4.3 Acute Abdomen, Bowel Obstruction & Perforation
Key Takeaways
The acute abdomen encompasses life-threatening surgical emergencies characterized by sudden abdominal pain, peritonism (involuntary guarding, board-like rigidity, rebound/percussion tenderness), and potential shock.
An erect chest radiograph detects pneumoperitoneum (subdiaphragmatic free gas) secondary to visceral perforation, mandating immediate fluid resuscitation, broad-spectrum antibiotics, and emergency surgical exploration.
Small bowel obstruction is caused predominantly by adhesions (~60%) and incarcerated hernias (~20%), showing centrally located dilated loops (>3 cm) with plicae circulares (valvulae conniventes) traversing the complete luminal diameter.
Large bowel obstruction is caused primarily by colorectal carcinoma (~60%), diverticular strictures, and volvulus; plain radiographs demonstrate peripheral dilated loops (>6 cm; caecum >9 cm) with non-circumferential haustra.
Sigmoid volvulus displays the pathognomonic 'coffee-bean sign' on abdominal X-ray and is decompressed first-line via flatus tube/sigmoidoscopy; caecal volvulus exhibits an embryo-shaped loop pointing to the LUQ and requires emergency surgical right hemicolectomy.
Acute Abdomen, Bowel Obstruction & Perforation
In UK emergency surgical practice (including Association of Surgeons of Great Britain and Ireland standards), the acute abdomen is a clinical syndrome characterized by sudden-onset, severe abdominal pain of less than 24 to 48 hours duration that may signify life-threatening intra-abdominal pathology requiring emergency surgical intervention. Rapid triage, accurate physical examination, targeted radiodiagnostics, and prompt resuscitation are critical to avert irreversible sepsis, necrosis, and multi-organ failure.
1. Clinical Evaluation of the Acute Abdomen & Peritonitis
Peritonitis represents inflammation of the peritoneal lining, divided into visceral (autonomic, poorly localized, dull/crampy) and parietal (somatic, sharp, exquisitely localized, aggravated by movement or coughing).
Clinical Hallmarks of Peritonism
- Involuntary Guarding: Reflex abdominal wall muscular spasm upon palpation that cannot be voluntarily suppressed by the patient; reflects localized parietal peritoneal irritation.
- Board-Like Rigidity: Involuntary, unrelenting, rock-hard contraction of the entire anterior abdominal musculature; denotes diffuse, generalized peritonitis.
- Percussion Tenderness: Sharp, focal pain elicited by light percussion over the affected abdominal quadrant. Clinically superior and far more humane than traditional "rebound tenderness" (Blumberg's sign), which causes unnecessary distress.
- Absent Bowel Sounds: Silent abdomen on auscultation over at least 2 minutes signifies paralytic ileus secondary to severe, generalized intra-abdominal sepsis.
Imaging: Pneumoperitoneum & Visceral Perforation
- Erect Chest Radiograph (CXR): The mandatory first-line screening investigation for suspected visceral perforation. It demonstrates free gas under the diaphragm (subdiaphragmatic crescent of air, visible in ~75% of perforated ulcers). The erect position must be maintained for at least 10 minutes prior to image acquisition to allow free air to ascend beneath the right hemidiaphragm (differentiated from gastric bubble on the left).
- Contrast-Enhanced CT Abdomen and Pelvis: The diagnostic gold standard for undifferentiated acute abdomen; precisely identifies perforation sites, extraluminal fluid, ischaemic bowel loops, abscess collections, and vascular occlusion.
Important
Visceral Perforation Emergency Protocol: Upon finding pneumoperitoneum with peritonitis:
- Establish immediate IV access with two large-bore cannulae.
- Commence IV fluid resuscitation with balanced crystalloids, reassessing response.
- Administer immediate IV broad-spectrum antibiotics per local guidelines (e.g. IV co-amoxiclav; cefuroxime plus metronidazole; or piperacillin-tazobactam for severe or hospital-acquired infection).
- Insert an indwelling urinary catheter and wide-bore nasogastric tube.
- Emergency surgical consultation for immediate exploratory laparotomy or emergency laparoscopy (e.g. Graham patch omental repair of a perforated peptic ulcer, or Hartmann's procedure for perforated diverticulitis).
