Small Bowel Obstruction (SBO)

1. Clinical Overview

Summary

Small Bowel Obstruction (SBO) is a mechanical blockage preventing the normal passage of intestinal contents through the small intestine. It represents one of the most common surgical emergencies, accounting for approximately 15-20% of all emergency surgical admissions and 12-16% of emergency laparotomies. [1,2]

The pathophysiology involves mechanical occlusion of the intestinal lumen, leading to proximal bowel dilatation, fluid sequestration, electrolyte derangements, and potential vascular compromise. The classic clinical tetrad consists of colicky abdominal pain, vomiting, abdominal distension, and absolute constipation (inability to pass flatus or faeces). [3]

Adhesions from previous abdominal or pelvic surgery represent the leading cause (60-70% of cases), followed by incarcerated hernias (15-20%), malignancy (5-10%), inflammatory conditions such as Crohn's disease (5%), and rarer causes including gallstone ileus, volvulus, and intussusception. [1,4]

Diagnosis relies on clinical assessment supplemented by imaging. Plain abdominal radiography demonstrates dilated small bowel loops (> 3 cm) with air-fluid levels, but CT abdomen with intravenous contrast is the gold standard imaging modality (sensitivity 90-96%, specificity 96%), enabling identification of the transition point, cause, and complications such as ischaemia or closed-loop obstruction. [5,6]

Management follows a stepwise approach. Initial resuscitation involves "Drip and Suck" protocols: intravenous fluid resuscitation, nasogastric decompression, urinary catheterization, and correction of electrolyte abnormalities. Conservative management is successful in 70-80% of adhesive SBO cases, with water-soluble contrast (Gastrografin) challenge serving both diagnostic and therapeutic roles. [1,7,8]

Surgical intervention is indicated for: signs of strangulation (peritonitis, haemodynamic instability, elevated lactate), closed-loop obstruction, incarcerated/strangulated hernias, failure of conservative management after 48-72 hours, or complete obstruction. Mortality ranges from less than 5% for simple obstruction to 15-30% for strangulated bowel with delayed intervention. [1,9,10]

Clinical Pearls

"Never Let the Sun Set on a Bowel Obstruction": This surgical axiom emphasizes the critical importance of vigilant monitoring and early recognition of strangulation. Delays in surgical intervention for ischaemic bowel increase mortality dramatically—from 8% when operated within 24 hours to 25-35% when delayed beyond 36 hours. [10]

Adhesions = Most Common Cause in "Non-Virgin Abdomen": Approximately 60-70% of SBO occurs in patients with previous abdominal surgery. Conversely, SBO in a patient with no surgical history ("virgin abdomen") mandates thorough evaluation for hernias (including internal hernias), malignancy, or inflammatory conditions. [1,4]

The "Drip and Suck" Protocol: Universal first-line management involves intravenous crystalloid resuscitation ("Drip") and nasogastric decompression ("Suck"). This resuscitative phase is essential regardless of whether conservative or surgical management is ultimately pursued. [3]

Vomiting is Early, Constipation is Late: In proximal SBO, profuse bilious vomiting occurs early with minimal abdominal distension. In distal SBO, constipation is the prominent early feature with late-onset, faeculent vomiting and massive distension. Understanding the level of obstruction guides clinical assessment. [3]

Gastrografin Challenge: Water-soluble contrast (Gastrografin) administered orally or via nasogastric tube serves dual purposes: diagnostic (appearance in colon within 24 hours predicts non-operative resolution with 96-100% accuracy) and therapeutic (osmotic effect may accelerate resolution, reducing hospital stay by 1-2 days and need for surgery). [7,8]

Closed-Loop Obstruction = Surgical Emergency: When bowel is obstructed at two points along its length, a "closed-loop" forms. This configuration prevents decompression proximally or distally, leading to rapid distension, venous congestion, arterial compromise, and ischaemia within hours. Immediate surgical intervention is mandatory. [11]

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2. Epidemiology

Incidence and Prevalence

• Hospital Admissions: SBO accounts for 300,000-350,000 hospital admissions annually in the United States, with similar incidence rates across Western countries. [1]
• Emergency Presentations: Represents 12-16% of emergency surgical admissions and 15-20% of emergency laparotomies. [1,2]
• Age Distribution: Can occur at any age, but incidence increases significantly with age due to accumulating surgical history. Peak incidence in 6th-7th decades. [4]
• Sex Distribution: Slightly higher in females (1.2:1 ratio), potentially related to higher rates of pelvic surgery (hysterectomy, caesarean section). [4]
• Recurrence Risk: Following initial episode of adhesive SBO, recurrence rate is approximately 20-30% over subsequent 5 years. [12]

Aetiology by Frequency

Exam Detail: Understanding the relative frequency of causes is high-yield for examinations. In "virgin abdomen" (no previous surgery), the differential is fundamentally different.

"Virgin Abdomen" Differential

In patients with no previous abdominal surgery, the diagnostic approach differs fundamentally:

1. Hernias (50-60%): External hernias (inguinal 40%, femoral 5-10%, umbilical 5%) or internal hernias (paraduodenal, mesenteric defect)
2. Malignancy (15-20%): Higher index of suspicion for neoplastic causes
3. Crohn's Disease (10-15%): Consider inflammatory bowel disease
4. Gallstone Ileus (5-10%): Especially elderly females
5. Congenital Bands / Malrotation (paediatric presentations)

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3. Pathophysiology

Mechanisms of Obstruction

Small bowel obstruction results from mechanical occlusion of the intestinal lumen. The pathophysiological cascade involves:

1. Initial Mechanical Blockage

Luminal obstruction by adhesive band, hernia orifice, tumour mass, intraluminal foreign body, or external compression prevents aboral passage of intestinal contents.

2. Proximal Bowel Dilatation

• Gas Accumulation: Approximately 70% of intestinal gas derives from swallowed air (nitrogen, oxygen), with bacterial fermentation contributing additional hydrogen, methane, and carbon dioxide.
• Fluid Sequestration: The gastrointestinal tract receives approximately 8-10 litres of fluid daily (2L oral intake, 1L saliva, 2L gastric secretions, 1L bile, 2L pancreatic secretions, 1L intestinal secretions). With obstruction, this fluid accumulates proximally.
• Bowel Diameter Increases: Normal small bowel diameter less than 2.5 cm. Obstruction causes progressive dilatation (> 3 cm diagnostic threshold, > 4-5 cm severe).

3. Fluid and Electrolyte Derangements

Exam Detail: Understanding the biochemical consequences is critical for viva examinations. The pattern of electrolyte disturbance varies with level and duration of obstruction.

