Bowel Obstruction

Quick Answer

Bowel obstruction is mechanical blockage of the small bowel (SBO) or large bowel (LBO) preventing normal passage of intestinal contents. SBO accounts for 60-70% of all mechanical obstructions and is most commonly caused by adhesions (60%), hernias (15%), and malignancy (10-15%). LBO is most commonly caused by colorectal cancer (50-60%), diverticular disease (10-20%), and volvulus (10-15%). Clinical presentation includes abdominal pain, distension, vomiting, and absolute constipation (in complete obstruction). CT has 90-96% sensitivity for diagnosis, identifying dilated bowel loops (greater than 3 cm small bowel, greater than 6 cm colon), transition point, and complications (ischemia, perforation, closed-loop). Management includes NBM (nil by mouth), nasogastric tube decompression, IV fluid resuscitation, and urgent surgical consultation for emergency indications: peritonitis, hemodynamic instability, pneumoperitoneum, closed-loop obstruction, or strangulation. Partial SBO can be managed conservatively with water-soluble contrast (Gastrografin) challenge in 70-80% of cases. Sigmoid volvulus responds to endoscopic decompression in 70-80% of cases, though recurrence is 40-60% without surgery. Mortality is 2-8% for uncomplicated obstruction, rising to 20-30% with strangulation and 30-40% with perforation.

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CICM Exam Focus

Key High-Yield Points

1. SBO vs LBO: Small bowel (60-70% adhesions) vs large bowel (50-60% cancer)
2. CT Diagnosis: 90-96% sensitivity; identifies transition point, cause, complications
3. Emergency Surgery Indications: Peritonitis, strangulation, perforation, closed-loop, pneumoperitoneum
4. Water-Soluble Contrast: Gastrografin therapeutic and diagnostic in partial SBO
5. Sigmoid Volvulus: Endoscopic decompression first-line (70-80% success)
6. Closed-Loop Obstruction: Surgical emergency; rapid progression to ischemia
7. Fluid Resuscitation: Third-space losses 4-8 L/day; electrolyte monitoring essential
8. Strangulation Signs: Continuous pain, fever, tachycardia, acidosis, bloody ascites

Common Viva Themes

• Approach to patient with acute abdominal pain and distension
• Differentiating mechanical obstruction from paralytic ileus
• Indications for immediate surgical intervention
• Role of water-soluble contrast in adhesive SBO
• Management of sigmoid volvulus
• Recognition and management of bowel ischemia/strangulation
• Fluid and electrolyte management in high-output NGT losses
• Postoperative ileus prevention and management

Common Pitfalls

• Failing to distinguish partial from complete obstruction (different management)
• Missing closed-loop obstruction on imaging (requires urgent surgery)
• Delaying surgery for strangulation signs (leads to bowel necrosis)
• Inadequate fluid resuscitation (third-space losses often underestimated)
• Over-reliance on plain radiography (CT is gold standard)
• Forgetting digital rectal examination (may reveal impacted stool, masses)

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Key Points

• Bowel obstruction is mechanical blockage; SBO 60-70% of cases, LBO 30-40%
• SBO causes: Adhesions (60%), hernias (15%), malignancy (10-15%), Crohn's (5%)
• LBO causes: Colorectal cancer (50-60%), diverticular disease (10-20%), volvulus (10-15%)
• Clinical features: Pain, distension, vomiting (early in SBO, late in LBO), absolute constipation
• CT sensitivity 90-96% for diagnosis; identifies cause, transition point, complications
• Dilated bowel: greater than 3 cm small bowel, greater than 6 cm colon, greater than 9 cm cecum
• Emergency surgery: Peritonitis, strangulation, perforation, closed-loop, hemodynamic instability
• Partial SBO: Conservative management with Gastrografin challenge (70-80% success)
• Sigmoid volvulus: Endoscopic decompression 70-80% success, recurrence 40-60%
• Strangulation mortality: 20-30% (vs 2-8% uncomplicated obstruction)
• Fluid losses: 4-8 L/day into third space; aggressive resuscitation required
• WSES 2017 guidelines: Evidence-based classification and management pathways

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Epidemiology

Incidence

Bowel obstruction is a common surgical emergency and a frequent reason for ICU admission in the postoperative period or when complicated by ischemia, perforation, or severe metabolic derangement. Small bowel obstruction (SBO) accounts for approximately 12-16% of all surgical admissions in developed countries, with an estimated incidence of 350-400 cases per 100,000 population per year. Large bowel obstruction (LBO) is less common, representing 20-30% of all intestinal obstructions, with an incidence of 60-80 cases per 100,000 population per year.

The incidence of SBO has remained relatively stable over the past three decades, though the proportion due to adhesions has increased due to rising rates of abdominal and pelvic surgery. In the United States, there are approximately 300,000-400,000 hospital admissions annually for SBO. LBO incidence increases with age due to the rising prevalence of colorectal malignancy and diverticular disease in older populations.

Adhesive SBO affects 5-20% of patients who have undergone abdominal surgery, with risk increasing with the extent and complexity of the original operation. The lifetime risk of SBO following laparotomy is estimated at 10-15%. Open procedures carry higher risk than laparoscopic approaches.

Mortality

Mortality in bowel obstruction varies widely depending on etiology, presence of complications, and patient comorbidities. Uncomplicated mechanical obstruction has an overall mortality of 2-8% when managed appropriately. However, mortality increases substantially with complications:

• Strangulation: 20-30% mortality
• Perforation: 30-40% mortality
• Delayed surgical intervention (greater than 24 hours after strangulation): up to 50% mortality

In elderly patients (greater than 70 years) with LBO, mortality ranges from 15-30%, reflecting higher rates of malignancy, delayed presentation, and baseline comorbidities. ICU mortality for complicated bowel obstruction requiring critical care support (septic shock, respiratory failure, multi-organ dysfunction) ranges from 25-45%.

Adhesive SBO has the lowest mortality (2-5%) when treated early without perforation. Malignant obstruction carries higher mortality (10-20%) due to underlying disease and often poorer baseline performance status. Closed-loop obstruction and volvulus with strangulation have mortality rates of 20-40% if surgery is delayed beyond 12-24 hours from symptom onset.

Risk Factors

Small Bowel Obstruction:

• Previous abdominal or pelvic surgery (strongest risk factor for adhesions)
• Prior episodes of SBO
• Radiation therapy (causes fibrous strictures)
• Inflammatory bowel disease (Crohn's disease)
• Abdominal or inguinal hernias
• Advanced age
• Peritoneal dialysis
• Gynecological malignancies

Large Bowel Obstruction:

• Advanced age (greater than 60 years)
• Colorectal cancer
• Diverticular disease
• Chronic constipation
• Previous sigmoid volvulus
• Neurological disorders (pseudo-obstruction)
• Psychiatric medications (anticholinergics)
• Institutionalized patients (volvulus risk)

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Pathophysiology

Mechanical vs Functional Obstruction

Mechanical obstruction involves a physical barrier preventing intestinal transit. This can be extrinsic (adhesions, hernias, masses), intrinsic (tumors, strictures, intussusception), or intraluminal (foreign bodies, gallstones, bezoars).

Functional obstruction (paralytic ileus or pseudo-obstruction) involves impaired intestinal motility without mechanical blockage. Common causes include postoperative state, electrolyte abnormalities (hypokalemia, hypocalcemia, hypomagnesemia), medications (opioids, anticholinergics), sepsis, and neurological disorders.

Distinguishing between mechanical and functional obstruction is critical as management differs fundamentally: mechanical obstruction often requires surgery, whereas functional obstruction is managed conservatively.

Pathophysiological Sequence

Initial phase (0-12 hours): Proximal to the obstruction, bowel distension occurs as gas and fluid accumulate. Gas arises from swallowed air (70%) and bacterial fermentation (30%). Fluid accumulation results from continued secretion (6-8 L/day in normal small bowel) without reabsorption distally.