2. Mechanical Bowel Obstruction: Cardinal Features & Pathophysiology
Mechanical bowel obstruction occurs when an intrinsic or extrinsic physical barrier prevents the normal aboral progression of intraluminal contents.
The Cardinal Tetrad of Bowel Obstruction
- Colicky Abdominal Pain: Intermittent, cramping pain corresponding to hyperperistaltic waves attempting to overcome the mechanical barrier. Pain becoming continuous and severe suggests strangulation and bowel ischaemia.
- Vomiting: Early, copious, bilious vomiting occurs in proximal small bowel obstruction; late, feculent vomiting occurs in distal small bowel or longstanding large bowel obstruction (feculent emesis is due to bacterial proliferation, not true faeces).
- Abdominal Distension: Minimal in high proximal jejunal obstruction; prominent and marked in distal ileal and large bowel obstruction.
- Absolute Constipation (Obstipation): Inability to pass either faeces or flatus. Patients may pass residual flatus or stool remaining distal to the obstruction point early in the disease course.
3. Small Bowel vs Large Bowel Obstruction: The "3-6-9 Rule"
| Diagnostic Parameter | Small Bowel Obstruction (SBO) | Large Bowel Obstruction (LBO) |
|---|---|---|
| Most Common Aetiologies | 1. Post-surgical Adhesions (~60–70%); 2. Incarcerated / Strangulated Hernias (~20%); 3. Crohn's disease strictures, neoplasms, intussusception, gallstone ileus | 1. Colorectal Malignancy (~60%); 2. Diverticular Stricture (~20%); 3. Volvulus (Sigmoid ~8%, Caecal ~2%) |
| Onset of Vomiting | Early, frequent, bilious | Late, infrequent; may become feculent |
| Degree of Distension | Moderate, central | Marked, prominent, peripheral |
| Abdominal Radiograph Distribution | Central loops of bowel crossing mid-abdomen | Peripheral loops framing the abdominal cavity |
| Mucosal Folds (Plies) | Valvulae Conniventes (Plicae Circulares): Thin mucosal lines that extend completely across the full diameter of the bowel lumen from wall to wall. | Haustra: Sacculated pouches whose mucosal indentations extend only partially across the luminal width (do not cross completely). |
| Luminal Diameter ("3-6-9 Rule") | Pathological dilatation: > 3 cm | Pathological dilatation: > 6 cm for colon; > 9 cm for caecum |
Conservative vs Surgical Management in SBO
- "Drip and Suck" Protocol: Nil-by-mouth (NPO), aggressive IV fluid resuscitation (Hartmann's solution), and wide-bore nasogastric (Ryle's) tube decompression to evacuate swallowed air and pooled secretions.
- Water-Soluble Contrast (Gastrografin) Challenge: Administer 50–100 mL of oral/NG Gastrografin followed by serial abdominal X-rays at 4 to 24 hours. Gastrografin is hyperosmolar, drawing fluid into the lumen and promoting peristalsis. If contrast reaches the colon within 24 hours, non-operative management succeeds in >90% of adhesive SBO cases.
- Immediate Surgical Indications: Peritonism, fever, localized abdominal tenderness, persistent tachycardia, refractory leukocytosis, elevated serum lactate, or an incarcerated / strangulated external hernia (groin examination is mandatory in every patient with bowel obstruction!).
4. Volvulus: Sigmoid vs Caecal
A volvulus occurs when a mobile segment of bowel twists around its mesenteric vascular axis, precipitating closed-loop bowel obstruction and strangulating mesenteric ischaemia.
Sigmoid Volvulus
- Epidemiology: Most common volvulus (~80%). Typical patients are elderly, bedbound, institutionalized nursing home residents, individuals with chronic constipation, or patients with chronic psychiatric or neurological disorders taking anticholinergic or antipsychotic medications.
- Radiological Sign: Abdominal X-ray shows the pathognomonic "coffee-bean sign" (a massive, inverted U-shaped, ahaustral loop of distended bowel arising from the pelvis and pointing towards the Right Upper Quadrant (RUQ)).
