Overview
Small Bowel Obstruction
1. Clinical Overview
Summary
Small bowel obstruction (SBO) is mechanical obstruction of intestinal transit. Adhesions from previous surgery account for 60-75% of cases, followed by hernias (10-15%) and malignancy (5-10%). Presentation includes colicky abdominal pain, vomiting, distension, and absolute constipation. CT with IV contrast is the gold standard investigation. Initial management is conservative ("drip and suck" - IV fluids, NG decompression, electrolyte correction) with surgical intervention for complications or failure to resolve. Strangulation is a surgical emergency with mortality rising from 8% to 25% when diagnosis is delayed.
Key Facts
- Incidence: 12% of surgical admissions; 300,000 operations/year (US)
- Causes: Adhesions (60-75%), Hernia (10-15%), Malignancy (5-10%)
- Classic Tetrad: Colicky pain, Vomiting, Distension, Constipation
- Imaging: CT abdomen with IV contrast (sensitivity 95%)
- Initial Management: "Drip and suck" - IV fluids + NG tube
- Surgery Indications: Strangulation, peritonitis, closed-loop, failure to resolve
Clinical Pearls
"Never Let the Sun Set on a Bowel Obstruction": Traditional teaching - though modern evidence supports 24-72h conservative trial for uncomplicated SBO if improving.
"Adhesive SBO Can Be Managed Conservatively": 65-80% of adhesive SBO resolves with non-operative management. Water-soluble contrast (Gastrografin) can be diagnostic AND therapeutic.
"Lactate is a Late Sign": By the time lactate is elevated, ischaemia may be irreversible. Don't wait for it - clinical signs of strangulation mandate surgery.
Why This Matters Clinically
SBO is one of the most common surgical emergencies. Early recognition of strangulation is critical. Delayed surgery for strangulated SBO increases mortality from 8% to 25%.
2. Epidemiology
Incidence
- 12-16% of acute surgical admissions
- 300,000+ hospitalisations/year (US)
- Second most common cause of acute abdomen (after appendicitis)
Demographics
- Increasing incidence due to more abdominal surgery
- Peak age: 50-70 years
- M = F
Aetiology
| Cause | Frequency | Notes |
|---|---|---|
| Adhesions | 60-75% | Post-surgical; especially pelvic/colorectal surgery |
| Hernia | 10-15% | Incarcerated inguinal, femoral, incisional |
| Malignancy | 5-10% | Primary or metastatic |
| Crohn's disease | 5% | Stricturing disease |
| Other | 5% | Gallstone ileus, intussusception, bezoars |
Risk Factors for Adhesive SBO
- Previous abdominal surgery (especially open pelvic surgery)
- Peritonitis
- Radiotherapy
- Foreign material (mesh)
3. Pathophysiology
Mechanism
- Mechanical obstruction → Bowel proximal to obstruction dilates
- Fluid sequestration → Third-spacing into bowel lumen (up to 6L/day)
- Bacterial overgrowth → Translocation risk
- Vascular compromise → Venous congestion → Arterial ischaemia → Necrosis
Types of Obstruction
| Type | Definition | Risk |
|---|---|---|
| Simple | Single point obstruction | Lower strangulation risk |
| Closed-loop | Two points of obstruction | High strangulation risk |
| Strangulated | Vascular compromise | Surgical emergency |
Strangulation Pathophysiology
- Mesenteric vessels compressed at adhesive band/hernia neck
- Venous obstruction first → Oedema
- Then arterial obstruction → Ischaemia → Necrosis
- Perforation → Peritonitis → Sepsis → Death
Why Decompression Helps
- Reduces intraluminal pressure
- Reduces wall tension (Laplace's law)
- May allow adhesive bands to "release"
4. Clinical Presentation