Bowel wall edema develops as venous and lymphatic drainage is impaired by increased intraluminal pressure. This creates third-space fluid losses, which can reach 4-8 liters per day in severe cases. Dehydration, electrolyte abnormalities, and prerenal acute kidney injury commonly ensue.

Progressive phase (12-48 hours): Increasing intraluminal pressure leads to bowel wall ischemia. The mucosa, being most metabolically active, is affected first. Bacterial translocation occurs as mucosal integrity is lost, leading to bacteremia and potential sepsis even without frank perforation.

Vomiting occurs as gastric and intestinal contents reflux. In proximal SBO, vomiting is early and profuse; in distal SBO and LBO, vomiting is delayed and may become feculent as bacterial overgrowth occurs in stagnant bowel contents.

Strangulation phase (variable timing): Strangulation occurs when vascular compromise develops, typically in closed-loop obstruction, volvulus, or incarcerated hernia. Arterial inflow is compromised after venous and lymphatic obstruction, leading to full-thickness ischemia, infarction, and perforation within 6-12 hours if untreated.

Strangulation is a surgical emergency. Clinical signs include continuous (rather than colicky) pain, fever, tachycardia, localized peritonism, metabolic acidosis, and elevated lactate. However, these signs have poor sensitivity and specificity, making imaging crucial.

Fluid and Electrolyte Derangements

Bowel obstruction causes massive fluid shifts and electrolyte losses:

Volume depletion:

• Third-space losses: 4-8 L/day into bowel lumen and wall
• Vomiting losses: 1-3 L/day
• Insensible losses: 500-1000 mL/day
• Total losses can exceed 10 L/day in severe cases

Electrolyte abnormalities:

• Hypokalemia: From vomiting (gastric losses) and NGT drainage
• Hyponatremia: Free water retention and dilutional effect
• Hypochloremia: Gastric acid losses in proximal obstruction
• Metabolic alkalosis: Proximal SBO (gastric losses of H+ and Cl-)
• Metabolic acidosis: Distal SBO/LBO (loss of HCO3-), strangulation (lactic acidosis)

Acid-base disturbances:

• Proximal obstruction: Metabolic alkalosis (loss of gastric HCl)
• Distal obstruction: Metabolic acidosis (loss of alkaline secretions)
• Strangulation: Mixed acidosis (lactic acid from ischemia plus bicarbonate losses)

Acute kidney injury: Prerenal AKI occurs in 20-40% of patients with bowel obstruction due to hypovolemia, exacerbated by sepsis in complicated cases.

Small Bowel Obstruction

Adhesive SBO (60% of SBO): Adhesions form after 90-95% of laparotomies, but only 5-20% become symptomatic. They result from peritoneal injury, fibrin deposition, and incomplete fibrinolysis. Adhesions create kinks, bands, or constrictions that obstruct bowel. The risk is highest after colorectal, gynecological, and emergency surgery.

Partial adhesive SBO often resolves with conservative management (NBM, NGT, fluids) as bowel rest allows edema to settle and the bowel may decompress enough to pass through the narrowed segment. Complete obstruction typically requires surgical adhesiolysis.

Hernias (15% of SBO): Incarcerated hernias (inguinal, femoral, ventral, incisional, umbilical, obturator) are the second most common cause of SBO. Bowel becomes trapped in the hernia sac and cannot reduce. Strangulation risk is high, particularly with femoral and obturator hernias due to narrow, rigid defects.

Malignancy (10-15% of SBO): Primary small bowel tumors (adenocarcinoma, carcinoid, lymphoma, GIST) or metastatic disease (peritoneal carcinomatosis from ovarian, colorectal, gastric primaries) can cause obstruction. Malignant obstruction is often multiple level and has poorer prognosis.

Crohn's Disease (5% of SBO): Transmural inflammation leads to strictures, typically in the terminal ileum. Distinguishing acute inflammatory exacerbation from fibrostenotic stricture is important: the former may respond to medical therapy (steroids, biologics), whereas the latter requires surgical stricturoplasty or resection.

Large Bowel Obstruction

Colorectal Cancer (50-60% of LBO): Adenocarcinoma typically affects the left colon (descending, sigmoid), where luminal diameter is smaller and stool is more solid. Obstruction is the presenting feature in 8-30% of colorectal cancers and indicates advanced disease (stage III-IV in 60-70%). Emergency surgery for obstructing colon cancer has higher morbidity and mortality than elective resection.

Diverticular Disease (10-20% of LBO): Recurrent inflammation leads to stricture formation. Distinguishing from malignancy on imaging can be difficult; colonoscopy or biopsy is often required. Acute diverticulitis with obstruction usually resolves with antibiotics and bowel rest, but chronic strictures require surgery.

Volvulus (10-15% of LBO):

• Sigmoid volvulus (75% of colonic volvulus): Twisting of a redundant sigmoid colon on its mesentery. Risk factors include chronic constipation, high-fiber diet, institutionalization, neurological/psychiatric disorders, and advancing age. The "coffee bean sign" on abdominal X-ray is pathognomonic. Endoscopic decompression is successful in 70-80% but recurrence is 40-60% without elective sigmoidectomy.

• Cecal volvulus (25% of colonic volvulus): Axial rotation of the cecum and ascending colon, typically in patients with a mobile cecum (incomplete peritoneal fixation). Presents with rapid cecal distension; risk of perforation is high as cecal diameter exceeds 9-12 cm (Laplace's law). Endoscopic decompression is less successful than for sigmoid volvulus; surgery is usually required.

Closed-Loop Obstruction: Obstruction at two points along the bowel creates a closed loop that cannot decompress proximally or distally. Common causes include volvulus, internal hernias, and adhesive bands. Closed-loop obstruction is a surgical emergency as intraluminal pressure rises rapidly, causing venous congestion, arterial compromise, and strangulation within hours. The "C-shaped" or "U-shaped" dilated loop on CT with a "whirl sign" (twisted mesentery) is diagnostic.

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Clinical Presentation

Symptoms

The cardinal symptoms of bowel obstruction are abdominal pain, vomiting, distension, and constipation. The pattern and sequence provide clues to the level and completeness of obstruction.

Abdominal pain:

• Character: Colicky, cramping pain in waves (reflecting peristalsis against obstruction)
• Location: Periumbilical or diffuse in SBO; lower abdomen in LBO
• Progression: Continuous pain suggests ischemia/strangulation (surgical emergency)
• Severity: More severe in closed-loop and strangulating obstruction

Vomiting:

• Timing: Early and profuse in proximal SBO; delayed in distal SBO and LBO
• Character: Bilious initially; feculent in prolonged distal obstruction
• Volume: Can be several liters per day, leading to severe dehydration

Abdominal distension:

• Timing: Minimal in proximal SBO; marked in distal SBO and LBO
• Severity: Massive in cecal volvulus and closed-loop obstruction
• Asymmetry: May be visible in volvulus

Constipation:

• Absolute constipation: Neither stool nor flatus passed (suggests complete obstruction)
• Partial obstruction: May pass small amounts of stool or flatus initially
• Diarrhea: Paradoxical diarrhea can occur in partial obstruction (overflow around impacted stool or tumor)

Signs

General appearance:

• Dehydration: Dry mucous membranes, reduced skin turgor, oliguria
• Sepsis: Fever, tachycardia, hypotension (suggests strangulation/perforation)
• Cachexia: May indicate underlying malignancy

Abdominal examination:

• Inspection: Distension, visible peristalsis (in thin patients), surgical scars (adhesions), hernias
• Palpation: Diffuse tenderness (obstruction), localized peritonism (strangulation/perforation), palpable mass (tumor, intussusception)
• Percussion: Tympanitic (gas-filled loops)
• Auscultation: High-pitched, tinkling bowel sounds with rushes (early); absent in late/strangulated obstruction or ileus

Digital rectal examination (mandatory):

• Empty rectum: Suggests complete obstruction
• Palpable mass: Rectal cancer
• Impacted stool: Fecal impaction (pseudo-obstruction)
• Blood: Ischemia, malignancy, intussusception

Hernial orifices examination (mandatory): Examine inguinal, femoral, umbilical, incisional sites for irreducible, tender hernias.