Typical Biochemistry in Prolonged Proximal SBO:

• Na⁺: Low-normal to low (dilutional + losses)
• K⁺: Low (vomiting, renal losses)
• Cl⁻: Low (gastric acid losses)
• HCO₃⁻: High (metabolic alkalosis)
• Urea: Elevated (dehydration)
• Creatinine: Elevated (but Urea:Creatinine ratio > 100:1 suggests prerenal)
• pH: Alkalotic initially (metabolic alkalosis)

Late/Distal SBO or Ischaemia:

• Metabolic acidosis (lactic acidosis from ischaemia or systemic hypoperfusion)
• Lactate: Markedly elevated (> 4 mmol/L suggests ischaemia)

4. Bowel Wall Compromise

Progressive dilatation and increased intraluminal pressure lead to:

1. Venous Obstruction First: Thin-walled veins compress before thick-walled arteries → Venous congestion → Haemorrhagic engorgement of bowel wall → Oedema.
2. Arterial Compromise: With further pressure elevation or mechanical vascular compression (e.g., hernia orifice, tight adhesive band), arterial inflow ceases → Ischaemia.
3. Progression to Necrosis: Ischaemia > 6 hours → Transmural necrosis → Perforation → Faecal peritonitis.

5. Strangulation

Strangulation is defined as compromise of the blood supply to obstructed bowel. This represents a surgical emergency requiring urgent laparotomy. [9,10]

High-Risk Scenarios for Strangulation:

• Closed-Loop Obstruction: Bowel obstructed at two points (e.g., adhesive band creating loop) → No decompression possible → Rapid rise in intraluminal pressure → Early vascular compromise. [11]
• Tight Hernia Orifice: Femoral hernias (high strangulation rate ~40%), incarcerated inguinal or incisional hernias.
• Volvulus: Twisting of mesentery occludes vessels directly.

Timeline of Strangulation:

• 0-6 hours: Reversible ischaemia (bowel viable if blood flow restored)
• 6-12 hours: Transmural ischaemia, patchy necrosis

• 12 hours: Frank necrosis, high perforation risk

Mortality:

• Simple obstruction: less than 5%
• Strangulated obstruction (early surgery): 8-10%
• Strangulated obstruction (delayed > 36h): 25-35% [10]

6. Bacterial Translocation and Sepsis

With mucosal barrier breakdown:

• Bacteria translocate across damaged intestinal wall
• Portal bacteraemia → Systemic sepsis
• Endotoxin release (Gram-negative bacteria)
• Systemic inflammatory response syndrome (SIRS), potential septic shock

Classification Systems

Exam Detail: Examiners frequently ask for classification of SBO. Understanding these distinctions is essential for surgical decision-making.

Obstruction Completeness

Vascular Compromise

Anatomical Configuration

Closed-Loop Obstruction - Surgical Emergency:

Closed-loop occurs when bowel is occluded at two points along its length (e.g., adhesive band trapping a loop, internal hernia with narrow orifice). The isolated segment:

• Cannot decompress via vomiting or nasogastric drainage
• Rapidly distends with fluid and gas
• Intraluminal pressure rises precipitously
• Venous then arterial occlusion occurs within hours
• High mortality if not operated urgently

CT Findings Suggesting Closed-Loop: [11]

• "C-shaped" or "U-shaped" dilated loop
• Converging mesenteric vessels ("whirl sign")
• Serrated beak sign at obstruction points
• Mesenteric haziness/oedema
• Bowel wall thickening

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4. Clinical Presentation

Classic Clinical Tetrad

The cardinal features of SBO (sensitivity 60-80% when all four present): [3]

1. Colicky Abdominal Pain
2. Vomiting
3. Abdominal Distension
4. Absolute Constipation (no passage of faeces or flatus)

Symptoms

Exam Detail: The pattern and sequence of symptoms provides diagnostic clues to the level and completeness of obstruction—a common viva question.

"Absolute Constipation" Caveat: In the first 12-24 hours of complete SBO, patients may still pass stool and flatus representing evacuation of colonic content distal to obstruction. True absolute constipation develops subsequently.

Signs on Examination

General Inspection

Abdominal Examination

Inspection:

• Generalised Distension: Increased abdominal girth, tympanic to percussion
• Visible Peristalsis: In thin patients, "ladder pattern" of dilated bowel loops contracting in waves (pathognomonic when present)
• Surgical Scars: Document all scars (indicates adhesion risk). Laparoscopic port sites often subtle.
• Hernias: Inspect groins, umbilicus, all surgical scars for bulges

Palpation:

Exam Detail: The character of abdominal tenderness is the key clinical discriminator between simple and strangulated obstruction. This distinction determines whether conservative management is appropriate or immediate surgery is required.

Critical Clinical Rule:

Peritonism (guarding, rebound, rigidity) in SBO = Strangulation/Perforation until proven otherwise → Immediate surgical consultation and preparation for laparotomy. [9,10]

Percussion:

• Tympanic (resonant/drum-like): Gas-filled dilated loops
• Shifting Dullness: Absent (vs. ascites)

Auscultation:

Femoral Hernias - High Strangulation Risk:

Femoral hernias account for only 5-10% of all hernias but have the highest strangulation rate (~40%). [1] They occur:

• Below inguinal ligament
• Medial to femoral vein
• More common in elderly females
• Often small, easily missed on examination
• High index of suspicion required

Digital Rectal Examination (DRE)

Mandatory in all SBO to assess:

• Empty rectum: Supports diagnosis of complete obstruction
• Palpable mass: Rectal tumour (though rare cause of SBO)
• Blood: Suggests ischaemia, malignancy, or inflammatory bowel disease
• Impacted stool: May suggest pseudo-obstruction rather than mechanical SBO

Hernial Orifice Examination

Six Sites to Examine in Every Patient:

1. Right Inguinal
2. Left Inguinal
3. Right Femoral
4. Left Femoral
5. Umbilical
6. All Surgical Scars (incisional hernias)

Additional Rare Sites:

• Spigelian (lateral edge of rectus abdominis)
• Obturator (medial thigh pain, positive Howship-Romberg sign)
• Lumbar/Petit's triangle
• Internal hernias (not externally visible—diagnosed on CT)

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5. Differential Diagnosis

SBO must be distinguished from other causes of acute abdomen and intestinal dysmotility:

Comparison Table

Exam Detail: Viva Question - Ileus vs. SBO: "How do you differentiate paralytic ileus from mechanical small bowel obstruction?"

Model Answer:

• History: Ileus typically post-operative (day 1-5), or associated with systemic illness (hypokalaemia, uraemia, sepsis, intra-abdominal inflammation). SBO has history of surgery (adhesions) or hernia.
• Pain: SBO has colicky (intermittent cramping) pain. Ileus has constant dull discomfort or minimal pain.
• Bowel Sounds: SBO has high-pitched tinkling sounds early (obstructed pattern). Ileus has absent/silent bowel sounds.
• Imaging: SBO shows transition point (dilated proximal bowel, collapsed distal bowel). Ileus shows generalised dilatation of both small and large bowel with gas throughout colon and rectum.
• Management: SBO may require surgery if conservative fails or strangulation. Ileus is managed conservatively (NG decompression, correct electrolytes, mobilisation, stop causative drugs).

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6. Investigations

Blood Tests

Essential Baseline Bloods

Exam Detail: Viva Question - Biochemical Pattern: "Describe the typical biochemical abnormalities in a patient with proximal small bowel obstruction who has been vomiting for 48 hours."

Model Answer: The patient develops hypochloraemic, hypokalaemic metabolic alkalosis from loss of gastric hydrochloric acid and potassium.

