Small bowel perforation

Overview

Full-thickness disruption of the small bowel wall causing peritoneal contamination, secondary peritonitis, and rapid progression to septic shock - a surgical emergency.

Causes

•Mechanical obstruction with ischaemia - strangulated hernia, adhesions, volvulus causing pressure necrosis

•Trauma - blunt deceleration injury (duodenojejunal flexure); penetrating; blast injury can cause delayed perforation 12-36 hours later

•Crohn's disease - transmural inflammation progressing to frank perforation

•Infection - typhoid fever (Salmonella typhi, Peyer's patch necrosis in terminal ileum), TB, CMV in immunocompromised

•Iatrogenic - colonoscopy, anastomotic dehiscence

•Mesenteric ischaemia - arterial/venous occlusion causing infarction then perforation

⚠️
Steroids can mask peritonitis signs - a patient on long-term corticosteroids may have a perforated viscus with deceptively mild tenderness. Maintain a high index of suspicion and do not withhold imaging.

Presentation

•Sudden-onset severe diffuse abdominal pain - constant, worsened by movement

•Peritonism - guarding (voluntary then involuntary), rigidity, rebound tenderness

•Absent bowel sounds - ileus from peritoneal contamination

•Fever, tachycardia, tachypnoea - SIRS/sepsis

•Haemodynamic instability - hypotension, septic shock in delayed presentations

Investigations

🥇 First-line

•erect CXR - pneumoperitoneum (free air under diaphragm); sensitivity ~70-80%

•FBC, U&E, CRP, serum lactate - leucocytosis, raised lactate (tissue ischaemia); ABG for acid-base status

•serum amylase - to exclude acute pancreatitis; urine pregnancy test in females of childbearing age

🏆 Gold standard

•CT abdomen and pelvis with IV contrast - confirms pneumoperitoneum, identifies site of perforation, assesses for abscess/free fluid/mesenteric ischaemia, guides operative planning

🎯
A normal erect CXR does NOT rule out perforation - up to 30% of perforations produce no visible free air on plain film. If clinical suspicion is high, proceed to CT.

Differential diagnosis

Key differentials
DiagnosisDistinguishing features
Acute pancreatitisEpigastric pain radiating to back; raised amylase/lipase; no pneumoperitoneum
Perforated peptic ulcerSudden epigastric pain; upper GI origin; managed with Graham patch repair
Large bowel perforationLeft iliac fossa pain preceding perforation; faeculent peritonitis
Mesenteric ischaemiaPain out of proportion to signs early on; raised lactate; CT angiography
Ectopic pregnancyFemales of childbearing age; positive pregnancy test; peritonism

Diagnosis	Distinguishing features
Acute pancreatitis	Epigastric pain radiating to back; raised amylase/lipase; no pneumoperitoneum
Perforated peptic ulcer	Sudden epigastric pain; upper GI origin; managed with Graham patch repair
Large bowel perforation	Left iliac fossa pain preceding perforation; faeculent peritonitis
Mesenteric ischaemia	Pain out of proportion to signs early on; raised lactate; CT angiography
Ectopic pregnancy	Females of childbearing age; positive pregnancy test; peritonism

Management

Resuscitation and definitive surgical treatment run in parallel - a patient with generalised peritonitis should be optimised and taken to theatre as quickly as possible.

Step 1 · Immediate resuscitation
1IV fluid resuscitation
2IV broad-spectrum antibiotics (e.g. piperacillin-tazobactam)
3Nil by mouth + nasogastric tube
4Urinary catheter (monitor urine output)
5Analgesia
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Step 2 · Confirm diagnosis
1CT abdomen and pelvis with IV contrast - site of perforation, operative planning
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Step 3 · Definitive surgery
1Midline laparotomy - exploration, control of contamination
2Repair, resection ± anastomosis or stoma depending on degree of contamination and bowel viability
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Step 4 · Postoperative care
1HDU/ICU - continued IV antibiotics, nutritional support (nasojejunal feeding or TPN)
2Monitor for anastomotic leak (deterioration day 3-5 post-op), intra-abdominal abscess

Complications

•Generalised peritonitis and septic shock - most immediately life-threatening

•Multi-organ failure - renal and hepatic dysfunction from prolonged sepsis

•Anastomotic leak - deterioration day 3-5 post-op; may require return to theatre

•Intra-abdominal abscess - may require CT-guided drainage

•Adhesion formation - long-term risk of small bowel obstruction

Prognosis

•Delays beyond 12-24 hours from perforation substantially increase mortality

•Highest operative risk: extremes of age, co-morbidities, immunosuppression, delayed presentation

•Mannheim Peritonitis Index - incorporates age, origin of sepsis, degree of contamination, organ failure, and malignancy to predict mortality