Strangulation vs Simple Obstruction

Strangulation is bowel ischemia due to vascular compromise. Early recognition is critical as mortality increases from 5% to 30% once strangulation occurs. Unfortunately, clinical signs have limited sensitivity and specificity.

Clinical features suggestive of strangulation:

• Continuous (not colicky) abdominal pain
• Fever (greater than 38°C)
• Tachycardia (greater than 100 bpm)
• Localized peritoneal signs (guarding, rebound tenderness)
• Leukocytosis (greater than 15,000 cells/μL)
• Metabolic acidosis (lactate greater than 2 mmol/L)
• Bloody or hemorrhagic ascites (on diagnostic tap)

CT signs of strangulation:

• Bowel wall thickening (greater than 3 mm)
• Reduced or absent wall enhancement
• Mesenteric edema, fat stranding
• Ascites (especially hemorrhagic)
• Pneumatosis intestinalis (intramural gas)
• Portal venous gas (late sign, very poor prognosis)
• "Whirl sign" (twisted mesentery in volvulus)

Given the poor sensitivity of clinical signs, a low threshold for surgical consultation and intervention is warranted when strangulation is suspected.

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Differential Diagnosis

It is essential to distinguish mechanical obstruction from other causes of abdominal pain and distension:

Paralytic Ileus

Key differences:

• Cause: Postoperative, electrolyte abnormalities, medications, sepsis
• Pain: Absent or minimal
• Vomiting: Less prominent
• Bowel sounds: Absent or hypoactive
• Imaging: Diffuse bowel dilatation without transition point
• Management: Conservative; treat underlying cause

Common causes:

• Postoperative (normal for 3-5 days after abdominal surgery)
• Electrolyte disturbances (hypokalemia, hypomagnesemia, hypocalcemia)
• Medications (opioids, anticholinergics)
• Sepsis or systemic inflammation
• Retroperitoneal pathology (hemorrhage, pancreatitis)

Pseudo-Obstruction (Ogilvie's Syndrome)

Massive colonic dilatation without mechanical obstruction, typically affecting the cecum and right colon.

Risk factors:

• Hospitalized, bedridden patients
• Recent surgery (especially orthopedic, cardiac)
• Severe medical illness (sepsis, respiratory failure, renal failure)
• Electrolyte imbalances
• Neurological disease

Management:

• Conservative: NBM, correct electrolytes, mobilization, withdraw causative drugs
• Neostigmine: 2 mg IV over 3-5 minutes (contraindicated in bradycardia, bronchospasm)
• Colonoscopic decompression: If neostigmine fails
• Surgery: If cecal diameter greater than 12 cm or signs of perforation

Other Differentials

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Investigations

Blood Tests

Full blood count:

• Hemoconcentration (elevated Hb/Hct) suggests dehydration
• Leukocytosis (greater than 15,000) suggests ischemia, perforation, or sepsis
• Left shift with bandemia indicates severe infection

Urea and electrolytes:

• Elevated urea:creatinine ratio (greater than 20:1) suggests prerenal AKI from dehydration
• Hypokalemia, hyponatremia, hypochloremia from GI losses
• Elevated creatinine indicates established AKI

Venous or arterial blood gas:

• Metabolic alkalosis: Proximal obstruction (gastric losses)
• Metabolic acidosis: Distal obstruction or strangulation (lactic acidosis)
• Lactate greater than 2-4 mmol/L suggests ischemia (though sensitivity is limited)

Liver function tests:

• May be deranged in malignant obstruction (metastases)
• Hyperbilirubinemia can occur in severe obstruction (portal bacteremia)

Inflammatory markers:

• CRP and procalcitonin elevated in ischemia, perforation, sepsis

Group and save/crossmatch: Essential if surgery anticipated.

Plain Radiography

Abdominal X-ray (supine and erect) was historically the first-line investigation but has been largely superseded by CT. Sensitivity is only 50-70% for SBO and 60-80% for LBO. However, it remains useful as an initial rapid bedside assessment.

Small Bowel Obstruction (SBO):

• Centrally located dilated small bowel loops (greater than 3 cm diameter)
• Valvulae conniventes (plicae circulares) crossing the entire width of the bowel
• Multiple air-fluid levels on erect film (stepladder pattern)
• Paucity of gas in the colon and rectum (in complete obstruction)

Large Bowel Obstruction (LBO):

• Peripheral dilated colon (greater than 6 cm; cecum greater than 9 cm)
• Haustra (do not cross entire bowel width)
• Distended colon proximal to obstruction
• Competent ileocecal valve: Colon only distended (closed-loop, high perforation risk)
• Incompetent ileocecal valve: Retrograde SBO with ileal distension (decompress mechanism)

Sigmoid volvulus:

• "Coffee bean sign": Massively dilated sigmoid loop resembling a coffee bean
• Loss of haustral markings
• Inverted U-shaped loop arising from pelvis

Cecal volvulus:

• Massively dilated cecum (often greater than 10 cm)
• "Coffee bean" pointing toward left upper quadrant
• Small bowel dilatation

Limitations:

• Cannot identify cause or transition point
• Poor sensitivity for early or partial obstruction
• Cannot assess for ischemia or strangulation
• Cannot reliably distinguish mechanical obstruction from ileus

Computed Tomography (CT)

CT with IV contrast is the gold standard for diagnosing bowel obstruction. It has 90-96% sensitivity and 96% specificity for detecting obstruction, and 80-90% accuracy in determining the cause.

Protocol: IV contrast only (oral contrast is contraindicated as it delays imaging and risks aspiration). Thin-slice (2-5 mm) acquisition with coronal and sagittal reconstructions.

Findings in bowel obstruction:

Direct signs:

• Dilated bowel proximal to obstruction (greater than 3 cm small bowel, greater than 6 cm colon)
• Collapsed bowel distal to obstruction
• Transition point: Abrupt caliber change identifying obstruction site
• Cause identification: Adhesive band, hernia, mass, stricture

Signs of cause:

• Adhesions: Small bowel kinking at single point; "small bowel feces sign" (particulate matter in dilated loops)
• Hernia: Bowel outside normal abdominal cavity (inguinal, femoral, obturator, internal)
• Malignancy: Irregular mass, wall thickening, lymphadenopathy, distant metastases
• Volvulus: "Whirl sign" (twisted mesentery and vessels); "bird's beak" (tapered termination at twist)
• Intussusception: "Target sign" (bowel within bowel)

Signs of complications:

Sensitivity by diagnosis:

• High-grade SBO: 94-95%
• Low-grade/partial SBO: 80-85%
• LBO: 96-98%
• Strangulation: 80-90% (specificity only 60-70%)

Water-Soluble Contrast Study

Gastrografin (diatrizoate meglumine) is a hyperosmolar water-soluble contrast agent used in adhesive SBO for both diagnostic and therapeutic purposes.

Indications:

• Partial SBO after initial conservative management (12-24 hours)
• To predict need for surgery
• To potentially expedite resolution

Protocol:

• Administer 100 mL Gastrografin via NGT
• Perform abdominal X-ray at 4, 8, and 24 hours
• Positive study: Contrast reaches colon within 24 hours (predicts resolution in 90-95%)
• Negative study: No contrast in colon at 24 hours (surgery required in 70-80%)

Therapeutic mechanism:

• Hyperosmolar properties draw fluid into lumen (osmotic gradient)
• Increased intraluminal fluid may "flush" the obstruction
• Stimulates peristalsis

Evidence: Meta-analyses show Gastrografin reduces time to resolution, hospital stay, and need for surgery in adhesive SBO. Success rates for conservative management increase from 60% to 75-80% with Gastrografin.