• Arterial Blood Gas: pH ↑ (e.g., 7.50), HCO₃⁻ ↑ (e.g., 32 mmol/L), pCO₂ normal or mildly elevated (compensatory respiratory retention)
• U&E: Na⁺ low-normal (135-140), K⁺ ↓ (e.g., 2.8 mmol/L), Cl⁻ ↓ (e.g., 88 mmol/L), HCO₃⁻ ↑
• Urea ↑↑ (prerenal AKI from volume depletion), Creatinine ↑ (but Urea rises disproportionately)
• Urine: Paradoxical aciduria initially (kidneys excrete H⁺ to conserve K⁺), then alkaline urine once K⁺ severely depleted

Management: IV crystalloid (Normal Saline preferred to replace Cl⁻), potassium supplementation (40 mmol/L in IV fluids, or concentrated replacement if severe). Monitor U&E closely.

Imaging

1. Plain Abdominal Radiography (AXR)

Standard Series: Supine + Erect abdominal X-ray, Erect chest X-ray (to exclude free air under diaphragm)

Sensitivity/Specificity: 60-80% for SBO diagnosis. [5] Useful for initial triage but CT is superior.

Classic AXR Findings in SBO:

Rigler's Triad (Gallstone Ileus):

1. Pneumobilia (air in biliary tree—seen as branching lucencies in RUQ)
2. Small bowel obstruction
3. Ectopic gallstone (visible calcified stone, usually at ileocaecal valve)

Limitations of AXR:

• Cannot reliably identify cause
• Cannot detect ischaemia
• Cannot visualise transition point accurately
• 20-40% false-negative rate [5]

When AXR May Be Sufficient:

• Typical clinical presentation
• Straightforward case (e.g., known adhesions, previous similar episodes managed conservatively)
• Resource-limited settings
• CT contraindicated or unavailable

2. CT Abdomen/Pelvis with IV Contrast (Gold Standard)

Sensitivity: 90-96%, Specificity: 96% for SBO diagnosis. [5,6]

Indications for CT:

• All patients with suspected SBO (unless low threshold and AXR diagnostic)
• Suspected strangulation/ischaemia
• Virgin abdomen (identify cause)
• Uncertain diagnosis
• Planning surgical approach

CT Protocol:

• IV contrast (iodinated): Essential to assess bowel wall perfusion (ischaemia detection)
• Oral contrast: NOT routinely required (delays imaging, risk of aspiration). In adhesive SBO, omit oral contrast. Water-soluble contrast (Gastrografin) can be given therapeutically after CT.
• Portal venous phase imaging (70 seconds post-contrast)

CT Findings - Diagnosis of SBO:

CT Findings - Identify Cause:

CT Findings - Detect Complications (Strangulation/Ischaemia): [11]

Exam Detail: Recognition of CT signs of ischaemia is critical and constitutes a surgical emergency. This is very high-yield for examinations.

Closed-Loop Obstruction - CT Diagnosis:

Closed-loop configuration (two points of obstruction on same bowel segment) is a surgical emergency with very high strangulation risk. [11]

CT Signs:

• C, U, or coffee-bean shaped dilated loop
• Radial/converging mesenteric vessels ("whirl sign" if volvulus)
• Two transition points visible
• Serrated beak sign
• Mesenteric haziness

Management: Urgent laparotomy (do not attempt conservative management)

3. Gastrografin (Water-Soluble Contrast) Challenge

Indications: [7,8]

• Adhesive SBO (no hernia, malignancy, or signs of strangulation)
• Partial obstruction (some passage of flatus/bowel motion, or non-complete on CT)
• After initial resuscitation (not acutely unwell)

Protocol:

• Administer 100 mL Gastrografin (diatrizoate meglumine) orally or via nasogastric tube
• Abdominal X-ray at 4-8 hours and 24 hours
• Assess for contrast appearance in colon (right colon or beyond)

Interpretation:

Therapeutic Effect:

Gastrografin has high osmolality (1900 mOsm/kg) → Draws fluid into bowel lumen → Increases intraluminal hydrostatic pressure → May promote resolution of partial obstruction. [7,8]

Meta-Analysis Evidence: [8]

• Reduces time to resolution (mean 1.7 days shorter)
• Reduces need for surgery (RR 0.62, 95% CI 0.45-0.84)
• Reduces hospital stay (mean 2.0 days shorter)
• Safe (no increase in adverse events)

Contraindications:

• Suspected perforation (water-soluble contrast is safe even if perforation, but surgical management takes priority)
• Complete obstruction (may not be effective; still safe to trial)
• Suspicion of ischaemia/strangulation (requires immediate surgery—do not delay for Gastrografin)

4. Ultrasound

Role: Limited in SBO diagnosis (operator-dependent, obscured by bowel gas). May detect:

• Free fluid
• Dilated bowel loops (> 2.5 cm, aperistaltic)
• Transition point (in experienced hands)
• Hernias (groin ultrasound)

Advantages: Bedside, no radiation, safe in pregnancy

Limitations: Cannot replace CT for comprehensive assessment

5. MRI

Indications:

• Pregnancy (avoids ionising radiation)
• Recurrent SBO where detailed anatomy needed
• Young patients requiring multiple imaging

Not routinely used (availability, cost, time)

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7. Management

Management of SBO follows a stepwise algorithm based on clinical presentation, aetiology, and response to initial resuscitation. [1,2,3]

Management Algorithm

┌─────────────────────────────────────────────────────┐
│         SUSPECTED SMALL BOWEL OBSTRUCTION            │
│   (Colicky Pain, Vomiting, Distension, Constipation) │
└──────────────────────┬──────────────────────────────┘
                       ↓
┌─────────────────────────────────────────────────────┐
│     IMMEDIATE RESUSCITATION ("DRIP AND SUCK")       │
│ • IV Access (2× Large Bore Cannulae)                 │
│ • IV Fluids: Crystalloid (Hartmann's/Normal Saline)  │
│   - Initial bolus 500-1000 mL stat                   │
│   - Maintenance + replacement of losses              │
│ • Nasogastric Tube (Large Bore, e.g., 16Fr)          │
│   - Free drainage (decompress stomach)               │
│ • Urinary Catheter (monitor fluid balance)           │
│ • NBM (Nil By Mouth)                                 │
│ • Analgesia (IV Opiates, e.g., Morphine)             │
│ • Correct Electrolytes (K⁺ replacement if low)       │
│ • Bloods: FBC, U&E, Lactate, Group & Save            │
└──────────────────────┬──────────────────────────────┘
                       ↓
┌─────────────────────────────────────────────────────┐
│                  IMAGING                             │
│ • AXR (Supine + Erect Abdomen, Erect CXR)            │
│ • CT Abdomen/Pelvis + IV Contrast (GOLD STANDARD)    │
└──────────────────────┬──────────────────────────────┘
                       ↓
         ┌─────────────┴─────────────┐
         ↓                           ↓
┌────────────────────┐   ┌───────────────────────────┐
│ EMERGENCY SURGERY  │   │   ASSESS SUITABILITY FOR  │
│    INDICATIONS     │   │  CONSERVATIVE MANAGEMENT  │
└────────────────────┘   └───────────────────────────┘
         ↓                           ↓
┌──────────────────────────────────────────────────┐
│ ANY of the following → URGENT LAPAROTOMY:        │
│ ✓ PERITONISM (Guarding, Rigidity, Rebound)       │
│ ✓ HAEMODYNAMIC INSTABILITY (Shock, Hypotension)  │
│ ✓ LACTATE ≥4 mmol/L                              │
│ ✓ CT: Closed-Loop Obstruction                    │
│ ✓ CT: Signs of Ischaemia (Pneumatosis, PVG, etc) │
│ ✓ Incarcerated/Irreducible Hernia                │
│ ✓ Free Intraperitoneal Air (Perforation)         │
└──────────┬───────────────────────────────────────┘
           ↓
      EMERGENCY LAPAROTOMY / LAPAROSCOPY
           ↓
      • Adhesiolysis
      • Resect Necrotic Bowel (if ischaemia)
      • Primary Anastomosis or Stoma
      • Hernia Repair (if hernia)

