Normal Bowel Preparation for Colonoscopy
The normal bowel preparation for colonoscopy consists of a split-dose regimen using either 2-4L of polyethylene glycol-electrolyte solution (PEG-ELS) or validated low-volume alternatives, combined with dietary modifications limited to the day before the procedure. 1
Standard Preparation Protocol
Purgative Selection
- No single bowel preparation purgative is superior to others for ambulatory patients at low risk for inadequate preparation 1
- 2L bowel preparation regimens are preferred over 4L regimens due to better tolerability while maintaining efficacy 1
- Available options include:
Timing: Split-Dose Administration (Strongly Recommended)
Split-dose administration is recommended for all patients, regardless of preparation volume 1, 3:
- First dose: Evening before colonoscopy 1, 2
- Second dose: Morning of colonoscopy, starting within 5 hours of the procedure and completing at least 2 hours before 3
- This approach achieves superior bowel cleansing compared to day-prior or same-day regimens 1, 3
Dietary Modifications
Dietary restrictions should be limited to the day before colonoscopy only 1:
- Low-residue and low-fiber foods or full liquids for early and midday meals on the day before colonoscopy 1
- Clear liquids only after starting the preparation 1
- A low-fiber diet for 72 hours is recommended for high-risk patients with previous inadequate preparation 4
Patient Education Requirements
Both verbal and written instructions must be provided for all components of the preparation 1:
- Instructions should cover what to expect, escort arrangements, dietary modifications, medication adjustments, and purgative administration 1
- Patient navigation (telephonic or virtual automated messaging) improves adequate preparation rates 1
Quality Benchmarks
Adequate bowel preparation is defined as cleanliness sufficient to assign standard screening/surveillance intervals and detect lesions >5mm throughout the colon 1, 4:
- Target rate: ≥85-90% of all colonoscopies should achieve adequate preparation 4, 5
- Quality is assessed after all washing and suctioning maneuvers during colonoscopy 1
High-Risk Populations Requiring Modified Protocols
Patients with Previous Inadequate Preparation
Use an intensive regimen achieving 90% success 1, 4:
- Low-fiber diet for 72 hours before procedure 1, 4
- 10mg bisacodyl on evening before 1, 4
- 1.5L PEG-ELS both evening before and morning of procedure 1, 4
Diabetic Patients
May require more aggressive regimens or higher volumes due to poorer response to standard preparations 1:
- Consider adding magnesium citrate to standard PEG preparation 1
- Good preparation achieved in only 62% of diabetics vs. 97% of non-diabetics with standard regimens 1
Patients with Prior Bowel Resection
Extended preparation protocols are necessary 1:
- Unsatisfactory preparation occurs in 60-65% with standard regimens 1
- Consider higher volumes or extended preparation timelines 1
Critical Contraindications and Safety Considerations
Avoid Sodium Phosphate Preparations In:
Sodium phosphate is contraindicated in patients with 2:
- Severe renal impairment (creatinine clearance <30 mL/min) 2
- Risk of fluid/electrolyte abnormalities 2
- Liver disease, hypoparathyroidism 4
- Patients taking diuretics, ACE inhibitors, or angiotensin receptor blockers 4, 6
Use PEG-Based Preparations Preferentially In:
- Elderly patients (risk of electrolyte abnormalities with alternatives) 1
- Patients with cardiovascular disease 6
- Patients with renal dysfunction 4, 6
Common Pitfalls to Avoid
- Do not stop preparation due to diarrhea: This is the intended therapeutic effect 6, 7
- Do not use day-prior regimens as standard: Split-dose is superior 1, 3
- Do not restrict diet for >24 hours in low-risk patients: Unnecessary and reduces compliance 1
- Do not administer medications within 1 hour of starting each dose: Risk of reduced absorption 2
- Ensure adequate hydration: Additional clear fluids must be consumed after every dose 2