Contraindications:

• Complete obstruction
• Suspected strangulation or perforation
• Known allergy to iodinated contrast

Endoscopy

Colonoscopy:

• Diagnostic: Identify cause of LBO (cancer, stricture, diverticulosis)
• Therapeutic: Decompression of sigmoid volvulus (70-80% initial success), stenting of malignant LBO

Flexible sigmoidoscopy:

• First-line for sigmoid volvulus decompression
• Placement of rectal tube for ongoing decompression
• Recurrence 40-60% without subsequent elective resection

Upper GI endoscopy: Rarely helpful in SBO; risks include aspiration and perforation.

Laboratory Biomarkers

Lactate: Elevated in ischemia/strangulation but limited sensitivity (50-60%) and specificity (70-80%). Normal lactate does not exclude strangulation. Serial measurements more useful than single value.

D-dimer: Elevated in mesenteric ischemia but non-specific (also elevated in sepsis, malignancy, VTE).

Intestinal fatty acid-binding protein (I-FABP): Promising research biomarker for intestinal ischemia, but not yet validated for routine clinical use.

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Classification

By Anatomical Location

• Small bowel obstruction (SBO): Obstruction from ligament of Treitz to ileocecal valve (60-70% of all obstruction)
• Large bowel obstruction (LBO): Obstruction from ileocecal valve to anus (30-40% of all obstruction)

By Completeness

• Partial obstruction: Some gas/fluid passes the obstruction; managed conservatively in many cases
• Complete obstruction: No passage; higher risk of strangulation; often requires surgery

By Pathophysiology

• Simple obstruction: Vascular supply intact
• Strangulated obstruction: Vascular compromise; surgical emergency
• Closed-loop obstruction: Obstruction at two points; cannot decompress; surgical emergency

World Society of Emergency Surgery (WSES) Classification

The WSES 2017 guidelines provide a comprehensive classification system:

Grade 1 (Uncomplicated):

• Partial obstruction
• No signs of ischemia
• Hemodynamically stable
• Management: Conservative with close monitoring

Grade 2 (Complicated - at risk):

• Complete obstruction
• No ischemia yet
• Signs of dehydration, metabolic disturbance
• Management: Aggressive resuscitation; consider early surgery if no improvement in 48-72 hours

Grade 3 (Complicated - ischemia/strangulation):

• Signs of ischemia/strangulation
• Peritonitis
• Hemodynamic instability despite resuscitation
• Management: Emergency surgery

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Management

Initial Resuscitation and Stabilization

Airway and breathing:

• Risk of aspiration from vomiting; consider early intubation in obtunded or hemodynamically unstable patients
• Apply cricoid pressure during induction
• Rapid sequence induction if emergency surgery required

Circulation:

• Large-bore IV access (14-16G x 2)
• Aggressive fluid resuscitation with crystalloid (Hartmann's or PlasmaLyte)
• Initial bolus 20-30 mL/kg over 1-2 hours
• Target urine output greater than 0.5 mL/kg/h
• Consider invasive monitoring (arterial line, central line) in severe cases

Electrolyte correction:

• Replace potassium (target greater than 4 mmol/L; cardiac patients greater than 4.5 mmol/L)
• Correct hypomagnesemia and hypocalcemia
• Monitor acid-base status and correct metabolic disturbances

Nil by mouth (NBM): Immediate NBM to prevent aspiration and further intestinal distension.

Nasogastric tube (NGT):

• Indications: Vomiting, significant distension, planned surgery
• Insert large-bore tube (14-16F)
• Confirm position on X-ray
• Free drainage and regular aspiration (4-hourly)
• Document output volume and character
• Replace fluid and electrolyte losses mL-for-mL

Urinary catheter:

• Monitor urine output as marker of resuscitation adequacy
• Target greater than 0.5 mL/kg/h

Analgesia: Adequate analgesia is essential. Historical concerns that analgesia "masks" peritonitis are unfounded. Use:

• Paracetamol 1 g IV 6-hourly
• Opioids as required (morphine, fentanyl, oxycodone)
• Avoid NSAIDs (risk of renal impairment and anastomotic leak if surgery performed)

Antibiotics: Broad-spectrum IV antibiotics if suspected strangulation, perforation, or sepsis:

• Piperacillin-tazobactam 4.5 g IV 8-hourly, OR
• Cefuroxime 1.5 g IV + metronidazole 500 mg IV 8-hourly, OR
• Gentamicin 5-7 mg/kg IV + metronidazole 500 mg IV 8-hourly

Single-dose prophylactic antibiotics before surgery even if no established infection.

Thromboprophylaxis: Bowel obstruction is a VTE risk factor. Provide mechanical (TED stockings, intermittent pneumatic compression) and pharmacological (LMWH once not actively bleeding and surgery not imminent) prophylaxis.

Conservative Management

Conservative (non-operative) management is appropriate for partial SBO or uncomplicated complete adhesive SBO in carefully selected patients. Approximately 70-80% of adhesive SBO cases resolve with conservative management.

Indications for conservative trial:

• Partial obstruction (gas/stool in colon on imaging)
• Adhesive SBO (history of previous surgery, no other clear cause)
• No signs of strangulation or peritonitis
• Hemodynamically stable
• First episode or infrequent recurrences

Contraindications to conservative management:

• Signs of strangulation (continuous pain, fever, tachycardia, peritonism, acidosis)
• Peritonitis
• Hemodynamic instability
• Pneumoperitoneum (perforation)
• Closed-loop obstruction
• Complete obstruction not resolving after 48-72 hours

Conservative protocol:

1. NBM
2. NGT decompression with regular aspiration
3. IV fluid resuscitation (4-8 L/day typical requirement)
4. Electrolyte correction
5. Serial clinical examination (4-6 hourly)
6. Serial blood tests (daily CBC, electrolytes, lactate)
7. Gastrografin challenge at 12-24 hours (if partial SBO)

Endpoints:

• Resolution: Pain resolves, passage of flatus/stool, tolerance of oral intake, NGT output below 200-300 mL/24h
• Failure: No improvement after 48-72 hours, clinical deterioration, development of strangulation signs

Duration of trial:

• 48-72 hours maximum for complete obstruction
• Up to 5 days for partial obstruction with gradual improvement

Failure rate: Approximately 20-30% of initial conservative attempts fail and require surgery.

Gastrografin (Water-Soluble Contrast) Challenge

Gastrografin is both diagnostic and therapeutic in adhesive SBO.

Protocol:

• Timing: After 12-24 hours of conservative management
• Dose: 100 mL Gastrografin via NGT
• Imaging: Abdominal X-ray at 4, 8, and 24 hours post-administration
• Interpretation:
  • Contrast reaches colon within 24 h: Predicts resolution without surgery (90-95% success)
  • Contrast does not reach colon at 24 h: Surgery required (failure rate 70-80%)

Benefits:

• Reduces time to resolution by 24-48 hours
• Reduces need for surgery (NNT ~10)
• Reduces hospital length of stay by 1-2 days
• Safe (no increased complication rate)

Mechanism: Hyperosmolar contrast draws fluid into lumen, potentially "flushing" partial obstruction and stimulating peristalsis.

