Introduction

Gastric mucosal visibility is essential for high-quality upper gastrointestinal (GI) endoscopy. While simethicone and N-acetylcysteine (NAC) have been shown to improve mucosal visibility, the optimal time interval between preparation and endoscopy remains undefined.

Aims & Methods

This randomized controlled trial evaluated the effect of timing on mucosal visibility and explored the upper limit beyond which visibility begins to decline.
In this single-center, randomized controlled trial, adult patients undergoing elective upper GI endoscopy were randomized into four groups: placebo, simethicone + NAC with endoscopy performed after 10–20 minutes, 20–30 minutes, and >30 minutes. The primary outcome was the proportion of patients achieving adequate gastric mucosal visibility (GMV), defined as a score of <7 on a validated visibility scale. A pre-specified subgroup analysis of the >30 minute group was performed by stratifying patients into 20-minute intervals (31–50, 51–70, and 71–90 minutes) to assess the durability of mucosal clarity over time.

Results

Comparison	Adequate gastric mucosal visibility (%)	P
10–20 min vs 20–30 min	27% vs 62%	0.001
10–20 min vs >30 min	27% vs 67%	0.001
10–20 min vs Placebo	27% vs 2.6%	0.001
20–30 min vs >30 min	62% vs 67%	0.174
20–30 min vs Placebo	62% vs 2.6%	0.001

1,140 patients (median age 42years, 63.2% males) were included in the study. Adequate GMV was significantly higher in all preparation groups compared to placebo (p < 0.001). The 20–30 minute and >30 minute groups demonstrated the highest rates of adequate visibility (61.5% and 73.5%, respectively), both significantly superior to the 10–20 minute group (26.9%) and placebo (2.6%). In the >30 minute subgroup analysis, the 31–50 minute interval demonstrated the highest adequacy (73.5%). The 51–70 minute group showed moderate adequacy (52.1%), which was not significantly different from the 20–30 minute group (p = 0.207). However, the 71–90 minute group had reduced adequacy (43.8%) and did not differ significantly from the 10–20 minute group (p = 0.145). No adverse events were reported across study arms.

Conclusion

Endoscopy performed between 20 and 50 minutes after mucosal preparation yields optimal gastric mucosal visibility. A decline in visibility beyond 50 minutes suggests a practical upper limit for endoscopy timing following preparation. These findings support structured, time-sensitive scheduling following mucosal cleansing to enhance procedural quality.

Disclosure

None

Introduction

Underwater endoscopic mucosal resection (UEMR) has been increasingly utilized due to its clinical benefits. However, in patients with poor bowel preparation, UEMR is limited by impaired endoscopic visualization due to luminal turbidity. Viscoclear®, a gel designed to secure endoscopic fields, has been available in Japan since 2020 and has demonstrated a 92.2% effectiveness rate in improving visibility during bleeding or inadequate bowel prep. While its usefulness during UEMR has been anticipated, clinical evidence remains limited. We conducted an image analysis study to evaluate the visibility enhancement effect of gel immersion compared to underwater.

Aims & Methods

This study was a prospective randomized crossover trial to compare the endoscopic visibility of colorectal adenomatous lesions (6-20 mm) between under-water and under-gel observation. Each lesion was observed alternately in both settings using white light imaging (WLI), blue laser imaging (BLI), and linked color imaging (LCI). Color difference (ΔE) between tumor and adjacent non-tumor areas was calculated using the Lab color space in Photoshop (Adobe Systems Inc.) to evaluate lesion margins. Based on preliminary retrospective data from our institution, a sample size of 72 was calculated (power: 0.8, one-sided α: 0.05). (jRCTs062220033)

Results

Between July 2022 and May 2024, 72 lesions were enrolled. Median tumor size was 8 mm (range: 6–18 mm). Histopathology revealed 65 adenomas (90.3%), 2 cancers (2.6%), 3 traditional serrated adenomas (4.1%), and 2 hyperplastic polyps (2.8%). Boston Bowel Preparation Scale Segment Scores (BBPS-SS) were 3 in 50 cases, 2 in 21 cases, and 1 in 1 case.
Median ΔE values in the underwater group were 10.0 (WLI), 15.7 (BLI), and 11.7 (LCI), while those in the under-gel group were 12.4 (WLI), 21.1 (BLI), and 13.1 (LCI). ΔE was significantly higher in the under-gel group than the underwater group under WLI and BLI (p = 0.01 and p < 0.01, respectively).
In subgroup analysis by BBPS-SS, under-gel observation showed significantly higher ΔE in WLI and BLI when BBPS-SS ≤2 (p = 0.03 and p < 0.01, respectively). No significant differences were seen when BBPS-SS was 3.

Conclusion

Under-gel observation improved the visibility of lesion margins under WLI and BLI compared to underwater observation, particularly in patients with suboptimal bowel preparation. Gel immersion endoscopy may therefore be a useful adjunct in difficult visualization conditions during colorectal UEMR.