What is the recommended bowel preparation before surgery?

Bowel Preparation Before Surgery

Mechanical bowel preparation (MBP) should NOT be used routinely for most elective colorectal surgeries, but combined MBP with oral antibiotics is strongly recommended when bowel preparation is indicated, particularly for rectal surgery with anastomosis. 1

General Principles for Colorectal Surgery

Standard Colonic Surgery

• Routine mechanical bowel preparation should be avoided for elective colonic resections, as it causes dehydration, electrolyte imbalances, patient discomfort, and provides no clinical benefit in reducing anastomotic leaks, wound infections, or mortality 1, 2
• High-quality evidence from 18 randomized trials (5,805 patients) demonstrates no difference in anastomotic leakage rates between MBP versus no preparation (4.4% vs 4.5%) 2
• MBP alone actually increases spillage of bowel contents and may worsen outcomes 1

Rectal Surgery - Selective Use

When MBP is indicated (specific scenarios below), always combine it with oral antibiotics rather than using MBP alone: 1, 3

• Low anterior resection with planned diverting ileostomy: MBP may be necessary, though evidence is limited 1
• Total mesorectal excision (TME) with diverting stoma: Consider MBP (weak recommendation due to low evidence) 1
• Laparoscopic low rectal surgery: One trial showed higher infectious morbidity without MBP when >80% had diverting stomas 1

Combined Bowel Preparation Protocol (When Indicated)

The optimal approach when bowel preparation is needed combines mechanical preparation with oral antibiotics: 1, 4, 3

• Timing: Begin preparation the day before surgery 4
• Mechanical component: Magnesium sulfate 30 mL of 50% solution (15g) at 10:00 AM, 2:00 PM, and 6:00 PM on pre-op day 2; then at 10:00 AM and 2:00 PM on pre-op day 1 4
• Oral antibiotics: Neomycin 1g plus erythromycin base 1g at 1:00 PM, 2:00 PM, and 11:00 PM on pre-op day 1 4
• Diet: Clear liquid diet on pre-op day 1 with IV fluid supplementation as needed 4

Evidence supporting combined preparation:

• Reduces surgical site infections by 61% compared to no preparation (OR 0.39) 3
• Reduces anastomotic leak by 47% (OR 0.53) 3
• Reduces organ space infections by 44% (OR 0.56) 3
• Analysis of 27,804 patients showed combined MBP/ABP superior to MBP alone or no preparation 3

Non-Colorectal Abdominal Surgery

Gynecologic Surgery

• Do not use routine MBP for elective gynecologic procedures 1
• No evidence supports benefit in this population 1

Urologic Surgery (Radical Cystectomy with Ileal Conduit)

• MBP provides no advantage and should not be routinely performed 5
• Randomized trial of 86 patients showed no difference in complications between MBP versus no preparation 5

Liver Surgery

• MBP is not indicated before hepatic resection 1
• No studies or evidence support its use in liver surgery 1

Preoperative Fasting Guidelines (All Surgery Types)

Modern fasting protocols replace the outdated "NPO after midnight" approach: 1, 6

• Clear liquids: Permitted until 2 hours before anesthesia induction 1
• Light meal: Permitted until 6 hours before induction 1, 6
• Full meal (meat, fatty/fried foods): Requires 8+ hours fasting 1
• Carbohydrate loading: 400 mL of complex carbohydrate drink (50g CHO) 2 hours before surgery reduces insulin resistance and improves outcomes 1, 6

This approach is supported by 22 randomized trials showing no increase in gastric content or aspiration risk compared to midnight fasting 1

Special Considerations for Colonoscopy

For diagnostic colonoscopy (not surgery), split-dose preparation is superior: 1

• Second portion should begin 4-6 hours before colonoscopy 1
• Must be completed at least 2 hours before procedure start 1
• Every additional hour between last purgative and colonoscopy decreases preparation quality by 10% 1
• Diet before colonoscopy: Low-residue diet is equivalent to clear liquid diet for bowel preparation quality but offers better patient tolerance and willingness to repeat (RR 1.17) 7

Common Pitfalls to Avoid

• Do not use MBP alone without oral antibiotics when bowel preparation is indicated - this provides no benefit and may cause harm 1, 3
• Do not routinely prepare the bowel for standard colonic resections - this is outdated practice not supported by evidence 1
• Do not enforce midnight fasting - this causes unnecessary patient discomfort and metabolic stress without safety benefit 1
• Do not assume laparoscopic surgery requires MBP - studies show laparoscopic colectomy is safe without preparation; use preoperative tattoo for tumor localization instead 1