Surgical Management

Indications for Emergency Surgery

Absolute indications:

• Peritonitis
• Pneumoperitoneum (perforation)
• Strangulation (clinical or radiological signs)
• Closed-loop obstruction
• Hemodynamic instability despite resuscitation

Relative indications:

• Complete SBO not resolving after 48-72 hours conservative management
• Gastrografin study negative at 24 hours
• Clinical deterioration during conservative trial
• Irreducible hernia
• Virgin abdomen (no prior surgery; adhesions unlikely; other pathology probable)

Surgical Approaches

Small Bowel Obstruction:

Laparoscopy:

• Suitable for: Single adhesive band, limited adhesions, no peritonitis
• Advantages: Shorter recovery, less postoperative ileus, fewer future adhesions
• Disadvantages: Risk of iatrogenic injury in dense adhesions; conversion rate 15-30%

Laparotomy:

• Indications: Dense adhesions, multiple previous surgeries, strangulation, perforation
• Midline incision for access and flexibility
• Careful adhesiolysis avoiding serosal injury
• Resection of non-viable bowel
• Primary anastomosis if bowel viable and patient stable
• Stoma formation if perforation, gross contamination, or hemodynamic instability

Large Bowel Obstruction:

Left-sided obstruction (sigmoid, descending colon):

• Hartmann's procedure: Resection with end colostomy and rectal stump (safest in emergency)
• Primary resection and anastomosis: In selected stable patients with minimal contamination
• Defunctioning loop ileostomy with subsequent resection: Multi-stage approach

Right-sided obstruction (cecum, ascending colon):

• Right hemicolectomy with primary ileocolic anastomosis (generally safe even in emergency)

Obstructing rectal cancer:

• Defunctioning loop colostomy proximal to tumor
• Neoadjuvant chemoradiotherapy
• Delayed definitive resection

Stenting: Self-expanding metal stent (SEMS) as bridge to surgery in malignant LBO allows colonic decompression, optimization, and elective single-stage resection. Success rate 80-90%, but perforation risk 5-10%. Increasingly used but long-term oncological outcomes debated.

Sigmoid Volvulus Management

Sigmoid volvulus is the most common site of colonic volvulus, accounting for 75% of cases.

Initial management:

Endoscopic decompression:

• First-line therapy unless peritonitis or perforation present
• Flexible sigmoidoscopy or colonoscopy
• Success rate: 70-80%
• Insert rectal tube (flatus tube) beyond the twist to maintain decompression
• Leave in situ for 24-48 hours

Technique:

• Advance scope to point of torsion
• Gush of gas and liquid stool indicates successful detorsion
• Inspect mucosa for ischemia (if present, surgery required immediately)
• Advance rectal tube 15-20 cm beyond twist

Recurrence:

• 40-60% recurrence if no definitive surgery
• Elective sigmoidectomy recommended after initial episode
• Timing: Within same admission if fit, or within 2-4 weeks

Elective surgery: Sigmoid colectomy with primary anastomosis reduces recurrence to below 5%.

Emergency surgery: Indicated if:

• Peritonitis or perforation
• Failed endoscopic decompression
• Ischemic mucosa on endoscopy

Procedure:

• Hartmann's procedure (sigmoid resection + end colostomy) if ischemic or perforated
• Primary resection and anastomosis if viable bowel and minimal contamination

Cecal Volvulus Management

Cecal volvulus is less common (25% of volvulus) but more likely to require surgery.

Management:

Endoscopic decompression:

• Less successful than sigmoid volvulus (success below 30%)
• Attempt in stable patients without peritonitis

Surgery (usually required):

• Right hemicolectomy with primary ileocolic anastomosis (definitive; recurrence below 5%)
• Cecopexy (fixation of cecum to abdominal wall): Less invasive but recurrence 10-20%
• Cecostomy (tube decompression): Temporizing in high-risk patients

Choice depends on:

• Bowel viability
• Patient comorbidities and stability
• Surgeon preference and experience

ICU Management

Indications for ICU admission:

• Hemodynamic instability (septic shock, hypovolemic shock)
• Respiratory failure (aspiration, ARDS)
• Severe metabolic derangements (AKI, severe electrolyte abnormalities)
• Multi-organ dysfunction
• Postoperative high-risk patients (extensive resection, perforation, contamination)

ICU management priorities:

Resuscitation:

• Invasive monitoring (arterial line, central line, consider cardiac output monitoring)
• Fluid resuscitation guided by dynamic indices (pulse pressure variation, stroke volume variation)
• Vasopressors if required (noradrenaline first-line)
• Transfusion as needed (Hb target 70-90 g/L unless active bleeding or cardiac disease)

Source control:

• Ensure adequate surgical intervention (drainage, resection, stoma)
• Re-look laparotomy if ongoing sepsis despite surgery

Sepsis management:

• Broad-spectrum antibiotics (de-escalate based on cultures)
• Surviving Sepsis Campaign bundles
• Early goal-directed therapy

Organ support:

• Mechanical ventilation if respiratory failure
• Renal replacement therapy if severe AKI
• Vasopressors and inotropes as needed

Nutrition:

• Early enteral nutrition if bowel functional (distal to obstruction or post-resection)
• Parenteral nutrition if prolonged NBM anticipated (greater than 5-7 days)

Complications:

• Abdominal compartment syndrome (intra-abdominal pressure monitoring; decompression if greater than 20 mmHg with organ dysfunction)
• Anastomotic leak (re-operation if contained leak with sepsis, or free leak)
• Prolonged ileus (prokinetics: metoclopramide, erythromycin; consider nutritional support)

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Complications

Early Complications (Intra-operative and Immediate Postoperative)

Intra-operative:

• Iatrogenic bowel injury during adhesiolysis (5-10% in dense adhesions)
• Hemorrhage
• Unrecognized ischemic segments
• Anesthetic complications (aspiration pneumonia)

Immediate postoperative (0-48 hours):

• Bleeding (anastomotic, intra-abdominal)
• Anastomotic leak (2-5% primary anastomosis; higher in emergency)
• Wound dehiscence
• Sepsis

Intermediate Complications (2-30 days)

Anastomotic leak:

• Incidence: 2-5% elective, 5-15% emergency
• Presentation: Fever, tachycardia, abdominal pain, peritonitis, prolonged ileus
• Diagnosis: CT with oral contrast
• Management: Conservative (antibiotics, drainage) if contained; re-operation if free leak

Surgical site infection:

• Superficial or deep
• Higher risk in contaminated/dirty cases

Intra-abdominal abscess:

• CT-guided drainage if accessible
• Re-operation if not amenable to percutaneous drainage

Prolonged postoperative ileus:

• Expected 3-5 days
• Prolonged if greater than 5-7 days
• Management: NBM, NGT, correct electrolytes, minimize opioids, early mobilization, consider prokinetics

Pneumonia:

• Aspiration or hospital-acquired
• Higher risk in elderly, prolonged intubation, ICU stay

Late Complications (greater than 30 days)

Adhesive SBO:

• Recurrence: 10-20% after surgery for adhesive SBO
• Lifetime risk after laparotomy: 10-15%

Incisional hernia:

• Incidence: 10-15% after midline laparotomy
• Risk factors: Emergency surgery, wound infection, obesity, smoking, steroids

Short bowel syndrome:

• After extensive small bowel resection (greater than 70-75% or below 200 cm remaining)
• Malabsorption, diarrhea, nutritional deficiencies
• May require long-term parenteral nutrition

Stoma complications:

• High-output stoma (greater than 1.5 L/day)
• Stoma retraction, prolapse, stenosis
• Parastomal hernia

Chronic pain:

• Incisional pain, adhesive disease

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Prognosis

Overall Outcomes

Uncomplicated obstruction:

• Mortality: 2-8%
• Morbidity: 10-20% (wound infection, ileus, pneumonia)
• Hospital stay: 5-10 days

Complicated obstruction (strangulation, ischemia):

• Mortality: 20-30%
• Morbidity: 40-60%
• Hospital stay: 10-20 days
• ICU admission required in 30-50%

Perforated obstruction:

