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 |