, confirm patient identity, obtain informed consent, verify anticoagulant medication status, and ensure vital signs are within normal limits.
The patient remains in the clinic recovery area for 30-60 minutes to monitor for immediate post-procedural complications. Patient must be instructed on diet restrictions, signs of perforation or bleeding, and to arrange for a follow-up appointment. Discharge occurs immediately upon stabilization.
Comprehensive Clinical Guide: Underwater Endoscopic Mucosal Resection (U-EMR)
1. Introduction and Overview
Underwater Endoscopic Mucosal Resection (U-EMR) represents a paradigm shift in the management of colorectal polyps and early-stage gastrointestinal neoplasia. Traditionally, Endoscopic Mucosal Resection (EMR) relied heavily on submucosal injection of saline or other viscous agents to elevate the lesion, creating a "cushion" to protect the muscularis propria from thermal injury during snare resection.
U-EMR, pioneered by Dr. Bin Bin Lu and popularized globally, eliminates the need for submucosal injection. By immersing the colonic lumen in water, the colon collapses around the lesion, leveraging gravity and the properties of water to naturally elevate the lesion toward the snare. This technique provides superior visualization, enhanced safety, and exceptional rates of complete resection for lesions that might otherwise be considered difficult or "non-lifting" under conventional methods.
2. Technical Specifications and Mechanism of Action
The core principle of U-EMR is the utilization of water as a medium for both distension and lesion elevation.
The Physics of U-EMR
- Lesion Elevation: In an air-filled colon, lesions are often flat or depressed. When the lumen is filled with water, the lesion naturally "floats" or becomes more prominent due to the difference in tissue density and the absence of air-induced tension on the colonic wall.
- The "Water-Cushion" Effect: Water provides a stable, non-compressible medium that allows the snare to capture the mucosal and submucosal layers without the risks associated with fluid-injected blebs, which can sometimes distort the morphology of the polyp.
- Visualization: Water acts as a natural lens, often clearing debris and providing a stabilized view that reduces the "shimmer" or movement associated with peristalsis.
Key Equipment
| Equipment | Specification/Requirement |
|---|---|
| Endoscope | High-definition (HD) colonoscope with water-jet functionality. |
| Snare | Braided, stiff-wire snares are preferred for better tissue capture. |
| Water Source | Sterile water or saline, room temperature. |
| Electrosurgical Unit | High-frequency generator set to "Endo-Cut" or "Pure Cut" modes. |
3. Clinical Indications and Usage
U-EMR is indicated for the resection of various gastrointestinal lesions, particularly those that are challenging to manage via conventional EMR.
Primary Indications
- Large Colorectal Polyps (>20mm): Especially those with a lateral spreading morphology.
- Fibrotic Lesions: Lesions that show a "non-lifting sign" due to prior biopsy or chronic inflammation.
- Lesions in Difficult Locations: Polyps located behind haustral folds or in the appendiceal orifice.
- Recurrent Polyps: Previously treated lesions that have regrown or possess scar tissue.
Patient Selection Criteria
- ASA Status: Patients should generally be ASA I-III.
- Coagulation Profile: Patients must be off therapeutic anticoagulation unless bridging protocols are strictly followed.
- Anatomical Suitability: The lesion must be accessible via colonoscopy.
4. Pre-Operative Preparation
Success in U-EMR is contingent upon meticulous preparation.
- Bowel Cleansing: A high-quality bowel preparation (e.g., split-dose PEG) is mandatory to ensure clear water and unobstructed views.
- Anticoagulation Management: Hold P2Y12 inhibitors and anticoagulants according to institutional guidelines.
- Patient Positioning: Left lateral decubitus is standard, but the patient may be repositioned during the procedure to use gravity to "float" the lesion into the optimal snare position.
- Prophylactic Measures: In large resections, consider the use of prophylactic clips to close the mucosal defect, particularly in the right colon.
5. Procedural Steps: The U-EMR Workflow
Step 1: Identification and Assessment
The lesion is inspected under air insufflation to determine morphology (Paris classification) and evaluate for signs of deep submucosal invasion (Kudo pit pattern/NICE classification).
Step 2: Desufflation and Immersion
Once the lesion is identified, all air is aspirated from the lumen. The colon is then filled with sterile water until the lesion is completely submerged and the colonic wall is collapsed around the polyp.
Step 3: Snare Placement
The snare is passed through the working channel. The operator maneuvers the snare over the lesion. Because the lesion is elevated by the water, the snare can often capture the lesion and a margin of healthy tissue more effectively than in air-filled conditions.