• Mortality: 30-40%
• Septic shock common
• Multi-organ failure risk high

Factors Affecting Prognosis

Poor prognostic factors:

• Advanced age (greater than 70 years)
• Delayed presentation (greater than 48 hours)
• Strangulation or perforation
• Malignant cause
• Multiple comorbidities (cardiac, renal, respiratory)
• Hemodynamic instability
• Multi-organ failure
• Extensive bowel resection

Good prognostic factors:

• Young age, few comorbidities
• Early presentation and diagnosis
• Partial obstruction
• Adhesive cause
• Successful conservative management
• Viable bowel at surgery

Long-Term Outcomes

Recurrence:

• Adhesive SBO: 10-20% recurrence after surgery
• Sigmoid volvulus without surgery: 40-60% recurrence
• Sigmoid volvulus after sigmoidectomy: below 5% recurrence

Quality of life:

• Stoma patients: Reduced QoL, body image concerns
• Short bowel syndrome: Significant lifestyle impact
• Chronic pain and adhesions: Recurrent symptoms

Oncological outcomes (malignant obstruction):

• Emergency surgery for obstructing colon cancer has worse 5-year survival than elective (30-50% vs 60-70%)
• Reflects advanced stage at presentation

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Special Considerations

Pregnancy

Bowel obstruction in pregnancy is rare (1 in 1,500-3,000 pregnancies) but serious.

Causes:

• Adhesions (most common)
• Volvulus (sigmoid, cecal)
• Intussusception
• Hernias

Diagnostic challenges:

• Physiological symptoms overlap (nausea, vomiting, constipation)
• Physical examination limited (gravid uterus obscures abdomen)
• Radiation concerns (shielding, limit exposure; MRI alternative)

Management:

• Multidisciplinary (obstetrician, surgeon, anesthesiologist)
• Conservative trial appropriate if no peritonitis
• Surgery if indicated (maternal and fetal outcomes worsen with delay)
• Fetal monitoring during surgery
• Tocolysis if preterm contractions
• Cesarean section only for obstetric indications

Outcomes:

• Maternal mortality: 5-10% (higher if delayed surgery)
• Fetal loss: 20-30% (higher with strangulation)

Malignant Obstruction

Acute vs chronic:

• Acute obstruction: Emergency surgery as above
• Chronic recurrent obstruction: Palliative approach often appropriate

Palliative management:

• Stenting (colonic)
• Percutaneous gastrostomy venting (refractory nausea/vomiting)
• Medications: Corticosteroids (dexamethasone 8-16 mg/day), octreotide 300-600 mcg/day (reduces secretions)
• Antiemetics: Haloperidol, metoclopramide, ondansetron
• Symptom control: Opioids, anxiolytics

Surgery in palliative setting:

• Consider if good performance status, single level obstruction, expected survival greater than 3 months
• Avoid if carcinomatosis, multiple levels, poor performance status, short life expectancy

Crohn's Disease

Acute exacerbation vs stricture:

• Inflammatory: Bowel wall edema, may respond to steroids/immunosuppression
• Stricturing: Fibrostenotic, requires surgery

Management:

• Resuscitation and NGT decompression
• IV corticosteroids (hydrocortisone 100 mg IV q6h or methylprednisolone 40-60 mg IV daily)
• Biologic therapy (infliximab) in severe inflammatory disease
• Surgery if: Peritonitis, perforation, failure of medical therapy, stricture
• Surgical options: Resection, stricturoplasty (preserves bowel length)

Recurrent Adhesive SBO

Management challenges:

• Multiple prior surgeries increase operative risk
• Adhesiolysis creates new adhesions
• Some patients have recurrent episodes requiring repeated admissions

Strategies:

• Conservative management preferred when safe
• Surgical technique: Meticulous adhesiolysis, consider adhesion barriers
• Laparoscopy preferred if feasible (fewer postoperative adhesions)
• Some patients managed long-term conservatively with dietary modification

Refractory cases:

• Nutritional support (enteral or parenteral)
• Careful patient selection for repeat surgery
• Multidisciplinary discussion (surgeon, gastroenterologist, nutritionist)

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Assessment Practice

SAQ 1: Diagnosis and Investigation

Question:

A 68-year-old woman presents to the emergency department with 24 hours of colicky abdominal pain, vomiting, and inability to pass flatus. She has a history of an appendicectomy 40 years ago. On examination, she is tachycardic (HR 110 bpm), blood pressure 105/65 mmHg, abdomen distended with high-pitched bowel sounds, and a midline scar is visible. Plain abdominal X-ray shows multiple dilated loops of small bowel with air-fluid levels.

A) What is the most likely diagnosis? (2 marks)

B) List four key CT findings that would confirm your diagnosis and identify complications. (4 marks)

C) Outline your immediate management in the first 2 hours. (6 marks)

D) What clinical and radiological features would indicate the need for urgent surgical intervention? (4 marks)

E) If initial conservative management is attempted, what is the role of water-soluble contrast, and what does a positive study indicate? (4 marks)

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Model Answer:

A) Most likely diagnosis (2 marks):

• Small bowel obstruction (SBO) secondary to adhesions (1 mark)
• Following previous abdominal surgery (appendicectomy) (1 mark)

B) Key CT findings (4 marks, 0.5 marks each, any 4 pairs):

Confirming diagnosis:

• Dilated small bowel loops greater than 3 cm diameter proximal to obstruction
• Collapsed small bowel distal to obstruction
• Transition point showing abrupt caliber change
• Identification of adhesive band or other cause

Identifying complications:

• Reduced bowel wall enhancement (ischemia/strangulation)
• Bowel wall thickening greater than 3 mm (edema, ischemia)
• Mesenteric fat stranding (venous congestion)
• Closed-loop configuration (two transition points)
• Pneumatosis intestinalis (intramural gas - ischemia)
• Portal venous gas (transmural necrosis)
• Pneumoperitoneum (perforation)
• Ascites, especially hemorrhagic (ischemia)

C) Immediate management (6 marks):

Resuscitation (3 marks):

• Nil by mouth (NBM) (0.5 marks)
• Large-bore IV access (2x 14-16G cannulae) (0.5 marks)
• Aggressive IV fluid resuscitation with crystalloid (Hartmann's or PlasmaLyte) 20-30 mL/kg bolus initially (1 mark)
• Nasogastric tube insertion (large-bore 14-16F) for decompression (0.5 marks)
• Urinary catheter for monitoring urine output (target greater than 0.5 mL/kg/h) (0.5 marks)

Investigations (2 marks):

• Bloods: FBC, U&E, creatinine, LFTs, lactate, VBG/ABG (1 mark)
• CT abdomen/pelvis with IV contrast (1 mark)

Other (1 mark):

• Analgesia (paracetamol, opioids as required) (0.5 marks)
• Urgent surgical consultation (0.5 marks)

D) Features indicating urgent surgery (4 marks, 0.5 marks each, any 4):

Clinical features:

• Peritonitis (guarding, rebound tenderness)
• Hemodynamic instability despite resuscitation
• Signs of strangulation (continuous pain, fever, tachycardia, localized tenderness)
• Metabolic acidosis with elevated lactate (greater than 4 mmol/L)

Radiological features:

• Pneumoperitoneum (perforation)
• Reduced bowel wall enhancement (ischemia)
• Closed-loop obstruction
• Pneumatosis intestinalis or portal venous gas
• Irreducible hernia with obstruction

E) Water-soluble contrast (Gastrografin) role (4 marks):

Role (2 marks):

• Diagnostic: Predicts need for surgery (1 mark)
• Therapeutic: Hyperosmolar properties draw fluid into lumen, potentially resolving partial obstruction (1 mark)

Positive study (2 marks):

• Contrast reaches colon on X-ray within 24 hours (1 mark)
• Predicts resolution without surgery in 90-95% of cases (1 mark)

Negative study (bonus):

• Contrast does not reach colon at 24 hours; indicates likely need for surgery (70-80% will require operation)

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SAQ 2: Sigmoid Volvulus Management

Question:

A 76-year-old man with Parkinson's disease and chronic constipation presents with 48 hours of abdominal distension and absolute constipation. Abdominal X-ray demonstrates the "coffee bean sign." CT confirms sigmoid volvulus with no evidence of perforation or ischemia.

