Bowel Obstruction
Bowel obstruction is a mechanical or functional blockage of the intestinal lumen preventing normal passage of contents. Adhesions are the commonest cause of small bowel obstruction (SBO).
Key Facts
Adhesions are the commonest cause of SBO (~60-75%); colorectal cancer is the commonest cause of large bowel obstruction (LBO) (~60%) Classical features: Colicky abdominal pain, vomiting (early in SBO, late in LBO), distension (more prominent in LBO), absolute constipation AXR: Dilated small bowel >3cm, large bowel >6cm, caecum >9cm — beyond these, perforation risk increases significantly CT abdomen/pelvis with IV contrast: Investigation of choice — identifies level, cause, and complications (strangulation, perforation) Strangulation is the most feared complication — compromised blood supply → bowel ischaemia → necrosis → perforation Closed-loop obstruction (e.g., sigmoid volvulus with competent ileocaecal valve) carries highest perforation risk — surgical emergency Initial management: 'Drip and suck' — IV fluids, NG tube decompression, NBM, catheter; reassess at 24-48 hours Gastrografin (water-soluble contrast) via NG tube may be therapeutic in adhesional SBO and aids decision-making (if contrast reaches caecum by 24 hours, likely to resolve conservatively)
Overview
Key Facts
Bowel obstruction is a common surgical emergency. The key clinical decision is whether to manage conservatively or operatively, based on the cause and presence of complications.
Epidemiology
SBO accounts for ~20% of acute surgical admissions. LBO is less common but more frequently requires surgical intervention. Adhesional SBO has a high recurrence rate (~20-30%).
Aetiology
Small bowel obstruction:
- Adhesions (~60-75%) — from previous surgery
- Hernias (~15%) — inguinal, femoral (especially in elderly women)
- Crohn's disease strictures
- Malignancy
- Intussusception (children), gallstone ileus (elderly)
Large bowel obstruction:
- Colorectal cancer (~60%)
- Diverticular disease/stricture (~15%)
- Volvulus (~10%) — sigmoid (most common) or caecal
Pathophysiology
- Mechanical obstruction → proximal bowel dilates with gas and fluid → intraluminal pressure rises
- Fluid sequestration into bowel lumen → dehydration, electrolyte imbalance
- If blood supply compromised (strangulation) → ischaemia → necrosis → perforation → peritonitis
- Vomiting (early in proximal SBO, late in distal/LBO) → metabolic alkalosis with hypokalaemia
Clinical Presentation
Small Bowel Obstruction
- Colicky central abdominal pain
- Early, profuse vomiting (may be bilious)
- Distension (moderate)
- Absolute constipation (may pass flatus/stool initially)
- Visible peristalsis (thin patients)
- High-pitched, tinkling bowel sounds
Large Bowel Obstruction
- Colicky lower abdominal pain
- Late vomiting (may become faeculent)
- Marked distension
- Early absolute constipation
- Resonant percussion
Sigmoid Volvulus
- Elderly, institutionalised, psychiatric patients, chronic constipation
- Massive distension ('coffee bean' sign on AXR)
- Treatment: Flexible sigmoidoscopic decompression → elective sigmoid colectomy
Red Flags (Strangulation)
- Constant (not colicky) pain — suggests ischaemia
- Peritonism (guarding, rebound)
- Fever, tachycardia
- Raised lactate
- Irreducible, tender hernia
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Paralytic ileus | Post-operative, metabolic cause, no mechanical blockage | CT — no transition point |
| Pseudo-obstruction (Ogilvie's) | LBO picture, usually post-surgical/medical; no mechanical cause | CT — no obstructing lesion |
| Constipation | Gradual, no acute obstruction features | AXR, clinical assessment |
| Mesenteric ischaemia | Pain out of proportion, AF, raised lactate | CT angiography |
| Acute pancreatitis | Epigastric pain, vomiting, ileus | Amylase/lipase, CT |
Diagnosis / Investigation
Bedside
- Observations: NEWS2
- NG tube: Decompress stomach, monitor aspirate volume
- Fluid balance: Strict input/output
Bloods
- FBC: WCC (strangulation/perforation)
- U&Es: Dehydration, hypokalaemia, metabolic alkalosis (vomiting)
- LFTs: Exclude biliary pathology
- Lactate: Raised in strangulation/ischaemia (>2 mmol/L concerning)
- ABG/VBG: Acid-base, lactate
- G&S: Pre-operative
Imaging
- AXR: Small bowel >3cm dilated; large bowel >6cm; caecum >9cm (perforation risk)
- CT abdomen/pelvis with IV contrast: Investigation of choice — identifies level, cause, transition point, strangulation, perforation
- Water-soluble contrast follow-through (Gastrografin): Via NG tube in adhesional SBO — therapeutic (osmotic) and prognostic (if contrast reaches caecum by 24 hours → likely to resolve conservatively)
Management
Conservative ('Drip and Suck')
- NG tube: Decompression — reduce vomiting, prevent aspiration
- IV fluids: Aggressive resuscitation (0.9% NaCl with KCl supplementation)
- NBM
- Urinary catheter: Monitor urine output
- VTE prophylaxis: LMWH
- Appropriate for adhesional SBO without signs of strangulation
- Reassess clinically and with AXR/CT at 24-48 hours
Gastrografin Challenge
- 100mL Gastrografin via NG tube
- AXR at 4-6 hours — if contrast in caecum, likely to resolve
- If no progress by 24 hours — consider surgery
Surgical
Indications for surgery:
- Strangulation (peritonism, raised lactate, constant pain)
- Closed-loop obstruction
- Hernia obstruction (irreducible)
- Failed conservative management (no improvement at 48-72 hours)
- LBO from cancer — resection ± stoma
- Sigmoid volvulus — sigmoidoscopic decompression → elective sigmoid colectomy
Procedures:
- Adhesiolysis (laparoscopic or open)
- Bowel resection if gangrenous
- Stoma if unsafe for primary anastomosis
Referral Criteria
- All suspected bowel obstruction — surgical team
- LBO — likely to need surgery; colorectal cancer pathway if appropriate
- Strangulation — emergency surgery
Prognosis
- Adhesional SBO: ~75% resolve with conservative management; recurrence ~20-30%
- Strangulated SBO: Mortality ~10-20% — increases with delayed surgery
- LBO from cancer: Depends on cancer stage — emergency surgery has higher morbidity than elective
- Sigmoid volvulus: Recurrence rate ~50-60% without definitive surgery; endoscopic decompression success ~80%
- Overall mortality: SBO ~3-5%; LBO ~10-15% (higher due to cancer and older population)
Other Relevant Information
SBO vs LBO Comparison
| Feature | SBO | LBO |
|---|---|---|
| Commonest cause | Adhesions | Colorectal cancer |
| Vomiting | Early, profuse | Late, faeculent |
| Distension | Moderate | Marked |
| AXR | Central, valvulae conniventes | Peripheral, haustra |
| Initial management | Conservative (drip and suck) | Usually surgical |