A 58-year-old man with a long-standing left inguinal hernia presents to the emergency department with acute onset colicky abdominal pain, abdominal distension, and bilious vomiting for 6 hours. On examination, the hernia is tender, firm, and irreducible. Bowel sounds are high-pitched and tinkling. Abdominal X-ray shows small bowel loops with air-fluid levels. Blood investigations reveal WBC 14,500/μL, serum lactate 3.2 mmol/L (normal <2), and serum amylase 180 U/L. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Strangulated Hernia ### Key Clinical Features **Key Point:** Strangulation is a surgical emergency characterized by compromised blood supply to hernia contents, leading to ischaemia, necrosis, and perforation if untreated. The clinical triad present in this patient: 1. **Irreducible, tender hernia** — indicates vascular compromise 2. **Systemic signs of tissue injury** — elevated WBC, raised lactate (marker of anaerobic metabolism and tissue hypoxia) 3. **Signs of bowel obstruction** — colicky pain, bilious vomiting, high-pitched bowel sounds, air-fluid levels ### Distinction: Incarceration vs Strangulation | Feature | Incarcerated Hernia | Strangulated Hernia | |---------|-------------------|---------------------| | **Definition** | Hernia contents trapped but blood supply intact | Hernia contents trapped WITH vascular compromise | | **Onset** | Gradual, may reduce spontaneously | Acute, irreducible | | **Local signs** | Tender but not severely inflamed | Severe tenderness, dusky/purple discoloration | | **Systemic signs** | Minimal or absent | Elevated WBC, raised lactate, fever | | **Bowel sounds** | May be normal or mildly altered | High-pitched (early) or absent (late) | | **Risk of perforation** | Low | High (within 6–12 hours if untreated) | | **Management** | Urgent surgery (within hours) | **Emergent surgery (within 1–2 hours)** | **High-Yield:** Elevated serum lactate (>2 mmol/L) in the setting of an irreducible hernia is a red flag for strangulation and tissue ischaemia. This patient's lactate of 3.2 mmol/L confirms tissue hypoxia. ### Pathophysiology of Strangulation ```mermaid flowchart TD A[Hernia contents trapped at neck]:::outcome --> B[Venous compression first]:::action B --> C[Venous congestion and oedema]:::action C --> D[Arterial flow compromised]:::action D --> E[Tissue ischaemia]:::outcome E --> F{Time elapsed?}:::decision F -->|< 6 hours| G[Reversible if decompressed]:::action F -->|6-12 hours| H[Necrosis begins]:::urgent F -->|> 12 hours| I[Transmural necrosis + perforation]:::urgent ``` **Clinical Pearl:** Venous obstruction precedes arterial obstruction in strangulation, which is why oedema and congestion occur before frank ischaemia. This is why time is critical — the "golden window" for salvage is 6–8 hours. ### Why Serum Amylase is Elevated The mildly elevated amylase (180 U/L) reflects **secondary hyperamylasaemia** from bowel ischaemia and mucosal injury, not primary pancreatitis. Amylase can be released from ischaemic bowel mucosa and absorbed into the bloodstream. **Warning:** Do not confuse secondary hyperamylasaemia (from bowel ischaemia) with acute pancreatitis. The clinical context (irreducible hernia, lactate elevation) points to strangulation, not pancreatic disease. ### Management Implications **Key Point:** Strangulated hernia is a **surgical emergency** requiring immediate operative intervention. Unlike incarcerated hernia (which may be attempted manual reduction), strangulated hernia requires urgent surgery to assess viability and resect necrotic bowel if necessary. **Mnemonic — RED FLAGS FOR STRANGULATION: VEIN** - **V**omiting (bilious, persistent) - **E**levated lactate and WBC - **I**rreducible, inflamed hernia - **N**ecrosis risk (time-dependent) [cite:Sabiston Textbook of Surgery 21e Ch 44]