- First-Line Emergency Management: Decompression via rigid or flexible sigmoidoscopy with insertion of a flatus tube. The tube bypasses the twisted neck, producing an explosive release of gas and liquid faeces, relieving obstruction in >80% of cases. The flatus tube is secured in situ for 24 hours.
- Definitive Treatment: Sigmoid volvulus recurs in >50% of patients. Following successful endoscopic decompression, elective sigmoid colectomy is planned during the same admission. Emergency surgery (Hartmann's procedure) is reserved for patients presenting with bowel ischaemia, perforation, or failed endoscopic detorsion.
Caecal Volvulus
- Epidemiology: Accounts for ~15–20% of volvulus cases; caused by congenital failure of peritoneal retroperitoneal fixation of the caecum (mobile caecum). More common in younger adults (30–50 years), during pregnancy, or in marathon runners.
- Radiological Sign: Abdominal X-ray demonstrates an embryo-shaped or comma-shaped gas-filled loop of bowel arising in the right lower quadrant and pointing towards the Left Upper Quadrant (LUQ) or epigastrium.
- Definitive Emergency Management: Immediate emergency surgical exploration (Right Hemicolectomy with primary ileocolic anastomosis or ileostomy). Endoscopic decompression is strictly contraindicated because of an exceptionally high failure rate (>95%) and catastrophic risk of caecal perforation.
5. Acute Appendicitis
Acute appendicitis is the most frequent surgical emergency worldwide, peaking in adolescents and young adults (10–30 years). It is initiated by luminal obstruction of the appendix by a faecolith (appendicolith), lymphoid hyperplasia (following a viral illness), or rarely a carcinoid tumour, resulting in bacterial proliferation, intraluminal hypertension, venous congestion, ischaemia, and gangrenous perforation.
Classical Clinical Progression
- Visceral Pain Phase: Early dull, periumbilical colicky discomfort transmitted via sympathetic visceral afferents entering the spinal cord at T10.
- Somatic Pain Phase: Over 12 to 24 hours, progressive transmural inflammation irritates the adjacent parietal peritoneum. Pain migrates to become sharp, constant, and exquisitely localized to the Right Iliac Fossa (RIF) at McBurney's point (one-third the distance along an imaginary line from the anterior superior iliac spine to the umbilicus).
- Systemic Symptoms: Anorexia (virtually universal; "the hamburger sign"), nausea, low-grade fever, and flushed appearance.
Named Physical Signs
- Rovsing's Sign: Palpation of the left lower quadrant reproduces pain in the right iliac fossa (due to retrograde displacement of colonic gas irritating the inflamed caecal region).
- Psoas Sign: Pain in the RIF elicited by passive hyperextension of the right hip (indicates retrocaecal appendicitis irritating the iliopsoas muscle).
- Obturator Sign: Pain in the RIF provoked by passive internal rotation of the flexed right hip (indicates pelvic appendicitis irritating the obturator internus muscle).
Diagnostic Pathway & Management
- Clinical Scoring: The Alvarado score integrates symptoms, signs, and laboratory markers (leukocytosis and neutrophilia). A score ≥7 strongly predicts acute appendicitis.
- Definitive Treatment: Intravenous fluid resuscitation, analgesia, pre-operative prophylactic broad-spectrum IV antibiotics covering enteric Gram-negatives and anaerobes (e.g. IV co-amoxiclav or cefuroxime + metronidazole), and prompt emergency laparoscopic appendicectomy.
6. Acute Mesenteric Ischaemia
Acute mesenteric ischaemia is a catastrophic abdominal vascular emergency resulting from sudden interruption of mesenteric arterial blood flow (predominantly the Superior Mesenteric Artery [SMA]). Overall mortality exceeds 60%.
Clinical Presentation & Cardinal Hallmark
- The Hallmark Discrepancy: Severe, excruciating, agonising central abdominal pain completely "out of proportion" to physical examination findings. In early stages, the abdomen remains soft, flat, and non-tender, because ischaemia is initially restricted to the mucosal and submucosal layers before transmural gangrene develops.
- Precipitating Factors: Embolic occlusion (~50%) arising from atrial fibrillation, recent myocardial infarction with mural thrombus, or severe peripheral vascular atherosclerosis.