Symptoms
| Feature | Description |
|---|---|
| Pain | Colicky, central/periumbilical, waves every 3-5 min |
| Vomiting | Early and profuse (proximal SBO); Late/faeculent (distal) |
| Distension | More prominent with distal obstruction |
| Constipation | Absolute (no flatus or stool) - late sign |
Proximal vs Distal SBO
| Feature | Proximal | Distal |
|---|---|---|
| Vomiting | Early, bilious | Late, faeculent |
| Distension | Minimal | Prominent |
| Pain | Severe, frequent colic | Less severe |
| Dehydration | Severe | Less severe |
Signs of Strangulation (SURGICAL EMERGENCY)
| Sign | Significance |
|---|---|
| Constant (not colicky) pain | Suggests ischaemia |
| Fever | Necrosis/perforation |
| Tachycardia | Sepsis/hypovolaemia |
| Peritonism | Localised or generalised |
| Shock | Late sign |
| Elevated lactate | Tissue hypoxia |
5. Clinical Examination
General Assessment
- Vital signs: Tachycardia, hypotension, fever
- Hydration status: Dry mucous membranes, reduced skin turgor
- Urine output: Oliguria suggests significant third-spacing
Abdominal Examination
| Finding | Notes |
|---|---|
| Inspection | Distension, surgical scars, visible peristalsis, hernias |
| Auscultation | High-pitched "tinkling" bowel sounds; Later silent |
| Percussion | Tympanic (gas-filled loops) |
| Palpation | Tenderness (localised = strangulation); Masses |
Essential Examination Points
- Check ALL hernia orifices: Inguinal, femoral, umbilical, incisional
- Digital rectal examination: Empty rectum supports obstruction
- Stoma check: If present - check for retraction, obstruction
6. Investigations
Bloods
| Test | Finding | Significance |
|---|---|---|
| FBC | Elevated WCC | Strangulation, sepsis |
| U&E | Hypokalaemia, raised urea | Dehydration, vomiting |
| Lactate | > mmol/L | Bowel ischaemia (late sign) |
| Amylase | May be mildly elevated | Non-specific |
| ABG | Metabolic acidosis | Severe SBO |
Imaging
| Modality | Findings | Notes |
|---|---|---|
| AXR | Dilated small bowel (>cm), Valvulae conniventes, No gas distally | Limited sensitivity (60%) |
| CT abdomen | Transition point, Dilated proximal/collapsed distal, Free fluid | Gold standard (sensitivity 95%) |
| CT signs of strangulation | Wall thickening, Mesenteric haziness, Reduced enhancement, Free fluid |
Water-Soluble Contrast Study (Gastrografin)
- Diagnostic: Contrast in colon at 24h predicts resolution
- Therapeutic: Hyperosmolar - draws fluid into lumen, may promote peristalsis
- Evidence: Reduces need for surgery and length of stay
7. Management
Initial Management ("Drip and Suck")
┌──────────────────────────────────────────────────────────┐
│ INITIAL MANAGEMENT OF SBO │
├──────────────────────────────────────────────────────────┤
│ 1. IV ACCESS + FLUIDS │
│ - Aggressive crystalloid resuscitation │
│ - May need 4-6L in first 24h │
│ │
│ 2. NBM + NG TUBE │
│ - Decompress stomach │
│ - Reduce vomiting and aspiration risk │
│ │
│ 3. URINARY CATHETER │
│ - Monitor urine output (>0.5ml/kg/h) │
│ │
│ 4. ELECTROLYTE CORRECTION │
│ - Especially potassium │
│ │
│ 5. VTE PROPHYLAXIS │
│ - LMWH + TED stockings │
│ │
│ 6. ANALGESIA │
│ - IV opioids (don't withhold) │
└──────────────────────────────────────────────────────────┘
Indications for Emergency Surgery
| Indication | Action |
|---|---|
| Peritonitis | Immediate laparotomy |
| Strangulation signs | Urgent laparotomy |
| Irreducible hernia | Urgent exploration |
| Closed-loop obstruction | High priority surgery |
Conservative Trial Duration
