What are the next steps for a colonoscopy with poor bowel preparation (prep)?

Management of Colonoscopy with Poor Bowel Preparation

For colonoscopies with poor bowel preparation, the procedure should be repeated with a more aggressive preparation regimen within 1 year for screening/surveillance colonoscopies, or as soon as possible for diagnostic indications with alarm symptoms or positive colorectal cancer screening tests. 1

Initial Assessment and Immediate Options

When poor bowel preparation is encountered during colonoscopy, there are several immediate options:

1. Preliminary assessment in rectosigmoid: If the preparation is clearly inadequate to detect polyps >5mm in the rectosigmoid, consider either:

   • Terminating and rescheduling the procedure
   • Attempting additional bowel cleansing strategies that day 1

2. Salvage options during the procedure:

   • Intraprocedural washing and suctioning: Can convert 75% of poor/fair preparations to good/excellent 1
   • Colonoscopic enema: Instillation of PEG (500-1000ml) or bisacodyl (10mg) enema into the right colon, followed by withdrawal and allowing the patient to evacuate before repeating the colonoscopy (success rates 53-99%) 1, 2
   • Additional oral purgative: Waking the patient from sedation for additional oral intake of purgative (2L of PEG is superior to 1L PEG enema) followed by same-day or next-day colonoscopy 1

Follow-up Recommendations Based on Indication

1. For screening/surveillance colonoscopies:

   • If preparation is inadequate to assign standard intervals, repeat colonoscopy within 12 months 1
   • For high-risk findings with inadequate preparation, shorter intervals than 1 year may be indicated 1

2. For diagnostic colonoscopies (alarm symptoms or positive FIT/stool DNA test):

   • Repeat with adequate bowel preparation as soon as possible 1

3. For average-risk screening with inadequate preparation:

   • If the descending colon, sigmoid, and rectum were well-visualized, consider:
     • Treating the examination as a flexible sigmoidoscopy (repeat in 5 years)
     • Offering alternative screening methods (FIT, stool DNA testing) 1
   • Note: 59% of patients prefer stool-based testing over repeating colonoscopy after inadequate preparation 1

Modified Preparation Regimen for Repeat Colonoscopy

For patients with previous inadequate preparation, use a more aggressive approach:

1. Dietary modifications:

   • Low-fiber/residue diet for 2-3 days before procedure 1, 3
   • Clear liquids only on the day before colonoscopy 1, 3
   • Restrict vegetables and legumes for 2-3 days before procedure 1

2. Medication adjustments:

   • Treat underlying constipation 1
   • Temporarily stop anticholinergics, opioids, or other constipating medications 1
   • Consider adding promotility agents 1

3. Preparation regimen:

   • Use high-volume bowel preparation regimens (4L PEG) 1, 4
   • Use split-dose administration (evening before and morning of procedure) 1, 3
   • Consider adding bisacodyl (10mg) the evening before 4

4. Enhanced patient education:

   • Provide clear, detailed instructions 1
   • Consider patient navigation services 1

Special Considerations

• Hospitalized patients often have poorer preparation quality and may require more intensive regimens 5
• Hard-to-prepare patients (elderly, IBD, renal insufficiency) may benefit from:
  • Prolonged low-fiber diet
  • Split preparation regimen
  • Colonoscopy within 5 hours of preparation completion 6
• Patients with renal insufficiency should use isotonic high-volume PEG solutions 3, 6

Common Pitfalls and Caveats

• Inadequate preparation significantly reduces adenoma detection rates (5% absolute lower ADR) 1
• Adenoma miss rates of 15-40% with poor preparation 1
• Patients with poor preparation are at high risk for repeat poor preparation (consider more aggressive approach) 1
• Next-day colonoscopies have better attendance rates than non-next-day appointments after preparation failure 1
• Documentation of preparation quality is essential for appropriate follow-up planning 7

Remember that the target for adequate bowel preparation rates should be 90% at both the individual endoscopist and unit level 1, 3.