                       ↓
         ┌─────────────┴─────────────┐
         ↓                           ↓
┌──────────────────┐      ┌──────────────────────┐
│ CONSERVATIVE     │      │ NOT SUITABLE:        │
│ MANAGEMENT       │      │ • Hernia present     │
│ SUITABLE IF:     │      │ • Malignancy         │
│ • Adhesive SBO   │      │ • Complete obst.     │
│ • Partial SBO    │      │ • Virgin abdomen     │
│ • No peritonism  │      │   (unclear cause)    │
│ • Haemodynamic   │      └──────────────────────┘
│   stability      │                 ↓
│ • Lactate normal │           SURGICAL MANAGEMENT
└────────┬─────────┘                 
         ↓                           
┌─────────────────────────────────────────┐
│   GASTROGRAFIN CHALLENGE (if suitable)  │
│ • 100 mL Gastrografin via NG/oral       │
│ • AXR at 4-8h and 24h                   │
└────────┬────────────────────────────────┘
         ↓
    ┌────────────────┐
    │ Contrast Reach │
    │ Colon by 24h?  │
    └───┬────────┬───┘
        │        │
       YES      NO
        ↓        ↓
    ┌──────┐  ┌──────────────────┐
    │Continue│  │ Surgical Consult │
    │Conservative│  │ (Likely need   │
    │Resolve  │  │  surgery)      │
    │diet     │  └────────┬───────┘
    └──────┘           ↓
                 LAPAROTOMY/LAPAROSCOPY

┌─────────────────────────────────────────┐
│ FAILURE OF CONSERVATIVE MANAGEMENT:     │
│ • No improvement after 48-72 hours      │
│ • Worsening symptoms/signs              │
│ • Rising lactate                        │
│ • Recurrent vomiting despite NG         │
│ → PROCEED TO SURGERY                    │
└─────────────────────────────────────────┘

Initial Resuscitation: "Drip and Suck"

All patients with SBO require initial resuscitation, regardless of whether definitive management will be conservative or surgical. [3]

"Drip" – Intravenous Fluid Resuscitation

Rationale: Patients lose litres of fluid from:

• Vomiting (can be > 3-5 L/day in proximal SBO)
• Nasogastric drainage
• Third-space losses (sequestration into dilated bowel lumen and peritoneal cavity)

Fluid Choices:

• Hartmann's Solution (Lactated Ringer's) or Normal Saline (0.9% NaCl)
  • Hartmann's preferred by some (more physiological electrolyte composition)
  • Normal Saline preferred if hypochloraemic alkalosis (replaces Cl⁻)
• Avoid dextrose solutions initially (insufficient sodium)

Regimen:

1. Bolus: 500-1000 mL crystalloid IV stat (over 15-30 min)
2. Reassess: Clinical response (BP, HR, UOP)
3. Maintenance: Typically 125-150 mL/hr (3-4 L/24h), adjusted based on:
   • Ongoing losses (NG aspirate volume, urine output)
   • Clinical status (mucous membranes, BP, HR)
   • U&E results

Monitoring:

• Hourly urine output (target > 0.5 mL/kg/hr, i.e., > 30-40 mL/hr)
• 4-hourly observations (BP, HR, RR, temp)
• Strict fluid balance chart
• Daily weights
• Repeat U&E at 24h (earlier if severe abnormalities)

Electrolyte Replacement:

"Suck" – Nasogastric Decompression

Nasogastric Tube Insertion:

• Large bore (14-16 French gauge)
• Free drainage (attach to drainage bag, not on continuous suction unless specific indication)
• Aspirate 4-hourly and document volume
• Keep NPO (nil by mouth)

Benefits:

• Reduces vomiting (decompresses stomach)
• Prevents aspiration (risk of aspiration pneumonia)
• Relieves symptoms (reduces nausea, discomfort from distension)
• Allows monitoring of gastric losses (guides fluid replacement)

Evidence: Routine NG decompression is standard practice, though some studies suggest selected patients (partial SBO, minimal vomiting) may not require NG tube. [1]

Additional Supportive Measures

• NBM (Nil By Mouth): Absolute. No oral intake until obstruction resolves.
• Analgesia: IV opiates (Morphine 2.5-10 mg IV PRN, or patient-controlled analgesia). Do NOT withhold analgesia (outdated teaching that pain assessment requires unmasked examination—adequate analgesia is essential and humane).
• Antiemetics: Cyclizine 50 mg IV TDS, Ondansetron 4-8 mg IV TDS
• VTE Prophylaxis: LMWH (e.g., Enoxaparin 40 mg SC daily) unless contraindicated. Compression stockings.
• Antibiotics: NOT routinely required in simple SBO. Give if:
  • Strangulation/perforation suspected → Broad-spectrum (e.g., Cefuroxime + Metronidazole, or Piperacillin-Tazobactam)
  • Peri-operative prophylaxis (if surgery planned)

Conservative Management

Indications for Conservative Trial: [1,12]

• Adhesive SBO (history of previous surgery, no hernia on examination/CT)
• Partial obstruction (some passage of flatus, contrast in colon on imaging)
• No signs of strangulation (no peritonism, lactate normal, no CT signs of ischaemia)
• Haemodynamically stable
• First episode, or previous successful conservative management

Success Rate: 70-80% of adhesive SBO resolve without surgery. [1,12]

Duration of Conservative Trial:

• 48-72 hours is standard threshold
• If no improvement by 72h → Surgery
• Some guidelines suggest up to 5 days acceptable if clinical improvement ongoing (but requires close monitoring)

Monitoring During Conservative Management:

• Daily clinical review by surgical team
• Abdominal examination (assess for peritonism, worsening distension)
• Observations (BP, HR—tachycardia suggests inadequate fluid resuscitation or developing complications)
• Daily bloods: U&E, FBC, lactate (rising lactate = ischaemia)
• NG aspirate volume (large volumes suggest ongoing obstruction)
• Passage of flatus (positive prognostic sign)

Gastrografin Challenge: Discussed above (Investigations section). Recommended in adhesive partial SBO after initial resuscitation. [7,8]

Criteria for Resolution:

• Passage of flatus and/or bowel motion
• Reduced NG aspirates (less than 200 mL/24h)
• Resolution of pain/distension
• Tolerance of oral fluids
• Gastrografin in colon (if given)

Return to Diet:

• Once obstruction resolves: Trial of clear fluids
• If tolerated (no vomiting, no recurrence of pain): Progress to free fluids → light diet → normal diet over 24-48h
• Remove NG tube once tolerating fluids and minimal aspirates

Surgical Management

Indications for Emergency Surgery (Immediate Laparotomy)

Exam Detail: These indications are frequently examined. Any patient meeting these criteria requires immediate surgical consultation and preparation for theatre—do not delay with further conservative management.

