What is the recommended bowel prep regimen for a patient undergoing colonoscopy?

Optimal Bowel Preparation for Colonoscopy

Split-dose polyethylene glycol (PEG) is the recommended bowel preparation regimen for colonoscopy, with the first dose taken the evening before the procedure and the second dose taken 4-6 hours before colonoscopy, completed at least 2 hours before the procedure start. 1, 2

Recommended Preparation Regimens

Standard Approach (First-Line)

• Split-dose regimen:
  • First half of preparation taken evening before colonoscopy
  • Second half taken 4-6 hours before the procedure
  • Must be completed at least 2 hours before procedure start
  • Superior cleansing quality compared to day-before regimens 1

Timing Based on Procedure Schedule

• Morning colonoscopies: Split-dose regimen strongly preferred 1
• Afternoon colonoscopies (after 10 AM):
  • Same-day regimen is an acceptable alternative (entire preparation on procedure day) 1, 2
  • May improve sleep quality but could cause more nausea 1

Preparation Volume Options

• Low-volume (2L) preparations are suggested over high-volume (4L) for better patient compliance 2
• Options include:
  • 2L PEG plus ascorbate
  • Sodium picosulphate plus magnesium citrate
  • 4L PEG (standard option, particularly for high-risk patients) 1, 2

Dietary Modifications

• Low-residue or low-fiber diet on the day before colonoscopy 2
• Clear liquids only after starting the bowel preparation 2
• Dietary restrictions should be limited to the day before colonoscopy for low-risk patients 2

Special Considerations

Patients with Renal Impairment

• PEG is the only recommended bowel preparation for patients with renal failure 3
• Avoid sodium phosphate preparations due to risk of acute kidney injury 2

Patients with Previous Inadequate Preparation

• Use split-dose 4L PEG + 15 mg bisacodyl 2
• Low-residue diet 3-2 days before colonoscopy 2
• Clear liquid diet the day before colonoscopy 2

Improving Patient Compliance and Outcomes

• Provide both verbal and written instructions to patients 2
• Consider patient navigation (telephone calls or automated messaging) 2
• Oral simethicone can be used as an adjunct to reduce bubbles during the procedure 2

Common Pitfalls and How to Avoid Them

1. Inadequate timing between preparation and procedure:

   • Ensure second dose is taken 4-6 hours before colonoscopy 1
   • Complete preparation at least 2 hours before procedure start 1
   • Quality decreases when interval exceeds 5 hours 1

2. Poor patient compliance:

   • Split-dose regimens significantly improve compliance compared to full-dose 4
   • Split-dose preparations decrease nausea and preparation discontinuations 4

3. Inappropriate preparation for patients with comorbidities:

   • Avoid hyperosmotic regimens in patients at risk for volume overload 2
   • Avoid sodium phosphate preparations in patients with renal impairment 3

4. Inadequate cleansing quality assessment:

   • Assess preparation quality after washing and suctioning 2
   • Target 90% adequate preparation at both individual endoscopist and unit levels 2
   • If preparation is inadequate, reschedule within 12 months 2

The evidence strongly supports split-dose regimens for superior bowel cleansing quality, better patient compliance, and fewer side effects compared to single-dose regimens 4, 5. For afternoon procedures, same-day preparation is a valid alternative with comparable efficacy 1.