- 24-72 hours: If no signs of strangulation and improving
- Gastrografin challenge: If no resolution at 24h
- Surgery if: No improvement, clinical deterioration, contrast not reached colon at 24h
Surgical Options
| Procedure | Indication |
|---|---|
| Adhesiolysis | Most common (laparoscopic or open) |
| Hernia repair | Incarcerated hernia |
| Bowel resection + anastomosis | Necrotic segment |
| Stoma formation | If anastomosis unsafe |
8. Complications
Of SBO
| Complication | Risk |
|---|---|
| Strangulation | 10-15% of SBO |
| Perforation | Following strangulation |
| Peritonitis | Life-threatening |
| Sepsis/MODS | High mortality |
| Aspiration | From vomiting |
Of Surgery
| Complication | Notes |
|---|---|
| Anastomotic leak | 3-5% |
| Surgical site infection | Common |
| Recurrent SBO | 10-30% over lifetime |
| Enterocutaneous fistula | Rare |
| Short bowel syndrome | If extensive resection |
9. Prognosis & Outcomes
Mortality
| Scenario | Mortality |
|---|---|
| Simple SBO (no strangulation) | 1-3% |
| Strangulated SBO (early surgery) | 8% |
| Strangulated SBO (delayed surgery) | 25-30% |
Recurrence
- 10-30% lifetime risk of recurrent SBO after adhesive SBO
- Higher with multiple previous episodes
Prognostic Factors
| Good | Poor |
|---|---|
| Single adhesive band | Matted adhesions |
| Early resolution | Delayed presentation |
| No strangulation | Strangulation/necrosis |
| Younger age | Elderly, comorbid |
10. Evidence & Guidelines
Key Guidelines
- Bologna Guidelines for SBO (WSES 2018)
- ASGBI: Management of Adhesive SBO (2017)
Key Evidence
Water-Soluble Contrast (Gastrografin)
- Meta-analysis: Reduces need for surgery (OR 0.62)
- Reduces length of stay by 1.8 days
- Safe; does not increase complications
Laparoscopic vs Open Adhesiolysis
- Laparoscopic feasible in 64-83% of selected cases
- Lower wound infection, shorter stay
- Higher conversion rate if matted adhesions
11. Patient/Layperson Explanation
What is Bowel Obstruction?
Bowel obstruction is when a blockage stops food and liquid from passing through your intestines normally. It's like a kink in a garden hose - the flow gets blocked.
What Causes It?
The most common cause is scar tissue (adhesions) from previous operations. It can also be caused by hernias or, less commonly, tumours.
What Are the Symptoms?
- Crampy tummy pain that comes in waves
- Being sick (vomiting)
- Swollen tummy
- Not being able to pass wind or open your bowels
How is it Treated?
Many cases can be treated without surgery by:
- Putting a tube down your nose to drain the stomach
- Giving you fluids through a drip
- Resting the bowel
If the blockage doesn't clear or there are warning signs, you may need an operation.
When to Seek Help
Go to A&E immediately if you have:
- Severe constant abdominal pain
- Vomiting that won't stop
- High fever
- A very swollen, hard tummy
12. References
Primary Guidelines
- Ten Broek RPG, et al. Bologna Guidelines for Diagnosis and Management of Adhesive Small Bowel Obstruction (ASBO): 2017 update of the evidence-based guidelines from the World Society of Emergency Surgery. World J Emerg Surg. 2018;13:24. PMID: 30305850
Key Studies
- Abbas S, et al. Oral water soluble contrast for the management of adhesive small bowel obstruction. Cochrane Database Syst Rev. 2007. PMID: 17636861
- Maung AA, et al. Evaluation and management of small-bowel obstruction: an Eastern Association for the Surgery of Trauma practice management guideline. J Trauma Acute Care Surg. 2012;73(5 Suppl 4):S362-9. PMID: 23114494