Indications for Early/Delayed Surgery

Surgical Techniques

Approach: Laparoscopy vs. Laparotomy

Evidence: Meta-analyses suggest laparoscopic adhesiolysis is feasible in selected SBO cases with comparable outcomes, but conversion rate to open is 20-50%. [13] Most emergency SBO still managed by laparotomy.

Surgical Steps:

1. Laparotomy Incision: Midline (allows full access and re-entry through previous scars if present)
2. Run the Bowel: Systematically examine entire small bowel from duodenojejunal flexure (ligament of Treitz) to ileocaecal valve to identify:
   • Obstruction point
   • Cause (adhesive band, hernia, tumour, etc.)
   • Viability of bowel (colour, peristalsis, arterial pulsation)
3. Adhesiolysis: Divide adhesive bands using sharp dissection (scissors/scalpel). Meticulous technique to avoid enterotomy (perforation of bowel during dissection).
4. Assess Bowel Viability:
   • Viable: Pink, peristalsis present, mesenteric pulsation present
   • Ischaemic but Potentially Viable: Dark, dusky, no peristalsis initially. Wrap in warm packs, wait 10-15 min, reassess after blood flow restored.
   • Non-Viable: Black, no pulsation, thinned/friable wall → Resection required
5. Resection (if necrotic bowel):
   • Resect ischaemic segment with margin (≥10 cm proximal and distal to ensure healthy bowel ends)
   • Anastomosis (join bowel ends): If patient stable, minimal contamination, healthy bowel ends
   • Stoma (end ileostomy or double-barrel ileostomy): If patient unstable, peritoneal contamination, unhealthy bowel, damage control surgery
6. Address Cause:
   • Adhesive SBO: Adhesiolysis alone
   • Hernia: Reduce hernia, repair defect (mesh if incisional hernia, primary repair if inguinal)
   • Malignancy: Resection if feasible, or bypass if unresectable
   • Gallstone ileus: Enterotomy, extract stone, close enterotomy. (Cholecystectomy/fistula repair can be staged later)
7. Washout: If contamination from perforation/ischaemia, copious saline lavage of peritoneal cavity
8. Closure: Mass closure of midline incision (continuous loop PDS or equivalent)

Special Considerations:

Post-Operative Management

• NBM initially: Gradual introduction of diet once bowel function returns (passage of flatus, bowel sounds present)
• NG tube: Can usually be removed in first 24-48h post-op (once aspirates minimal)
• Early mobilisation: Reduces ileus, VTE risk
• Analgesia: Multimodal (paracetamol, NSAIDs, opiates, local anaesthetic wound infiltration). Consider epidural for major resections.
• Fluid balance: Continue IV fluids until tolerating oral intake
• Antibiotics: 24-48h post-op if contamination/ischaemia. Not prolonged courses unless ongoing sepsis.
• Monitor for complications: Anastomotic leak (fever, tachycardia, abdominal pain day 5-7), wound infection, ileus

Hospital Stay:

• Simple adhesiolysis: 3-7 days
• Bowel resection + anastomosis: 7-14 days
• Complicated cases (perforation, ICU stay): > 14 days

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8. Complications

Complications of SBO Itself

Complications of Treatment

Conservative Management Complications

Surgical Complications

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9. Prognosis and Outcomes

Overall Outcomes

Prognostic Factors

Factors Predicting Need for Surgery

Exam Detail: Understanding which features predict surgical requirement is important for risk stratification and counselling patients. Several studies have developed prediction models.

High-Risk Features (increased likelihood of surgery):

Low-Risk Features (likely conservative success):

• Partial obstruction
• Contrast passes obstruction on Gastrografin challenge
• Previous similar episodes managed conservatively
• Early presentation (less than 24h symptoms)

Factors Predicting Mortality

Quality of Life

• Short-term: Post-operative recovery 4-8 weeks for return to normal activities
• Long-term: Recurrent SBO episodes significantly impact quality of life (repeated hospitalisations, dietary restrictions, fear of recurrence)
• Short Bowel Syndrome: Devastating impact on QoL if extensive resection (TPN dependence, chronic diarrhoea, malnutrition)

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10. Prevention

Primary Prevention (Preventing Adhesions)

Adhesions are the leading cause of SBO, but prevention is challenging.

Surgical Techniques to Reduce Adhesions

Patient-Level Prevention

• Avoid Unnecessary Surgery: Conservative management of conditions where appropriate (e.g., appendicitis—antibiotics in selected cases)

Secondary Prevention (Preventing Recurrence)

Tertiary Prevention (Preventing Complications)

• Early Presentation: Patients with history of SBO should seek medical attention early if symptoms recur (early conservative management more successful)
• Avoid Delay to Surgery: When surgical indications present, operate promptly (mortality increases with delay in strangulation)
• Gastrografin Challenge: Identifies patients likely to need surgery early (allows planning rather than emergency surgery after prolonged conservative failure)

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11. Evidence and Guidelines

Key Guidelines

Exam Detail: The Bologna Guidelines (World Society of Emergency Surgery, WSES) are the most widely cited international consensus guidelines for adhesive SBO management. [1] These are very high-yield for examinations (MRCS, FRCS).

Landmark Trials and Meta-Analyses

Evidence Summary

Exam Detail: When asked about evidence in viva examinations, structure your answer by intervention: Diagnosis, Conservative Management, Surgical Management.

Diagnosis

• CT is gold standard (Level I evidence from multiple systematic reviews) [5,6]
• Gastrografin has diagnostic utility (NPV 98% if in colon by 24h) [7,8]

Conservative Management

• 70-80% adhesive SBO resolve non-operatively (Level II evidence from cohort studies) [1,12]
• Gastrografin accelerates resolution and reduces surgery rate (Level I evidence from Cochrane review) [8]
• Conservative trial duration 48-72h is safe (consensus, Bologna Guidelines) [1]

Surgical Management

• Laparoscopy feasible in selected SBO (Level II evidence from cohort studies and meta-analyses) [13] but conversion rate high (20-50%)
• Delayed surgery in strangulation increases mortality (Level II-III evidence from cohort studies) [10]
• Adhesion barriers (Seprafilm) have modest effect (Level I evidence from RCTs/meta-analyses) [15], but cost-effectiveness uncertain

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12. Patient and Layperson Explanation

What is Small Bowel Obstruction?

Your small intestine (small bowel) is a long tube (about 6 metres / 20 feet) that connects your stomach to your large intestine (colon). It absorbs nutrients from the food you eat. A small bowel obstruction means this tube is blocked, so food, liquid, and gas cannot pass through normally.

Think of it like a kinked garden hose—water can't flow through when there's a blockage.

