What is the recommended bowel clean out protocol for adults?

Bowel Clean Out Protocol for Adults

For standard colonoscopy preparation in adults, use a split-dose regimen of 4L polyethylene glycol-electrolyte solution (PEG-ELS) or low-volume alternatives (2L PEG-ELS with adjuncts), with the second dose taken on the morning of the procedure to optimize cleansing quality. 1

Standard Preparation Protocols

First-Line Regimens

Split-dose administration is superior to same-day or day-before-only dosing, achieving 75% good/excellent cleansing versus 43% with non-split dosing 2. The US Multi-Society Task Force on Colorectal Cancer provides strong recommendations for the following approaches 1:

• 4L PEG-ELS split-dose: Administer 2L the evening before (between 5:00-9:00 PM) and 2L on the morning of colonoscopy (at least 5 hours prior but no more than 9 hours before procedure) 1
• Low-volume alternatives: 2L PEG-ELS with adjuncts (bisacodyl, ascorbic acid, or sodium sulfate) are non-inferior to 4L preparations in healthy, non-constipated individuals 1, 2
• Sodium picosulfate/magnesium citrate: Two packets separated by 6 hours, with split-dosing (evening before and morning of) achieving 84% success versus 74% with comparator 3

Dietary Modifications

• Low-fiber diet for 72 hours before the procedure 1
• Clear liquid diet on the day before colonoscopy (24 hours prior) 3

Timing Considerations

Colonoscopy should be performed within 8 hours of the last fluid intake to maximize cleansing effectiveness 2. Maximum cleansing quality deteriorates significantly when procedures occur more than 8 hours after the final preparation dose 2.

High-Risk Populations Requiring Intensified Protocols

Patients with Prior Failed Preparation

For patients with previously inadequate bowel preparation, an intensive regimen achieves 90% success 1:

• Low-fiber diet for 72 hours followed by clear liquids the day before 1
• 10 mg bisacodyl on the evening before the procedure 1
• 1.5L PEG-ELS on the evening before 1
• Second 1.5L PEG-ELS dose on the morning of colonoscopy 1

Diabetic Patients

Diabetic patients have significantly poorer response to standard preparations (only 62% adequate versus 97% in non-diabetics with 6L PEG) 4. Consider more aggressive regimens or higher volumes in this population, regardless of insulin use, glycemic control, or presence of neuropathy 4.

Contraindications to Specific Agents

Avoid sodium phosphate preparations in patients with 5:

• Liver disease
• Hypoparathyroidism
• Renal impairment
• Risk of fluid and electrolyte abnormalities

Use PEG-based preparations preferentially in these high-risk populations 5.

Salvage Strategies for Inadequate Preparation

Pre-Procedure Assessment

Assess effluent quality before sedation: Patients reporting brown liquid or solid stool have a 54% chance of inadequate preparation 1. In these cases, administer additional oral laxatives or large-volume enemas before proceeding 1, 5.

Intra-Procedure Salvage

If inadequate preparation is discovered during colonoscopy, through-the-scope enema techniques achieve 96-100% success 1, 5:

• Phosphate enema (133 mL/19 g) followed by bisacodyl enema (37 mL/10 mg), or two bisacodyl enemas, instilled through the colonoscope accessory channel 1
• 500 mL polyethylene glycol solution instilled at the hepatic flexure level via biopsy channel 1
• Wake patient from propofol sedation to evacuate residual fluid in the bathroom 1

Same-Day or Next-Day Completion

Next-day colonoscopy reduces repeat failure risk (OR 0.31,95% CI 0.1-0.92) compared to delayed rescheduling 1, 5. Same-day completion after additional oral cathartic administration is associated with better outcomes than delayed colonoscopy 1.

Quality Benchmarks and Follow-Up

Adequacy Standards

The rate of adequate bowel cleansing should be at least 85% for any endoscopist or practice 1. Adequate preparation means the colonoscopist can recommend standard screening/surveillance intervals and detect lesions >5 mm throughout the colon 1.

Management of Inadequate Preparation

• If cecum reached but preparation inadequate: Repeat colonoscopy within 1 year with more aggressive preparation regimen 1, 5
• If procedure terminated due to inadequate preparation: Assess quality in rectosigmoid region; only terminate if clearly inadequate to detect polyps >5 mm 1, 5
• Shorter intervals than 1 year indicated when advanced neoplasia detected with inadequate preparation 1

Common Pitfalls to Avoid

• Do not use day-before-only dosing when split-dose is feasible—this reduces success by 32% 2
• Do not delay colonoscopy beyond 8 hours after last preparation dose—cleansing quality deteriorates significantly 2
• Do not ignore brown effluent reports at check-in—these patients need salvage measures before sedation 1
• Do not use sodium phosphate in renal, liver, or electrolyte-disorder patients—serious complications can occur 5
• Do not assume standard doses work in diabetics—they require more aggressive protocols 4