- Metabolic Derangement: The pathognomonic laboratory triad is severe metabolic acidosis with marked hyperlactataemia (lactate >4.0 mmol/L), profound leukocytosis, and an elevated anion gap.
- Definitive Diagnostic Modality: Immediate emergency contrast-enhanced CT mesenteric angiography (imaging during arterial phase). Standard non-contrast CT, plain radiographs, and abdominal ultrasound cannot exclude mesenteric ischaemia and cause fatal diagnostic delays.
- Emergency Treatment: Immediate fluid resuscitation, broad-spectrum IV antibiotics, therapeutic unfractionated heparin, and emergent vascular/general surgical intervention (catheter-directed embolectomy, surgical revascularisation, and resection of non-viable gangrenous bowel).
A 78-year-old bedbound woman residing in a nursing home is admitted to the surgical assessment unit with a 2-day history of progressive abdominal distension, mild crampy pain, and absolute constipation. She takes regular haloperidol and co-codamol for chronic agitation and osteoarthritis. On examination, her abdomen is massively distended and tympanitic to percussion, but soft and non-tender without guarding or rebound tenderness. Bowel sounds are high-pitched and metallic. Digital rectal examination reveals an empty rectal vault. A plain abdominal radiograph demonstrates a hugely distended, smooth, ahaustral loop of bowel originating from the pelvis and extending toward the right upper quadrant, resembling a bent inner tube or coffee bean. What is the most appropriate first-line emergency management for this patient?
Urgent colonoscopy with self-expanding metal stent (SEMS) deployment across the lesion
Emergency exploratory laparotomy and total abdominal colectomy with end-ileostomy
High-volume oral polyethylene glycol bowel preparation and intravenous neostigmine
Rigid or flexible sigmoidoscopy with insertion and placement of a flatus tube
A 72-year-old woman with a documented history of persistent atrial fibrillation and severe generalized peripheral vascular disease is brought to the emergency department with sudden-onset, excoriating central abdominal pain that began 3 hours ago. She has vomited twice and passed one loose stool. On physical examination, she appears distressed and diaphoretic. Her pulse is 124 bpm and irregular, blood pressure is 108/66 mmHg, and respiratory rate is 26 breaths/min. Abdominal palpation reveals a soft, non-distended abdomen with only mild, vague periumbilical tenderness; there is no guarding, rigidity, or percussion tenderness. Arterial blood gas analysis reveals: pH 7.26 (normal 7.35–7.45), pO2 11.2 kPa, pCO2 3.8 kPa, standard bicarbonate 14 mmol/L (normal 22–26 mmol/L), base excess -10 mmol/L, and lactate 5.4 mmol/L (normal <2.0 mmol/L). What is the most appropriate definitive diagnostic investigation?
Erect plain chest radiograph to rule out subdiaphragmatic pneumoperitoneum
Plain abdominal radiograph to assess for small bowel obstruction
Urgent contrast-enhanced CT mesenteric angiography
Transabdominal ultrasound examination of the gallbladder and biliary tree
A 52-year-old man presents to the emergency department with a 3-hour history of sudden-onset, agonising epigastric pain that rapidly spread across his entire abdomen. He has a history of chronic osteoarthritis for which he takes naproxen 500 mg twice daily. On physical examination, he lies completely motionless on the trolley with shallow respirations. His blood pressure is 104/68 mmHg, heart rate is 114 bpm, and temperature is 37.9°C. Abdominal examination reveals a rock-hard, board-like abdomen with severe generalized percussion tenderness and involuntary guarding throughout all four quadrants. Bowel sounds are absent. An erect chest radiograph demonstrates crescent-shaped radiolucency beneath the right hemidiaphragm. What is the most appropriate definitive management for this patient?
Insertion of a wide-bore nasogastric tube and conservative management with intravenous omeprazole infusion
Immediate intravenous fluid resuscitation, broad-spectrum antibiotics, and emergency exploratory laparotomy
Urgent contrast-enhanced CT scan of the abdomen to locate the precise perforation site prior to surgical review
Urgent diagnostic upper gastrointestinal endoscopy to cauterise the bleeding ulcer base
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