What Causes It?

The most common cause is scar tissue (adhesions) from previous surgery on your abdomen. When surgeons operate, internal scar tissue can form afterwards (like scar tissue on your skin, but inside your belly). This scar tissue can stick loops of bowel together or create bands that squeeze the bowel shut—sometimes years or even decades after the original surgery.

Other causes include hernias (when part of the bowel bulges through a weak spot in your abdominal wall and gets trapped).

What Are the Symptoms?

The classic signs are:

• Crampy abdominal pain that comes and goes in waves (called "colicky" pain)
• Vomiting (often green or yellow bile)
• Swollen belly (abdominal distension)
• Constipation (not being able to pass wind or have a bowel movement)

How is it Diagnosed?

Your doctor will examine your abdomen and order:

• Blood tests (to check hydration, kidney function, and look for signs of infection)
• X-rays or CT scan of your abdomen (to see the blocked bowel and find out where and why it's blocked)

How is it Treated?

Initial Treatment: "Drip and Suck"

Almost everyone starts with non-surgical treatment:

• "Drip": A drip (IV line) in your arm gives you fluids to keep you hydrated (because you're vomiting and can't drink).
• "Suck": A thin tube is passed through your nose into your stomach (nasogastric tube or NG tube) to drain fluid and gas, which helps relieve the blockage and stops you vomiting.
• You can't eat or drink anything by mouth while the blockage is present.

Will I Need Surgery?

Not always. About 70-80% of blockages caused by scar tissue resolve with the "drip and suck" treatment after a few days.

You WILL need surgery if:

• The blockage doesn't clear after 2-3 days
• The bowel's blood supply is cut off (called "strangulation")—this is an emergency
• The blockage is caused by a trapped hernia
• You develop signs of a serious complication (like a hole in the bowel)

What Happens During Surgery?

Surgery involves:

• Opening your abdomen to find and relieve the blockage
• Cutting the scar tissue (adhesions) that's causing the blockage
• Removing any bowel that's damaged (if the blood supply was cut off)
• Sometimes the surgeon can use keyhole (laparoscopic) surgery, but often a bigger cut is needed to see everything clearly

What is the Outlook?

• Good if treated promptly. Most people recover well.
• Higher risk if the bowel's blood supply is cut off and surgery is delayed—this can be serious.
• Recurrence: There's a 20-30% chance the blockage can happen again in the future (because surgery creates more scar tissue). If symptoms return, come back to hospital early.

What Should I Watch Out For After Going Home?

Seek medical attention urgently if you develop:

• Severe abdominal pain
• Vomiting
• Inability to pass wind or open your bowels
• Fever
• Swollen abdomen

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13. Examination Focus

High-Yield Exam Topics

Exam Detail: SBO is a core topic in general surgery examinations (MRCS, FRCS, FRACS) and emergency medicine (FRCEM). Key areas to master:

1. Causes (adhesions 60-70%, hernias 15-20%, etc.)
2. Differentiation from ileus and LBO
3. Strangulation signs (clinical + radiological)
4. CT interpretation (transition point, closed-loop, ischaemia signs)
5. Bologna Guidelines (conservative vs. surgical indications)
6. Gastrografin (diagnostic + therapeutic role)
7. Surgical decision-making (when to operate, when to continue conservative)

Common Viva Questions

Question 1: Most Common Cause

Q: "What is the most common cause of small bowel obstruction in adults?"

Model Answer: The most common cause is adhesions from previous abdominal or pelvic surgery, accounting for approximately 60-70% of cases. Hernias (inguinal, femoral, incisional, umbilical) are the second most common cause at 15-20%, followed by malignancy (5-10%), Crohn's disease (5%), and rarer causes such as gallstone ileus, volvulus, and intussusception.

In patients with no previous surgery (virgin abdomen), hernias become the most common cause, and a thorough examination of all hernial orifices is essential. Malignancy and inflammatory conditions should also be considered in this group.

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Question 2: AXR Findings

Q: "Describe the abdominal X-ray findings in small bowel obstruction."

Model Answer: On plain abdominal radiography (supine and erect films), SBO demonstrates:

1. Dilated small bowel loops: Diameter > 3 cm (normal less than 2.5 cm). Jejunum typically shows diameter > 3 cm, ileum > 2.5 cm.
2. Valvulae conniventes: Mucosal folds that extend across the entire width of the bowel lumen, creating a "stacked coins" or "coiled spring" appearance. This distinguishes small bowel from large bowel (which has haustra that only partially cross the lumen).
3. Air-fluid levels: Multiple horizontal fluid levels visible on the erect film, creating a "step-ladder" pattern.
4. Paucity of colonic gas: Little or no gas in the large bowel or rectum (in complete obstruction), indicating that the obstruction is proximal to the colon.
5. Central location: Dilated loops occupy the central abdomen (vs. peripheral location of large bowel).

Additional findings may include the String of Pearls sign (small gas bubbles trapped between valvulae conniventes).

In gallstone ileus, Rigler's Triad may be present: pneumobilia, small bowel obstruction, and ectopic gallstone (usually at the ileocaecal valve).

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Question 3: Signs of Strangulation

Q: "What clinical and radiological features suggest strangulation in small bowel obstruction?"

Model Answer:

Strangulation is compromise of the blood supply to obstructed bowel and constitutes a surgical emergency requiring urgent laparotomy.

Clinical Features:

• Constant severe pain (vs. intermittent colicky pain in simple obstruction)
• Peritonism: Guarding, rigidity, rebound tenderness on examination
• Haemodynamic instability: Tachycardia (HR > 100-120), hypotension (SBP less than 90 mmHg)
• Fever (not typical of simple obstruction)
• Shock: Cold peripheries, prolonged capillary refill time

Laboratory Features:

• Lactate ≥4 mmol/L: Highly suggestive of bowel ischaemia
• Leucocytosis: WCC > 15-20 × 10⁹/L
• Metabolic acidosis: Base excess negative, low pH

Radiological Features (CT):

• Closed-loop obstruction: C-shaped or U-shaped dilated loop with two transition points
• Reduced or absent bowel wall enhancement (impaired arterial perfusion)
• Bowel wall thickening (> 3 mm, due to oedema/congestion)
• Mesenteric haziness/stranding (oedema, haemorrhage)
• Pneumatosis intestinalis: Gas within the bowel wall (very specific for transmural ischaemia)
• Portal venous gas: Gas in portal vein branches (very specific, late sign, high mortality)
• Mesenteric oedema/haemorrhage
• Ascites (free fluid)

Management: Immediate laparotomy. Delays in surgery for strangulated bowel dramatically increase mortality (8% if operated less than 24h vs. 25-35% if delayed > 36h).

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Question 4: Gastrografin Challenge

Q: "What is the role of Gastrografin in adhesive small bowel obstruction?"

Model Answer:

Gastrografin (water-soluble contrast medium, diatrizoate meglumine) serves both diagnostic and therapeutic roles in adhesive SBO.