Step 4: Resection
The snare is closed slowly. The operator must ensure that the muscularis propria is not captured. The electrosurgical current is applied using a "cut" or "blend" mode. The water acts as a heat sink, potentially reducing the risk of thermal damage to the deeper layers of the wall.
Step 5: Retrieval and Inspection
The resected tissue is retrieved. The base of the defect is inspected for evidence of bleeding or perforation. If the base is clean, the water is aspirated, and the procedure is concluded.
6. Post-Operative Recovery and Protocol
- Immediate Post-Op: Monitor for signs of abdominal pain, tachycardia, or fever (indicators of perforation or post-polypectomy syndrome).
- Dietary Restrictions: Clear liquid diet for the first 12–24 hours, transitioning to a low-fiber diet for 3–5 days.
- Activity: Avoid heavy lifting or strenuous exercise for 1 week.
- Follow-up: Surveillance colonoscopy is typically scheduled at 6–12 months, depending on the pathology report (R0 vs. R1 resection).
7. Risks, Side Effects, and Contraindications
Risks and Complications
- Bleeding: Delayed post-polypectomy bleeding can occur in 2–5% of cases.
- Perforation: While U-EMR is considered safer, full-thickness injury remains a risk, especially in thin-walled areas like the cecum.
- Post-Polypectomy Syndrome: Transmural inflammation resulting in focal abdominal pain without perforation.
- Incomplete Resection: Failure to capture the entire lesion, necessitating further intervention.
Contraindications
- Suspected Invasive Cancer: U-EMR is not intended for T2 or higher invasive malignancies.
- Severe Diverticulitis: Risk of perforation is significantly elevated.
- Uncorrectable Coagulopathy: High risk of uncontrollable hemorrhage.
8. Alternative Treatments
While U-EMR is highly effective, it is not the only modality available:
* Conventional EMR (C-EMR): Standard for smaller, non-fibrotic polyps.
* Endoscopic Submucosal Dissection (ESD): Indicated for larger (>30mm) lesions with suspected early invasive cancer, allowing for en-bloc resection.
* Surgical Resection: Reserved for lesions with high-risk features for malignancy or those inaccessible by endoscopic means.
9. Frequently Asked Questions (FAQ)
1. Is U-EMR safer than conventional EMR?
Yes, U-EMR is generally considered safer because the water provides a thermal heat sink and the natural buoyancy of the lesion reduces the need for aggressive submucosal injections, which can sometimes lead to complications.
2. Can U-EMR be performed on all polyps?
No. It is primarily indicated for large, benign-appearing, or fibrotic polyps. It is not appropriate for lesions with deep invasive features.
3. Does the water blur the image?
On the contrary, water acts as a refractive medium that can actually enhance visibility by smoothing out the mucosal irregularities and providing a stable background.
4. How long does the procedure take?
U-EMR is often faster than conventional EMR because it eliminates the time-consuming step of submucosal injection.
5. What if the lesion is on a flat surface?
U-EMR is particularly effective for flat lesions, as the water causes the lesion to stand out relative to the surrounding wall.
6. Are there specific complications related to the water?
The primary risk is aspiration if the patient is under deep sedation. Proper airway management and positioning are essential.
7. Does U-EMR increase the risk of infection?
Using sterile water minimizes the risk. Irrigation of the lumen is a standard endoscopic practice and does not significantly increase infection rates.
8. Is special training required?
Yes, while the technique is intuitive for experienced endoscopists, specific training in water-immersion techniques is recommended to ensure safety.
9. What is the "Non-lifting sign"?
This is a clinical sign where a lesion does not elevate after saline injection. U-EMR is the gold standard for "non-lifting" lesions that are still deemed endoscopically resectable.
10. How do I determine if a lesion is suitable for U-EMR?
Suitability is determined by endoscopic assessment of size, morphology, and the presence of high-risk indicators (e.g., ulceration, deep depression) which would suggest invasive cancer.
10. Summary and Clinical Outlook
Underwater Endoscopic Mucosal Resection has fundamentally changed the approach to complex colonic lesions. By leveraging the physical properties of water, clinicians can achieve higher rates of complete resection with a favorable safety profile. As technology advances, the integration of U-EMR with advanced imaging (NBI/LCI) will likely further improve the detection and treatment of early GI neoplasia, ultimately reducing the need for surgical intervention.
Disclaimer: This guide is intended for educational purposes for healthcare professionals. It does not replace institutional clinical protocols or formal surgical training. Always consult the latest clinical guidelines from the ASGE or ESGE when performing endoscopic procedures.