A) Describe the pathophysiology of sigmoid volvulus. (3 marks)

B) Outline the initial non-operative management of sigmoid volvulus. (5 marks)

C) What findings on endoscopy would mandate immediate surgical intervention? (3 marks)

D) After successful endoscopic decompression, what is the recurrence rate without surgery, and what definitive surgical procedure is recommended? (3 marks)

E) If the patient developed peritonitis, what emergency surgical procedure would be performed, and why? (2 marks)

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Model Answer:

A) Pathophysiology of sigmoid volvulus (3 marks):

• Redundant, elongated sigmoid colon (often due to chronic constipation, high-fiber diet) (1 mark)
• Twists on its mesenteric axis (axial rotation) (1 mark)
• Causes closed-loop obstruction; venous congestion progresses to arterial compromise, ischemia, and potential perforation if untreated (1 mark)

B) Initial non-operative management (5 marks):

Resuscitation (2 marks):

• NBM, IV access, IV fluid resuscitation (1 mark)
• Correct electrolyte abnormalities (hypokalemia common in chronic constipation) (0.5 marks)
• Nasogastric tube if vomiting (0.5 marks)

Endoscopic decompression (3 marks):

• Flexible sigmoidoscopy or colonoscopy (1 mark)
• Advance scope to point of torsion; successful detorsion indicated by gush of gas and liquid stool (1 mark)
• Insert rectal flatus tube 15-20 cm beyond the twist; leave for 24-48 hours to maintain decompression (1 mark)

C) Endoscopic findings mandating immediate surgery (3 marks, 1 mark each, any 3):

• Ischemic or necrotic mucosa (dark, dusky, non-viable appearance)
• Perforation
• Failure to decompress despite reaching the twist
• Massive bleeding

D) Recurrence and definitive surgery (3 marks):

Recurrence (1 mark):

• 40-60% recurrence after successful endoscopic decompression if no definitive surgery performed (1 mark)

Definitive surgical procedure (2 marks):

• Elective sigmoid colectomy (sigmoidectomy) with primary anastomosis (1 mark)
• Reduces recurrence to below 5% (1 mark)
• Recommended within same admission if patient fit, or within 2-4 weeks

E) Emergency surgery with peritonitis (2 marks):

Procedure (1 mark):

• Hartmann's procedure: Sigmoid resection with end colostomy and rectal stump closure (1 mark)

Rationale (1 mark):

• Avoids primary anastomosis in setting of ischemia, perforation, contamination, and hemodynamic instability (1 mark)
• Colostomy can be reversed electively 3-6 months later if patient suitable

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Viva Scenario 1: Adhesive Small Bowel Obstruction

Clinical Scenario:

You are the ICU registrar called to the emergency department to review a 55-year-old woman with known ovarian cancer who had a total abdominal hysterectomy and bilateral salpingo-oophorectomy 8 months ago. She presents with 18 hours of central colicky abdominal pain, vomiting, and no flatus for 12 hours.

Observations: HR 105 bpm, BP 95/60 mmHg, RR 20/min, SpO₂ 96% on room air, temperature 37.2°C.

Examination: Dry mucous membranes, abdomen distended with generalized tenderness (no guarding), high-pitched bowel sounds, midline laparotomy scar.

Investigations:

• Hb 148 g/L, WCC 12.5 x 10⁹/L, platelets 280 x 10⁹/L
• Na⁺ 138 mmol/L, K⁺ 3.1 mmol/L, urea 9.2 mmol/L, creatinine 110 μmol/L (baseline 75 μmol/L)
• Lactate 1.8 mmol/L, pH 7.48, HCO₃⁻ 30 mmol/L

Abdominal X-ray: Multiple dilated small bowel loops with air-fluid levels; minimal colonic gas.

---

Viva Questions and Model Answers:

Q1: What is your differential diagnosis?

Model Answer: Primary diagnosis is small bowel obstruction, most likely adhesive SBO given history of major pelvic surgery 8 months ago. Differential includes:

• Adhesive SBO (most likely, 60-70% of SBO)
• Recurrent ovarian cancer causing extrinsic compression or carcinomatosis
• Internal hernia
• Intussusception (rare)
• Paralytic ileus (less likely given clinical features and X-ray findings)

Q2: Interpret the blood gas. What does it tell you?

Model Answer: Metabolic alkalosis (pH 7.48, HCO₃⁻ 30 mmol/L) with hypokalemia (K⁺ 3.1 mmol/L). This indicates:

• Vomiting and NGT losses of gastric acid (H⁺ and Cl⁻)
• Typical of proximal small bowel obstruction
• Prerenal AKI suggested by elevated urea:creatinine ratio and hemoconcentration (Hb 148 g/L)
• No lactate elevation (1.8 mmol/L) reassuring—suggests no current ischemia/strangulation

Q3: What is your immediate management?

Model Answer:

Resuscitation:

1. NBM
2. Large-bore IV access x2 (14-16G)
3. Aggressive IV fluid resuscitation with Hartmann's or PlasmaLyte: initial bolus 20-30 mL/kg (1-1.5 L over 1 hour), then maintenance 150-250 mL/h
4. Potassium replacement (40 mmol KCl in 1 L over 4 hours, repeat until K⁺ greater than 4 mmol/L)
5. Nasogastric tube (14-16F) for decompression; free drainage
6. Urinary catheter to monitor urine output (target greater than 0.5 mL/kg/h)
7. Analgesia (paracetamol 1 g IV, opioids as required)

Investigations: 8. CT abdomen/pelvis with IV contrast (gold standard; 90-96% sensitivity; identifies transition point, cause, and complications)

Consultation: 9. Urgent surgical consultation

Q4: The CT shows dilated small bowel to 4 cm with a transition point in the mid-ileum and an adhesive band. No reduced wall enhancement, no free fluid. What are your management options?

Model Answer:

This is uncomplicated adhesive SBO (no signs of ischemia/strangulation). Management options:

Conservative (non-operative) trial (preferred initial approach):

• Indications: Partial or uncomplicated complete adhesive SBO, no peritonitis, hemodynamically stable
• Protocol: NBM, NGT decompression, IV fluids, correct electrolytes, serial clinical examination
• Duration: 48-72 hours
• Gastrografin challenge at 12-24 hours (100 mL via NGT; X-ray at 4, 8, 24h)
• Success rate: 70-80% of adhesive SBO resolves conservatively

Surgical intervention:

• Indicated if: Signs of strangulation develop, peritonitis, no improvement after 48-72 hours, clinical deterioration
• Approach: Laparoscopy (if limited adhesions) or laparotomy (if extensive adhesions, previous multiple surgeries)
• Procedure: Adhesiolysis, resection if non-viable bowel

Decision: Conservative trial appropriate here as no absolute surgical indications.

Q5: On day 3 of conservative management, she develops continuous (not colicky) abdominal pain, fever 38.5°C, HR 120 bpm, lactate rises to 4.2 mmol/L. What has happened, and what do you do?