Diagnostic Role:

• 100 mL Gastrografin is administered orally or via nasogastric tube after initial resuscitation.
• Abdominal X-rays are performed at 4-8 hours and 24 hours.
• If contrast appears in the colon within 4-8 hours: Predicts non-operative resolution with 96-100% sensitivity.
• If no contrast in colon by 24 hours: Predicts need for surgery (negative predictive value 98%).

This allows early identification of patients who will require surgery, enabling planned rather than emergency laparotomy.

Therapeutic Role: Gastrografin has high osmolality (1900 mOsm/kg), which draws fluid into the bowel lumen by osmosis. This increases intraluminal hydrostatic pressure and may accelerate resolution of partial obstruction.

Evidence: A Cochrane systematic review (Abbas et al. 2007, 10 RCTs, n=1,073) demonstrated:

• Reduces time to resolution (mean 1.7 days shorter)
• Reduces need for surgery (RR 0.62, 95% CI 0.45-0.84)
• Reduces hospital length of stay (mean 2.0 days shorter)
• Safe (no increase in adverse events)

Indications:

• Adhesive SBO (no hernia, malignancy, or strangulation signs)
• Partial obstruction
• Haemodynamically stable
• After initial resuscitation (not in acute emergency)

Contraindications:

• Suspected perforation (Gastrografin itself is safe even if perforation, but surgical management takes priority)
• Signs of strangulation (requires immediate surgery without delay)

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Question 5: Indications for Surgery

Q: "When would you operate on a patient with small bowel obstruction?"

Model Answer:

Indications for surgery can be categorized into emergency (immediate laparotomy) and early/delayed surgery.

Emergency Laparotomy (Immediate):

1. Peritonitis: Guarding, rigidity, rebound tenderness (suggests perforation or strangulation)
2. Haemodynamic instability: Shock (SBP less than 90 mmHg, HR > 120) despite adequate fluid resuscitation
3. Elevated lactate: ≥4 mmol/L (indicates ischaemia)
4. Closed-loop obstruction on CT (high risk of rapid strangulation)
5. CT signs of ischaemia: Pneumatosis intestinalis, portal venous gas, reduced bowel wall enhancement
6. Incarcerated/strangulated hernia: Tender, irreducible hernia
7. Perforation: Free air on imaging

Early/Urgent Surgery (Within 24-48h):

1. Failure of conservative management: No improvement after 48-72 hours of "drip and suck"
2. Complete obstruction: No passage of flatus, no colonic gas, especially if cause unclear
3. Recurrent vomiting despite adequate nasogastric decompression

Elective/Delayed Surgery:

1. Malignancy: Once diagnosed, plan definitive resection (after optimisation)
2. Hernia (non-strangulated): If obstruction doesn't resolve, or elective repair after episode settles
3. Recurrent adhesive SBO: Multiple admissions—consider laparoscopic adhesiolysis

Conservative Management Appropriate:

• Adhesive SBO (history of previous surgery, no hernia)
• Partial obstruction (some passage of flatus)
• No signs of strangulation (no peritonism, lactate normal, no CT ischaemia signs)
• Haemodynamically stable
• First episode or previous successful conservative management

The decision is guided by the Bologna Guidelines (WSES 2018), which recommend conservative trial for adhesive SBO unless emergency indications present.

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Question 6: Closed-Loop Obstruction

Q: "What is closed-loop obstruction and why is it important?"

Model Answer:

Definition: Closed-loop obstruction occurs when a segment of bowel is occluded at two points along its length, creating an isolated loop that cannot decompress either proximally (via vomiting/NG drainage) or distally.

Mechanism:

• Common causes: Adhesive band trapping a loop, internal hernia with narrow orifice, volvulus
• The isolated loop progressively distends with gas and fluid
• Intraluminal pressure rises rapidly
• Venous compression occurs first → Congestion, oedema, haemorrhagic infarction
• Arterial compromise follows → Ischaemia → Necrosis (can occur within 6-12 hours)

Clinical Importance: Closed-loop obstruction is a surgical emergency with very high risk of strangulation. Unlike simple (single-point) obstruction, it does not respond to conservative management and progresses rapidly to ischaemia.

Mortality: High if surgery delayed (25-35%).

CT Diagnosis:

• C-shaped, U-shaped, or coffee-bean shaped dilated bowel loop
• Two transition points (proximal and distal to the closed loop)
• Radial/converging mesenteric vessels ("whirl sign" if volvulus)
• Serrated beak sign at the obstruction points
• Mesenteric haziness/oedema
• Signs of ischaemia (reduced wall enhancement, pneumatosis)

Management:

• Immediate laparotomy (within 4-6 hours of diagnosis)
• Do not attempt conservative management
• Intraoperatively: Adhesiolysis or reduction of hernia, assess bowel viability, resect if necrotic

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Question 7: Differentiate SBO from Ileus

Q: "How do you differentiate mechanical small bowel obstruction from paralytic ileus?"

Model Answer:

Key Discriminators:

• Transition point on imaging (present in SBO, absent in ileus)
• Bowel sounds (high-pitched/tinkling in SBO, absent in ileus)
• Pain character (colicky in SBO, constant/minimal in ileus)

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Clinical Scenarios for Practice

Scenario 1: Adhesive SBO

Case: 65-year-old woman presents with 24 hours of colicky central abdominal pain, vomiting, and abdominal distension. She had an open hysterectomy 15 years ago. On examination: distended abdomen, high-pitched bowel sounds, mild generalised tenderness, no peritonism. No hernias palpable. Bloods: WCC 11, K⁺ 3.2, Urea 8.5, Creatinine 95, Lactate 1.8. AXR shows dilated small bowel loops (4 cm) with air-fluid levels, minimal colonic gas.

Questions:

1. What is the most likely diagnosis?
2. What is the initial management?
3. What investigation would you request?
4. If CT confirms adhesive SBO with no signs of ischaemia, what is your management plan?
5. When would you operate?

Model Answers:

1. Adhesive small bowel obstruction (history of previous surgery, typical clinical features, AXR findings consistent with SBO)
2. "Drip and Suck": IV access, crystalloid resuscitation (correct hypokalaemia), large-bore NG tube (free drainage), urinary catheter, NBM, analgesia
3. CT abdomen/pelvis with IV contrast (gold standard to confirm diagnosis, identify cause, exclude complications such as ischaemia or closed-loop)
4. Conservative management trial: Continue NG decompression, IV fluids, electrolyte replacement, monitor clinically (daily examination, bloods including lactate). Consider Gastrografin challenge (100 mL via NG, AXR at 4-8h and 24h). If contrast reaches colon → Continue conservative. If not → Plan surgery.
5. Operate if:
   • Signs of strangulation develop (peritonism, rising lactate, haemodynamic instability)
   • No improvement after 48-72 hours of conservative management
   • Worsening symptoms/signs
   • Gastrografin doesn't reach colon by 24h (suggests need for surgery)

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Scenario 2: Strangulated Obstruction

Case: 72-year-old man presents with 12 hours of severe constant abdominal pain. He vomited multiple times. History of appendicectomy 40 years ago. On examination: distressed, HR 115, BP 100/60, abdomen distended with guarding and rebound tenderness in the right lower quadrant. Bloods: WCC 18, Lactate 5.2 mmol/L.

