Is it safe to perform an underwater colonoscopy?

Is Underwater Colonoscopy Safe?

Yes, underwater colonoscopy techniques are safe and may offer advantages over conventional air insufflation colonoscopy, with comparable or lower complication rates and reduced patient discomfort.

Safety Profile of Underwater Colonoscopy

Perforation Risk

• No perforations were reported in a systematic review of 508 colorectal lesions removed using underwater EMR across 10 studies 1
• A prospective study of 62 large sessile colorectal polyps (mean size 34 mm) treated with underwater EMR reported zero perforations 2
• A randomized controlled trial comparing underwater versus conventional EMR for small polyps (4-9 mm) found no perforations in either group 3
• For context, diagnostic colonoscopy perforation rates range from 0-0.2%, while the overall colonoscopic perforation rate is approximately 0.04-0.07% 4

Bleeding Risk

• Delayed bleeding occurred in 2.85% (95% CI, 1.64-4.90%) of underwater EMR procedures in the systematic review 1
• In the prospective study of large polyps, delayed bleeding occurred in 3 of 60 patients (5%) and was managed conservatively without intervention 2
• The randomized trial showed early bleeding in 1.4% of both underwater and conventional EMR groups, with no postprocedural bloody stool in the underwater group versus 3.1% in the conventional group 3
• These rates are comparable to or lower than the 2-5% delayed bleeding risk reported for conventional underwater EMR techniques 4

Overall Adverse Event Rate

• The pooled adverse event rate for underwater EMR was 3.31% (95% CI, 1.97-5.52%) 1
• No cases of postpolypectomy syndrome were reported in the prospective study of 60 patients 2

Mechanism of Safety

Why Underwater Technique May Be Safer

• Water immersion causes the mucosa and submucosa to involute as folds while the muscularis propria remains circular, creating natural separation between resectable tissue and the muscular layer 4
• This eliminates the need for submucosal injection in many cases, avoiding injection-related complications and submucosal scarring 2
• Minimal air insufflation reduces barotrauma risk, which is a recognized cause of perforation during conventional colonoscopy 4
• Water immersion minimizes colonic distension, reducing mechanical stress on the bowel wall 5

Pain Reduction as a Safety Indicator

• Water infusion colonoscopy significantly reduces pain compared to air insufflation (mean difference -1.57 on 0-10 scale, 95% CI -2.00 to -1.14) 6
• Pain during colonoscopy indicates risk of bowel perforation, and the water-immersion method's ability to reduce pain without sedation promotes patient safety by preserving this important warning signal 5
• Significantly fewer participants requested on-demand sedation/analgesia with water infusion (risk ratio 1.20,95% CI 1.14-1.27) 6

Clinical Efficacy Supporting Safety

Resection Outcomes

• Complete resection rate was 96.36% (95% CI, 91.77-98.44%) for underwater EMR 1
• En bloc resection rate was 57.07% (95% CI, 43.20-69.91%) for underwater EMR, with one study achieving 55% en bloc resection for large lesions (median 30 mm) 1, 2
• Recurrence rate was 8.82% (95% CI, 5.78-13.25) at mean 7.7 months follow-up 1

Cecal Intubation

• Cecal intubation rate was similar between water infusion and standard air insufflation (risk ratio 1.00,95% CI 0.97-1.03) 6
• Adenoma detection rate was slightly improved with water infusion (risk ratio 1.16,95% CI 1.04-1.30), potentially detecting adenomas in an additional 3% of screening patients 6

Important Caveats and Contraindications

When to Exercise Caution

• One case report exists of perforation of a proximal colon lesion removed with underwater EMR in retroflexion, suggesting caution with this specific maneuver 4
• The British Society of Gastroenterology historically recommended avoiding colonoscopy in severe colitis due to toxic megacolon or perforation risk, though more recent evidence suggests limited unprepared sigmoidoscopy with minimal air insufflation can be performed safely by experienced endoscopists 4
• CO2 insufflation is preferred over air when insufflation is needed, as it minimizes bowel distension and perforation risk (Recommendation Grade 1B) 4

Technical Considerations

• Underwater EMR should be performed by endoscopists experienced in conventional EMR, who report a short learning curve for the technique 4
• For large polyps (>30 mm), submucosal lift was needed in 30% of lesions and correlated with polyp size >30 mm 4
• The technique requires full water immersion of the segment containing the lesion and appropriate electrocautery settings (Drycut, effect 5, 60W) 4

Comparison to Conventional Techniques

Safety Advantages

• Underwater EMR eliminates submucosal injection-related risks including submucosal scarring that can make subsequent resection more difficult and increase perforation risk 2
• The zero perforation rate in multiple studies compares favorably to the maximum acceptable ICP rate of ≤0.1% for diagnostic colonoscopy and ≤1% for complex polypectomy 4
• Bleeding rates are within or below the acceptable range for therapeutic colonoscopy 1, 3