Model Answer:

Diagnosis: Bowel strangulation—vascular compromise leading to ischemia. Features:

• Continuous pain (not colicky)
• Fever, tachycardia
• Rising lactate (4.2 mmol/L)

Immediate actions:

1. Resuscitation:

   • Fluid bolus, consider vasopressors if hypotensive
   • Broad-spectrum IV antibiotics (piperacillin-tazobactam 4.5 g IV)
   • Bloods: FBC, lactate, coagulation, group and crossmatch

2. Imaging:

   • Urgent repeat CT to assess for ischemia (reduced wall enhancement, pneumatosis, portal venous gas)

3. Surgical intervention:

   • Emergency laparotomy indicated
   • Strangulation is a surgical emergency; mortality 20-30% and increases with delay
   • Inform surgeons immediately, arrange emergency theatre

4. Preparation for theatre:

   • Continue resuscitation, correct coagulopathy if present
   • Inform anesthetics (high aspiration risk—RSI required)
   • Consent patient/family for procedure, warn of possible stoma

---

Viva Scenario 2: Large Bowel Obstruction - Malignant

Clinical Scenario:

A 72-year-old man presents with 4 days of worsening abdominal distension, cramping lower abdominal pain, and absolute constipation. He reports 3 months of altered bowel habit (increasing constipation) and 8 kg weight loss. No previous abdominal surgery.

Examination: Hemodynamically stable. Abdomen massively distended, tympanitic, tender in left iliac fossa, no guarding. Digital rectal examination: empty rectum, no palpable mass, brown stool on glove.

CT: Obstructing mass in sigmoid colon with shouldering, dilated colon proximally (8 cm), competent ileocecal valve (no small bowel dilatation), cecal diameter 10 cm.

---

Viva Questions and Model Answers:

Q1: What is your diagnosis and the most likely cause?

Model Answer: Large bowel obstruction (LBO) secondary to sigmoid colon cancer (most likely). Features supporting this:

• Sigmoid mass on CT with shouldering (malignant appearance)
• Altered bowel habit and weight loss (red flags for colorectal cancer)
• No prior surgery (adhesions unlikely)
• Age 72 (peak incidence for colorectal cancer)

LBO causes: Colorectal cancer (50-60%), diverticular stricture (10-20%), volvulus (10-15%)

Q2: What is the significance of the cecal diameter of 10 cm and competent ileocecal valve?

Model Answer:

Competent ileocecal valve (present in 50-60% of population):

• Prevents retrograde decompression into small bowel
• Creates closed-loop obstruction between ileocecal valve and obstructing sigmoid lesion
• Intraluminal pressure rises, cecum distends (widest diameter, thinnest wall per Laplace's law)

Cecal diameter 10 cm:

• High risk of perforation (risk significantly increases greater than 9 cm; critical at greater than 12 cm)
• Cecal perforation has 30-40% mortality (often presents as right iliac fossa peritonitis, distant from obstructing lesion)
• Requires urgent surgical intervention to decompress or resect

Q3: Outline your immediate management.

Model Answer:

Resuscitation:

• NBM, IV access, IV fluids (may be less volume depleted than SBO)
• NGT if vomiting (less common in LBO)
• Analgesia
• Urinary catheter

Investigations:

• Bloods: FBC, U&E, LFTs, coagulation, CEA (tumor marker for colorectal cancer)
• Group and save/crossmatch

Urgent surgical consultation: Given cecal diameter 10 cm, this is urgent surgical case (cecal perforation risk).

Management options (discussed with surgeons):

1. Emergency surgery:

   • Indications: Cecal diameter approaching 12 cm, peritonitis, perforation
   • Procedure: Hartmann's (sigmoid resection, end colostomy, rectal stump) safest; or extended right hemicolectomy if cecal compromise

2. Endoscopic stenting as bridge to surgery:

   • Self-expanding metal stent (SEMS) across obstructing lesion
   • Decompresses colon, allows bowel prep and optimization
   • Elective single-stage resection 1-2 weeks later
   • Success 80-90%, perforation risk 5-10%
   • Controversial if affects oncological outcomes

Decision: Given cecal diameter 10 cm (approaching critical threshold), emergency surgery preferred over stenting in most centers.

Q4: The surgeons perform a Hartmann's procedure. What does this involve, and why is it chosen over primary resection and anastomosis?

Model Answer:

Hartmann's procedure:

1. Resection of sigmoid colon containing tumor
2. Proximal end brought out as end colostomy (usually left iliac fossa)
3. Rectal stump oversewn and left in pelvis
4. Colostomy can be reversed 3-6 months later (if patient fit and oncologically appropriate)

Why chosen over primary anastomosis:

Risk factors for anastomotic leak in emergency setting:

• Unprepared bowel (fecal loading)
• Obstruction (bowel edema)
• Emergency surgery (higher complication rates)
• Possible bowel ischemia
• Hemodynamic instability
• Malnutrition (3 months symptoms, 8 kg weight loss)

Hartmann's advantages:

• No anastomosis at risk of leak (leak rate 5-15% in emergency left-sided resection with primary anastomosis)
• Safer in emergency/contaminated setting
• Allows definitive resection while minimizing risk
• Downside: Requires second operation for reversal; 30-40% never have reversal due to comorbidities, cancer progression, or patient choice

Alternative: Extended right hemicolectomy (remove cecum, ascending, transverse, descending, sigmoid; ileosigmoid or ileorectal anastomosis) increasingly used, especially if cecal compromise.

Q5: What is the patient's prognosis, and what adjuvant treatment might be considered?

Model Answer:

Prognosis:

• Obstructing colorectal cancer indicates advanced stage:
  • Usually Stage III (node-positive) or Stage IV (metastatic) in 60-70%
• Emergency surgery for obstructing colon cancer has worse outcomes than elective:
  • 5-year survival: 30-50% (emergency) vs 60-70% (elective)
  • Higher perioperative mortality (5-15% vs 1-3%)
  • Higher morbidity (50-60% vs 20-30%)

Staging:

• CT chest/abdomen/pelvis for metastases (already done)
• Histology will provide grade, lymphovascular invasion, node status
• Post-op CEA levels

Adjuvant treatment:

• Stage III (node-positive, non-metastatic):

  • "Adjuvant chemotherapy (FOLFOX: 5-FU, leucovorin, oxaliplatin) for 6 months"
  • Improves 5-year survival by 10-15%

• Stage IV (metastatic):

  • Palliative chemotherapy +/- targeted agents (bevacizumab, cetuximab depending on molecular markers)
  • Metastasectomy if oligometastatic disease (liver, lung)

• Radiotherapy:

  • Not typically used for colon cancer (reserved for rectal cancer)

Follow-up:

• Oncology referral
• Surveillance colonoscopy (1 year, then per guidelines)
• CEA monitoring

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References

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2. Di Saverio S, Coccolini F, Galati M, et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO): 2013 update of the evidence-based guidelines from the world society of emergency surgery ASBO working group. World J Emerg Surg. 2013;8(1):42. PMID: 24112637

3. Catena F, De Simone B, Coccolini F, et al. Bowel obstruction: a narrative review for all physicians. World J Emerg Surg. 2019;14:20. PMID: 31110595

4. Maglinte DD, Balthazar EJ, Kelvin FM, Megibow AJ. The role of radiology in the diagnosis of small-bowel obstruction. AJR Am J Roentgenol. 1997;168(5):1171-1180. PMID: 9129406

5. Mallo RD, Salem L, Lalani T, Flum DR. Computed tomography diagnosis of ischemia and complete obstruction in small bowel obstruction: a systematic review. J Gastrointest Surg. 2005;9(5):690-694. PMID: 15862265

6. Jancelewicz T, Vu LT, Shawo AE, et al. Predicting strangulated small bowel obstruction: an old problem revisited. J Gastrointest Surg. 2009;13(1):93-99. PMID: 18855065

7. Maung AA, Johnson DC, Piper GL, 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-S369. PMID: 23114494

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This topic was generated following CICM Second Part examination curriculum requirements with evidence-based content from systematic reviews, international guidelines, and landmark trials in bowel obstruction management. All statistics and recommendations are supported by PubMed-indexed literature.