Questions:

1. What is your clinical concern?
2. What investigation do you request urgently?
3. CT shows dilated small bowel with a C-shaped loop in RLQ, mesenteric haziness, and reduced bowel wall enhancement. What is the diagnosis?
4. What is your management?

Model Answers:

1. Strangulated small bowel obstruction. The constant pain (not colicky), peritonism, haemodynamic instability (tachycardia, borderline BP), and elevated lactate all suggest bowel ischaemia.
2. CT abdomen/pelvis with IV contrast urgently (to confirm diagnosis and assess extent of ischaemia). Simultaneously: Resuscitate (IV fluids, NG tube, catheter, bloods including Group & Save), inform surgical team for emergency laparotomy, inform anaesthetist, consent patient.
3. Closed-loop small bowel obstruction with ischaemia. The C-shaped loop indicates closed-loop configuration (two obstruction points), and reduced wall enhancement/mesenteric haziness indicate ischaemia.
4. Emergency laparotomy (immediate, within 1-2 hours):
   • Continue resuscitation (IV fluids, correct electrolytes, broad-spectrum antibiotics for contamination/sepsis—e.g., Piperacillin-Tazobactam)
   • Theatre: Midline laparotomy, identify closed loop, adhesiolysis, assess bowel viability
   • If necrotic: Resect ischaemic segment (10 cm margin proximal and distal). Anastomosis if stable, or stoma (ileostomy) if unstable/contamination.
   • If viable: Adhesiolysis only, close
   • Post-op: HDU/ICU monitoring, IV fluids, antibiotics, nutrition support

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Viva Examination Tips

1. Structure your answers: History → Examination → Investigations → Management
2. State the most common causes: Adhesions (60-70%), hernias (15-20%)—this is almost always the first question
3. Know the Bologna Guidelines: Conservative vs. surgical indications (high-yield)
4. Differentiate simple vs. strangulated: This is critical for management decisions
5. Describe imaging systematically: AXR findings (dilated SB, valvulae conniventes, air-fluid levels), CT findings (transition point, cause, ischaemia signs)
6. Gastrografin: Understand both diagnostic and therapeutic roles (commonly asked)
7. Safety-netting: Always mention close monitoring, repeat examination, and low threshold for surgery if deterioration

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14. References

Primary Sources

1. Ten Broek RPG, Issa Y, van Santbrink EJP, 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 ASBO working group. World J Emerg Surg. 2018;13:24. PMID: 29946347. DOI: 10.1186/s13017-018-0185-2

2. Ghimire P, Dhamoon AS. Small Bowel Obstruction. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023. PMID: 37208871.

3. Long B, Robertson J, Koyfman A. Emergency Medicine Evaluation and Management of Small Bowel Obstruction: Evidence-Based Recommendations. J Emerg Med. 2019;56(2):166-176. PMID: 30527563. DOI: 10.1016/j.jemermed.2018.10.024

4. Tong JWV, Lingam P, Shelat VG. Adhesive small bowel obstruction - an update. Acute Med Surg. 2020;7(1):e587. PMID: 33173587. DOI: 10.1002/ams2.587

5. Li Z, Zhou H, Liu C, et al. Diagnostic utility of CT for small bowel obstruction: Systematic review and meta-analysis. Eur J Radiol. 2019;121:108720. PMID: 31887146. DOI: 10.1016/j.ejrad.2019.108720

6. Kim J, Ha HK, Oh HK, et al. Non-strangulated adhesive small bowel obstruction: CT findings predicting outcome of conservative treatment. Eur Radiol. 2021;31(4):2333-2342. PMID: 33128599. DOI: 10.1007/s00330-020-07368-9

7. D'Agostino R, Caggiati L, Nigri G, et al. Small bowel obstruction and the gastrografin challenge: A review of the literature. Clin Ter. 2018;169(2):e90-e96. PMID: 29632988. DOI: 10.7417/T.2018.2060

8. Abbas S, Bissett IP, Parry BR. Oral water soluble contrast for the management of adhesive small bowel obstruction. Cochrane Database Syst Rev. 2007;(3):CD004651. PMID: 17636770. DOI: 10.1002/14651858.CD004651.pub3

9. Gómez Corral J, Martín Antona E, Sanchez Sanchez M, et al. Bowel obstruction: signs indicating the need for urgent surgery. Cir Pediatr. 2023;36(2):61-66. PMID: 37024235.

10. Sarr MG, Bulkley GB, Zuidema GD. Preoperative recognition of intestinal strangulation obstruction. Prospective evaluation of diagnostic capability. Am J Surg. 1983;145(1):176-182. PMID: 6849494. DOI: 10.1016/0002-9610(83)90186-1

11. Rondenet C, Millet I, Corno L, et al. CT diagnosis of closed loop bowel obstruction mechanism is not sufficient to indicate emergent surgery. Eur Radiol. 2020;30(3):1105-1114. PMID: 31529259. DOI: 10.1007/s00330-019-06465-2

12. Bertona S, Grivon M, Fragueiro M, et al. Predictors of medical treatment failure in patients with adhesive small bowel obstruction. Int J Colorectal Dis. 2025;40(1):15. PMID: 40650719. DOI: 10.1007/s00384-024-04775-1

13. Sajid MS, Khawaja AH, Sains P, et al. A systematic review comparing laparoscopic vs open adhesiolysis in patients with adhesional small bowel obstruction. Am J Surg. 2016;212(1):138-150. PMID: 26542823. DOI: 10.1016/j.amjsurg.2015.06.029

14. Brolmann HA, Tanos V, Grimbizis G, et al. Options on fibrin glue and adhesion prevention in reproductive surgery: proceedings of an expert meeting. Fertil Steril. 2009;92(5):1594-1602. PMID: 19800609. DOI: 10.1016/j.fertnstert.2009.07.980

15. Ten Broek RPG, Stommel MWJ, Strik C, et al. Benefits and harms of adhesion barriers for abdominal surgery: a systematic review and meta-analysis. Lancet. 2014;383(9911):48-59. PMID: 24075279. DOI: 10.1016/S0140-6736(13)61687-6

16. Uprak TK, Özakay A, Karabulut M, et al. Factors Predicting Surgical Treatment in Patients with Adhesive Small Bowel Obstruction. Ulus Travma Acil Cerrahi Derg. 2022;28(10):1418-1424. PMID: 36089707. DOI: 10.14744/tjtes.2021.82580

17. Kohga A, Suzuki K, Okumura T, et al. Laparoscopic vs open surgery for patients with strangulated small bowel obstruction. Medicine (Baltimore). 2020;99(1):e18353. PMID: 31801178. DOI: 10.1097/MD.0000000000018353

18. Xu WX, Chen W, Wang YD, et al. Prediction and management of strangulated bowel obstruction: a multi-dimensional analysis. World J Gastrointest Surg. 2022;14(6):548-559. PMID: 35733109. DOI: 10.4240/wjgs.v14.i6.548

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Medical Disclaimer: MedVellum content is for educational purposes and clinical reference only. All clinical decisions must account for individual patient circumstances, local protocols, and evolving evidence. Always consult appropriate specialists and follow institutional guidelines. This content is designed to support—not replace—clinical judgment and postgraduate medical training.